IR and Raman spectroscopy correlation with the structure of (La/Pr)1−x(Pr/Nd)xGaO3 solid solution crystals

The Czochralski and floating zone methods are used to grow single crystals of gallium perovskites solid solutions with rare earth elements La, Pr and Nd for structural, Raman and IR spectroscopy investigations. The contraction of the unit cell results from decreasing of the averaged radius of rare earth ions and causes increasing tilting and deformation of GaO6 octahedra. The volume of the GaO6 octahedra increases despite the decrease of the unit cell volume. Thus, the ratio of the perovskite unit cell to the octahedron volume decreases with the decrease of the unit cell volume and is determined to be 5.72 in LaGaO3 and 5.5 in NdGaO3. The temperature dependence of the Raman spectra demonstrates a first order phase transition at about 150 °C. The shift of the Raman modes slightly decreases with x increasing independently of the rare earth ion type. Evolution of the IR spectra with x is also discussed.