Double-ReO3-type structure compound NaSbF6 undergoes a low-temperature rhombohedral to high-temperature cubic phase between 303 and 323 K, as revealed by temperature-dependent X-ray diffractions. Although many double-ReO3-type fluorides exhibit either low thermal expansion or negative thermal expansion (NTE), NaSbF6 exhibits positive thermal expansion (PTE) with a large volumetric coefficient of thermal expansion, αv = 62 ppm/K, in its cubic phase. Raman spectroscopy reveals that the low-frequency transverse vibration of fluorine atoms is stiffened in NaSbF6, compared with the typical NTE compound CaZrF6 with the same structure. The related weak contraction associated with the polyhedral rocking would be overcome by the notable elongation of the Na–F bond length on heating, thus leading to the large volumetric PTE. Unlike ScF3 and CaZrF6 which are insulators with a wide band gap, a relative small band gap of 3.76 eV was observed in NaSbF6. The small band gap can be attributed to the hybridization between the Sb 5s and F 2p orbitals.

•c-Axis oriented (Bi2Ba3O4−δ)b1/b2CoO2 films are prepared by a solution method.•Annealing temperature effects on microstructures and TE properties are reported.•The optimized annealing temperature is as low as 600 °C.•Transport mechanisms for (Bi2Ba3O4−δ)b1/b2CoO2 films are deeply investigated.(Bi2Ba3O4−δ)b1/b2CoO2 (BBC) thin films are prepared on LaAlO3 (001) single crystal substrates by chemical solution deposition. The annealing temperature effects on the thin film microstructures as well as transport properties are investigated. The results of X-ray diffraction, energy dispersive spectrometry and transmission electron microscopy confirm the formation of stoichiometric BBC thin films with c-axis orientation. Annealing temperature plays a very important role in determination of resistivity and Seebeck coefficient due to the variations of grain size, carrier concentration and mobility. The resistivity behaviors for the different temperature-annealed thin films obey different electrical transport mechanisms at low, medium and high measured temperature ranges. The optimized BBC thin film is annealed at 600 °C, showing a metal-insulator transition at about 100 K and the resistivity and Seebeck coefficient at 300 K is of 8.7 mΩ cm, 74.4 μV K−1, respectively. The results will provide an effective route to fabricate BBC thin films as well as a guidance for investigation about its transport properties.

Recent progress in transparent conducting components stimulates the extensive exploration of p-type transparent conducting oxide (TCO) materials. Here, we report the synthesis of a class of p-type delafossite Ag-based TCO thin films, AgCrO2 (ACO), using a facile chemical solution route in an open condition. Firstly, the evolution of microstructure, morphology, and optical properties with respect to annealing temperature is reported. The stoichiometric ACO thin films show self-assembled c-axis orientation. The 500 °C-annealed ACO thin film presents a relatively high quality, dense surface and good optical transmittance amongst all the derived thin films. Then, to improve the conductivity, Mg doping effects are investigated. Upon Mg doping, p-type conductivity is obtained for thin films of AgCr1−xMgxO2 (0.04 ≤ x ≤ 0.20). The conductivity initially increases from 3.1 × 10−3 to 67.7 × 10−3 S cm−1 with x increasing from 0.04 to 0.12 and then slightly decreases with further increasing Mg concentration. The Hall results display that the hole concentration gradually increases with increasing Mg dopant concentration, and the carrier mobility first increases with x increasing from 0.04 to 0.12, while decreases with x further increasing from 0.12 to 0.20. A high magnitude of optical transmittance near 60% in the visible region and wide optical bandgaps (3.41–3.66 eV) of the AgCr1−xMgxO2 thin films are observed. The facial fabrication of ACO thin films in an open condition will provide a start for the synthesis of Ag-based delafossite thin films.

•The field-induced effect of the magnetization indicates the strong spin-lattice coupling.•Below 35 K, the spiral spin order becomes obvious.•Gilbert damping parameter α shows an abnormal behavior due to the local lattice distortion.In this work we present a detailed magnetization, electron spin resonance (ESR) and specific capacity study on spinel MnCr2O4 single crystals in an extended temperature range of 5–300 K. The field-induced effect of the magnetization indicates the strong spin-lattice coupling in MnCr2O4 single crystal. The following results are obtained by the ESR investigation: (i) Below 35 K, since the spiral spin order, a driving force of the multiferroic (MF) effect, becomes obvious, the line shape of ESR shows asymmetric characters and the ferromagnetic resonance (FMR) model of Smit and Beljers formulation is invalid; (ii) The temperature dependence of Gilbert damping parameter α, reflecting the strength of the spin-lattice coupling, shows an abnormal behavior due to the local lattice distortion in MnCr2O4 single crystal. And the distortion is a triggering force for the formation of spiral spin order. Moreover, our research helps to understand the origin of the MF effect in MnCr2O4.Download high-res image (325KB)Download full-size image

GaNMn3/Epoxy composites were prepared by using negative thermal expansion GaNMn3 powders as the metallic filler. By increasing the loading level of GaNMn3 powders, the hardness and heat conductivity were improved comparing with that of neat epoxy. When the loading level lies in 42 vol.% - 58 vol.% for GaNMn3-0.7 μm and 26 vol.% - 43 vol.% for GaNMn3-2.3 μm, the composites present low thermal expansion (the absolute value of linear thermal coefficient is less than 10 ppm/K), weak dielectric loss (less than 0.04), and the dielectric constants exceed 25, exhibiting great potential for applications in embedded-capacitor fields.

The electronic and magnetic properties of ZrS2 nanoribbons (NRs) are investigated based on first principles calculations. It is found that the ZrS2 NRs with armchair edges are all indirect band gap semiconductors without magnetism, and the band gap exhibits odd–even oscillation behavior with the increase of the ribbon width. For the NRs with zigzag edges, those with both edges S-terminated are nonmagnetic direct band gap semiconductors, and the gap decreases monotonically as a function of the ribbon width. However, the NRs with one edge S-terminated and the other edge Zr-terminated are ferromagnetic half-metals, while those with both edges Zr-terminated tend to be ferromagnetic half-metals when the width N ≥ 9. The magnetism of both systems mainly originates from the unsaturated edge Zr atoms. Depending on the different edge configurations and ribbon widths, the ZrS2 NRs exhibit versatile electronic and magnetic properties, making them promising candidates for applications in electronics and spintronics.

