Low-temperature thermal properties and features of the phonon spectrum of lutetium tetraboride

摘要

The coefficients of thermal expansion to the c axis (α||, α⊥ were measured for lutetium tetraboride over the temperature range 4.2-300 K. The heat capacity data for lutetium tetraboride were used for the calculation of tetraboride phonon spectrum moments and also for the development of a simplified tetraboride spectrum model. The use of the heat capacity and thermal expansion data allowed the temperature changes of the Gruneisen parameters Г, Г_||, Г_⊥ for tetraboride to be calculated. As a result of the approximation of Г_⊥(T), Г ||(T) temperature dependencies in accordance with the chosen phonon spectrum model have been found: the anomalies of Г_⊥(T), Г_||(T) are at about 25 K and then drop at lower temperatures due to the Einstein vibrations of boron sublattices.