Chalcopyrite CuGaTe2 is under research for its high thermoelectric performance. Different routes have been investigated recently for enhancing its thermoelectric parameters. In this work we report the synthesis of chalcopyrite CuGa1−xMnxTe2 (x = 0.0, 0.01, 0.02, and 0.03) by a solid state method and through which an enhanced power factor was obtained. The samples were characterized for electrical, thermal and thermoelectric transport properties in the temperature range 325–870 K after performing stability analysis using TG-DTA data. XRD patterns confirm a phase pure tetragonal structure for all nominal compositions with the space group I2d. The electrical conductivity σ increases drastically by Mn2+ doping which increases the hole carriers, while the Seebeck coefficient S still retains large positive values. As a result, the power factor of CuGa0.99Mn0.01Te2 reaches 1.55 mW K−2 m−1 at 718 K. Calculations using the relationship of S and ln σ suggest that the power factor observed for Mn-doped samples is higher than that expected for CuGaTe2 with optimized carrier concentration, suggesting that the Mn-doping brings additional effects other than simple carrier tuning. The total thermal conductivity is reduced by Mn doping, with a minimum thermal conductivity of 1.6 W m−1 K−1 for the x = 0.01 sample. The maximum value for ZT reached at 870 K was 0.83, which is more than 40% enhancement as compared to that of pure CuGaTe2. Strong interactions between the magnetic moments of Mn and charge carriers are inferred by the large negative Weiss temperature in the magnetic susceptibility and distinct anomalous Hall effect, the latter of which develops in accordance with the increase of magnetization at low temperature. These results suggest that the carrier–magnetic moment interaction plays an essential role in the enhancement of the thermoelectric properties of CuGa1−xMnxTe2.

Physical properties of the ternary compound YbPdSi are investigated. The polycrystalline sample of YbPdSi has been characterized by powder X-ray diffraction, showing the orthorhombic YPdSi-type structure. Magnetization measurements reveal ferromagnetic ordering takes place at 8 K. Specific heat data are analyzed by the crystalline electric field model, which indicates that only the ground state doublet participate in the magnetic ordering. At low temperature, a heavy fermion state with the electronic specific heat coefficient γ∼300mJ/molK2 is suggested. The coexistence of the heavy fermion state and the ferromagnetic ordering implies that the Kondo and theta; RKKY interactions are competing in YbPdSi.Highlights► New compound where ferromagnetism and heavy fermion behavior coexists. ► Ferromagnetic transition is observed in YbPdSi at 8 K. ► Crystal field splitting scheme is obtained from the specific heat analysis. ► Heavy fermion behavior with γ∼ 300 mJ/mol K2 is observed. ► Competition of the Kondo effect and the RKKY interaction is prominent in YbPdSi.

Single-crystalline samples of a new Zintl compound, Eu3Ga2P4, have been synthesized by a Ga-flux method. Eu3Ga2P4 is found to crystallize in a monoclinic unit cell, space group C2/c, isostructural to Ca3Al2As4. The structure is composed of a pair of edge-shared GaP4 tetrahedra, which link by corner-sharing to form Ga2P4 two-dimensional layers, separated by Eu2+ ions. Magnetic susceptibility showed a Curie–Weiss behavior with an effective magnetic moment consistent with the value for Eu2+ magnetic ions. Below 15 K, ferromagnetic ordering was observed and the saturation magnetic moment was 6.6 μB. Electrical resistivity measurements on a single crystal showed semiconducting behavior. Resistivity in the temperature range between 280 and 300 K was fit by an activation model with an energy gap of 0.552(2) eV. The temperature dependence of the resistivity is better described by the variable-range-hopping model for a three-dimensional conductivity, suggesting that Eu–P bonds are involved in the conductivity. A large magnetoresistance, up to −30%, is observed with a magnetic field H = 2 T at T = 100 K, suggesting strong coupling of carriers with the Eu2+ magnetic moment.

