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 data was also used to for the first time confirm that the structure of NaMgF3 is analogous to the orthorombically distorted perovskite structure of GdFeO3 space group Pnma (no. 62). Looking for new ternary hydrides in the NaH-MgH2 system, the only new compound found was NaMgH3 which is isotypic with NaMgF3. The positions of the D atoms in Na(3)AID(6), isotypic with the low temperature phase of Na(3)AIF(6), space group P2(t) / n (no. 14), could for the first time be determined from neutron diffraction data. The degree of distortion was discussed from the point of bonding distances and angles in the octahedra of the hydrides and fluorides. In the case of NaMgH3 and NaMgF3, the angles of which the octahedra are rotated (phi) and atomic coordinates were calculated. Both NaMgH3 and Na3AlH6 appear to be less tilted but more deformed than their corresponding fluorides. (C) 2000 Elsevier Science S.A. All rights reserved.