Dielectric properties and phase transitions in K_1-xLi_xTa_1-yNb_yO₃ :Cu

Abstract

The epsilon'(T,f) and tan [delta(T,f)] (10-300 K, 100 Hz - 1 MHz) behavior is studied in K1.xLixTa1-yNbyO3:Cu (0.012 %wt. in batch) with estimated x(1) = 0.0014, y = 0.024 (KLTN 0.14/2.4) and x(2) = 0.0028, y(2) = 0.013 (KLTN 0.28/1.3). In KLTN 0.14/2.4 a strong dipole relaxation is found in the 40-80 K region, with epsilon'(T)(max) = 16 000 at 47 K for 100 Hz, and a phase transition dominated by the soft mode coupled with a relaxation freezing mode is displayed at 39 K. Below, at 15.5 K, a nondispersive epsilon'(T) cusp-shaped maximum with epsilon'(T)(max) approximate to 25 000 was found. KLTN 0.28/1.3 reveals a similar behavior, namely, Li+-related dielectric dispersion with epsilon'(T)(max) = 8300 at 47 K For 100 Hz, and a phase transition at similar to 35 K. At lower temperatures, epsilon' increases with a weak shoulder at similar to 27 K. The so-called ``277'' species of KLTN:Cu (1900 ppm), with x = 0.001, y = 0.025 stated by content analysis, whose unusual properties were marked recently([1,2]), reveal a sharp phase transition, accompanied by dielectric dispersion with a very high epsilon'(T)(max) approximate to 86000 and increased conductivity in the transition region.