Abstract
Crystal structures of rare-earth gallium perovskitesLaGaO3,PrGaO3,NdGaO3 and Pr1−xNdxGaO3 (x = 0.25, 0.50, 0.75) solid solutions were investigated in the temperature range12–300 K by high-resolution powder diffraction using synchrotron or neutronradiation. The previously reported negative thermal expansion in theb direction of thePrGaO3 lattice has been foundto be persistent in Pr1−xNdxGaO3 solid solutions and its magnitude has been revealed as proportional tothe amount of praseodymium. Evaluation of the obtained temperatureevolution of cell dimensions indicated a weak anomalous behaviour of theb latticeparameter in NdGaO3, and its origin is supposed to be the same as inPrGaO3, i.e. a coupling of the crystal electric field levels with phonon excitations of about 23–25 meVenergy. The performed bond length analysis revealed an anomalous behaviour of bothLnO12 (Ln—rare-earth)and GaO6 coordination polyhedra, which can be a structural manifestation of anomalous thermalexpansion in the considered compounds.
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