HEAT-CAPACITY OF TAV2HX(DX) - EVIDENCE FOR A LOW-TEMPERATURE PHASE-TRANSITION

The heat capacities of the C15-type hydrides TaV2H1.1, TaV2H1.3 and TaV2D1.3 have been measured over the temperature range from 3.5 to 300 K. The electronic specific-heat coefficients-gamma are found to be considerably lower than in the hydrogen-free TaV2. For all the studied samples the heat capacity shows a peak which can be attributed to H(D) ordering. The ordering temperature increases with increasing hydrogen content and shows the isotope effect. We discuss the possible relation between this phase transition and the anomalous low-temperature motion of H(D) in TaV2Hx(Dx).