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

High Temperature-Insensitive Electrostrain Obtained in (K, Na)NbO3-Based Lead-Free Piezoceramics

Over the last decades, notable progress is achieved in (K, Na)NbO3 (KNN)-based lead-free piezoceramics. However, more studies are conducted to increase its piezoelectric charge coefficient (d33). For actuator applications, piezoceramics need high electric-field induced strain under low electric fields while maintaining exceptional temperature stability across a wide temperature range. In this study, this work developes Li/Sb-codoped KNN (LKNNS) ceramics with high electrostrain by defect engineering and domain engineering. A remarkable strain of 0.43%, along with a giant d33* value of 2177 pm V-1, is attained in the LKNNS ceramic at 20 kV cm-1. The ceramic exhibits a minimal performance decrease of less than 15% over a temperature range from room temperature to 150 °C. The exceptional strain is attributed to the presence of A-site vacancy-oxygen vacancy (V A ' - V O • • ${\mathrm{V}}_{\mathrm{A}}^{{\prime}}{\mathrm{ - V}}_{\mathrm{O}}^{{\mathrm{ \bullet \bullet }}}$ ) defect dipoles and the increase in nano-domains. The hierarchical domain configuration andV A ' - V O • • ${\mathrm{V}}_{\mathrm{A}}^{{\prime}}{\mathrm{ - V}}_{\mathrm{O}}^{{\mathrm{ \bullet \bullet }}}$ defect dipoles impede the switched domains from reverting to their original state as temperature increases, furthermore, the elongated dipole moments ofV A ' - V O • • ${\mathrm{V}}_{\mathrm{A}}^{{\prime}}{\mathrm{ - V}}_{\mathrm{O}}^{{\mathrm{ \bullet \bullet }}}$ caused by rising temperatures compensate for strain reduction results in exceptional temperature stability. This study provides a model for designing piezoelectric materials with exceptional overall performance under low electric fields and across a wide temperature range.

Polarity Modulation Induced High Electrostrain Performance with Near-Zero Hysteresis in a (Sr0.7Bi0.2□0.1)TiO3-Based System

High-precision piezo actuators necessitate dielectrics with high electrostrain performance with low hysteresis. Polarity-modulated (Sr_0.7Bi_0.2□0.1)TiO₃-based ceramics exhibit extraordinarily discrete multiphase coexistence regions: (i) the relaxor phase coexistence (RPC) region with local weakly polar tetragonal (T) and pseudocubic (Pc) short-range polar nanodomains and (ii) the ferroelectric phase coexistence (FPC) region with T long-range domains and Pc nanodomains. The RPC composition features a specially high and pure electrostrain performance with near-zero hysteresis (S ∼ 0.185%, Q₃₃ ∼ 0.038 m⁴·C^-2), which is double those of conventional Pb(Mg_1/3Nb_2/3)O₃-based ceramics. Particular interest is paid to the RPC and FPC with multiscale characterization to unravel local structure-performance relationships. Guided by piezoelectric force microscopy, scanning transmission electron microscopy, and phase-field simulations, the RPC composition with multiphase low-angle weakly polar nanodomains shows local structural heterogeneity and contributes to a flat local free energy profile and thus to nanodomain switching and superior electrostrain performance, in contrast to the FPC composition with a macroscopic domain that shows stark hysteresis. This work provides a paradigm to design high-precision actuator materials with large electrostrain and ultralow hysteresis, extending our knowledge of multiphase coexistence species in ferroelectrics.

Comparison of contribution to phase boundary from A-site aliovalent dopants in high-performance KNN-based ceramics

Different influence of A-site aliovalent dopants, Bi3+ and Ca2+, on phase boundary and electrical properties in KNN-based ceramics.