Characterisation of doped-lanthanum gallates by X-ray diffraction and Raman spectroscopy

Abstract

La1−xSrxGaO3−z (x=0–0.2) and LaGa1−yMyO3−z (y=0–0.2, M=Cr, Mg) were synthesised using the standard solid state technique. The structural changes, with increase in dopant concentration, were investigated using powder X-ray diffraction and Raman spectroscopy. The X-ray diffraction of Sr-doped LaGaO3 shows a shift in the orthorhombic pattern with increase in dopant concentration. At 20 mol% Sr doped on the A-site of LaGaO3 the XRD pattern contains the secondary phase SrLaGa3O7 and a third unidentified phase. LaGaO3 B-site doped with Cr shows little change with increase in Cr dopant level, up to 20 mol%. There is, however, a splitting of peaks, indicating a new phase is formed at >5% Cr dopant. LaGaO3 B-site doped with Mg shows a gradual shift in the orthorhombic pattern of LaGaO3 with the formation of La4Ga2O9 and a third unidentified phase. Raman spectra of Mg-doped LaGaO3 show a second phase of La4Ga2O9 formed at Mg dopant concentrations greater than 5 mol%. This is distinguished by bands at 243, 295 and 356 cm−1 which become significant at 20 mol% Mg. Raman spectra of pure LaGaO3 at room temperature shows 18 bands and only 14 at −196°C, of a predicted 24 modes.