Superconductivity of transition metal dichalcogenide 1T-TiTe2 under high pressure was investigated by first-principles calculations. Our results show that the superconductivity of 1T-TiTe2 exhibits very different behavior under hydrostatic and uniaxial pressure. The hydrostatic pressure is harmful to the superconductivity, while the uniaxial pressure is beneficial to the superconductivity. The superconducting transition temperature TC at ambient pressure is 0.73 K, and it reduces monotonously under the hydrostatic pressure to 0.32 K at 30 GPa, while TC increases dramatically under the uniaxial pressure along the c axis. The established TC of 6.34 K under the uniaxial pressure of 17 GPa, below which the structural stability is maintained, is above the liquid helium temperature of 4.2 K. The increase of the density of states at the Fermi level, the red-shift of the phonon density of states/Eliashberg spectral function F(ω)/α2F(ω), and the softening of the acoustic modes with pressure are considered as the main reasons that lead to the enhanced superconductivity under uniaxial pressure. In view of the previously predicted topological phase transitions of 1T-TiTe2 under the uniaxial pressure (Q. Zhang et al., Phys. Rev. B: Condens. Matter Mater. Phys., 2013, 88, 155317), we consider 1T-TiTe2 as a possible candidate in transition metal chalcogenides for exploring topological superconductivity.

•The doped Cu2+ ions are determined to be located at trigonal prism sites.•The magnetization steps are sensitive to magnetic field during cooling process.•The electrical transport properties can be well described by 1D-VRH model.•Compared to un-doped sample, the ZT of sample with x = 0.6 can be enhanced 60 times.The effect of Cu doping on the structural, magnetic, electrical and thermal transport properties of Ca3Co2-xCuxO6 single crystals has been investigated systematically. Based on the analysis of the structural parameter and x-ray photoelectron spectroscopy spectra, the valence state of Cu is considered to be +2. All samples undergo a long-range spin density wave (SDW) transition at TN and a glass-like magnetic transition at Tf with decreasing temperature. Both TN and Tf decrease monotonously with increasing Cu-doping content. A series of magnetization steps can be observed in the M(H) curve of Ca3Co2O6, and the magnetization steps are sensitive to the sample cooling magnetic field and Cu doping content x. With the increase of x, the resistivity along c-axis decreases while the thermopower increases. As a result, the figure of merit (ZT) increases considerably and the room-temperature ZT value of the sample with x = 0.6 is nearly 60 times larger than that of the un-doped crystal.Download high-res image (287KB)Download full-size image

The increase of a thermoelectric material's figure of merit (ZT value) is limited by the interplay of the transport coefficients. Here we report the greatly enhanced thermoelectric performance of a ZrS2 monolayer by the biaxial tensile strain, due to the simultaneous increase of the Seebeck coefficient and decrease of the thermal conductivity. Based on first-principles calculations combined with the Boltzmann transport theory, we predict that the band structure of the ZrS2 monolayer can be effectively engineered by the strain, and the Seebeck coefficient is significantly increased. The thermal conductivity is reduced by the applied tensile strain due to the phonon softening. At the strain of 6%, the maximum ZT value of 2.4 is obtained for the p-type doped ZrS2 monolayer at 300 K, which is 4.3 times larger than that of the unstrained system. Moreover, the temperature dependence of the ZT values is investigated, and compared with the unstrained system, the ZT values of the p- and n-type doping are much more balanced by the applied strain.

Single-phase antiperovskite nitride GeNCo3 with space group Pm3̅m is successfully synthesized by a solid–gas reaction. The crystal structure, magnetism, specific heat at low temperatures, Hall effect, and electrical and thermal transport properties are widely investigated. Exhilaratingly, a canonical spin-glass (SG) behavior is observed in GeNCo3 with a freezing temperature T0 = 79.43 K, dynamical exponent zν = 6.156, and flipping time τ0 = 5.0 × 10–12 s. The origin of the SG state in GeNCo3 is likely due to the atomic disorder introduced by the Ge vacancies. This is further proven by the measurements of Ge0.9NCo3 with more Ge deficiencies.

Mn1−xZnxCr2O4 (0 ≤ x ≤ 1) single crystals have been grown using the chemical vapor transport (CVT) method. The crystallographic, magnetic, and thermal transport properties of the single crystals were investigated by room-temperature X-ray diffraction, magnetization M(T) and specific heat CP(T) measurements. Mn1−xZnxCr2O4 crystals show a cubic structure, the lattice constant a decreases with the increasing content x of the doped Zn2+ ions and follows the Vegard law. Based on the magnetization and heat capacity measurements, the magnetic evolution of Mn1−xZnxCr2O4 crystals has been discussed. For 0 ≤ x ≤ 0.3, the magnetic ground state is the coexistence of the long-range ferrimagnetic order (LFIM) and the spiral ferrimagnetic one (SFIM), which is similar to that of the parent MnCr2O4. When x changes from 0.3 to 0.8, the SFIM is progressively suppressed and spin glass-like behavior is observed. When x is above 0.8, an antiferromagnetic (AFM) order presents. At the same time, the magnetic specific heat (Cmag.) was also investigated and the results are coincident with the magnetic measurements. The possible reasons based on the disorder effect and the reduced molecular field effect induced by the substitution of Mn2+ ions by nonmagnetic Zn2+ ones in Mn1−xZnxCr2O4 crystals have been discussed.

•Chemical doping effects on thermoelectric properties of Sn1−xMxCCo3 were systematically reported.•ZT of Sn1−xMxCCo3 can be enhanced by hole doping, while decreased by equivalent/electron doping.•Enhanced ZT is mainly due to an increased density of states near Fermi level.•Compared to other low-temperature TE systems, our optimized ZT has an advantage.We report the effects of chemical doping on thermoelectric properties of metal-based thermoelectric materials Sn1−xMxCCo3 (M = Ag, In, Ge, Pb, Sb, Te, and Bi) with antiperovskite structure. Compared to parent compound SnCCo3, both Seebeck coefficient (S) and figure of merit (ZT) can be effectively enhanced by hole doping, while a decreased S and ZT appear in equivalent- and electron-doped SnCCo3. Among all the doped samples, the maximum ZT value of 0.045(1) is obtained in Sn0.95Ag0.05CCo3, which is about 50% larger than that of parent compound SnCCo3 (ZT ∼ 0.03). This enhanced ZT is mainly attributed to the increased S induced by locally modified density of states near Fermi level. In addition, our optimized ZT value (∼0.045, at 235 K) is relatively large compared with other typical low-temperature thermoelectric materials.We systemically investigated the effects of chemical doping on thermoelectric properties of antiperovskite metal-based thermoelectric materials Sn1−xMxCCo3 (M = Ag, In, Ge, Pb, Sb), and found an enhancement of thermoelectric performance induced by hole doping.Figure optionsDownload full-size imageDownload as PowerPoint slide

