Binary and Pseudobinary Invar Materials based on Intermediate Valence Compounds

Resumo

A new type of binary and pseudobinary invar materials based on intermediate valence samarium compounds Sm_0.8B₆, Sm_1 – xLa_xB₆ (x = 0, 0.1, 0.22, and 0.5), Sm_0.67Y_0.33S, Sm_0.55Y_0.45S, and Sm_2.75C₆₀ are developed. The Weiss two-level invar model is used to describe the anomalous contribution to the coefficient of thermal expansion (CTE) for Sm_0.8B₆ and Sm_1 – xLa_xB₆ (x = 0, 0.1, 0.22, and 0.5). The minimum position of the CTE of samarium hexaboride as a function of the degree of lanthanum doping is determined. The obtained dependence allows one to predict the CTE minimum position for Sm_1 – xLa_xB₆ compounds in the temperature range from 40 to 180 K and to optimize the developed composite invar materials, where the positive CTE of the functional material is compensated by the negative CTE of the valence-unstable system.