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Crystal structure and thermal expansion of PrGaO3 in the temperature range 10-1253 K

Leonid Vasylechko 3Anatoliy Senyshyn 3Michael Knapp 2Marek Berkowski 4Carsten Paulmann 1Ulrich Bismayer 1A. Matkovskii 3

1. University of Hamburg, Mineralogisch-Pertographisches Institut, Hamburg, Germany
2. Technische Universitat Darmstadt, Darmstadt, Germany
3. Lviv Polytechnic National University, 12 Bandera, Lviv 79013, Ukraine
4. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland


Crystal structure and thermal expansion of PrGaO3 have been investigated in the temperature range 10-1253 K by means of single crystal and high-resolution powder diffraction techniques using synchrotron radiation. Single crystal and powder diffraction experiments were carried out at the beamlines F1 and B2 at HASYLAB/DESY. PrGaO3 possesses an orthorhombically distorted GdFeO3 type structure in the whole temperature range investigated. The changes in lattice parameters and cell volume are anisotropic and nonlinear with increasing temperature. Negative thermal expansion in [010]- and [100]-directions were detected in the temperature ranges 10-180 K and 10-50 K, respectively. Negative thermal volume expansion is observed in the temperature range 10-50 K. Due to pronounced anisotropy of the thermal expansion, the normalized values of the lattice parameters bp and cp become equal at 1200 K. For the average interatomic distances (PrO)8-(PrO)12, (GaO)6 and (OO)8 a linear increase with temperature is observed. For the temperature dependencies of the (PrPr)6, (PrGa)8 and (GaGa)6 average distances a change of slope occurs at 200-300 K.
A Reduction of the bond-length distortion in the corresponding polyhedra with temperature and an increase of the values of the observed tolerance factors indicate a decrease of the perovskite structure deformation in PrGaO3. From extrapolation of the experimental values of the interatomic distances and their ratios, the temperature of the predicted orthorhombic-to-rhombohedral phase transition could be estimated to 1840-1875 K.
Acknowledgement. This work was supported by WTZ (UKR-012-97), Ukrainian Ministry of Science (Project No. "Ion") and Polish Committee for Scientific Research (Grant N 7 T08A 00520).


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Presentation: poster at E-MRS Fall Meeting 2003, Symposium B, by Leonid Vasylechko
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-10 10:10
Revised:   2009-06-08 12:55