Crystal structure of an unusual polytype: 7H-Ba{sub 7}Nb{sub 4}MoO{sub 20}
- Univ. Complutense, Madrid (Spain)
A new cation deficient hexagonal perovskite with the unusual polytype 7H (hhchhcc) has been obtained in the Ba-Mo-Nb-O system for the Ba{sub 7}Nb{sub 4}MoO{sub 20} composition. It crystallizes in the P{bar 3}m1 space group (No. 164) with hexagonal lattice parameters a = 5.8644(2) {angstrom} and c = 16.5272(4) {angstrom}. The crystal structure has been studied by means of X-ray powder diffraction, electron diffraction, high-resolution electron microscopy, and neutron powder diffraction. The unit cell of Ba{sub 7}Nb{sub 4}MoO{sub 20} can be seen as an ordered intergrowth along the c-axis of the structural units corresponding to the 12R and the palmierite polytypes. Both types of blocks are isolated through the cationic vacancies, giving rise to a layered structure. The existence of two cationic empty sites per unit cell is probably the reason for the 7H polytype containing two hh pairs being adopted.
- OSTI ID:
- 329072
- Journal Information:
- Chemistry of Materials, Journal Name: Chemistry of Materials Journal Issue: 2 Vol. 11; ISSN CMATEX; ISSN 0897-4756
- Country of Publication:
- United States
- Language:
- English
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