Evidence for self-organization processes in PbTe-Bi 2 Te 3 semiconductor solid solutions
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Theoretical & Experimental Physics Department, National Technical University “Kharkov Polytechnic Institute,” 61002 Kharkov, Ukraine (Received 12 January 2011; accepted 9 May 2011)
The dependences of unit cell parameter, x-ray diffraction line width B, and microhardness H on the composition of PbTe-Bi2Te3 (0–10 mol% Bi2Te3) semiconductor alloys, subjected to different types of heat treatment, were obtained. In the concentration ranges ;0.5–1.5 and 3–4 mol% Bi2Te3 within the homogeneity region of PbTe (0–6 mol% Bi2Te3), anomalous constancy or decrease in B and H was observed. A long room temperature aging leads to a more distinct manifestation of these effects. It is suggested that the observed peculiarities in the concentration dependences of the properties are connected with percolation effects and self-organization processes in the solid solution.
I. INTRODUCTION
In a large number of solid solutions based on binary and ternary compounds, in the range of small impurity concentrations (;0.5–1.0 at.%), we observed anomalies in the property-composition dependences (e.g., see Refs. 1–7) and attributed them8 to the manifestation of critical phenomena accompanying concentration phase transitions of percolation type occurring under the transition from diluted solid solutions, in which the interaction between impurities can be neglected, to concentrated ones, in which so-called infinite cluster is formed.9 After the impurity continuum is formed, states with spatially correlated distribution of atoms (long- or shortrange ordering) corresponding to the minimum in the crystal-free energy can be realized. If an impurity is introduced into the matrix in the form of a chemical compound, chemical interaction between the constituents of the compound may take place in the solid solution and lead to a short-range ordering, in particular the formation of neutral complexes whose composition corresponds to the composition of the introduced compound or that of intermediary phases. Analyzing the concentration dependences of properties and using the phenomenological method of cluster components, we made the conclusion about a microheterogeneous structure of semiconductor solid solutions based on SnTe.10–14 As percolation effects and ordering processes in solid solutions significantly influence structure and physical properties of crystals, it is of interest to expand the range of objects and properties to be studied. PbTe-based solid solutions are widely applied in thermoelectricity, optoelectronics, IR devices, holography, and other fields of science and technology.15–17 Bismuth is a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.165 J. Mater. Res., Vol. 26, No. 13, Jul 14, 2011
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one of the most important donor impurities in PbTe. Introducing bismuth, one can change electron concentration and thus maximize values of thermoelectric figure of merit in crystals and thin films, optimize parameters of p-n junctions in laser diodes, and s
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