The anisotropic thermal expansion and anisotropy of lattice volume change in Y4Al2O9at 1370°C were confirmed by high-temperature neutron diffraction of the sintered polycrystalline sample. The cell volume of the high-temperature phase is approximately 0.4% smaller than that of the low-temperature phase. The crystal structure of the high-temperature phase was determined by Rietveld analysis. It crystallizes in a monoclinic cell,a=7.4804(4) Å,b=10.5461(5) Å,c=11.2057(7) Å, andβ=108.927(4)° at 1518°C,Z=4 with space groupP21/c, which is identical to the space group of the low-temperature phase. The phase transition was concluded to be diffusionless by comparison of the crystal structures of the high- and low-temperature phases. At the transition, the atoms in the unit cell move cooperatively on the slip planes of oxygen atoms parallel to the (010) plane along theaaxis.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry