Hg0.04Zn3.96Sb3: Synthesis, Crystal Structure, Phase Transition, and Thermoelectric Properties

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• 作者：B. L. Pedersen ; H. Birkedal ; E. Nishibori ; A. Bentien ; M. Sakata ; M. Nygren ; P. T. Frederiksen ; B. B. Iversen
• 刊名：Chemistry of Materials
• 出版年：2007
• 出版时间：December 11, 2007
• 年：2007
• 卷：19
• 期：25
• 页码：6304 - 6311
• 全文大小：703K
• 年卷期：v.19,no.25(December 11, 2007)
• ISSN：1520-5002

文摘

The thermoelectric material Zn₄Sb₃ was mercury doped by introduction of 1 at. % Hg into the synthesis mixture, resulting in Hg_0.04Zn_3.96Sb₃. 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, ΔT = 10 K) reveal a significant change in the α–α′–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 α–α′ transition for the undoped sample, whereas the largest transition enthalpy is found in the α′–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 α-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.