Formation Entropies of MgH2 and PdHx Calculated fromSpectroscopic Entropy and the Consistency between Them andExperimentally Calculated Entropies

摘要

The standard formation entropy (ΔfS°) of non-stoichiometric compound palladiumhydride (PdHx) conventionally evaluates from PCT (Pressure-Composition-Temperature)curves or heat capacity measurement.On the other hand,we reported that ΔfS° ofstoichiometric compound magnesium hydride (MgH2) calculated by spectroscopic entropybased on statistical thermodynamics agreed with one evaluated by plateau pressure in PCTcurves.1 This relationship apply to evaluation of ΔfS° for non-stoichiometric compoundPdHx.When ΔfS° of PdHx calculates with the spectroscopic entropy by referencing the ΔfS°evaluated by few hysteresis PCT curves at each temperature,the configuration entropy ofhydrogen atoms in Pd lattice can be estimated.In this work,the configuration entropywhich is assumed to arrange not only octahedral site but also tetrahedral site at a certainratio is estimated by experimentally evaluated ΔfS° by PCT curves.