Design on improving piezoelectric strain and temperature stability of KNN‐based ceramics

Abstract Lead‐free 0.99(0.96K 0.46 Na 0.54 Nb 1‐ x Ta x O 3 ‐0.04Bi 0.5 (Na 0.82 K 0.18 ) 0.5 ZrO 3 )‐0.01CaZrO 3 (0.99(0.96KNNTa x ‐0.04BNZ)‐0.01CZ) ceramics were prepared by a solid‐state sintering method. Ta 2 O 5 doped in the 0.99(0.96KNNTa x ‐0.04BNZ)‐0.01CZ ceramics results in a phase structure transition from the orthorhombic (O)/tetragonal (T) phase to the rhombohedral (R)/T phase. The Ta 2 O 5 dopant induces a decrease in the average grain size from ~1.70 to ~0.69 μm. At x = 0.02 and 0.04, the ceramics have a high reverse piezoelectric coefficient (~500 pm/V under 25 kV/cm). The ceramics with x = 0.04 show an optimal level of unipolar strain, reaching 0.17% under 35 kV/cm at room temperature, and their field‐induced strain varies <10% in the temperature range from 25 to 135°C. The presence of the O phase in the polymorphic phase boundary (PPB) improves the temperature stability the reverse piezoelectric coefficient ( ). Obtaining KNN‐based ceramics with good piezoelectric properties and weak temperature sensitivity by designing a R/O/T phase boundary and controlling the average grain size to the submicrometer level is highly feasible.