Dielectric, ferroelectric and piezoelectric proprieties of GdCoO3 doped (K0.5Na0.5)NbO3

• GdCoO3 doping stabilizes the room temperature orthorhombic phase.
• High Curie temperatures were observed.
• A ferroelectric softening effect was noticed.
• An improved planar coupling factor of 39.5% was obtained for 0.75 mol% GdCoO3.
• The mechanical quality factor decrease for all compositions studied.

Lead free piezoelectric ceramics (1 − x)(K0.5Na0.5)NbO3–xGdCoO3 (0 ⩽ x ⩽ 5 mol%) were prepared by conventional ceramic process. The effect of GdCoO3 content on the crystalline structure, microstructure, dielectric, ferroelectric and piezoelectric proprieties were investigated. The results show that all composition posses an orthorhombic crystal structure at room temperature, and GdCoO3 doping slightly shift the high temperature phase transitions orthorhombic–tetragonal (To−T) and tetragonal–cubic (Curie temperature, TC). Good and dense microstructure was obtained, with an average grain size decreasing for higher doping degrees. Compared to the reference sample (K0.5Na0.5)NbO3, GdCoO3 addition reduce the coercive field Ec of all compositions studied, and increases the remnant polarization Pr for 0 ⩽ x ⩽ 1 mol%. The mechanical quality factor Qm is decreasing for all doped samples, but planar electromechanical coupling factor kp increases for 0 ⩽ x ⩽ 1 mol%. The optimum composition was found to be 0.9925(K0.5Na0.5)NbO3–0.0075 GdCoO3, with a measured density of 4.3366 g/cm3, dielectric constant of 535 and dielectric loss of 0.04 at room temperature, To−T = 198 °C, TC = 408 °C, Pr = 18.58 μC/cm2, Ec = 13.31 kV/cm, Qm = 263 and kp = 0.395. These properties make this material a potential candidate for soft piezoelectric devices suitable for high temperature application.