Properties of lithium hydride I. Single crystals

Abstract Single crystals of optical quality LiH have been prepared by slow crystallization of the melt under hydrogen gas at moderate pressure. Measured and reported values of the physical, thermal, chemical, and optical properties of LiH and LiD are compared to those of LiF and NaCl. These properties bear out the predominantly ionic nature of crystalline LiH. The optical properties of LiH differ from those expected by a comparison with the properties of the alkali halides or the other alkali hydrides. This difference is related to distortion and polarization effects on the hydride ion in the LiH crystal lattice. There is a tendency toward covalency which may contribute to the binding energy of crystalline LiH, and this also may be responsible for its somewhat anomalous behavior.