The effect of the annealing temperature on the structure and electrical properties of Li/Ta-modified (K0.5Na0.5)NbO3-based piezoelectric crystals

As we all known that the piezoelectric single crystals exhibit unique and outstanding performance and therefore have been used widely in many electronic devices, including sensors, actuators, and transducers. Recently, large lead-free K0.5Na0.5NbO3(KNN)-based piezoelectric single crystals were prepared using a seed-free solid-state crystal growth (SFSSCG) method. However, there are some defects in the crystals prepared by this method. The defects would inhibit the domain-wall movement and increase the leakage currents in the crystals and then prevent the improvement of performance of the crystals. Here, an approach to considerably enhance the piezoelectric properties of the KNN-based crystals by annealing treatment is reported. The effect of the annealing temperature on the structure and electrical properties of the crystals was studied. The results show that the annealing temperature has a little effect on the crystalline structure but great effect on the natural surface morphology, domain structure, and electrical properties of the single crystals. When the annealing temperature is in the range of 550 similar to 800 degrees C, it can enhance significantly the piezoelectric, ferroelectric, and dielectric properties of the crystals and decrease their dielectric loss. The crystal annealed at 700 degrees C shows excellent properties: d(33) = 591pC/N, epsilon(r) = 580, tan delta = 0.01, k(t) = 0.715, and T-c = 417 degrees C. The effects of the annealing treatment on the leakage current density and conduction mechanism in the crystals were also studied. The results indicate that the annealing treatment enables the crystals to far outperform the unannealed crystals and comparable to the lead-based materials.

Automated summary

Annealing treatment can significantly enhance the performance of KNN-based piezoelectric single crystals, including their piezoelectric, ferroelectric, and dielectric properties. The optimal annealing temperature is in the range of 550 to 800 degrees Celsius.