Understanding the Nature of Temperature Stability in Potassium Sodium Niobate Based Ceramics from Structure Evolution under External Field.

Preferable temperature stability of ferroelectric and strain properties can be achieved in potassium sodium niobate (KNN)-based ceramics compared to that of other lead-free piezoelectric material systems, giving it greater potential for use in electronic devices once the temperature reliability issue related to the piezoelectric constant (d33) can be further resolved. Through exploration of the nature of the temperature stability from the evolution of a crystal structure under external fields, it has been determined that the electric field has no effect on the temperature stability of d33, resulting in almost the same trend of changes in d33 with temperature under both in situ and ex situ measurements, which is totally unlike the close relationship between the electric field and the strain temperature stability. With analysis of multiple factors including intrinsic phase coexistence, electric-field-induced domain texturing, lattice distortion, and thermally induced domain detexturing, the intrinsic contribution of phase evolution plays a dominant role in the temperature stability of d33 because of the mutual counteraction of domain texturing, lattice distortion, and thermal domain detexturing. Our research provides a systematic approach to understanding the nature of the d33 temperature stability in KNN-based ceramics and proposes some favorable suggestions on the future design of materials with good temperature reliability.