Thermodynamic properties and lattice dynamics investigation of LuB2C: experiment and ab initio calculations

Magnetic phase transition and lattice dynamic features in ErB2C borocarbide

A sample of erbium borocarbide ErB₂C was synthesized from a stoichiometric mixture of erbium, boron, and pyrographite hydride. Temperature dependent magnetic susceptibility, heat capacity and lattice parameters of borocarbide at 2-300 K were experimentally investigated, the Raman spectrum was determined and analyzed. Sharp anomalies in the heat capacity and magnetic properties of ErB₂C nearT= 16.3 K, caused by the transition to the antiferromagnetic state, as well as diffuse anomalies at a higher temperature, caused by the effect of the crystal field (Schottky anomalies) were revealed. It was found that the magnetic phase transition does not cause measurable anomalies in the lattice parameters of borocarbide due to the weak coupling between the Er³⁺ion subsystem and the B-C layers. Almost zero thermal expansion of erbium borocarbide in the basal plane (alongaandbaxes) (anisotropic invar effect) as well as an unusual character of thec-axis thermal expansion were observed. The first of these features is due to the high bonding energy in the B-C layers and the weak bond between the layers in the borocarbide crystal lattice. It was found that the anomalous expansion along thecaxis is a consequence of the action of the crystal field. The splitting scheme for the ground level of Er³⁺ions by crystal field was determined from the analysis of the Schottky anomaly of the heat capacity.