In this work, we demonstrate abrupt, reversible switching of resistance in 1T-TaS2 using dc and pulsed sources, corresponding to an insulator–metal transition between the insulating Mott and equilibrium metallic states. This transition occurs at a constant critical resistivity of 7 mohm-cm regardless of temperature or bias conditions and the transition time is significantly smaller than abrupt transitions by avalanche breakdown in other small gap Mott insulating materials. Furthermore, this critical resistivity corresponds to a carrier density of 4.5 × 1019 cm–3, which compares well with the critical carrier density for the commensurate to nearly commensurate charge density wave transition. These results suggest that the transition is facilitated by a carrier driven collapse of the Mott gap in 1T-TaS2, which results in fast (3 ns) switching.

We report the synthesis, structure, and magnetic and electrical/thermal transport properties of a Cr-based antiperovskite compound PdNCr3, which crystallizes in MgCNi3-type cubic structure (space group Pmm, No. 221). Interestingly, the spin-glass (SG) behavior, which is confirmed by the corresponding characteristic parameters (the freezing temperature T0 = 61.4(2) K, the dynamical exponent zν = 7.103(3), and the flipping time τ0 = 2.714(2) × 10−11 s), is observed in PdNCr3. Furthermore, the value of the Sommerfeld–Wilson ratio (RW ∼ 1.024(3)) for PdNCr3 is much smaller than those of cluster glass systems (RW > 100) and Kondo cluster glass systems (RW = 20–30), indicating that PdNCr3 is a canonical SG system. Density functional theory calculation shows that the origin of SG in PdNCr3 is attributed to the disordering located N vacancies, which is further confirmed by the measurement of sample PdN0.75Cr3 with more N deficiency. On the other hand, infrequently, the zero-field-cooled exchange bias (ZFC-EB) with an exchange bias field (HE) of about 350 Oe is observed after zero-field cooling from an unmagnetized state in PdNCr3. The values of HE are found to depend strongly on temperature and measuring magnetic field. For PdNCr3, the ferromagnetic unidirectional anisotropy, which is the origin of our ZFC-EB effect, is formed around the ferromagnetic–SG interface isothermally during the initial magnetization process below the blocking temperature. In addition, the training effect of ZFC-EB in PdNCr3 is observed after the zero-field cooling process and has been explained well in terms of the spin configurational relaxation model.

We report the superconductivity of CaSn3 single crystals with a AuCu3-type structure, namely cubic space group Pmm. The superconducting transition temperature TC = 4.2 K is determined by the magnetic susceptibility, electrical resistivity, and heat capacity measurements. The magnetization versus magnetic field (M–H) curve at low temperatures shows a typical-II superconducting behavior. The estimated lower and upper critical fields are about 125 Oe and 1.79 T, respectively. The penetration depth λ(0) and coherence length ξ(0) are calculated to be approximately 1147 nm and 136 nm by the Ginzburg–Landau equations. The estimated Sommerfeld coefficient of the normal state γN is about 2.9 mJ mol−1 K−2. ΔC/γNTC = 1.13 and λep = 0.65 suggest that the CaSn3 single crystal is a weakly coupled superconductor. Electronic band structure calculations show a complex multi-sheet Fermi surface formed by three bands and a low density of states (DOSs) at the Fermi level, which is consistent with the experimental results. Based on the analysis of electron–phonon coupling of AX3 compounds (A = Ca, La, and Y; X = Sn and Pb), we theoretically proposed a way to increase TC in the system.

Preparation of antiperovskite thin films is challenging work due to their complex phase diagram and easy decomposition during processing, which hinder the fundamental studies and applications. Herein, we report the preparation of antiperovskite CuNCo3 (CNC) thin films on several different single crystal substrates by chemical solution deposition. The results show that the derived CNC thin films are c-axis oriented regardless of the substrate orientation, suggesting the self-assembled c-axis orientation. The microstructures as well as the physical properties are investigated, showing that the CNC thin films are metallic and can be considered as a new type of soft-magnet with a ferromagnetic Curie temperature higher than 650 K. The results will provide an effective route for fabricating antiperovskite cobalt-based thin films as well as provide a prototype for the investigation of the growth mechanisms of complex metal nitride thin films by solution methods.

Weak ferromagnetism arising from uncompensated surface spins (USS) is usually expected when an antiferromagnetic (AFM) material is diminished to nanoscale in size. Here we report strong ferromagnetism beyond the USS-mechanism in the AFM ground state of nanocrystalline GaCMn3. The enhanced ferromagnetism can be attributed to an AFM to ferromagnetic (FM) transformation in the shell with a finite thickness of a crystallite. As the average crystallite size (<D>) decreases, the FM shell expands relative to the AFM core, leading to strengthening ferromagnetism. Through the AFM/FM interface the rotation of FM spins under a magnetic field is impeded by the AFM spins, leading to a large coercivity (HC). The largest HC (∼6.4 kOe at 5 K) was observed in the sample with a critical <D> of ∼15 nm. In contrast, USS-type weak ferromagnetism was observed in nanocrystalline GaNMn3. Our results suggest a new approach to achieving strong FM order beyond the prediction of the USS mechanism, as well as to designing AFM-core/FM-shell nanostructures based on nanosized AFM materials.

