Calorimetric properties of C14 and C15 YMn_2 and YMn_2(H,D)_6

摘要

The capacity of YMn_2 to undergo reversible hydrogenization makes this compound a potential candidate for hydrogen storage. This report describes the successful synthesis of YMn_2H_6 from hexagonal C14 YMn_2 as well as calorimetric studies of hexagonal C14 YMn_2, cubic C15 YMn_2 and their isostructural derivatives, YMn_2H_6 and YMn_2D_6. Complementary structural and physical property characterizations include X-ray diffraction, electrical resistivity, and magnetic susceptibility measurements. Of particular interest is a hysteretic first-order phase transition in C15 YMn_2 near 100 K, which does not occur in C14 YMn_2. Analysis of a specific heat anomaly that is associated with this transition reveals a substantial latent heat of 330 J/mol. No such anomalous specific heat exists in YMn_2D_6, suggesting that the transition is suppressed upon deuterization.