(K,Na)NbO3-based lead-free ceramics with enhanced temperature-stable piezoelectricity and efficient red luminescence

There has been a surge of research interest in the promising lead-free potassium−sodium niobate (KNN)-based ceramics, applications of which could be significantly promoted by improving thermal stability of piezoelectricity. Besides, endowing the KNN-based ceramics with photoluminescence property by rare-earth-ion doping can make them more completive lead-free counterparts in potential applications such as novel multifunctional sensing devices. Herein, a novel KNN-based ceramic material doped with Eu was elaborately designed to simultaneously obtain enhanced temperature-stable piezoelectricity and good luminescence property. By the introduction of diffused phase transition and the modulation of unit cell distortion, a large piezoelectric strain coefficient (d*33) with a small variation (590±59 pm/V) over a wide temperature range (from room temperature to 110 ℃) was realized. The optimal composition also exhibited a considerable piezoelectric coefficient (d33) with small fluctuation (330±33 pC/N) from 20 to 80 ℃. In addition to the enhanced temperature-stable piezoelectricity, the luminescence of these ceramics was slightly enhanced with the elevation of BaZrO3 (BZ) doping contents, which could be attributed to the increased compositional disorder and the decreased unit cell distortion of the matrix material. Moreover, an optical characteristic was more prominent at ultra-low temperatures. This work unprecedentedly provides a novel paradigm for the design of multifunctional KNN-based ceramics with enhanced temperature-stable piezoelectricity and good luminescence property, revealing the great potential of the rare-earth-element-doped KNN material for future applications in the novel multifunctional devices.