Dielectric properties and phase transitions in K1−xLixTa1−yNbyO3:Cu

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The ε’(T, f) and tan [δ(T, f)] (10–300 K, 100 Hz – 1 MHz) behavior is studied in K1−xLixTa1−yNbyO3:Cu (0·012 %wt. in batch) with estimated x1 = 0·0014, y = 0·024 (KLTN 0·14/2·4) and x2 = 0·0028, y2 = 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 ε’(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 ε’(T) cusp-shaped maximum with ε’(T)max≈25 000 was found. KLTN 0·28/1·3 reveals a similar behavior, namely, Li+-related dielectric dispersion with ε’(T)max = 8300 at 47 K for 100 Hz, and a phase transition at ∼35 K. At lower temperatures, ε’ increases with a weak shoulder at ∼ 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 ε’(T)max ≈86000 and increased conductivity in the transition region.