Hydride formation in the intermetallic compounds cepd₃ and cerh₃

The intermetallic compounds CePd₃ and CeRh₃ were hydrogenated at hydrogen pressures up to 24 MPa and temperatures up to 540 K, and investigated by X-ray and neutron powder diffraction and X-ray photoelectron spectroscopy (XPS). Both compounds retain their AuCu₃ type arrangement upon hydrogen uptake. The cubic lattice parameters increase from 412.5(1) and 402.57(2) pm in CePd₃ and CeRh₃, respectively, to 413.5(1) and 406.27(3) pm in the corresponding hydrides. In contrast to the rhodium, compound CePd₃H_x forms only under high pressure and room temperature and releases hydrogen quickly in air. From neutron powder diffraction on CeRh₃D_0.84 deuterium atoms were found to occupy 84.4(8) % of octahedral interstices formed solely by rhodium, atoms, [Rh₆], in a statistical fashion, resulting in a deficient cubic anti-perovskite type structure (space group Pm3̄m (No. 221), a = 407.248(7) pm at T = 299(2) K). Rhodiumdeuterium (203.62(1) pm) and cerium-deuterium distances (352.69(1) pm) are consistent with typical interatomic distances in other hydrides. XPS measurements reveal mixed valency in CePd₃.