Control of phase transition of (K_0.5Na_0.5)(Nb_0.8Ta_0.2)O₃ lead-free ceramics by alkaline metal modification

ABSTRACT

(Na_0.5K_0.5)(Nb_0.8Ta_0.2)O₃ lead-free ceramics with variation of alkaline metal elements were investigated. It has been found that the phase transition temperature of the ceramics can be widely adjusted by A-site doping. Li⁺ doping could increasing T_C, while other alkaline metal elements Na⁺, K⁺, Rb⁺ and Cs⁺ doping couldn't stabilize orthorhombic phase. T_C increased to 377°C from the initial 306°C as the Li⁺ amount increasing from 0.02 to 0.10, meanwhile, T_O-T decreased from 82°C to −38°C. It is indicated that T_C can be influenced by tolerance factor t. An enhanced d₃₃ = 185 pC/N and k_p = 44% at room temperature were observed in the ceramics with Li⁺ content of x = 0.04, probably because the corresponding T_O-T of the ceramics is moved to room temperature at x = 0.04 Li⁺ amount. The enhanced piezoelectric properties indicate that the modified (Na_0.5K_0.5)NbO₃ lead-free materials are promising candidates to complement Pb(Zr,Ti)O₃ based solid solutions on certain occasions and the expanded phase-transition temperature range can be beneficial to the service circumstances of the materials.

KEYWORDS:

• Lead-free piezoelectric ceramics
• phase transition
• Li⁺ doping
• Curie temperature