Low-temperature structural and Raman studies on rare-earth gallates

Measurements of lattice parameters and structural refinement were made for a LaGaO3, PrGaO3, NdGaO3, La0.34Pr0.33Nd0.33GaO3, and La0.63Nd0.37GaO3 samples by powder-diffraction method using synchrotron radiation. The final structure refinement was performed in space group Pbnm at 12 K and room temperature. Anisotropic negative thermal expansion for PrGaO3 samples was detected. Some anomalies of NdGaO3 thermal behavior of lattice parameters were observed. The thermal dependence of the Raman spectra of NdGaO3 single crystals at low temperatures was investigated. Strong interaction of the Ag phonon and the crystal-field excitation of the Nd3+4f electrons of the same symmetry was observed. This leads to a renormalization of the wave function and the energy of the phonon and the crystal-field excitation