•A new series of layered oxyselenides Nd2(Fe1−xMnx)2Se2O3 has been synthesized.•They crystallize in the layered tetragonal structure with I4/mmm space group.•They are semiconductors with polaronic transport type.•The parent compound shows a frustrated antiferromagnetic (AFM) ground state.•The intermediate alloys show a rich magnetic phase diagram.A new series of layered oxyselenides Nd2(Fe1−xMnx)2Se2O3 (0 ⩽ x ⩽ 0.5) was synthesized via solid state reaction method. Their structure and properties were investigated by the X-ray powder diffraction, magnetic bulk, electrical and thermal transport measurements along with specific heat experiments. The compounds crystallize in the layered tetragonal structure with I4/mmm space group and show semiconducting behavior. The large discrepancy between activation energy for conductivity, Eρ (0.153–0.177 eV), and thermopower, ES (7.0–14.8 meV), indicates the polaronic transport mechanism. Heat capacity and bulk magnetization indicate an increased ferromagnetic component of the long-range magnetic order and possible increased degree of frustration. Atomic disorder on Fe/Mn sites suppresses the temperature of the long-range order whereas intermediate alloys show a rich magnetic phase diagram.

Thermoelectric properties of the Ca3Co4O9 system have been enhanced through an exotic route: Na doping at Co site, namely misplaced substitution. To compare, we have also performed the research of Na doping at Ca site and Co vacancy. In view of the analysis of XRD, XPS, and Raman data, Na+ ions could be suggested to enter into Co sites of [CoO2] layers in Ca3Co4–xNaxO9 (x = 0, 0.05, 0.10) and Ca sites of [Ca2CoO3] layers in Ca2.90Na0.10Co4O9, respectively. And Co ions are omitted from [CoO2] layers in Ca3Co3.90O9. Among all samples, Ca3Co3.90Na0.10O9 shows the maximum ZT value, which at room temperature reaches to ∼0.0117. Such a value is about 150% larger than that of Ca3Co4O9 and 63% larger than that of Ca2.90Na0.10Co4O9. The results indicate that the misplaced substitution is more beneficial to enhance the thermoelectric performance of Ca3Co4O9 system, compared with the traditional idea with Na doping at Ca site. Such an enhancement is mainly attributed to the combined action of electronic correlation, locally modified band structure near Fermi level, and carrier concentration.

Epitaxial antiperovskite superconducting CuNNi3 thin films have been grown by chemical solution deposition. The film is a type II superconductor and shows a Tc of 3.2 K with a transition of 0.13 K. The Hc2(0) and ξ0 are estimated to be 8.1 kOe and 201 Å, respectively.

Transparent conducting p-type Bi2Sr2Co2Oy thin films have been first grown on SrTiO3 substrates by a chemical solution deposition, showing c-axis self-orientation. The figure of merit can reach as high as 800 MΩ−1, which is the highest value for p-type transparent conducting thin films by solution methods.

We report the magnetic, electrical, and thermoelectric properties of SnCCo3, where good thermoelectric performance [figure of merit ZT ∼ 0.035(2), 258 K] and strong electron correlation (Kadowaki–Woods ratio RKW ∼ 4a0) are observed. The thermoelectric properties of ACCo3 (A = Al, Ga, Ge) and SnCM3 (M = Mn, Fe) were also investigated for comparison. As a result, the ZT value of SnCCo3 is the largest among all of those samples, which is mainly attributed to the large Seebeck coefficient caused by the strong electron correlation and low carrier density. Moreover, the ZT value can be effectively enhanced by proper chemical doping in SnCCo3.

•The copper-deficiency increases when Co is substituted by Mn.•The doping of Mn introduces the FM interaction in the Co/MnO2 planes.•The competition of AFM and FM results in the appearance of the SG state.•The coexistence of AFM order and SG state is observed.We have synthesized and investigated the magnetic properties of the layered oxyselenides Sr2Co1−xMnxO2Cu2−δSe2 (0 ⩽ x ⩽ 1). They crystallize in an unusual intergrowth structure with Cu2Se2 and (Co,Mn)O2 layers separated by Sr ions. The refinement of the X-ray diffraction data reveals an increase in the copper-deficiency when Co is substituted by Mn, which is caused by oxidization of Mn2+ ions. The antiferromagnetic (AFM) transition temperature (TN) shifts to lower temperature and the dominant in plane interaction changes from AFM to ferromagnetic (FM) with Mn doping. The coexistence of AFM order and SG state is observed for compositions with 0.25 ⩽ x ⩽ 0.5.

CrN thin films are first prepared by a facile chemical solution deposition method. The results show that the derived CrN thin films are nanocrystalline with the grain size of 30–60 nm. X-ray photoelectron spectroscopy measurement shows the stoichiometry of the derived thin film. The temperature dependent resistivity within the range of 2–300 K shows a semiconductor-like behavior with dρ/dT < 0 and a discontinuity in resistivity at 253 K is observed due to the antiferromagnetic transition. At 10 K the magnetoresistance is as low as −0.06% under 45 kOe. The first growth of CrN thin films by the facile chemical solution deposition will provide an alternative route to prepare CrN thin films, especially for large-area CrN thin films with low-cost.

In this work, BiFeO3 (BFO) thin films were prepared on metallic Ni (200) tapes with and without a La0.5Sr0.5TiO3 (LSTO) buffer layer at different temperatures by chemical solution deposition. The effects of the annealing temperature as well as the LSTO buffer layer on the dielectric, leakage and ferroelectric properties have been studied in detail. The crystallite size, dielectric constant and leakage current density increase, while the coercive field decreases with increasing annealing temperature. The BFO thin films deposited directly on the Ni tapes are prone to wrinkling, while the wrinkles are smoothed by introducing a thin LSTO buffer layer. Decreased compressive microstrain as well as improved ferroelectric and leakage properties are observed in the BFO thin films deposited on the LSTO buffered Ni tapes. The results will provide an instructive route to optimize BiFeO3-based thin films on metallic tapes by chemical solution deposition methods.

•Polycrystalline samples of GeCr3, GeCCr3, and GeNCr3 are synthesized by using solid state reaction method.•A good quality of our samples is verified by the Rietveld refinement and electrical transport measurement.•We present a comprehensive understanding of physical properties of GeCr3, GeCCr3, and GeNCr3.We report the synthesis of GeCr3, GeCCr3, and GeNCr3 polycrystalline compounds, and present a systematic study of this series by the measurements of X-ray diffraction (XRD), magnetism, electrical/thermal transport, specific heat, and Hall coefficient. Good quality of our samples is verified by quite small value of residual resistivity and considerably large residual resistivity ratio. Based on the Rietveld refinement of XRD data, the crystallographic parameters are obtained, and, correspondingly, the sketches of crystal structure are plotted for all the samples. The ground states of GeCr3, GeCCr3, and GeNCr3 are paramagnetic/antiferromagnetic metal, and even a Fermi-liquid behavior is observed in electrical transport at low temperatures. Furthermore, the analysis of the thermal conductivity data suggests the electron thermal conductivity plays a major role in total thermal conductivity for GeCr3 at low temperatures, while the phonon thermal conductivity is dominant for GeCCr3 and GeNCr3 at high temperatures. The negative value of Seebeck coefficient and Hall coefficient indicate that the charge carriers are electron-type for GeCr3, GeCCr3, and GeNCr3.

