•Series NiTex nanorods with excellent crystallinity were synthesized.•NiTe exhibits paramagnetic behavior.•While NiTe2 change from diamagnetism to paramagnetism at 57.8 K•Te atoms enhance the diamagnetism and reduce the transition temperature.NiTex nanorods (x = 1.00, 1.15, 1.33, 1.60, 1.80, 2.00) with average diameter of 150 nm have been selectively synthesized by a simple hydrothermal process. The nanorods with various x share similar hexagonal structure and morphology. NiTe nanorods present paramagnetic property at both high and low temperature while NiTe2 nanorods exhibit a diamagnetic characteristic at high temperature and a paramagnetic behavior below 58 K. The magnetic moment reduces with the increase in tellurium content. The difference in magnetic behaviors of NiTex nanorods is mainly attributed to the competition between the diamagnetism and paramagnetism based on the experimental observation.Download high-res image (81KB)Download full-size image

A multifunctional material, Na2Fe2Ti6O16 (NFTO), was synthesized via a simple hydrothermal method for the first time. NFTO nanosheets with a long hexagonal plate shape enjoy double absorption, high magnetic moment and strong adsorption. The magnetic property allows for the convenient collection of the NFTO adsorbent from aqueous solution during recycling and double absorption in the visible-light region could be applied in visible-light harvesting. The double absorption and magnetic property originate from the d–d transitions of Fe3+, due to the effect of the crystal field. The adsorption process was evaluated by a methylene blue removal experiment and was found to have good agreement with the pseudo-second-order kinetics model and Langmuir isotherm. The NFTO nanosheets exhibit excellent recyclability, a high kinetic adsorption rate and a maximum adsorption capacity of 165.8 mg g−1 at equilibrium pH. These results are greatly significant for multifunctional NFTO as a promising adsorbent material used in water purification.

Direct magnetoelectric (DME) and converse magnetoelectric (CME) effects are two opposite processes in magnetoelectric (ME) materials. An ME theoretical model about the longitudinal vibration was proposed to research their relationships in a laminate composite based on equivalent circuit. Following the piezoelectric and magnetostrictive constitutive equations, we deduced magnetic-mechanical-electric equations, and then built a symmetric equivalent circuit about the ME coupling, based on which we analyzed the CME and DMD effects equivalently. A simple laminate composite was prepared by bonding Terfenol-D and Pb(Zr,Ti)O3 plates together for a experimental research. Theoretical calculations meet the experimental results very well. The CME and DME effects exhibit enhanced energy transitions at the resonance frequency with a large phase shift of about π. The ME composite shows CME and DME frequency multiplying behaviors and inhomogeneous CME and DMD responses. The CME and DME as well as their resonance frequencies present nonlinear characteristics with the bias magnetic field. The CME resonance frequency is lower than the DME resonance frequency in a same sample. CME decreases while DME increases with the magnetostrictive layer. The theoretical model plays an important role in the comprehensive understanding of ME properties, especially the CME effect, and design of ME devices such as magnetic-electric field sensors, energy harvesting transducers and solid tunable transformers.

Single-crystalline BiFeO3 nanorods have been prepared with a hydrothermal method under magnetic fields. The nanorods exhibit enhanced magnetization in comparison with the microcubes synthesized without the magnetic field. The nanorods display anomalous Raman behaviors, i.e., frequency shift of E-1, A1-1 and A1-2 modes and an enhanced intensity of the A1-2 mode, meaning there is magnetic anisotropy in the BiFeO3 lattice. The enhanced magnetization and anomalous Raman change are mainly attributed to the modulated spin structure from the distorted lattice caused by the magnetic field.

