Ceramics in the system (Bi_0.5K_0.5)TiO₃-BiFeO₃ have good electromechanical properties and temperature stability. However, the high conductivity inherent in BiFeO₃-based ceramics complicates measurement of the ferroelectric properties. In the present work, doping with niobium (Nb) is carried out to reduce the conductivity of (Bi_0.5K_0.5)TiO₃-BiFeO₃. Powders of composition 0.4(K_0.5Bi_0.5)Ti_1-xNb_xO₃-0.6BiFe_1-xNb_xO₃ (x = 0, 0.01 and 0.03) are prepared by the mixed oxide method and sintered at 1050 °C for 1 h. The effect of Nb doping on the structure is examined by X-ray diffraction. The microstructure is examined by scanning electron microscopy. The variation in relative permittivity with temperature is measured using an impedance analyzer. Ferroelectric properties are measured at room temperature using a Sawyer Tower circuit. Piezoelectric properties are measured using a d₃₃ meter and a contact type displacement sensor. All the samples have high density, a rhombohedral unit cell and equiaxed, micron-sized grains. All the samples show relaxor-like behavior. Nb doping causes a reduction in conductivity by one to two orders of magnitude at 200 °C. The samples have narrow P-E loops reminiscent of a linear dielectric. The samples all possess bipolar butterfly S-E loops characteristic of a classic ferroelectric material. Nb doping causes a decrease in d₃₃ and S_max/E_max.

Seo-Hee Jang

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