Phase stability of the type-I clathrate compound Ba8AlxSi46−x and the thermoelectric property dependence on chemical composition are presented. Polycrystalline samples were prepared by argon arc melting and annealing. Results of powder X-ray diffraction and electron microprobe analysis show that the type-I structure is formed without framework deficiency for 8≤x≤15. Lattice constant a increases linearly with the increase of x. Thermoelectric properties were measured for x=12, 14 and 15. The Seebeck coefficients are negative, with the absolute values increasing with x. The highest figure of merit zT=0.24 was observed for x=15 at T=1000 K, with carrier electron density n=3×1021 cm−3. A theoretical calculation based on the single parabolic band model reveals the optimum carrier concentration to be n∼4×1020 cm−3, where zT∼0.7 at T=1000 K is predicted.Graphical AbstractBa8AlxSi46−x is found to crystallize in the type-I clathrate structure without framework deficiency for 8≤x ≤15. Thermoelectric figure of merit reaches zT=0.24 for x=15 at 1000 K, and calculation predicts zT∼0.7 for a lower carrier concentration.Highlights► Phase relation of the type-I clathrate Ba8AlxSi46−x is clarified. ► Thermoelectric performance becomes higher with the increase of Al content x. ► Low lattice thermal conductivity comparable to glasses is observed. ► Figure of merit zT=0.7 is predicted from calculation at the carrier concentration n∼4×1020 cm−3.

We investigated the phase stability and superconducting properties of YbGaxSi2−x. Polycrystalline samples were synthesized by argon arc melting and subsequent annealing. The composition range of the phase with the AlB2-type structure was determined to be 1.12(1) ≤ x ≤ 1.49(3) by powder X-ray diffraction and electron probe microanalysis. The lattice constants, both a and c, increase linearly with x throughout the single-phased region. Electrical resistivity showed metallic behavior for all samples, and the superconducting transition was observed to occur at critical temperatures ranging from TC = 2.4 K for x = 1.15 to less than 1.8 K for x = 1.41. The extent of the decrease in TC with x is comparable to that in MGaxSi2−x (M = Ca, Sr, Ba) for x > 1. The negative sign of the Seebeck coefficient measured for x = 1.20 indicates that the dominant carriers are electrons. The temperature dependence of the magnetic susceptibility below room temperature showed almost nonmagnetic behavior suggesting the nearly divalent state of Yb. However, Yb was found to be in the mixed valent state Yb2.3+ based on a precise measurement using X-ray absorption spectroscopy in the partial fluorescence yield mode at the Yb LIII absorption edge. Comparison is made with the nonsuperconducting YbGaGe from the viewpoint of the relation of the crystal structure and superconductivity.

The Yb2Cu2In compound with the tetragonal Mo2B2Fe structure has been prepared using a high-pressure technique. The lattice volume is found to be considerably larger than that expected for the system with usual Yb3+ configuration. The temperature dependence of the magnetic susceptibility and the electrical resistivity shows that this system is almost non-magnetic. These results indicate that the Yb ion in this system is very close to the divalent state.

Chalcopyrite CuGaTe2 is under research for its high thermoelectric performance. Different routes have been investigated recently for enhancing its thermoelectric parameters. In this work we report the synthesis of chalcopyrite CuGa1−xMnxTe2 (x = 0.0, 0.01, 0.02, and 0.03) by a solid state method and through which an enhanced power factor was obtained. The samples were characterized for electrical, thermal and thermoelectric transport properties in the temperature range 325–870 K after performing stability analysis using TG-DTA data. XRD patterns confirm a phase pure tetragonal structure for all nominal compositions with the space group I2d. The electrical conductivity σ increases drastically by Mn2+ doping which increases the hole carriers, while the Seebeck coefficient S still retains large positive values. As a result, the power factor of CuGa0.99Mn0.01Te2 reaches 1.55 mW K−2 m−1 at 718 K. Calculations using the relationship of S and lnσ suggest that the power factor observed for Mn-doped samples is higher than that expected for CuGaTe2 with optimized carrier concentration, suggesting that the Mn-doping brings additional effects other than simple carrier tuning. The total thermal conductivity is reduced by Mn doping, with a minimum thermal conductivity of 1.6 W m−1 K−1 for the x = 0.01 sample. The maximum value for ZT reached at 870 K was 0.83, which is more than 40% enhancement as compared to that of pure CuGaTe2. Strong interactions between the magnetic moments of Mn and charge carriers are inferred by the large negative Weiss temperature in the magnetic susceptibility and distinct anomalous Hall effect, the latter of which develops in accordance with the increase of magnetization at low temperature. These results suggest that the carrier–magnetic moment interaction plays an essential role in the enhancement of the thermoelectric properties of CuGa1−xMnxTe2.