Investigation of phase structure, microstructure, and electrical properties of LaAlO₃-modified alkali niobate lead-free perovskite

LaAlO₃ as an effective additive for modification of KNN system has never been systemically discussed before. Here, (0.96−x)K_0.48Na_0.52NbO₃–0.04Bi_0.5Na_0.5ZrO₃–xLaAlO₃ (KNN–BNZ–xLA) ceramics have been synthesized by traditional solid-state sintering with a special emphasis on the influences of LaAlO₃ components on the crystallographic structure, microstructure, and electrical properties. XRD and Rietveld refinements were performed to explore the effects of LaAlO₃ on the phase evolution and the crystallographic structure, respectively, which revealed a coexistence of tetragonal and orthogonal phases. And through the results of the temperature-dependent dielectric constant (ε _r−T), we found the phase boundary shifted to low temperature slowly with the increase of LaAlO₃ components. As a resut, the samples with x = 0.004 demomstrated the excellent properties of d ₃₃ ~ 354 pC/N, k _p ~ 46%, T _C ~ 325 °C, P _r ~ 21.8 μC/cm², tan δ ~ 3.9%, together with a high strain value as high as 0.18% at 50 kV cm⁻¹, which are originated to the contributions of the crystallographic structure transition and dense microstructure. Additionally, it is worth noting that such a good thermal stability of piezoelectricity (e.g., d ₃₃ ≥ 303 pC/N, T ≤ 300 °C) was also observed by thermal depoling method and temperature-dependent P–E hysteresis loops. Not only is this work itself scientifically fascinating but it also renders these materials appealing for practical applications as a candidate for lead-based ones.