The effect of Ca-doping on the structural, magnetic, electrical, and thermal transport properties has been investigated in Dy1−xCaxVO3 (0 ⩽ x ⩽ 0.2) ceramics. Substituting Ca2+ for Dy3+ leads to a shrinkage of lattice due to the introduction of V4+ with a smaller ionic radius. The parent compound DyVO3 undergoes three spin/orbital ordering (OO/SO) transitions with decreasing temperature at TOO, TSO1 and TSO2, respectively. Increasing the doping level of Ca decreases TSO1, the magnetization above TSO1 and below 50 K, whereas increases TSO2, indicating the Ca-doping has a suppressing effect on the ordering state in DyVO3 system. The thermopower of DyVO3 decreases sharply near TOO while it is not observed in the Ca-doped samples. The result shows that the x = 0.05 Ca-doping is sufficient to melt the OO state in DyVO3 system. Both the thermopower and resistivity decrease significantly with increasing the Ca-doping content. The decreased thermopower is suggested to originate from the combined effect of the increased carrier concentration and decreased spin/orbital degeneracies.Highlights► Combined effect of orbital entropy and carrier concentration on thermopower. ► Ca-doping effect on the ordering states of DyVO3. ► Composition dependent magnetization, resistivity, thermopower and thermal conductivity.

•The effects of Mn doping on physical properties of ZnCFe3−yMny were reported.•The effects of dual doping on physcial properties of ZnC1−xNxFe3−2xMn2x werereported.•The magnetocaloric working temperature is around 300 K for ZnC0.5N0.5Fe2Mn.•The magnetic entropy change and RCP are 2.86 J/kg K and 220 J/kg for ZnC0.5N0.5Fe2Mn.In this paper we report the effects of Mn substitution on the structural and magnetic properties of ZnCFe3−yMny (0 ⩽ y ⩽ 1). It is found that with increasing the doping level y the increased lattice constant, enhanced Curie temperature (TC), and decreased saturated magnetization (MS) are obtained. However, the enhancement of TC (>380 K) in ZnCFe3−yMny is not suitable to explore room-temperature magnetocaloric material. Therefore, we carry out a dual doping by N and Mn on C and Fe sites of ZnCFe3, respectively. As a result, with increasing x the lattice parameter increases while the TC and MS decrease gradually for ZnC1−xNxFe3−2xMn2x (0 ⩽ x ⩽ 1). In particular, for ZnC0.5N0.5Fe2Mn (x = 0.5) the TC (∼302 K) is tuned just at the room temperature. Correspondingly, around the TC of ZnC0.5N0.5Fe2Mn the magnetocaloric effect is considerably large with a magnetic entropy change of 2.86 J/kg K (ΔH = 4.5 T) as well as a relative cooling power (RCP) of 220 J/kg (ΔH = 4.5 T). Given the considerably large RCP, inexpensive and innoxious raw materials, and suitable operating temperature, ZnC0.5N0.5Fe2Mn is suggested to be a promising candidate for room-temperature magnetic refrigeration.

•Valence state of doped Sb ions is variational as Sb-doping level increases.•The spin-density-wave state is more stable in the Sb-doped samples.•The ZT value of Ca3Co3.90Sb0.10O9 is two times larger than that of Ca3Co4O9.•Sb-doping may be effective to improve thermoelectric performance of Ca3Co4O9.The structure, magnetic, electrical and thermal transport properties of Ca3Co4−xSbxO9 (0 ⩽ x ⩽ 0.2) have been investigated systematically. Base on the analysis of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), the valence state of the doped Sb ions is suggested to be +3 in the x = 0.05 sample, and its content increases monotonously along with the gradual introduction of Sb5+ ions as x further increases. The resistivity and the metal–insulator-transition temperature increase with increasing x, indicating the more stable spin-density-wave state in the Sb-doped samples. The thermopower decreases first as x = 0.05, and then increases monotonously with increasing x till to 0.15. The thermal conductivity decreases obviously due to Sb-doping. As a result, the Ca3Co3.90Sb0.10O9 sample has the largest thermoelectric figure-of-merit ZT value of 0.012 at room temperature, which is about two times larger than that of Ca3Co4O9. The results are suggested to originate from the variations of carrier concentration and electronic correlation via Sb-doping with the different valence states.

We have synthesized a series of layered cobaltite Bi2Sr2−xCaxCo2Oy (0≤x≤0.3). Reduced resistivity was observed with x≤0.2 due to the possible chemical pressure induced charge transfer between the Bi2Sr2O4 layer and CoO2 layer. Enhanced thermoelectric power S was also observed in the Ca-doped samples with the largest S as for x=0.2. The variation of S(T) could reflect the change of electronic correlation or the modification of local density of states and band structure near the Fermi energy. In addition, magnetic measurements show that the samples with x=0.0 exhibit abnormal and abrupt changes, revealing a possible thermally excited spin-state transition. It is found that the thermoelectric performance is obviously enhanced by the low Ca-doping.Highlights► Reduced resistivity was observed in low Ca-doped Bi2Sr2Co2Oy. ► Enhanced thermopower and ZT was observed in low Ca-doped Bi2Sr2Co2Oy. ► A possible thermally excited spin-state transition was found in Bi2Sr2Co2Oy.

We present the structure, magnetization, and resistivity results of the spinel Al-doped MnV2O4. When small amount of Al ions substitutes V ones, the structural transition accompanying orbital order of MnV2O4 disappears. With further Al doping, the paramagnetic–ferrimagnetic transition temperature TC increased firstly and then decreased. The magnetic phase diagram is discussed in terms of the competition among the lattice shrinkage and the non-magnetic substitution aroused by Al3+ ions doping and the different degree of freedoms of lattice, spin and orbit in Mn(V1−xAlx)2O4. We also study the resistivity of these samples and find that the doping of Al ions does not change the electric transport mechanism, but increases the difficulty of electron hopping as shown in the obvious increasing of the activation energy.Highlights► Doping effect of the V3+ ions by Al3+ ions in MnV2O4 is systematically studied. ► The orbital order of V3+ ions is gradually broken by orbital quenched Al3+ ions. ► Construct a magnetic phase diagram for different Al-doped MnV2O4. ► The doping of Al3+ ions increases the difficulty of electron hopping.

