X-ray study of defects in the GeTeAg2TeBi2Te3 system

Georgieva

Один

1991

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Equilibrium polycrystalline samples of GeTe‐rich (GeTe)1−x[(Ag2Te)1‐y(Bi2Te3)y]x (y = 0.4667, 0.5000, and 0.5333) SS are prepared. On the base of different experimental investigations the T‐x projection of the phase equilibrium diagram of SS with y = 0.4667 is drawn. The GeTe‐rich SS keep the crystal structure of GeTe. The phase transition temperature Tc decreases with increasing amount of the ternary compound and reaches 300 K at x of about 0.23. From a comparision of the power coefficient S2σ of SS with different y at 300 K it is found that a deviation in stoichiometry of the ternary compound towards Ag2Te (y = 0.4667) or Bi2Te3 (y = 0.5333) influences unfavorably the thermoelectric parame‐ters.

Section: T-x Projection Of the Phase Diagramsupporting

confidence: 67%

Solid State Transformations and Electrophysical Properties of GeTe-Rich Solid Solutions in the GeTe-Ag2Te-Bi2Te3 System

Georgieva

Один

1991

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“…In order to obtain the E ( k ) relationship for finite temperatures, Bangert [20] has taken into account two matrix elements R , and R , neglected in his zero-temperature calculations [19], which represent the contribution from the interband electron-phonon interactions. The energy-momentum relationship in this case is given by A is related to the optical deformation potential E by A = EU (12) with u being the relative sublattice displacement. The energy gap E, in the rhombohedral phase at the T point is related to the energy gap in the cubic phase E,, by…”

Section: The Band Structure Of the Iv-vi Compounds In Cubic And Rhombmentioning

confidence: 99%

Thermoelectric Power of Some Compositions of GeTe-Rich (GeTe)1—x(AgBiTe2)2 Solid Solution

Georgiev

1993

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A method of preparation of single phase ingots of GeTe-rich solid solutions (x s 0.20) in the system (GeTe), _JAgBiTe,), is developed. The temperature dependence (77 to z 900 K) of thermoelectric power is measured. The curves for GeTe and GeTe-rich solid solutions are of similar shape. Using the conventional transport theory the lattice and electronic contributions to this effect are obtained. To explain the behavior of diffusion and phonon drag terms the metallic expressions for both are used. On the basis of band-edge models of GeTe and AgBiTe, and the nonparabolic two-band Kane model of IV-VI compounds and separate values of the electronic parts of the thermoelectric power an information about the Fermi energy and the degree of degeneracy is received. A qualitative interpretation of the temperature dependence of S , is made.

Structural Study of (GeTe)1–x[(Ag2Te)0.5333(Bi2Te3)0.4667]xSolid Solutions

Georgieva

1991

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The reversible cubic ↔ rhombohedral (O h5 ↔ C 5V3) phase transition of GeTe‐rich (GeTe)1–x[(Ag2Te)0.5333(Bi2Te3)0.4667]xsolid solutions is studied by means of high temperature X‐ray analysis. Temperature and composition changes of the rhombohedral lattice parameters are found. They prove the displacive nature of the solid solution phase transition. With increasing amount of heterovalent Ag and Bi atoms replacing Ge cations the phase transition temperature Tc decreases.