Thermoelectric properties of a metastable (Ba,K)Zn₂As₂ crystallized in the ThCr₂Si₂-type structure

We obtained a high temperature β-phase of Ba_1−xK_xZn₂As₂ crystallized in the ThCr₂Si₂-type structure as a metastable state at a room temperature by quenching. It's thermoelectric properties were evaluated in the range of 0.00 ≤ x ≤ 0.10. The maximum dimensionless figure-of-merit ZT was relatively high for a ThCr₂Si₂-type structure to be ZT = 0.30 at 773 K for x = 0.03 with the lattice thermal conductivity of less than 1 W/mK. The quite low lattice thermal conductivity could be attributed to lattice instability between the β-phase and the equilibrium α-phase crystallized in the α-BaCu₂S₂-type structure. The stability of the metastable β-phase was examined by powder X-ray diffraction measurements over a wide temperature range. Phase diagram of the metastable β-phase was determined and temperature dependence of its atomic parameters was obtained by Rietveld analysis. The results demonstrate the potential of compounds crystallized in the ThCr₂Si₂-type structure and the effectiveness of a metastable state for achieving a high-performnace thermoelectric-property.