The effects of Rh doping on the structural, magnetic, electrical, and thermal transport properties of Ca3Co4–xRhxO9 (0 ≤ x ≤ 0.4) samples have been investigated systematically. XRD and XPS results show that the doped Rh ions are in the form of Rh3+. Only a metal–insulator transition (MIT) and an anomaly of the slope related to the transition from a Fermi liquid to an incoherent metal at low temperatures were observed in the resistivity curve for the undoped sample. As Rh ions were doped into the samples, an additional anomaly and MIT occurred in the resistivity curve near room temperature, which are suggested to originate from the spin-state transition (SST) of Co ions. The low-temperature MIT temperature increased with increasing Rh-doping content, indicating that the spin-density-wave state became stable as a result of the enhanced random Coulomb potential in CoO2 octahedral block layers induced by Rh substitution. Based on an analysis of the thermopower and XPS data, Rh3+ ions are suggested to substitute at the Co3+ sites of CoO2 layers. The substitution induced a partial SST of Co4+ ions from the low-spin to the high-spin state, leading to the formation of a spin-state polaron. The evolution of the electrical and magnetic properties with Rh doping is summarized in a single phase diagram for Ca3Co4–xRhxO9. It should be noted that the thermopower of the system did not change obviously with Rh doping, but the thermal conductivity decreased significantly. As a result, the ZT value increased markedly with increasing Rh-doping content. The ZT value at room temperature for Ca3Co3.6Rh0.4O9 reached 0.014, which is about 2.4 times larger than that of Ca3Co4O9. The results show that Rh doping might be an effective route to improving the thermoelectric performance of the Ca3Co4O9 system.

Single-phase Bi0.85La0.15FeO3 ceramics were synthesized under various magnetic fields (Ha=0 T, 3 T, 5 T). Substantially reduced leakage current and hence modified ferroelectric (FE) properties were obtained with magnetic field annealing (MA). The largest magnetization and lowest leakage current with large FE polarization (Pr∼33 μC/cm2) were found in the sample annealed with Ha=3 T. Great changes were also observed in the Raman spectra. All the observed features originate mainly from the different FE domain wall structures induced by MA. These results demonstrate that MA is an effective way to tune the multiferroic and magnetoelectric properties in BiFeO3-based materials.Graphical abstractBright field TEM micrograph of the representative domain structures in the samples (a) BLF0, (b) BLF3 and (c) BLF5.Highlights► Bi0.85La0.15FeO3 ceramics were synthesized under various magnetic fields. ► Substantially reduced leakage current with improved ferroelectricity were obtained. ► Enhanced magnetization with moderate annealing magnetic field

The electron paramagnetic resonance (EPR) properties of the electron-doped manganite La1−xTexMnO3 (0.1 ≤ x ≤ 0.2) are investigated based on the data of EPR spectra, resistivity, and magnetic susceptibility. With decreasing temperature from 400 K, the EPR linewidth ΔHPP decreases and passes through a minimum at Tmin, then substantially increases with further decreasing temperature. The broadening of the EPR linewidth above Tmin can be understood in terms of the increase in the relaxation rate of spin of eg polarons to the lattice with increasing temperature due to the similarity between the temperature dependence of the linewidth ΔHpp(T) and the conductivity σ(T). For the samples with x = 0.1 and 0.15, the conductivity activation energy Eσ is comparable with the activation energy Ea deduced from the linewidth. Whereas for the x = 0.2 sample, there is a large difference between Eσ (0.2206 eV) and Ea (0.0874 eV).

ZnO:Al thin films were prepared on n-type (1 0 0)-oriented Si and glass slide substrates by chemical solution deposition method. The effects of Al content, the annealing temperature in air, the annealing temperature in reducing atmosphere and the solution concentration on the structural, morphological, electrical and optical characteristics have been investigated systematically. The results show that the processing parameters play an important role in the microstructures as well as the properties. The lowest resistivity value (0.091 Ω cm) was observed by optimization of the processing parameters.

RMoO4 (RMO, R = Ca, Sr, Ba) films were fabricated on LaAlO3 (LAO) substrates using chemical solution deposition method. The derived RMO films are highly (00l)-orientated with good crystallization. The photoluminescence (PL) emission spectra show that the CaMoO4 (CMO) and SrMoO4 (SMO) films have an intrinsic broad green emission band centered at 500 nm whereas BaMoO4 (BMO) film has a broad orange emission band resulting from the PL of molybdate group with an oxygen ion deficiency. The highly (00l)-oriented CMO film on LAO has better PL property than that of CMO film on Si substrate, which is ascribed to higher crystalline integrity and lower light scattering.

2H-Ni0.02TaSe2 single crystals were successfully grown via the iodine vapor transport technique. The typical dimension of the crystal is about 3×2×0.5 mm3. Compared with the parent compound 2H-TaSe2 with a superconducting transition temperature TC=0.14TC=0.14 K, the electronic transport, specific-heat and magnetization results indicate that the superconductivity of the Ni0.02TaSe2 single crystal is obviously enhanced (TC=2.79TC=2.79 K). In addition, it is found that the incommensurate charge-density-wave (ICDW) disappears while the commensurate charge-density-wave (CCDW) shifts to about 96.2 K with the intercalation of a little of Ni. It clearly indicates that there is a competition between superconductivity (SC) and charge-density-wave (CDW) order for 2H-TaSe2 system and that between SC and ICDW is more drastic.

Nickel–zinc (Ni–Zn) ferrite Ni0.7Zn0.3Fe2O4 thin films were fabricated on Si(0 0 1) substrate by a simple chemical method. The microstructure and magnetic properties were systematically investigated. X-ray diffraction results show that all samples have a single-phase spinel structure with the space group of Fd3¯m. The results of field-emission scanning electronic microscopy show that the mean grain size increases from 10 to 32 nm with increasing the annealing temperature from 500 to 900 °C. The magnetic properties of Ni0.7Zn0.3Fe2O4 ferrite thin films exhibit a strong dependence on the annealing temperature. The coercivity increases from 25 to 80 Oe and the saturation magnetization increases from 146 to 283 emu/cm3 with increasing the annealing temperature, which is in favor of modern electronic device miniaturization.

