New Role of Relaxor Multiphase Coexistence in Potassium Sodium Niobate Ceramics: Reduced Electric Field Dependence of Strain Temperature Stability

The influence of relaxor behavior on strain behavior is less investigated in potassium sodium niobate [(K, Na)NbO₃, KNN] ceramics. Here, we report novel phenomena in the temperature-dependent strain behavior with the electric field of KNN-based ceramics with relaxation characteristics. The strain temperature stability is electric field dependent below the threshold electric field: temperature-dependent strain can be effectively improved by increasing the applied electric fields, while it remains almost electric field independent above the threshold electric field. Such a macroscopic property change can be well consistent with the following microscopic domain structure evolution. Little voltage dependence is found above a certain voltage by employing voltage-dependent piezoresponse hysteresis loops and domain switching under different temperatures, implying the contribution of domain behavior to the change of strain. Ergodic polar nanoregions (PNRs) are induced by the high-density domain walls among nanodomains in the relaxor samples, as revealed by the atomic-resolution polarization mapping with Z-contrast. The facilitated domain switching due to the lowered energy barrier and nearly vanished polarization anisotropy based on the PNRs with nanoscale multiphase coexistence can promote the electric field compensation for temperature effect. This work demonstrates the contribution of relaxor behavior to the electric field dependence of strain temperature stability in KNN-based ceramics.