Thermal Reliability of Alkaline Niobate-Based Lead-Free Piezoelectric Ceramics

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Alkaline niobate-based (K,Na,Li,Ba,Sr)(Nb,Ta,Zr)O3 (ANSZ) ceramics were prepared by conventional sintering process, and their piezoelectric properties were measured. The Curie temperature ($T_{\text{C}}$) of the ANSZ ceramic was 278 °C. The electromechanical coupling factor ($k_{\text{p}}$) and the piezoelectric constant ($d_{33}$) were 45.5% and 295 pC/N, respectively, and the dielectric permittivity ($\varepsilon_{33}^{\text{T}}/\varepsilon_{0}$) was 1610 at room temperature. The thermal reliability was tested by 1000 cycles of thermal shock with temperatures ranging from $-55$ to 125 °C. The change in $d_{33}$ of ANSZ was compared with that of commercial Pb(Zr,Ti)O3 after 1000 cycles of thermal shock. The phase transition behavior of ANSZ was investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC) simultaneous measurement. No appreciable endothermic peak accompanied by a polymorphic phase transition was observed on the DSC curve. The crystalline structure was investigated in detail by XRD measurement with high-energy synchrotron radiation. The coexistence of two ferroelectric phases in a wide temperature range (from $-175$ to 150 °C) was observed.
2009-09-25