Novel rhombohedral and tetragonal phase boundary with high T C in alkali niobate ceramics

Abstract

We design a new composition to establish rhombohedral and tetragonal phase coexistence in alkali niobate ceramics. The composition of (1−x)[0.94(K0.48Na0.52)NbO3–0.045Bi0.5Na0.5ZrO3−0.015CaTiO3]–xLi0.2Na0.8NbO3 has been synthesized by conventional solid-state reaction method. XRD patterns and curves of permittivity versus temperature show that the phase of this kind of perovskite structure ceramics convert tetragonal phase (x ≤ 0.4) into rhombohedral phase (x ≥ 0.5), and the rhombohedral and tetragonal (R-T) phases coexistence has been confirmed at x = 0.425 ~ 0.475. Around this phase boundary, the ceramics with x = 0.425 show an optimum piezoelectric properties (d 33 ~ 178 pC/N and k p ~ 38.5%) with high T C ~ 400 °C. Moreover, the ceramics exhibited strong temperature stability. This work exhibits obviously different piezoelectric properties from other R-T coexistence systems in KNN-based ceramics, the underlying physical mechanism has been discussed. It is believed that this method could promote the further development of alkali niobate ceramics.