Remarkably High-Temperature Stability of Bi(Fe1-xAlx)O3-BaTiO3 Solid Solution with Near-Zero Temperature Coefficient of Piezoelectric Properties

The 0.72Bi(Fe1-xAlx)O-3-0.28BaTiO(3) (x=0, 0.01, 0.03, 0.05, and 0.07, abbreviated as BFAx-BT) lead-free high-temperature ceramics were prepared by the conventional ceramic processing. Systematic investigation on the microstructures, crystalline structures, dielectric and piezoelectric properties, and high-temperature stability of piezoelectric properties was carried out. The crystalline structures of BFAx-BT ceramics evolve from rhombohedral structure with x<0.01 to the coexistence of rhombohedral structure and pseudocubic phases with x approximate to 0.01, finally to pseudocubic phases when x>0.03. Remarkably high-temperature stability with near-zero temperature coefficient of piezoelectric properties (TCk(p)), together with improved piezoelectric properties has been achieved for x=0.01 BFAx-BT ceramics. The BFAx-BT(x=0.01) ceramics simultaneously show the excellent piezoelectric properties of d(33)=151 pC/N, k(p)=0.31 and super-high-temperature stability of T-d=420 degrees C, TCk(p)=1x10(-4). It is considered that the observed strong piezoelectricity and remarkably high-temperature stability should be ascribed to the phase coexistence of rhombohedral and pseudocubic phases. The rhombohedral phases have a positive TCk(p) value and the pseudocubic phases possess a negative TCk(p) value. Thus, the TCk(p) value of BFAx-BT ceramics can be tuned by composition of x.