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Crystal lattice disorder and characteristic features of the low-temperature thermal properties of higher borides

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Abstract

Heat capacity CP(T) and lattice parameters a(T), b(T) and c(T) of LuB44Si3.5 borosilicide are experimentally studied as a function of temperature in the range of 2–300 K. The results are compared with those of pseudo-isostructural LuB50 boride. At the lowest temperatures, it is shown that the CP(T) dependence of borosilicide changes linearly with temperature. This is attributed to the effect of glass-like behaviour of the heat capacity due to the disorder in the sublattice of non-metals. The presence of defects in the B–Si sublattice and the irregular form of the cages in the B–Si matrix, which are occupied by Lu3+ ions, lead to the formation of two-level systems (TLS) in the Lu3+ subsystem. The TLS make a characteristic bell-like low-temperature contribution to the heat capacity of borosilicide. We show that there is a wide temperature range (5–150 K) of negative thermal expansion of borosilicide, which is attributed to the influence of quasi-independent vibrations of Lu3+ ions in the cages of the borosilicide crystal structure.

Graphical abstract: Crystal lattice disorder and characteristic features of the low-temperature thermal properties of higher borides

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Article information


Submitted
30 Dec 2019
Accepted
22 Jan 2020
First published
22 Jan 2020

Dalton Trans., 2020, Advance Article
Article type
Paper

Crystal lattice disorder and characteristic features of the low-temperature thermal properties of higher borides

V. V. Novikov, A. V. Matovnikov, N. V. Mitroshenkov, A. V. Shevelkov and S. L. Bud'ko, Dalton Trans., 2020, Advance Article , DOI: 10.1039/C9DT04919C

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