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We have previously described the enhancement of piezoelectricity in low crystallinity Bi${}_{12}$TiO${}_{20}$–BaTiO₃ (BTO-BT) nanocomposites. This poses a question regarding the effect of the crystallinity on piezoelectricity. Here, the variation of crystallinity and structure that was developed along the temperature gradient was confirmed. The magnitude of the piezoelectric constant was found to have great relationship with the crystallinity and distortion of BiO₅ polyhedra of amorphous Bi${}_{12}$TiO${}_{20}$. The highest piezoelectric constant of 13pC/N was obtained together with the lowest crystallinity and highest degree of distortion of BiO₅ polyhedra. These results highlight the key role of the amorphous phase and further confirm the importance of distortion of BiO₅ polyhedra in influencing the piezoelectricity. In this view, one may also expect that macroscopic polarity could be improved by increasing the amorphous content and the degree distortion of the BiO₅ bonding units in the system.

Lead–free Sr${}_{1-x}$Ca_xTiO₃ ($x=0,0.4$) ceramics were synthesized via a solid state reaction technique at room temperature. The effects of ionic substitutions in A-sites between strontium and calcium on the structural and dielectric properties were investigated. XRD technique was used to identify the crystal structure and to demonstrate the phase purity. SEM observations have shown homogeneous morphologies for all samples. Dielectric measurements were investigated for a wide range of frequency (100Hz–1GHz) and temperature (25${}^{\circ }$C–250${}^{\circ }$C). Strontium substitution by calcium has not only led to a decrease in the dielectric permittivity value, but also to the loss tangent value by a considerable factor. Interesting values of the quality factor and the quite constant value ${\epsilon }^{\prime }\sim 200$ in extended frequency and temperature ranges show that SCT ceramic could be a real candidate for the development of monolithic ceramic capacitors dedicated to high-frequency lead-free components and/or to extremely high-temperature environments.

Ceramic has a great broad application in high-temperature environment due to its favorable mechanical, antioxidant and corrosion resistance properties. However, it tends to exhibit severe crack or fail under thermal shock resulting from its inherent brittleness. Microstructure property is a vital factor and plays a critical role in influencing thermal shock property of ceramic. The present study experimentally tested and characterized thermal-shock crack and residual strength of ceramic under different quench temperature, while two kinds of alumina ceramics with different grain size are employed. A two-dimensional (2D) numerical model based on statistical mesoscopic damage mechanics is introduced to depict the micro-crack propagation of ceramic sheet under water quenching. The effects of grain size on critical thermal shock temperature, crack characteristics and residual strength are studied. And the microscopic mechanism of the influence of grain size on thermal shock resistance of ceramic is discussed based on the crack propagation path obtained from experimental and simulation results. The qualitative effect and evolution change of grain size on thermal shock property of alumina ceramic will be summarized.