Raman spectra and extended X-ray absorption fine structure characterization of La_[(2-x)/3]Na_xTiO_3 and Nd_[(2-x)/3]Li_xTiO_3 microwave ceramics

摘要

A-site deficient perovskite compounds, La_[(2-x)/3]Na_xTiO_3 (0.02 < = x < = 0.5) and La_[(2-x)/3]Na_xTiO_3(0.1 < = x < = 0.5) microwave ceramics, were investigated by Raman scattering. La_[(2-x)/3]Na_xTiO_3 (0.1 < = X < = 0.5) was also investigated by extended X-ray absorption fine structure (EXAFS) measurement. The Raman shifts of the E (239cm~(-1)) and A_1 (322cm~(-1)) modes of La_[(2-x)/3]Na_xTiO_3 were found to decrease with x. However, the E (254 cm~(-1)) and A_1 (338 cm~(-1)) of Nd_[(2-x)/3]Li_xTiO_3 were found to blueshift with x, which was caused by Li substitution. The redshift of the A_1 (471 cm~(-1))phonon of Nd_[(2-x)/3]Li_xTiO_3 (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)/3]Li_xTiO_3.