Preparation and properties of nanocrystalline BNT-BTx piezoelectric ceramics by sol-gel and spark plasma sintering

(Bi0.5Na0.5)TiO3 was doped in situ with 5, 8, and 11 mol% BaTiO3 (BNT-BTx; x = 0.05, 0.08 and 0.11) using a sol-gel technique. The resulting powders from gel precursors showed microstructures consisting of nano-sized grains and crystalline perovskite structure. Spark plasma sintering (SPS) technique was used to prepare high densified (98–99%ρtheor) BNT-BTx ceramics from these nanopowders. The results confirm the spark plasma sintering method applied to nano-scale powders, obtained by sol-gel, as a viable route in producing nanostructured ceramics. The evolution of the structure and electrical properties of the ceramics with BaTiO3 concentration (x) was investigated. The permittivity of BNT-BT0.08 ceramic is higher (εr = 2090, at 100 kHz) than that for x = 0.05 (εr = 1350) and x = 0.11 (εr = 1800). BNT-BT0.08 ceramic shows maximum values for the frequency constants (Np, Nt), piezoelectric charge coefficient (d31) and piezoelectric voltage coefficient (g31), and minimum values for the electromechanical coupling factor (kp) and piezoelectric charge coefficient (d33). The electrical properties of these ceramics are influenced by grains size, oxygen deficiency and non-uniform internal stresses due to these oxygen deficiencies. BNT-BTx ceramics sintered by SPS seem to be good ceramic resonators with high mechanical quality factor (Qm).