A new-type of semiconductor photocatalyst Na0.9Mg0.45Ti3.55O8 (NMTO) was prepared by a simple hydrothermal method for the first time. NMTO single crystal nanosheets with dominant {0 0 1} facets were obtained at 300 °C with 1 M NaOH over 40 min. HRTEM and XPS analyses confirmed the well crystallized nanosheets. NMTO was demonstrated as a direct semiconductor with a band gap of about 3.55 eV. Pure NMTO exhibited high photodegradation ability for methylene blue (MB) under UV-visible light irradiation. The trapping experiments indicated that the photogenerated holes were mainly responsible for the MB photodegradation. The presence of H2O2 significantly improved the photocatalytic activity of NMTO by inhibiting the electron–hole recombination through capturing the photogenerated electrons. A possible mechanism for the photodegradation of MB over NMTO is proposed. This work highlights the potential application of NMTO in the field of energy conversion.

BiFeO3 ceramics were sintered in the temperature range of 700–900 °C by using the pure BiFeO3 powders hydrothermally synthesized at 250 °C. The low reaction temperature and low sintering temperature prevent the element volatilization and phase decomposition. The ceramics sintered at 800 and 850 °C exhibit much dense microstructure with clear grains and grain boundaries. They also show high dielectric constant, dielectric dispersion and low loss tangent. At room temperature, the dielectric behaviors of BiFeO3 ceramics are mainly attributed to the transition of localized charge carriers and the microstructure of grains and grain boundaries. The temperature dependence of dielectric constant and loss tangent confirms that the localized charge carriers are a main contribution to the dielectric permittivity. Activation energy Eα of relaxation process for the BiFeO3 ceramic sintered at 850 °C is 0.397 eV. The obtained BiFeO3 ceramics show magnetic responses, which are relative to the grain size.Graphical abstractHighlights► Low sintering temperature prevents the element volatilization and phase transition. ► The ceramic exhibits much dense microstructure with clear grain and grain boundary. ► The ceramics enjoy high dielectric constant and dielectric dispersion. ► The magnetic properties of BiFeO3 ceramics are relative to the grain size.

Large-scale polyhedral bismuth ferrite (BiFeO3) particles were synthesized with a hydrothermal method under a series of experimental conditions. X-ray diffraction revealed that the BiFeO3 powders had a perovskite structure. Scanning electron microscopy images showed different BiFeO3 particles were formed, including sphere, octahedron, truncated octahedron, cubo-octahedron and truncated cube. The experimental results showed that the concentration of KOH, reaction time, heating and cooling rates had important impacts on the size and morphology of the BiFeO3 particles. The formation mechanism and change process of the large-scale polyhedral BiFeO3 particles were discussed in detail. The obtained BiFeO3 showed ferroelectric behavior and magnetic response, which approved the multiferroic property of the BiFeO3 crystallization. The optical behaviors of BiFeO3 particles revealed the band gap energy of about 2 eV, which is smaller than the BiFeO3 bulk due to the nano-crystallites.Research highlights► Large-scale polyhedral bismuth ferrite (BiFeO3) particles, with different morphologies of sphere, octahedron, truncated octahedron, cubo-octahedron and truncated cube, were synthesized by carefully controlling the hydrothermal conditions. ► The formation of the large-scale BiFeO3 polyhedron is attributed to the selective aggregation and dissolution-recrystallization. ► The large compact truncated cubes were obtained by reducing the cooling rate.

The colossal magnetodielectric effect is reported in Pb(Zr,Ti)O3/Terfenol-D laminate composite under low magnetic field. When the composite is placed in an external a.c. magnetic field, magnetoelectric effect is produced, as a result, the dielectric properties of the Pb(Zr,Ti)O3 is changed, i.e. magnetodielectric effect. Both the amplitude and resonance frequency change with the external magnetic field. The colossal magnetodielectric coefficient of 5 × 104% at low magnetic field of 20 Oe is achieved near the electromechanical resonance frequency.

A magnetoelectric composite transformer is proposed. The voltage step-up ratio can be adjusted by an applied magnetic field based on the direct and converse magnetoelectric effects. The nonlinear relationship between the voltage step-up ratio and magnetic field is caused by the nonlinear relationship of the magnetoelectric effect in magnetic field.

