Common features of gallium perovskites

The Czochralski and floating zone methods have been used to grow single crystals of gallium perovskites solid solutions with rare earth elements La, Pr, Nd, Sm and with Sr. The structure of the crystals has been investigated by powder X-ray, synchrotron radiation and neutron diffraction methods over a wide temperature range. The unit cell volume at room temperature varies from approximately 228 to 236 Angstrom (3) in Sm0.75Nd0.25GaO3 and La0.88Sr0.12GaO3-delta, respectively. Position of atoms in the unit cell and evolution of perovskite lattice deformation induced by continuously varying average rare earth ionic radius is discussed. The unit cell parameters including atoms positions, thermal expansion coefficients, segregation coefficients and phase transition temperature scale with the unit cell volume in all investigated crystals. All these parameters may be represented as a function of average ionic radius of rare elements, however, this value is not well determined in these compounds because of ill determined coordination number

Growth and structural investigations of La1-xPrxCaO3 solid solution single crystals

Growth of single crystals in the pseudobinary LaGaO3-PrGaO3 system by the Czochralski and floating-zone methods was investigated. It has been found that solid solution crystals La1-xPrxGaO3 exist in the whole concentration range x, The segregation coefficients of Pr in LaGaO3 and La in PrGaO3 have been found to be k(eff)(Pr) approximate to 0.84 and k(eff)(La) approximate to 1.19. The structure of the crystals was investigated by X-ray diffraction method. With increasing Pr concentration x, the lattice parameters a and c decrease, whereas b remains almost constant, the volume of the unit-cell decreases. At x = 0.51 parameters a and b become equal and the crystal adopts a pseudo-tetragonal structure. The differential thermal analysis proved that the temperature of the first-order phase transition observed in LaGaO3 at similar to 150 degreesC rises linearly with Pr concentration I at the rate of 13.3 degreesC/Pr mol%. (C) 2001 Elsevier Science B.V. All rights reserved