Role of antimony in the phase structure and electrical properties of potassium-sodium niobate lead-free ceramics

In the past ten years, antimony has been reported to strongly affect the developments in the piezoelectric properties of (K,Na)NbO₃ (KNN) lead-free ceramics, that is, its enhanced piezoelectric activity is closely related to the doped antimony as well its content. In this work, we clarified the role of Sb⁵⁺ in the construction of a phase structure and the enhancement of electrical properties of a pure KNN ceramic. Research has shown that doping with Sb⁵⁺ can simultaneously move their orthorhombic-tetragonal phase transition temperature (T_O-T) and rhombohedral-orthorhombic phase transition temperature (T_R-O) forward to room temperature, benefiting the formation of three types of phase boundaries. The coexistence of rhombohedral and orthorhombic phases was established in the Sb⁵⁺ composition range of 0.07-0.09 by this regulation. In addition, their grain sizes were determined by the Sb⁵⁺ content, that is, the optimum Sb⁵⁺ content (x ≤ 0.05) induces grain growth, and their grain sizes become considerably smaller when the compositions deviate from x > 0.05. More importantly, their electrical properties could be also tuned by changing the Sb⁵⁺ content. Their dielectric, ferroelectric, and piezoelectric properties are strongly dependent on the antimony content, whereas the strain behavior is mainly ascribed to the multi-phase transition region as well as the structural change of phase transitions. As a result, this work would help to further understand the underlying physical origin for enhanced electrical properties in alkali niobate ceramics.