Ferroelectric Materials for High Temperature Piezoelectric Applications

Electronic control and operation in almost all advanced devices or machines involve use of various sensors and actuators, many of which are based on piezoelectric (PE) effect. Ferroelectric (FE) materials forming a sub-group of piezoelectric materials have additional applications. Subject to success in materials and related developments, PE and FE devices perform competitively with alternative devices but at lower cost in most cases. There is increasing commercial and technical interest for PE actuators (ranging from electronic muscles, fuel injectors and inkjet printers to various vibrators), PE sensors (pressure and other sensors and motion detection to energy recovery), and ultrasonic imaging devices. PE to non-PE transition temperature (Curie temperature for FE PE materials) and piezoelectric coefficients together decide the choice of the right material for any particular application. Since most of these applications, including medical ultrasonic imaging, are done at or near room temperature, low Curie temperature (but otherwise attractive) piezoelectric materials, based on barium titanate (BT), lead zirconate titanate (PZT) and relaxor ferroelectric ceramics, have served us well. However, a few important applications, in automobile and rocket exhausts, in some engines and gadgets, and inside high pressure molten metal in nuclear Fast Breeder Reactors (FBRs) involve high temperatures (HTs), higher than or nearing the Curie temperature of even PZT. These applications including FBRs, generating nuclear fuel and power, demand development of high temperature piezoelectric materials. FBRs can close the nuclear fuel cycle by partially using the nuclear waste (containing U-238) and thus minimize waste disposal problem. That makes nuclear energy a better green energy. Working on Th-232 from monazite sand, FBRs can breed Th-233, a nuclear fuel, with simultaneous generation of electricity. Ranging and imaging of nuclear fuel rods and control rods through the liquid metal coolant in FBRs, especially during insertion and withdrawal, help correct positioning of the rods to avoid any misalignment and possible nuclear accident. This “viewing” through the optically opaque liquid metal or alloy coolant, is possible by ultrasonic imaging of the rods using HT PE ultrasonic-generators and-detectors, an active area of research. Lithium niobate with T(Curie) > 1000°C and orthorhombic PbNb 2 O 6 with T(Curie) > 570°C are two of many HT PE materials under development or in trial runs. In the present work, world-wide R & D on HT piezoelectric materials has been reviewed after an outline of the basics.