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

Lead‐free 0.99(0.96K0.46Na0.54Nb1‐xTaxO3‐0.04Bi0.5(Na0.82K0.18)0.5ZrO3)‐0.01CaZrO3 (0.99(0.96KNNTax‐0.04BNZ)‐0.01CZ) ceramics were prepared by a solid‐state sintering method. Ta2O5 doped in the 0.99(0.96KNNTax‐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 Ta2O5 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 (d33∗). 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. [ABSTRACT FROM AUTHOR]