Improvement of the electrical properties of textured BNKT-modified (K, Na)NbO₃ lead-free ceramics in the broad operating temperature range

In this study, the improvement in the electrical properties of textured BNKT-modified (K, Na)NbO₃ ceramics was extensively investigated across a broad, high operating temperature range. Herein, the two crucial issues of phase transitions and microstructure improvement of BNKT-modified (K, Na)NbO₃ ceramics were discussed utilizing the crystal orientation technique. Additionally, we have verified the existence of phase transition temperatures for the R–O phase (T_R–O), O–T phase (T_O–T), and T–C phase (T_C). This is based on the research on the temperature-dependent characteristics of the random and textured BNKT-modified (K, Na)NbO₃ lead-free ceramics in the temperature range of −100 to 420 °C. The experimental results revealed a significant improvement in the electrical properties of ceramics, which was attributed to the strategy of shifting T_R–O and T_O–T phase transitions to near RT, forming R–O–T phase boundaries. Besides, the textured KNLNS-BNKT ceramic with 82% grain orientation demonstrated better dielectric, piezoelectric, and ferroelectric properties compared to those randomly fabricated by the traditional ceramic method (the ε_r of 1223, the P_r of 13.5 μC/cm², the d₃₃ of 245 pC/N, and the k_p of 0.4 increased by 11.7%, 8%, 25%, and 11%, respectively). Moreover, the normalized strain (d₃₃*) achieved a maximum value of 495 pm/V at 50 °C under an electric field of 24 kV/cm.