Thermodynamical stability and electronic structure of a perovskite-type hydride, NaMgH3

Thermodynamical stability and electronic structure of a perovskite-type hydride, NaMgH3, exhibiting reversible decomposition and recombination reactions, were studied experimentally. NaMgH3 decomposes in two steps accompanying hydrogen desorption reactions, and the enthalpy change (ΔH) and the entropy change (ΔS) are calculated to be ΔH(1) = −93.9(6) kJ/mol H2 and ΔS(1) = −116.2(9) J/K mol H2 for the first step, and ΔH(2) = −102.2(4) kJ/mol H2 and ΔS(2) = −125.9(6) J/K mol H2 for the second step, respectively. Maximum entropy method (MEM)/Rietveld analysis of synchrotron X-ray diffraction profiles indicated that NaMgH3 contains two hydrogen anions at the different occupation sites.