Raman spectra and extended X-ray absorption fine structure characterization of La_(2-x)/3Na_xTiO₃ and Nd_(2-x)/3Li_xTiO₃ microwave ceramics

A-site deficient perovskite compounds, La_(2-x)/3Na_xTiO₃ (0.02 ≤ x ≤ 0.5) and Nd_(2-x)/3Li_xTiO₃ (0.1 ≤ x ≤ 0.5) microwave ceramics, were investigated by Raman scattering. Nd_(2-x)/3Li_xTiO₃ (0.1 ≤ x ≤ 0.5) was also investigated by extended X-ray absorption fine structure (EXAFS) measurement. The Raman shifts of the E (239 cm^-1) and A₁ (322 cm^-1) modes of La_(2-x)/3Na_xTiO₃ were found to decrease with x. However, the E (254 cm^-1) and A₁ (338 cm^-1) of Nd_(2-x)/3Li_xTiO₃ were found to blueshift with x, which was caused by Li substitution. The redshift of the A₁ (471 cm^-1) phonon of Nd_(2-x)/3Li_xTiO₃ (0.1 ≤ x ≤ 0.3) indicates that O-Ti-O bonding forces lessen with Li concentration, which is consistent with the EXAFS result that Ti-O bond lengths increase for 0.1 ≤ x ≤ 0.3. For x > 0.3, the EXAFS result shows that Ti-O bond lengths decrease. Moreover, Ti-O bond lengths show strong correlation with the microwave dielectric constants of Nd_(2-x)/3Li_xTiO₃.