Strain mechanism for order-parameter coupling through successive phase transitions in PrAlO3

Carpenter, M. A. and Howard, C. J. and Kennedy, B. J. and Knight, K. S. (2005) Strain mechanism for order-parameter coupling through successive phase transitions in PrAlO3. Physical Review B, 72 (2, 024). DOI

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High-resolution powder neutron diffraction data have been collected at ∼50 temperatures between 4.2 and 300 K for perovskites Pr1−xLaxAlO3 with x=0, 0.05, 0.1, and 0.25. Structural and lattice parameter data extracted by Rietveld refinement have then been used to follow details of octahedral tilting and spontaneous strains associated with the sequence of phase transitions Pm3̅ m↔R3̅ c↔Imma↔C2∕m. These are interpreted in terms of strain/order parameter coupling using a single Landau free-energy expansion for a Pm3̅ m reference structure with two instabilities (R4+ and Γ3+ active). Data from the literature relating to the Pm3̅ m↔R3̅ c transition are consistent with second-order character and an extrapolated transition temperature of 1864±31 K. The R3̅ c↔Imma transition is first order in character and can be understood as occurring because coupling takes place between tilting and electronic order-parameter components via a common tetragonal strain. Strains for the Imma↔C2∕m transition conform closely to the Landau solution for a proper ferroelastic transition with second-order character and low-temperature saturation. The acoustic anomaly reported at 118 K appears to be associated with a metrically tetragonal structure which develops, as an accidental strain degeneracy, at a temperature between ∼110 and ∼120 K. Differences in saturation temperatures for the order parameters associated with tilting and electronic ordering are probably responsible for small additional anomalies in the evolution of strains below ∼110 K.

Item Type: Article
Uncontrolled Keywords: 2005 AREP 2005 P IA49
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
Journal or Publication Title: Physical Review B
Volume: 72
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 29 Jul 2011 10:26
Last Modified: 23 Jul 2013 09:58

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