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  • Title: Thermal evolution of the crystal structure and phase transitions of KNbO3.
    Author: Skjærvø SL, Høydalsvik K, Blichfeld AB, Einarsrud MA, Grande T.
    Journal: R Soc Open Sci; 2018 Jun; 5(6):180368. PubMed ID: 30110437.
    Abstract:
    The thermal evolution of the crystal structure and phase transitions of KNbO3 were investigated by high-temperature powder X-ray diffraction and Rietveld refinement of the diffraction data. Two phase transitions from orthorhombic (Amm2) to tetragonal (P4mm) and from tetragonal to cubic ( Pm3¯m ) were confirmed, both on heating and cooling. Both phase transitions are first order based on the observed hysteresis. The mixed displacive and order-disorder nature of the tetragonal to cubic transition is argued based on symmetry and apparent divergence of the atomic positions from pseudo-cubic values. The transition between the orthorhombic and tetragonal phase shows no temperature-dependence for atomic positions and only thermal expansion of the unit cell parameters and is thus discussed in relation to a lattice dynamical instability.
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