IMF2017

Bismuth sodium titanate (Bi_0.5Na_0.5)TiO₃ (BNT) based ceramics which are near the morphotropic phase boundary (MPB) have piezoelectric properties comparable to those of lead‑containing Pb(Zr,Ti)O₃ (PZT) but concerns arise regarding thermal stability during long term operation due to lower depolarization temperatures. A previous study showed that T_d was remarkably improved to ~152 °C for the 0.2% Mn composition, demonstrating that Mn doping improves structural thermal stability in BNT7.5BT at increased temperatures. Ceramic disks of each composition were prepared and sintered for 2 hours at 1170ºC. Disks coated with silver paste were placed in an oven and connected to an impedance gain-phase analyzer. Runs from 100 ºC to 600 ºC in 50 ºC steps were made at frequencies from 0.1 Hz to 1 MHz in 71 logarithmic steps. Two samples were run for each Mn concentration, the first to 500 ºC and the second to 600 ºC. The 0% Mn samples had activation energies near 0.75 eV. The 0.2% Mn samples showed high E_a near 1.64 eV indicative of electronic conductivity. The 1% Mn samples showed low E_a near 0.71 eV characteristic of ionic conductivity, and had the lowest resistivity of all the samples. The first 2% Mn sample showed a low E_a indicating ionic conductivity to 400 ºC. The second sample had similar results to 400 ºC showing ionic conductivity at lower temperatures, but additional data points to 600 ºC revealed a curved semi-log plot ending in straight lines showing electronic conductivity dominating at higher temperatures.