Effects of Bismuth Deficiency on Piezoelectric Properties of (Bi0.5-xNa0.5TiO3)0.94(BaTiO3)0.06 Ceramics

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High-density ceramics with compositions of (Bi0.5-xNa0.5TiO3)0.94(BaTiO3)0.06 (BNBT-6), where x=0−0.03, were fabricated to develop potentially useful lead-free piezoelectric materials with high mechanical quality factors, Qm. Effects of Bi-deficiency on the physical properties of the fabricated ceramics were investigated. Microstructures of the samples with a Bi-deficiency of x≥0.015 showed no appreciable grain boundaries. This is due to the liquid-phase sintering that occurs for a Bi-deficiency concentration of x≥0.015. The mechanical quality factors for the radial vibration mode and the thickness vibration mode exhibited a maxima at x=0.022 and 0.024 with values of 674 and 128, respectively. The temperature coefficients of resonant and antiresonant frequencies (TCF) of the BNBT-6 samples with x=0.019−0.030 were almost constant with TCFfr1=−400 ppm/°C for the fundamental resonant frequency and TCFfa1=−320 ppm/°C for the fundamental antiresonant frequency, respectively. This method of creating a deficiency of a very small quantity of Bi in the BNBT-6 composition produces substantial improvement in Qm characteristics without deterioration of other piezoelectric parameters.