Crystal Structure of Lanthanum, Cerium and Praseodymium Hydrides

The Hydrides of the Rare-Earth Metals

“…Rossi 34 ' 35 found that a specimen containing 200 cm 3 H 2 per g of metal (LaH 2 . 5 ) has a cubic lattice with a = 5.63-5.64 k. Work by Holley, Zachariasen and others (involving X-ray and neutron diffraction studies 31 ) on the dependence of the equilibrium pressure on the temperature and concentration 32 showed, together with microstructural examination, that below a hydrogen content corresponding to the composition LaH 2 (1.43 wt.…”

“…Until recently the only such work was by Rossi 35 , who reported that cerium hydride has a face-centred cubic lattice with lattice parameter a = 5.61 A. Removal of hydrogen by evacuation at 530° leads to the appearance of a second phase with a slightly smaller lattice period.…”

The crystal structure of the deuterides of ytterbium and europium

“…X-ray powder photographs for the hydrides of lanthanum, cerium, and praseodymium were first reported by Rossi (1934). Dreyfus-Alain & Viallard (1953) have reported such photographs for lanthanum hydride.…”

High temperature allotropy of the rare-earth elements

“…The structure of cerium at room temperature was found to be fee by Quill (3) and by others (1,5,12,22) for samples as pure as 99.9 per cent, whereas for samples containing as much as 10 per cent Impurities, the fee phase was found to coexist with the hep phase by Hull (23) and by Ziegler (6).…”

“…At room temperature, lanthanum has been reported to ex hibit a hexagonal closest packed (hep) structure by McLennan and McKay (2) and by others (3,4,5,6, 7), a face centered cubic (fee) structure by Klemm and Bommer (1) and by others (8,9), or a mixture of both by James et al (10) and by Ziegler et al (7). According to Zintl and Neumayr (4) and others (6,7,11) annealing of lanthanum at 350°C tends to stabilize the fee structure at room temperature.…”