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Issue 7, 2020
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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., 2020,49, 2138-2144
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, 49, 2138
DOI: 10.1039/C9DT04919C

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