Temperature dependence of the coefficient of linear thermal expansion of single-crystal SmS
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RUCTURE AND NONELECTRONIC PROPERTIES OF SEMICONDUCTORS
Temperature Dependence of the Coefficient of Linear Thermal Expansion of Single-Crystal SmS V. V. Kaminskiœa^, S. M. Luguevb, Z. M. Omarovb, N. V. Sharenkovaa, A. V. Golubkova, L. N. Vasil’eva, and S. M. Solov’eva aIoffe
Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia ^e-mail: [email protected] bInstitute of Physics, Dagestan Scientific Center, Russian Academy of Sciences, ul. 26 Bakinskikh komissarov 94, Makhachkala, 367003 Russia Submitted April 24, 2006; accepted for publication May 10, 2006
Abstract—The coefficient of linear thermal expansion of single-crystal SmS has been measured in the temperature range 300–850 K by dilatometry and X-ray diffraction. It is shown that the difference in the results obtained by these two methods is due to the heating-induced formation of SmS phases with small lattice parameters (5.62–5.8 Å) close to that for the metallic SmS phase. PACS numbers: 65.40.De DOI: 10.1134/S1063782607010010
Samarium monosulfide (SmS) is a rare-earth semiconductor with n-type conductivity; it has a lattice of the NaCI type with the lattice parameter a = 5.97 Å at a temperature T ≈ 300 K. The most interesting properties of SmS are based on the ability of Sm ions to relatively Sm3+ + e) under easily change their valence (Sm2+ the action of external factors. One such property is the generation of an emf upon uniform sample heating in the absence of external temperature gradients [1]. This effect is based on the change in the valence of defect (displaced from regular lattice sites) Sm ions. Further investigation showed the fundamental possibility of using this effect for direct transformation of thermal energy to electrical by fabricating corresponding SmSbased semiconductor structures [2]. Samarium monosulfide should be grown on different substrates and matched with commutation elements of thermal converters. This circumstance provokes interest in the temperature dependence of the coefficient of linear thermal expansion α of SmS. In addition, investigation of the temperature dependence of the relative elongation of a sample makes it possible to estimate the stability of the crystal structure with increasing temperature, which ensures the stability of emf generation. The contribution of thermally excited defects to α at low temperatures is insignificant in comparison with their contribution at high temperatures since their partial concentration N rapidly increases with temperature according to the exponential law [3]. The problem consists in determining the temperatures above which thermally excited defects begin to contribute to α. These temperatures can be estimated from comparison of the temperature dependences of the relative elongation ∆l/l0 of a sample
obtained by dilatometry and the relative increase in the lattice parameter ∆a/a0 obtained for the same sample. In this case, for different temperatures, N = 3 [ ( ∆l/l 0 ) – ( ∆a/a 0 ) ],
(1)
where l0 and a0 are,
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