O-site and T-site Occupation of α-phase PdH[subscript x] and PdD[subscript x]

Abstract

An important study of the solubility of hydrogen in α-phase PdH[subscript x] and deuterium in α-phase PdH[subscript x] over a wide temperature range was published by Clewley et al. (J. Chem. Soc., Faraday Trans. 1: Phy. Chem. Condensed Phases 69 (1973) 449–458). An analysis of the data based on an empirical solubility model based on O-site occupation allows for an understanding of the data at low temperature, but probably is not a good starting place for understanding the solubility at high temperature. We have applied a recently developed empirical model for both O-site and T-site occupation to this data set, and find good agreement between data and a basic version of the model which assumes that the O-site and T-site partition functions are taken to be harmonic oscillator partition functions. Even better agreement is obtained when a more realistic O-site partition function is used. A range of optimum models with different assumptions about the T-site partition function is considered, and it is found to be possible to select one that matches the T-site occupation at zero loading inferred from neutron diffraction measurements of Pitt and Gray (Europhys. Let. 64 (2003) 344). The O-site to T-site excitation energy is assumed independent of temperature in these models, and we obtain specific model values of 105.3 meV for α-phase PdH[subscript x] and 106.5 meV for α-phase PdH[subscript x]. Keywords: Empirical model; Mean-field lattice gas model; Solubility; α-phase PdH[subscript x] and PdD[subscript x]; Tetrahedral occupation