Crystal structure and thermal annealing behaviors of high d ₃₃ Aurivillius-phase ceramics Li_0.04Ce_0.04Na _(0.46-x/2)Bi_(4.46+x/2)Ti_(4-x)Sc _x O₁₅ with the Sc³⁺/Bi³⁺ co-substitution

Modified Aurivillius-type-structured piezoelectric ceramics, Li _0.04Ce_0.04Na_(0.46-x/2)Bi _(4.46+x/2)Ti_(4-x)Sc _x O₁₅ (LiCe-NBT-Sc-x, x = 0, 0.025, 0.075, 0.125, 0.15, 0.175) were synthesized by using conventional solid-state reaction process. Rietveld refinement for the x = 0.125 modified sample was carried out by using powder X-ray diffraction and LiCe-NBT-Sc-0.125 was confirmed to be a four-layer Aurivillius oxide with orthorhombic space group A2 ₁ am [a = 5.45814(7) Å, b = 5.43029(7) Å, c = 40.8547(4) Å and V = 1,210.902(26) ų; Z = 4], at room temperature. The Sc³⁺/Bi ³⁺ substitution led to an increase in Curie temperatures (T _c) and an enhancement in piezoelectric property, and the LiCe-NBT-Sc-0.125 ceramic with a T _c of 675 °C had a high piezoelectric activity (d ₃₃) of 32 pC/N. Variable thermal-annealing d ₃₃ and resistivity (ρ) of the LiCe-NBT-Sc-0.125 ceramic were investigated; the d ₃₃ of the O₂ annealed sample reached up to 37 pC/N, and its resistivity was about 6.8 × 10⁶ Ω cm at 575 °C and about 6.5 × 10⁵ Ω cm at 650 °C.