The meta-stable orthorhombic phase of lead meta-niobate (PbNb 2 O 6 ), as obtained by quenching, is piezoelectric, but difficult to prepare in pure state as a few competing phases like the non-piezoelectric rhombohedral PbNb 2 O 6 tend to form during the preparation. However, it can have an attractively high Curie temperature above 570 • C. High Curie temperature piezoelectric sensors are desirable for imaging and other applications in certain industrial and research sectors. Presently, both phases have been synthesized as single phase samples as shown here from structural Rietveld analysis of their XRD. Characterization of both compounds by FTIR and XRD have been carried out and presented.

Electro-magnetic interference (EMI) affects delicate electronic devices and living beings. Composites of a polymeric binder with fine metallic turnings (copper and brass), powders of conducting inorganic compounds (suitably fired cadmium oxide), ferroelectric powders (BaTiO3 and orthorhombic PbNb2O6), and with their combinations have been prepared as cloth-like sheets, and characterized in a Vector Network Analyzer (VNA) with respect to EMI shielding and reflection capabilities. Input power (Pin) for the EMI shield (above-mentioned test materials), the reflected power (Prefl) and the transmitted power (Pout) have been measured by the VNA as a function of EM wave frequency in two technically important frequency bands - in 700 MHz to 3 GHz part of the ultra-high frequency (UHF) band and in the X-band, covering 8 to 12 GHz. From the measured data, Shielding Effectiveness in dB unit = 10 log (Pout / Pin) and Reflection Effectiveness in dB = 10 log (Prefl / Pin) have been calculated and studied for all the samples, with the results presented and discussed. In particular, our substitution of expensive metal powders by fine metallic turnings, available as waste from mechanical workshops, reduces the cost of polymer-metal composites substantially, retaining high shielding i.e. low transmission (down to -33dB in 08 to 12 GHz range).

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 PbNb2O6with 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.

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