High-pressure studies of LaH3−δ (δ = 0.00, 0.15)

Compressibility of LaH3−δ (δ = 0.00, 0.15) has been studied in the pressure range from ambient up to 25 GPa using the diamond anvil cell (DAC) technique. In case of stoichiometric lanthanum trihydride, no structural phase transition has been detected by energy dispersion X-ray diffraction (ED-XRD) and LaH3.00 has been shown to retain the initial fcc structure up to 25GPa. Experimental molar volume–pressure dependence has been fit by Murnaghan model of equation of state (EOS) estimating bulk modulus (B0) to be about 90 GPa with its first pressure derivative (B0′) fixed at 4. In contrast to LaH3.00, a reversible structural change has been observed for the substoichiometric lanthanum trihydride, LaH2.85. A possible tetragonal distortion of the initial fcc structure is considered to explain the observation.