Crystal Structures and Thermoelectric Properties of Layered Compounds in the ATe-Bi_2Te_3 (A = Ge, Sn, Pb) Systems

摘要

Single-crystal and powder x-ray diffraction studies of compounds in the nATe · mBi_2Te_3 (A = Ge, Sn, Pb) homologous series in the pseudobinary systems ATe-Bi_2Te_3 reveal a marked dissimilarity of the GeTe-Bi_2Te_3 system from SnTe-Bi_2Te_3 and PbTe-Bi_2Te_3. The GeTe-Bi_2Te_3 system contains, along with GeBi_2Te_4 (n/m =1), GeTe-rich (n/m > 1) and Bi_2Te_3-rich (n/m < 1) members of the nGeTe · mBi_2Te_3 series. In contrast, the Sn and Pb systems contain only Bi_2Te_3-rich compounds (n/m < 1). This dissimilarity is interpreted in terms of the crystal structures of GeTe, SnTe, and PbTe. The thermoelectric properties of nPbTe · mBi_2Te_3 compounds are studied in a broad temperature range. The thermoelectric figures of merit of unoptimized n-type PbBi_4Te_7 and PbBi_2Te_4 are ZT=0.5 and 0.4 at 600 and 650 K, respectively. Comparison of the thermoelectric properties of the isostructural 12-layer compounds GeBi_4Te_7, SnBi_4Te_7, and PbBi_4Te_7 indicates that the maximum in ther-mopower shifts to higher temperatures in going from the Ge to Sn and Pb compounds.