Barium zirconate-titanate/barium calcium-titanate ceramics via sol-gel process: novel high-energy-density capacitors

Lead-free barium zirconate-titanate/barium calcium-titanate, [(BaZr0.2Ti0.80)O-3](1-x)-[(Ba0.70Ca0.30)TiO3](x) (x = 0.10, 0.15, 0.20) (BZT-BCT) ceramics with high dielectric constant, low dielectric loss and moderate electric breakdown field were prepared by the sol-gel synthesis technique. X-ray diffraction patterns revealed tetragonal crystal structure and this was further confirmed by Raman spectra. Well-behaved ferroelectric hysteresis loops and moderate polarizations (spontaneous polarization, P-s similar to 3-6 mu C cm(-2)) were obtained in these BZT-BCT ceramics. Frequency-dependent dielectric spectra confirmed that ferroelectric diffuse phase transition (DPT) exists near room temperature. Scanning electron microscope images revealed monolithic grain growth in samples sintered at 1280 degrees C. 1000/epsilon versus (T) plots revealed ferroelectric DPT behaviour with estimated gamma values of similar to 1.52, 1.51 and 1.88, respectively, for the studied BZT-BCT compositions. All three compositions showed packing-limited breakdown fields of similar to 47-73 kV cm(-1) with an energy density of 0.05-0.6 J cm(-3) for thick ceramics (> 1 mm). Therefore these compositions might be useful in Y5V-type capacitor applications.