Structural, magnetic, and transport properties of the compounds Bi0.3Ca0.7Mn1−xVxO3 with 0 ≤ x ≤ 0.1 have been experimentally investigated. This substitution introduces non-magnetic dopant V5+(3d04S0, S = 0) in the Mn–O–Mn network, which results in the variation of the Mn3+/Mn4+ ratio. It is suggested that Mn4+ ions are substituted by V5+ ions, which gives rise to the increase of Mn3+ ions. The electronic transport and magnetization results show that the temperature of charge ordering increases with increasing V-doping content. In addition, for all the samples, the temperature of resistivity in the temperature range above the charge ordering transition can be described by the adiabatic hopping of small polaron model, whereas below the charge ordering transition, Mott's variable range hopping mechanism is seen to be valid. The enhanced charge ordering caused by V-doping is suggested to originate from the enhanced Jahn–Teller distortion of the MnO6 octahedrons due to increased Mn3+ ions.

Single phase CuAlO2 thin films were first successfully prepared on (0 0 0 1) sapphire substrates by chemical solution deposition method. Additionally, in order to improve the transmittance and conductivity of single phase CuAlO2 thin films, effects of citric acid as additive on phase structure, morphology and optical–electrical property of CuAlO2 thin films were investigated. Appropriate contents of citric acid do not inhibit the formation of single phase CuAlO2 thin films, and are also in favor of improvement of transmittance. Excessive citric acid not only introduces secondary phases, but also deteriorates the quality of the film surface. The mean transmittance in visible region is approximately 50% in the film prepared with 5 unit contents of citric acid and its direct and indirect optical band gaps are 3.24 eV and 1.8 eV, respectively. The films with or without citric acid behave like semiconductors. The resistivity and the activation energy of the film prepared with 5 unit contents of citric acid are evaluated as 2.5 × 102 Ω cm at 290 K and 300.5 meV, respectively.

Mn-substituted Bi0.8Ca0.2FeO3 ceramics Bi0.8Ca0.2Fe1−xMnxO3 (0 ≤ x ≤ 0.5) were synthesized by a solid-state reaction method. Powder X-ray diffraction investigations performed at room temperature show that the crystal structure is rhombohedral for x ≤ 0.1 and orthorhombic for 0.2 ≤ x ≤ 0.5. Compared to the undoped Bi0.8Ca0.2FeO3 compound, enhanced magnetization and electric polarization were observed in the samples with x ≤ 0.1. A further increase in the magnetization with increasing x took place in the samples with 0.2 ≤ x ≤ 0.5. All the Mn-substituted samples studied are basically antiferromagnetic accompanied by the appearance of weak ferromagnetism, which is similar to the BiFeO3 compound. The conductivity of the samples with x ≥ 0.3, measured between 140 and 380 K, is of the semiconducting type.

La0.7Sr0.3MnO3 (LSMO) and SrFe12O19 (SFO) samples were synthesized by chemical coprecipitation method. The composites of (1 − x)LSMO:xSFO (x is mass%) were prepared using solid-state cosintering. The microstructure, electrical transport, and magnetic properties of the derived composites were systematically investigated. Compared with pure LSMO, the enhancement of low-field magnetoresistance (LFMR) is observed in the composites. The magnetoresistance (MR) value at 300 K for the sample with x = 0.05 is about 2.9 times larger than that of the pure LSMO. The enhanced MR was attributed to the enhanced spin-dependent intergrain tunneling at the interfaces and grain boundaries due to the enhanced magnetic disorders and antiferromagnetic (AFM) couplings near boundaries between LSMO and SFO grains.

The magnetocaloric effect and the critical behavior of La2NiMnO6 are investigated by measurement of the magnetization around TCTC. The magnetic entropy change |ΔS||ΔS| of La2NiMnO6 for a field change of 0–45 kOe near the Curie temperature is about 5% of the theoretical expectation. The critical behavior of the La2NiMnO6 deviates from the mean field theory. These abnormal phenomena are understood in the context of the strong spin–phonon coupling in La2NiMnO6. It is suggested that a method of modulating this coupling would enhance the magnetic entropy change greatly, which makes the La2NiMnO6 a promising candidate for room-temperature magnetic refrigeration.

Superconductivity was discovered in a Ni0.05TaS2 single crystal. A Ni0.05TaS2 single crystal was successfully grown via the NaCl/KCl flux method. The obtained lattice constant cc of Ni0.05TaS2 is 1.1999 nm, which is significantly smaller than that of 2H–TaS2 (1.208 nm). Electrical resistivity and magnetization measurements reveal that the superconductivity transition temperature of Ni0.05TaS2 is enhanced from 0.8 K (2H–TaS2) to 3.9 K. The charge-density-wave transition of the matrix compound 2H–TaS2 is suppressed in Ni0.05TaS2. The success of Ni0.05TaS2 single crystal growth via a NaCl/KCl flux demonstrates that NaCl/KCl flux method will be a feasible method for single crystal growth of the layered transition metal dichalcogenides.

Sr2FeMoO6 samples with different grain sizes were prepared by the sol–gel method. X-ray diffraction (XRD) patterns and field-emission scanning electron microscopy (FE-SEM) of the Sr2FeMoO6 samples show that the samples are in the nanometer range. The average grain sizes DD for these samples are 34.5, 39.7 and 44.3 nm, increasing with the sintering temperature. The transport measurements show that the Sr2FeMoO6 samples behave like semiconductors at low temperatures, dominated by the carrier scattering at the grain boundaries (GBs). And the resistivities of the samples are 1.6, 1.2 and 0.5 mΩ cm at 10 K, respectively, increasing with decreasing grain size. The temperature dependences of the magnetization and resistance clearly demonstrate the coexistence of ferromagnetic metal and antiferromagnetic (or paramagnetic) insulator, which is believed to induce a metal–insulator transition at the Curie temperature (TC)(TC).

