Effects of excess lead-oxide and bismuth-oxide content on the electrical properties of high-temperature bismuth scandium lead titanate ceramics

Aeronautic and aerospace applications require piezoelectric materials that can operate at high temperatures. The air-breathing aeronautic engines can use piezoelectric actuators for active combustion control for fuel modulation to mitigate thermo-acoustic instabilities and/or for gas flow control to improve efficiency. The principal challenge for the insertion of piezoelectric materials is their limitation for upper use temperature and this limitation is due to low Curie temperature and increasing conductivity. We investigated processing, microstructure and property relationship of (1-x)BiScO
₃
-(x)PbTiO
₃
(BS-PT) composition as a promising high temperature piezoelectric. The effect of excess Pb and Bi and their partitioning in grain boundaries were studied using impedance spectroscopy, ferroelectric, and piezoelectric measurement techniques. Excess Pb addition increased the grain boundary conduction and the grain boundary area (average grain size was 24.8μm, and 1.3μm for compositions with 0at.% and 5at.% excess Pb, respectively) resulting in ceramics with higher losses (tan δ= 0.9 and 1.7 for 0at.% and 5at.% excess Pb at 350 °C and at 10kHz) that were not resistive enough to pole. Excess Bi addition increased the resistivity (ρgrain = 4.1×10
¹⁰
Ω.cm and 19.6 × 10
¹⁰
Ω.cm for compositions with 0at.% and 5at.% excess Bi, respectively), improved poling, and increased the piezoelectric coefficient from 137 to 197 pC/N for 5at.% excess Bi addition. In addition, loss tangent decreased more than one order of magnitude at elevated temperatures (<300 °C). For all compositions the activation energy of the conducting species was similar (≈ 0.35-0.40 eV).