Five compacted samples of thermoelectric Zn4Sb3 have been prepared from the same synthesis batch by spark plasma sintering. Four samples were made from powder with a grain size <45μm, and one sample from powder with grain size >45μm. Thermoelectric properties were evaluated, and an apparent strong correlation with sample density is found. ZnSb impurity contents obtained from powder x-ray diffraction cannot explain the variation in properties, which the authors’ suggest may be caused by slight changes in Zn content. The results show that minute changes in sample compaction conditions can have a larger effect on ZT than doping.

The effects of Cd substitution in M x Zn4−x Sb3 on the high-temperature thermal stability, low-temperature phase transitions and thermoelectric properties have been studied on three samples with a substitution degree of 0.1, 1, and 2 at % Cd (x = 0.004, 0.04, 0.08). The high-temperature thermal stability in atmospheric air of a 1% substituted sample is compared with an unsubstituted Zn4Sb3 sample. Multitemperature synchrotron powder diffraction data reveals that while only ∼42 wt % of the original Zn4Sb3 phase remains in the unsubstituted sample after three heating cycles to 625 K, 78 wt % is preserved in the Cd-substituted sample. Thus, Cd-substitution provides a significant improvement of the thermal stability of Zn4Sb3. Multitemperature synchrotron powder diffraction data measured between 90 and 300 K reveal that Cd substitution has a suppressing effect on the α′−α−β phase transitions. With increasing substitution, there is also a significant change in the individual Zn site occupancies. Differential scanning calorimetry shows an apparent correlation between Cd content and phase transition temperature. Thermoelectric properties have been measured from 2 to 400 K for all samples, and although some physical properties are significantly affected by doping, no immediate improvement of ZT was achieved.

High-temperature thermoelectric properties of the double-perovskite ruthenium oxide (Sr1−xLax)2ErRuO6 J. Appl. Phys. 112, 073714 (2012) Thermoelectric properties of n-type Mn3−xCrxSi4Al2 in air J. Appl. Phys. 112, 073713 (2012) Thermoelectric effect in a graphene sheet connected to ferromagnetic leads J. Appl. Phys. 112, 073712 (2012) Thermoelectric properties of p-type Bi0.5Sb1.5Te2.7Se0.3 fabricated by high pressure sintering method J. Appl. Phys. 112, 073708 (2012) Dimensional crossover of charge density wave and thermoelectric properties in CeTe2−xSbx single crystals

The thermoelectric material Zn 4 Sb 3 was mercury doped by introduction of 1 at. % Hg into the synthesis mixture, resulting in Hg 0.04 Zn 3.96 Sb 3 . The doped compound and an undoped reference were characterized by multitemperature short wavelength synchrotron X-ray powder diffraction, SEM/EDX, differential scanning calorimetry (DSC), and physical property measurements. Rietveld refinements suggest that mercury substitution takes place solely on the Zn1 framework site of the disordered room temperature β-phase crystal structure, while the interstitial positions are mercury-free. The refined composition suggests a doping level of 0.6%. The remaining mercury is present as elemental Hg as evidenced by SEM/EDX analysis, the presence of peaks corresponding to crystalline Hg below the Hg freezing temperature, and the presence of a drop in the resistivity at the superconducting transition temperature of Hg. Rietveld refinements of multitemperature synchrotron X-ray powder diffraction data (180 K < T < 290 K, ∆T ) 10 K) reveal a significant change in the R-R′-β phase transition temperatures between undoped and 1% Hg-doped samples. This is corroborated by DSC data that show that the transition enthalpies are very small, about 0.1-0.4 J/g. The largest enthalpy change is observed in the R-R′ transition for the undoped sample, whereas the largest transition enthalpy is found in the R′-β transition for the Hg-doped compound. Complete thermoelectric properties have been measured in the temperature range 2-400 K on dense samples prepared by spark plasma sintering. The Hg doping has a very large effect on the transport properties in the ordered R-phase crystal structure but only a minor influence on the properties in the disordered β-phase. The thermoelectric figure of merit, ZT, is found to be ∼0.3 for both the undoped and the Hg-doped sample at 300 K.