Structural and dielectric characterizations of the mixed crystal Li0.8Na0.2NbO3

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Abstract

Ferroelectric mixed crystals Li0.8Na0.2NbO3 were grown from the melt by the Czochralski method. It has been found from the structural analysis that a mixed crystal Li0.8Na0.2NbO3 is rhombohedral with a hexagonal unit cell of dimensions aH = 5.1736 Å and cH = 13.938 Å at 25°C. To confirm the thermal expansion, high-temperature X-ray diffraction was carried out in the temperature range from 25 to 900°C, and the longitudinal thermal expansion coefficients turned out to be α = 11.501 × 10−5°C−1 and α33 = 7.712b310−5°C−1. The temperature characteristics of dielectric constants and a.c. conductives of the mixed crystals Li0.8Na0.2NbO3 have been investigated in detail from room temperature to above the Curie temperature, 1108°C. Significant low frequency dielectric dispersions were observed over a wide temperature range, including the Curie temperature. It is believed that this low frequency relaxation process is due to mobile charged-point defects presumably connected with the substitution of Na+ for Li+ in the LiNbO3 frame.

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