High-quality cc-axis-oriented La2/3Sr1/3MnO3−δ (LSMO) films have been grown directly on Si(001) wafers by DC-magnetron sputtering without prechemical treatment of the substrate surface. The highly-oriented films have flat surface morphology and bean-like grains on the surface. It is suggested that self-assembly growth may be the intrinsic growth mechanism of these cc-axis-oriented LSMO films on Si. The magnetic and electrical transport properties are measured and it is found that there exists a large low-field magnetoresistance (LFMR) over a wide temperature range down to 5 K, which is attributed to spin-dependent scattering at grain boundaries in the films.

The compound In0.95CNi3 has been synthesized and the basic properties have been investigated. It has the typical antiperovskite structure (space group Pm3m  , lattice parameter 3.7836 Å). The electronic specific coefficient γγ and Debye temperature ΘDΘD are found to be 14.1 mJ/mol K2 and 372 K, respectively. It behaves as a ferromagnetic metal below the Curie temperature (577 K). The emergence of ferromagnetism is suggested to originate from the deviation of the Ni/In atomic ratio from the ideal stoichiometry. The possible mechanisms have been discussed in detail in terms of this deviation.

Systematic studies of the structural, transport, magnetic and specific heat behavior have been performed on the perovskite molybdates SrMo1−xNixO3 (0.02≤x  ≤0.08). Ni doping at the Mo site does not change the structure of all samples, but increases the lattice parameter aa monotonically. All of the doped samples keep their metallic behavior. The magnetic properties keep a Pauli paramagnetism in the high-temperature region, but have a ferromagnetic (FM) transition at about 50 K. The resistivity, ρρ, and magnetic susceptibility, χχ, increase, while the electronic specific heat coefficient, γeγe, decreases monotonically with the increase of Ni doping content, xx. The electronic transport of all samples shows a T2T2 dependence in the low-temperature region and a TT dependence in the high-temperature region, respectively. The temperature dependence of the specific heat can be well described by the formula Cp(T)/T=γe+βpT2Cp(T)/T=γe+βpT2 in the low-temperature range. These behaviors can be explained by the competition between the decrease in the density of states (DOS) at the Fermi level and the electron localization due to the disorder effect induced by the random distribution of Ni at the Mo site in the samples.

Polycrystalline Si1−xMnx (x=0.005x=0.005, 0.01, and 0.015) samples were prepared by the arc-melting method. Powder x-ray diffraction analysis demonstrates that the light Mn doping does not change the crystalline structure of silicon. Magnetic studies reveal that the ferromagnetism can be developed in all Mn-doped samples and the Curie temperature (TC)(TC) increases with increasing Mn doping content xx. The effective magnetic moments are 4.15, 4.05μB/Mn for the samples with x=0.01x=0.01 and 0.015, respectively. The undoped sample shows semiconducting behavior in the whole studied temperature range, whereas a metal–insulator transition can be observed near TCTC for all doped samples. The thermally activated conducting mechanism dominates the low temperature transport properties of the doped samples. The activation energy obtained from the fitting decreases monotonously with increasing xx. In addition, the anomalous Hall effect below TCTC was observed from the magnetic field dependence of the Hall resistivity curves.

The effect of Cu-doping at Mo-site on structural, magnetic, electrical transport and specific heat properties in molybdates SrMo1−xCuxO3 (0≤x≤0.2) has been investigated. The Cu-doping at Mo-site does not change the space group of the samples, but decreases the structural parameter a monotonously. The magnetic properties change from Pauli-paramagnetism for x=0 to exchange-enhanced Pauli-paramagnetism for x=0.05 and 0.10, and then ferromagnetism for x=0.15 and 0.20. All samples exhibit metallic-like transport behavior in the whole temperature range studied. The magnitude of resistivity increases initially to x=0.10 and then decreases with increasing Cu-doping concentration. The results are discussed according to the electron localization due to the disorder effect induced by the random distribution of Cu at Mo site in the samples. In addition, the temperature dependence of specific heat for the Cu-doped sample has also been studied.

Systematic studies of resistivity, thermoelectric power, and thermal conductivity have been performed on polycrystalline bilayered manganites LaSr2Mn2−xCrxO7 (0≤x≤0.2). It is found that the temperature dependence of both Seebeck coefficient S(T) and resistivity ρ(T) in the high temperature region follows the small polaron transport mechanism for all the samples. But in the low temperature region, variable-range-hopping (VRH) model matches the experimental data better. In addition, the maximum of absolute S(T) at low temperatures is gradually suppressed for the sample with Cr-doping level of x>0.04, implying that a new FM order probably arises. With decreasing the temperatures further, S(T) has a sign change and becomes positive for the sample with Cr-doping level of x>0.04, indicating that there may occur a variation of the type of charge carrier. As to thermal conduction κ(T), the low-temperature peak is suppressed due to Cr-doping. The variation of κ(T) is analyzed based on the combined effect due to the suppression of local Mn3+O6 Jahn–Teller (JT) lattice distortion because of the substitution of Cr3+ ions for Mn3+ ions, which results in the increase in thermal conduction, and the introduction of the disorder due to Cr-doping, which contributes to the decrease in thermal conduction.

The magnetization, resistivity ρ, thermoelectric power (TEP) S, and thermal conductivity κ in perovskite cobalt oxide Gd0.7Sr0.3CoO3 have been investigated systematically. Based on the temperature dependence of susceptibility χg(T) and Seebeck coefficient S(T), a combination of the intermediate-spin (IS) state for Co3+ and the low-spin (LS) state for Co4+ can be suggested. A metal–insulator transition (MIT) caused by the hopping of σ* electrons (localized or delocalized eg electrons) from the IS Co3+ to the LS Co4+ is observed. Meanwhile, S(T) curve also displays an obvious phonon drag effect. In addition, based on the analysis of the temperature dependence of S(T) and ρ(T), the high-temperature small polaron conduction and the low-temperature variable-range-hopping conduction are suggested, respectively. As to thermal conduction κ(T), rather low κ values in the whole measured temperature range is attributed to unusually large local Jahn–Teller (JT) distortion of Co3+O6 octahedra with IS state.

The effect of Pr-doping on structural, electronic transport, magnetic properties in perovskite molybdates Sr1−xPrxMoO3 (0≤x≤0.15) has been investigated. The Pr-doping at Sr-site does not change the space group of the samples, but decreases the lattice parameter a. The magnitude of resistivity ρ increases initially (x≤0.08) and then decreases with further increasing Pr-doping level x and ρ(T) behaves as T2 and T dependence in the low-temperature range blow T* and high-temperature range of 150 K