Pb(Zr0·52Ti0·48)O3 (PZT) powders were prepared by hydrothermal method. The effects of experimental parameters, including Pb/(Zr, Ti) ratio, alkaline concentration, reaction temperature and time on the product powders were studied in detail. Pure PZT powders were synthesized at suitable experimental conditions and Raman spectra confirmed the PZT with a perovskite-type structure. The homogeneous PZT powders with cubic-shaped morphology were formed at alkaline concentration of 1·2 M after reacting at 230°C for 2 h. The pure PZT powders obtained at low temperature and low alkaline concentration were attributed to precursors, TiCl4, with high activity and mineralizer NaOH with small cation radius.

(Mg0.95Zn0.05)2(Ti0.8Sn0.2)O4 powder was synthesized by a solid state reaction. Then, Ni0.4Zn0.6Fe2O4 was grown on the (Mg0.95Zn0.05)(Ti0.8Sn0.2)O4 particles in a hydrothermal environment to form a core-shell structure. (1-x)(Mg0.95Zn0.05)2(Ti0.8Sn0.2)O4@xNi0.4Zn0.6Fe2O4 composite ceramics were sintered at 1200 °C with these powders. XRD, SEM, TEM analyses indicated that high dense core-shell ceramics without any foreign phase were obtained. Different types of sharp interfaces were self-assembled owing to the minimization of direct elastic energy in the hydrothermal environment. The composites enjoy good magnetic and dielectric properties, especially, good microwave dielectric properties with high saturation magnetization when the ferrite content is 0.3–0.5. The results provided a powerful experimental basis for the sensor and transducer.

Nanocrystalline NiFe2O4 powders with different crystal sizes were hydrothermally synthesized with different alkali concentrations at 230 °C. Then the NiFe2O4 nanopowders were sintered at various temperatures to obtain NiFe2O4 ceramics with different grain sizes. The NiFe2O4 ceramic properties were strongly dependent on the grain size. With the increase in the grain size, saturation magnetization (Ms) and magnetic permeability (μ) increased, Curie temperature (Tc) decreased. Dielectric constant enhanced and dielectric loss decreased in nanoferrites. The possible mechanism of grain size dependences was discussed in detail.Graphical abstractWe prepared NiFe2O4 ceramics with different grain size. These ceramics show different magnetic and electric properties relative to the grain size.Download full-size imageHighlights► We researched the grain size effects on the magnetic and dielectric properties of the NiFe2O4 ceramics. ► Saturation magnetization and magnetic permeability increased with the grain sizes. ► Curie temperature decreased in a consistency with finite size scaling theory.

A new-type of semiconductor photocatalyst Na0.9Mg0.45Ti3.55O8 (NMTO) was prepared by a simple hydrothermal method for the first time. NMTO single crystal nanosheets with dominant {0 0 1} facets were obtained at 300 °C with 1 M NaOH over 40 min. HRTEM and XPS analyses confirmed the well crystallized nanosheets. NMTO was demonstrated as a direct semiconductor with a band gap of about 3.55 eV. Pure NMTO exhibited high photodegradation ability for methylene blue (MB) under UV-visible light irradiation. The trapping experiments indicated that the photogenerated holes were mainly responsible for the MB photodegradation. The presence of H2O2 significantly improved the photocatalytic activity of NMTO by inhibiting the electron–hole recombination through capturing the photogenerated electrons. A possible mechanism for the photodegradation of MB over NMTO is proposed. This work highlights the potential application of NMTO in the field of energy conversion.

Single-crystalline BiFeO3 nanorods have been prepared with a hydrothermal method under magnetic fields. The nanorods exhibit enhanced magnetization in comparison with the microcubes synthesized without the magnetic field. The nanorods display anomalous Raman behaviors, i.e., frequency shift of E-1, A1-1 and A1-2 modes and an enhanced intensity of the A1-2 mode, meaning there is magnetic anisotropy in the BiFeO3 lattice. The enhanced magnetization and anomalous Raman change are mainly attributed to the modulated spin structure from the distorted lattice caused by the magnetic field.