V. S. Zemskov

Composition and Properties of Layered Compounds in the GeTe–Sb2Te3System

The 620-K section of the Ge–Sb–Te phase diagram was mapped out using x-ray diffraction, microstructural analysis, and microhardness measurements. The transport properties of the layered tetradymite-like compounds nGeTe · mSb2Te3(n, m= 1–4) were studied in wide temperature ranges (Hall effect and electrical resistivity, from 77 to 800 K, and thermoelectric power, from 90 to 450 K). The results show that the nGeTe · mSb2Te3compounds are degeneratep-type semiconductors with a fairly high hole concentration due to the high density of intrinsic point defects. The temperature dependences of the Hall coefficient and resistivity exhibit anomalies related to solid-state phase transitions. The room-temperature lattice thermal conductivity ofnGeTe · mSb2Te3is fairly low, in the range 8–10 mW/(cm K).

X-ray Diffraction Study of Mixed-Layer Compounds in the PbTe–Bi2Te3System

PbTe–Bi2Te3alloys were studied by x-ray diffraction (XRD) and microstructural analysis. Single-crystal XRD studies of cleaved surfaces showed that the PbTe–Bi2Te3system contains an nPbTe · mBi2Te3homologous series of layered compounds with n= 1, 2 and m= 1–4. In addition to the known compounds PbBi2Te4and PbBi4Te7 , three new layered compounds with n/m< 1 were identified: PbBi6Te10(n= 1,m= 3), PbBi8Te13(n= 1, m= 4), and Pb2Bi6Te11(n= 2,m= 3). The 51-layer structure of PbBi6Te10was refined by single-crystal XRD (positional and thermal parameters, bond distances). No mixed-layer compounds with n/m> 1 were identified in the PbTe–Bi2Te3system, in contrast to GeTe–Bi2Te3and GeTe–Sb2Te3 .

Thermoelectric Properties of nGeTe · mSb2Te3Layered Compounds

The Hall coefficient, electrical conductivity, and thermoelectric power of Ge3Sb2Te6, Ge2Sb2Te5, GeSb2Te4 , and GeSb4Te7were measured over a wide temperature range (RHand σ from 77 to 800 K and Sfrom 90 to 450 K). The carrier concentration was varied via compositional changes within the homogeneity regions of the compounds. All of the materials studied were found to be p-type. Some of the alloys have a low lattice thermal conductivity and are, therefore, candidate p-type thermoelectric materials. The temperature-dependent hole mobility data suggest that both acoustic phonons and point defects contribute to the scattering of charge carriers at low temperatures.

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

Abstract Single crystals and powders of the ternary mixed layered homologous series of compounds n GeTe· m Bi 2 Te 3 have been investigated by X-ray diffraction (XRD). It is found that a character of cleaved (00 l ) face XRD patterns for the n GeTe· m Bi 2 Te 3 (0 n / m ≤3) single crystals varies in a regular manner with increasing ratio n / m 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 ≤9) 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.

Homologous series of layered tetradymite-like compounds in the Sb-Te and GeTe-Sb2Te3 systems

AbstractThe structures of layered compounds in thenSb2 ·mSb2Te3 andnGeTe ·mSb2Te3 homologous series were studied by x-ray diffraction. GeSb6Te10 (n = 1,m = 3) was shown to have a 51-layer structure (sp. gr.

Thermoelectric Properties of the Layered Compound GeBi4Te7 Doped with Copper

R\bar 3m

Structural and electrical properties of layered tetradymite-like compounds in the GeTe—Bi2Te3 and GeTe—Sb2Te3 systems

) withc = 10.202(1) nm. In the structure of GeSb6Te10, Sb2Te3 five-layer slabs and GeSb2Te4 sevenlayer slabs are stacked along thec axis in the ordered sequence -557 557 557-. Crystallographic data for this compound are presented. The specific and common structural features of the layered compounds in thenSb2 ·mSb2Te3 andnGeTe ·mSb2Te3 homologous series are discussed.

X-ray diffraction study of ternary layered compounds in the PbSe-Bi2Se3 system

AbstractX-ray diffraction studies of cleaved single-crystal specimens and powders demonstrate that the SnTe–Bi2Te3 system contains a homologous series of nSnTe · mBi2Te3 layered compounds (n = 1, 2; m = 1–3). In addition to the known compound SnBi2Te4, the compounds SnBi4Te7 (n = 1, m = 2) and SnBi6Te10 (n = 1, m= 3), structural analogues of GeBi4Te7 and GeBi6Te10, are identified. SnBi4Te7 has a 12-layer structure with lattice parameters a = 0.4392(1) nm andc = 2.399(1) nm (sp. gr. P