Abstract
Ceramics in the system (Bi0.5K0.5)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 (Bi0.5K0.5)TiO3-BiFeO3. Powders of composition 0.4(K0.5Bi0.5)Ti1−xNbxO3-0.6BiFe1−xNbxO3 (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 Smax/Emax.
Highlights
Solid solutions containing perovskite BiFeO3 have recently been attracting attention for use as lead-free piezoelectric ceramics
Incorporation of Nb causes a small increase in the unit cell parameter and a small decrease in the rhombohedral distortion
The incorporation of Nb causes an increase in the second phase content of both calcined powders and sintered ceramics
Summary
Solid solutions containing perovskite BiFeO3 have recently been attracting attention for use as lead-free piezoelectric ceramics. In order to improve the electrical properties, solid solutions of BiFeO3 with other perovskites such as BaTiO3 and PbTiO3 have been studied [10,11,12]. Compositions close to the MPB have good piezoelectric properties (d33 > 100 pC/N, bipolar strain of ~0.15% at an electric field of 6 kV/mm) and good temperature stability [10,12,14,15].
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