Synthesis and crystal growth of SrLiH3 and EuLiH3; Ternary hydrides with the perovskite structure

Abstract

The ternary metal hydrides, MLiH3, with M = Sr2+ and Eu2+ which crystallize in the cubic perovskite structure were synthesized by direct reaction between lithium hydride and the appropriate metal dihydride. The reactants were obtained by direct reaction of the vacuum distilled (10-5 Torr) parent metals with ultrapure hydrogen. Large single crystals of both SrLiH3 and EuLiH3 were grown from the melt using a modification of the Bridgman-Stockbarger technique. Contrary to a previous report these materials melt incongruently rather than congruently, and it was necessary to utilize an initial charge composition of 40% MH2-60% LiH to prevent the precipitation of MH2 upon melting. The peritectic melting point of EuLiH3 was determined as 780 ± 5°C using DTA. Crystals of SrLiH3 were orange-brown and those of EuLiH3 were deep-red in color. The absorption edge at room temperature, determined by optical transmission measurements, was about 4.0 eV for SrLiH3 and 1.8 eV for EuLiH3. The room temperature resistivity of both materials was about 107 ohm-cm. The crystals were quite brittle, quite sensitive to thermal shock, and tended to fracture conchoidally when cleavage was attempted by ordinary means. Chemical analysis suggested that the major impurities in both hydrides were oxygen and nitrogen and that these hydrides are not grossly non-stoichiometric with respect to hydrogen content.