Peculiarities of the lattice thermal properties of rare-earth tetraborides

The temperature dependences of the a(T) and c(T) crystal structure parameters for HoB4 and ErB4 at temperatures of 5–300 K are experimentally investigated. Anomalies of these dependences for tetraborides studied at magnetic ordering temperatures were found for HoB4TN1 = 5.7 K, TN2 = 7.1 K and for ErB4TN1 = 15.4 K. The regular lattice alat(T) and clat(T) contribution to the thermal expansion of the rare-earth tetraborides studied in the present work and in the authors previous works were calculated. The temperature changes in the lattice components of the tetraborides thermal expansion, as well as their heat capacity of previous works of the authors, are considered within the Einstein and Debye approximations. The characteristic temperatures θDi,θE\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\theta _{{\rm Di}}, \theta _{{\rm E}}$$\end{document} of the examined rare-earth tetraborides were found. A slight decrease in the characteristic temperatures for RB4 tetraborides was observed with an increase in the rare-earth metal atomic number in the Periodic Table, which is conditioned by the predominant effect of the R3+ ion mass on the lattice dynamics of the analyzed borides in comparison with the lanthanide reduction.