Bulk and interfacial polarization phenomena OF La /SUB 1-x/ Ba /SUB x/ F /SUB 3-x/ crystals

The small-signal a.c. response of single-crystalline LaF/sub 3/ and the anion-deficient solid solutions La /SUB 1-x/ Ba /SUB x/ F /SUB 3-x/ with ionically blocking Pt electrodes has been studied up to 1300 K in the frequency range 10/sup -2/-10/sup 5/ Hz. A complex nonlinear least-squares analysis of the admittance and impedance spectra has been employed to obtain a detailed equivalent circuit and the relevant parameter values. At low and moderate temperatures the a.c. bulk response can be modeled with a Debye-type circuit. The circuit parameters are not associated with a dielectric with dipoles, but with free charge carriers migrating over inequivalent sites. At higher temperatures the Debye circuit reduces to a resistance, indicating fast exchange of the mobile species between inequivalent anion lattice sites. To model the a.c. interface response, a constant-phase element of the form Y /SUB Q/ = K /SUB j/ (i..omega..) /SUP aj/ in parallel wit a resistance has been employed over the entire temperature range. The role of interfacial impurity oxygen diffusion is discussed.