Preparation and properties of lithium hydride

The properties and preparation of Li hydride are presented primarily from a thermodynamic point of view. Several preparations and fabrication methods are briefly described. The crystal structure is given along with the thermal expansion and compressibility. The thermodynamics are described for three regions: the a- region which is the solubility of hydrogen in Li metal, the $\alpha$ region which is the description of the defect region of the Li hydride and the ($\alpha + \beta$) or plateau region. The $\alpha$ region is best described by the regular solution theory of hydrogen dissolved in Li. The $\beta$ region is described by the assumption that both Li ion and hydrogen ion vacancies are present. This assumption is supported by the spectroscopic and diffusion data, although the possibility of hydrogen interstitials has not been eliminated. The equilibrium two phase region and the heat capacity of pure LiH(D) are well characterized both above and below the melting point of LiH(D). The possibility and evidence of a Curie point at about 12 K for pure LiH(D) is presented