Influence of pH values on the surface and properties of BCZT nanopowders synthesized via sol-gel auto-combustion method

To investigate the preparation of lead-free nano-powder for piezoelectric thin film coating applications, in this work, barium calcium zirconate titanate (Ba0·85Ca0.15Zr0·1Ti0.9O3 or BCZT) was synthesized by the sol-gel auto-combustion method with controlled pH values. The change in pH value of 5, 7 and 9 was carried out by adjusting NH4OH content while the molar ratio of metal and citric acid was fixed at 1:1. The as-burnt powder was calcined at 900 °C for 2 h and was then characterized in terms of chemical bonding, crystal structure and morphology using Raman, FTIR spectroscopy, XRD and TEM techniques. Particle size and tetragonality of the powder increased with increasing pH value. Raman spectrum peaks of as-burnt powders showed an amorphous phase which was in agreement with XRD result. The calcined powders showed a broad peak at ~ 562 cm− 1 corresponding to the stretching vibration of TiO and ZrO bonds in perovskite structure. Crystallite size calculated using Scherrer's equation was in a range of 32-35 nm. SAED pattern showed that the calcined powders were polycrystalline with respective indices of perovskite unit cell. The pH 7 synthesis condition, which was found to be optimum for producing nano-sized powder with narrow size distribution, suggested that chemically neutral environment was an important factor for good reactivity with well-controlled nucleation and growth of BCZT particles.