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

Abstract

Lead-free barium zirconate-titanate/barium calcium-titanate, [(BaZr 0.2 Ti 0.80 )O 3 ] 1− x –[(Ba 0.70 Ca 0.30 )TiO 3 ] 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 ∼ 3–6 µC 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 °C. 1000/ε versus ( T ) plots revealed ferroelectric DPT behaviour with estimated γ values of ∼1.52, 1.51 and 1.88, respectively, for the studied BZT–BCT compositions. All three compositions showed packing-limited breakdown fields of ∼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.