title: Electron diffraction and microscopy study of the structure and microstructure of the hexagonal perovskite Ba3Ti2MnO9.
abstract: This paper reports a structural and microstructural investigation of the hexagonal perovskite Ba(3)Ti(2)MnO(9) using electron microscopy and diffraction. Convergent-beam electron diffraction (CBED) revealed the structure has the non-centrosymmetric space group P6(3)mc (186) at room temperature and at approximately 110 K. Compared with the centrosymmetric parent structure BaTiO(3), with space group P6(3)/mmc, this represents a break in mirror symmetry normal to the c axis. This implies the Ti and Mn atoms are ordered on alternate octahedral sites along the 0001 direction in Ba(3)Ti(2)MnO(9). Using high-resolution electron microscopy (HREM), we observed occasional 6H/12R interfaces on (0001) planes, however, no antiphase boundaries were observed, as were seen in Ba(3)Ti(2)RuO(9). Using powder X-ray Rietveld refinement we have measured the lattice parameters from polycrystalline samples to be a = 5.6880 +/- 0.0005, c = 13.9223 +/- 0.0015 A at room temperature.
authors.affiliation: Brockhouse Institute for Materials Research, McMaster University, Hamilton L8S 4L9, Canada. maunder@mcmaster.ca
authors.forename: Christian
authors.initials: C
authors.lastname: Maunders
authors.forename: Harold J
authors.initials: HJ
authors.lastname: Whitfield
authors.forename: David G
authors.initials: DG
authors.lastname: Hay
authors.forename: Joanne
authors.initials: J
authors.lastname: Etheridge