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.