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Review article of the solid-state crystal growth (SSCG) technique and the progress of lead-free ferroelectric single crystals for piezoelectric applications.

The route to phase-pure BiFeO3 (BFO) ceramics with excellent ferroelectric and electromechanical properties is severely impeded by difficulties associated with the perovskite phase stability during synthesis. This has meant that dopants and solid solutions with BFO have been investigated as a means of not only improving the functional properties, but also of improving the perovskite phase formation of BFO-based ceramics. The present work focuses on Sm-modified BFO ceramics of composition Bi0.88Sm0.12FeO3. The polarization and strain behaviors were investigated as a function of the phase composition, microstructure, and chemical composition. Addition of Sm reduces the susceptibility of the BFO perovskite to phase degradation by Si impurities. Si was observed to react into Sm-rich grains dispersed within the microstructure, with no large increases in the amount of bismuth-parasitic phases, namely Bi25FeO39 and Bi2Fe4O9. These as-prepared ceramics exhibited robust polarization behavior showing maximum remnant polarizations of ~40 to 50 μC/cm(2). The electric-fieldinduced strain showed an appreciable stability in terms of the driving field frequency with maximum peak-to-peak strains of ~0.3% and a coercive field of ~130 kV/cm.

16The photooxidative stability of an aromatic segmented poly(urethane-urea) (PUU) elastomer, 17 stabilised with a range of carbon black fillers, was assessed after very low UVA doses as a means to 18 identify components that are highly susceptible to UV degradation, and suggest better design of such 19 materials. Fourier-transform infrared (FTIR) analysis indicated rapid degradation of the urea bonds 20 in the hard segments, followed by chain scission and photo-Fries reaction of the urethane linkages. In 21 the soft segments, the oxidation of the original ether groups resulted in the formation of large 22 amounts of ester groups, while some crosslinking of the ether groups was also evident. Carbon black 23 provided moderate protection against degradation, with the smallest-sized particles being the most 24 effective. Protection was evidenced by reduced surface cracking as well as an increased resistance to 25 chemical changes in both the soft segments and hard segments. Even so, significant degradation was 26 still evident at low UV doses suggesting that further stabilisation is required to increase the UV 27 durability of these elastomers and improve their long-term performance. 28 29 Keywords: UV ageing; aromatic poly(urethane-urea); carbon black 30 system. PUUs have been found to exhibit better photostability than their polyurea counterparts [19]. 53However, due to limited work in this area, a complete description of the PUU photodegradation 54 process and how the UV irradiation affects the properties of PUU remain unclear. 55 effects of three types of carbon black with different structural characteristics on the UV stability of 77 this PUU were also studied. The photodegradation processes were analysed using Fourier-transform 78 infrared (FTIR) studies of the PUU surface chemistry over the monitoring period, along with other 79 techniques such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), 80 119 2.3 Accelerated UV ageing 120 Samples were cut from 2.5-3.5 mm thick flat sheets and loaded into custom-built extensometers 121 according to ASTM D1149-16 using Method B, Procedure B1 -Straight Specimens (Static 122 Elongation). The accelerated ageing method was adapted from UV Resistance MIL-STD-810G, 123Method 505.5, Procedure II (A2). Briefly, samples were loaded into a QUV accelerated weathering 124 tester (Q-Lab, Ohio, USA) that was equipped with UVA-340 lamps. The samples were held at 50°C 125 143 X-ray photoelectron spectroscopy (XPS) 144Surface analysis was performed on a Kratos Axis ULTRA X-ray photoelectron spectrometer 145 (XPS) using monochromatic Al Kα (hν = 1486.6 eV) radiation. Curve fitting was undertaken using a 146Gaussian-Lorentzian peak shape and Shirley background function. The binding energy was poly (etherurethane urea)

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Ultrasonic techniques alone or in combination with electrical methods are increasingly being used for the detection and/or location of partial discharge (PD) in high-voltage transformers and other electrical plants. Ultrasonic transducers used for fault location are traditionally coupled externally on to the transformer wall. Mounting transducers inside the transformer steel tank has certain definite advantages like better noise immunity, increased sensitivity due to better acoustic matching to oil, and less complicated signals (only longitudinal waves). Transformers are filled with mineral oil whose temperature could rise up to 110 °C during normal operation. Also, there are large electric and magnetic fields and strong mechanical vibrations as well inside the transformer. The authors has developed 1–3 piezopolymer composite transducers which are capable of operating in this adverse environment. These transducers were life tested in mineral oil at 130 °C for over 500 days and their kt values monitored as a function of time. Life test and vibration test data for several transducers as well as sensitivity, frequency response, pulse width, and constructional details are presented.