Abstract
The anisotropic coefficients of thermal expansion and the peritectic transformation of orthorhombic-Hf6Ta2O17 to tetragonal-HfO2 plus liquid at 2250 °C have been studied by in-situ X-ray powder diffraction from room temperature to complete melting (∼2450 °C) in air, using a quadrupole lamp furnace (QLF) and a conical nozzle levitator (CNL) equipped with a CO2 laser. The topotactic, peritectic transformation has been fully described by extracting the orientation relationship, lattice variant deformation and a motif (grouping) of cations that relates the two structures at the transformation temperature. The calculation of these two important parameters as well as identification of the motif is facilitated by a knowledge of the anisotropic coefficients of thermal expansion as a function of temperature. Symmetry decomposition has been performed to show that the orthorhombic-Hf6Ta2O17 and tetragonal-HfO2 structures are simply related by polyhedral rotations and loss of 1 mol of oxygen.
Original language | English (US) |
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Pages (from-to) | 127-137 |
Number of pages | 11 |
Journal | Acta Materialia |
Volume | 161 |
DOIs | |
State | Published - Dec 2018 |
Keywords
- Crystalline oxides
- In-situ high temperature X-ray diffraction
- Phase transformations
- Thermal expansion
- X-ray synchrotron radiation
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Polymers and Plastics
- Metals and Alloys