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Hydrogen-induced atomic rearrangement in MgPd3 |
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| Authors: | H Kohlmann G Renaudin K Yvon B Harbrecht |
| Institution: | a Laboratoire de Cristallographie, Université de Genève, 24 Quai Ernest Ansermet, 1211 Genève 4, Switzerland b Institut fur Anorganische und Analytische Chemie und Radiochemie, Universität des Saarlandes, 66041 Saarbrücken, Germany c Laboratoire des Matériaux Inorganiques, Université Blaise Pascal de, Clermont-Ferrand, 24 avenue des Landais, 63177 Aubière Cedex, France d Fachbereich Chemie, und Wissenschaftliches Zentrum für Materialwissenschaften Philipps-Universität Marburg, 35032 Marburg, Germany |
| Abstract: | The hydrogenation behavior of MgPd3 has been studied by in situ X-ray powder diffraction and by neutron powder diffraction. At room temperature and p ≈500 kPa hydrogen pressure its structure is capable of incorporating up to one hydrogen atom per formula unit (α-MgPd3H≈1), thereby retaining a tetragonal ZrAl3-type metal atom arrangement. Upon heating to 750 K in a hydrogen atmosphere of 610 kPa it transforms into a cubic modification with AuCu3-type metal atom arrangement (β-MgPd3H≈0.7). Neutron diffraction on the deuteride reveals an anion deficient anti-perovskite-type structure (β-MgPd3D0.67, a=398.200(7) pm) in which octahedral sites surrounded exclusively by palladium atoms are occupied by deuterium. Complete removal of hydrogen (480 K, 1 Pa) stabilizes a new binary modification (β-MgPd3, a=391.78(2) pm) crystallizing with a primitive cubic AuCu3-type structure. Mechanical treatment (grinding) transforms both α and β modifications of MgPd3 into a cubic face-centered solid solution Mg0.25Pd0.75 showing a random distribution of magnesium and palladium atoms. |
| Keywords: | Metal hydrides Intermetallic compounds Neutron diffraction X-ray diffraction Phase transition Crystal structure determination |
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