Investigation of the perovskite related structures of NaMgH3, NaMgF, and Na3AlH6

Two perovskite related metal hydrides, NaMgH3 and Na3AlH6 were structurally investigated using powder diffraction techniques. Single crystal X-ray dat a was also used to for the first time confirm that the structure of NaMgF3 is analogous to the orthorombically distorted perovskite structure of GdFeO 3 space group Pnma (no. 62). Looking for new ternary hydrides in the NaH-Mg H2 system, the only new compound found was NaMgH3 which is isotypic with Na MgF3. The positions of the D atoms in Na(3)AID(6), isotypic with the low te mperature phase of Na(3)AIF(6), space group P2(t) / n (no. 14), could for t he first time be determined from neutron diffraction data. The degree of di stortion was discussed from the point of bonding distances and angles in th e octahedra of the hydrides and fluorides. In the case of NaMgH3 and NaMgF3 , the angles of which the octahedra are rotated (phi) and atomic coordinate s were calculated. Both NaMgH3 and Na3AlH6 appear to be less tilted but mor e deformed than their corresponding fluorides. (C) 2000 Elsevier Science S. A. All rights reserved.