Low-temperature specific heat of non-stoichiometric β-ytterbium deuteride

Abstract

Heat capacity measurements on a β-ytterbium deuteride sample with the composition D/Yb=2.71 have been carried out over a temperature range from 1.9 to 260 K. Two anomalies were observed at 4 K and 230 K, respectively. On the grounds of the separated Schottky contribution to the specific heat, the influence of the crystal field on the splitting of the (2J+1)-fold degenerate ground state J=7/2 of the Yb3+ ion is analysed. The existence of two sublattices (sort of an electronic phase separation) of hydrogen atoms arranged by the two different ytterbium atom valencies is suggested. The sharp discontinuity in the specific heat at 230 K in YbD2.71 resembles that observed in the light rare earth hydrides REHx in the composition range 2.7<x<2.92 and attributed to a metal-semiconductor transition. X-ray diffraction measurements in the range 50–300 K indicate that the anomaly in Cp(T) at 230 K is accompanied by the probable tetragonal distortion of the cubic structure at low temperatures. The metal-insulator/semiconductor transformation is likely induced when the deuterium/hydrogen atoms order in the structure.