Enhancing temperature stability in potassium-sodium niobate ceramics through phase boundary and composition design

Phase boundaries and composition design were explored to achieve both high piezoelectricity and favorable temperature stability in potassium-sodium niobate ceramics, using (1-x)(K,Na)(Nb,Sb)O-3-xBi(Na,K)(Zr,Sn,Hf)O-3 ceramics. A rhombohedral-tetragonal (R-T) phase boundary was constructed at x =0.035-0.04 by co-doping with Sb5+ and Bi(Na,K)(Zr,Sn,Hf)O-3. More importantly, a superior temperature stability was observed in the ceramics with x = 0.035, accompanying with a stable unipolar strain at room temperature to 100 degrees C. The ceramics with x = 0.035 also exhibited improved piezoelectric properties (e.g., piezoelectric coefficient d(33) similar to 465 pC/N and electromechanical coupling factor k(p) = 0.47) and Curie temperature (T-c similar to 240 degrees C). The Rietveld refinement and in-situ temperature-dependent piezoresponse force microscopy (PFM) results indicated that the enhancement of the piezoelectric properties was caused by the easy domain switching, high tetragonal fraction, and tetragonality, while the improved temperature stability mainly originated from the stable domain structures.