The effects of sintering atmospheres on piezoelectric performances of Co-doped Ba0.88Ca0.12Zr0.12Ti0.88O3 ceramics

This work investigates the effects of content ratio Co3+/Co2+ on piezoelectric properties of lead-free Ba0.88Ca0.12Zr0.12Ti0.88O3 (BCZT) ceramics. For this purpose, 0.10 wt% Co ions using a CoO powder doped BCZT ceramics were sintered under various atmospheres (ranging from pure nitrogen to 100 vol% oxygen concentration) to vary the ratio value Co3+/Co2+. X-ray photoelectron spectroscopy analysis revealed the coexistence of Co3+ and Co2+ for oxygen concentration below 40 vol% and the single oxidation state of Co3+ for oxygen concentration over 50 vol%. Co2+ substitution could induce more oxygen vacancy to accelerate densification and grain growth, whereas Co3+ substitution usually leads to larger lattice distortion to generate a stable asymmetric structure. When oxygen concentration was 30 vol% and Co3+/Co2+ near to 1.0, the respective superiority of Co3+ and Co2+ is brought into full play, and the ceramic showed the highest piezoelectric constant d(33)* similar to 518 pm/V (380 pm/V for undoped BCZT) and the relatively high Curie temperature T-c similar to 105 degrees C (95 degrees C for undoped BCZT). This study suggests that optimizing sintering atmosphere might be an effective way to enhance the piezoelectric properties for some composition-modified piezoelectric BCZT ceramics.