X-ray diffraction study and electrical and thermal transport properties of the nGeTe•mBi2Te3 homologous series compounds

Single crystals and powders of the ternary mixed layered homologous series of compounds nGeTe.mBi(2)Te(3) have been investigated by X-ray diffraction (XRD). It is found that a character of cleaved (00l) face XRD patterns for the nGeTe.mBi(2)Te, (0 <n/m less than or equal to3) single crystals varies in a regular manner with increasing ratio Win as far as the occupation of empty cation layers prevails. The hexagonal l-indices for these patterns are represented in generalized form as a function of two integers: n and m. X-ray powder diffraction of high members of the homologous series demonstrates that the alloys enriched by GeTe (3 <n/m less than or equal to9) contain a mixture of domains of different members of the homologous series. These alloys are characterized by extremely low thermal conductivity due to the high degree of lattice disorder. A plateau region in the temperature dependencies of the lattice thermal conductivity in the compounds with n/m >3 ratio is like that for amorphous materials. Hall coefficient and electrical resistivity were measured in the temperature range of 77-800 K. Seebeck coefficient and thermal conductivity were determined in the 90-450-K and 80-350-K temperature intervals, respectively. (C) 2001 Elsevier Science B.V. All rights reserved.