Heat capacity of α-AlH₃ and α-AlD₃ at temperatures up to 1000 K

The densest α modification of AlH₃ and AlD₃ is thermodynamically stable at high hydrogen pressures. At ambient pressure, α-AlH₃ and α-AlD₃ rapidly and irreversibly decompose to Al and H₂ or D₂ gas when heated to about 420 and 520K, respectively. In the present paper, the heat capacities at constant volume (C_V) and at constant pressure (C_P) are calculated for α-AlH₃ and α-AlD₃ at a pressure of 1atm and temperatures 0-1000K using the phonon densities of states determined earlier by inelastic neutron scattering at helium temperatures (Kolesnikov et al 2007 Phys. Rev. B 76 064302). The C_P(T) dependence of AlH₃ is also measured at temperatures 6-30K and 130-320K and that of AlD₃ at 130-320K in order to compensate for the scatter in the literature data and to improve the accuracy of the calculated C_V and C_P dependences at low temperatures.