High-frequency dielectric properties of K1-xLixTaO3 ceramics compared to crystals

Second harmonic generation (SHG) and high-frequency dielectric properties of Li-doped KTaO3 (K1-xLixTaO3, KLT100x) ceramics, KLT5 and KLT10, are studied in the 15-300 K temperature range. Using the resonant microwave spectroscopy at 5.8 GHz, time-domain THz spectroscopy (-10-40 cm-1) and far-infrared reflectivity (-30-650 cm-1) in conjunction with the dielectric properties earlier published in the 100 Hz - 100 MHz frequency range, a broad-band dielectric response of ceramics in the whole 100 Hz - 20 THz range is obtained and compared with that recently published for KLT4.3 and KLT8 crystals. According to SHG, unlike in crystals, the ferroelectric phase transition temperature in both ceramics appears near 100 K. The dielectric soft mode softening is less pronounced, and the low-frequency permittivity increases less on cooling, when compared with crystals. The relaxational behavior below the microwave range is very similar and the main relaxations follow the same Arrhenius law as in the crystals.