Raman spectra and extended X-ray absorption fine structure characterization of La(2−x)/3NaxTiO3 and Nd(2−x)/3LixTiO3 microwave ceramics

A-site deficient perovskite compounds, La(2−x)/3NaxTiO3 (0.02 ≤ x ≤ 0.5) and Nd(2−x)/3LixTiO3 (0.1 ≤ x ≤ 0.5) microwave ceramics, were investigated by Raman scattering. Nd(2−x)/3LixTiO3 (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)/3NaxTiO3 were found to decrease with x. However, the E (254 cm−1) and A1 (338 cm−1) of Nd(2−x)/3LixTiO3 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)/3LixTiO3 (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)/3LixTiO3.