Narrow Results

We present a mathematical model for linear magneto-electro-thermo-elastic continua, as sensors and actuators can be thought of, and prove the well-posedness of the dynamic and quasi-static problems. The two proofs are accomplished, respectively, by means of the Hille–Yosida theory and of the Faedo–Galerkin method. A validation of the quasi-static hypothesis is provided by a nondimensionalization of the dynamic problem equations. We also hint at the study of the convergence of the solution to the dynamic problem to that to the quasi-static problem as a small parameter — the ratio of the largest propagation speed for an elastic wave in the body to the speed of light — tends to zero.

We study the redistribution of mobile charge carriers in a composite fiber of piezoelectric dielectrics and non-piezoelectric semiconductors in extensional deformation under a uniform temperature change. The macroscopic theory of piezoelectricity and the drift-diffusion theory of semiconductor are used, coupled by doping and mobile charges. A one-dimensional model for extension is developed. Through a theoretical analysis, it is shown that under a temperature change the mobile charges in the semiconductor redistribute themselves under the polarization and electric field produced through thermoelastic, pyroelectric and piezoelectric effects. The results suggest the possibility of using composite structures for thermally manipulating mobile charges in semiconductors and have potential applications in piezotronics.

In order to develop miniaturized X-ray devices that provide localized X-ray radiation for medical applications, the dependences of the X-ray intensity on the ambient gas pressure and the inner diameter of the case made of stainless steel were investigated for LiNbO₃ single crystals polarized parallel to the c-axis in a N₂ atmosphere. The smallest inner diameter (16 mm) is slightly larger than the diagonal (14 mm) of the square crystal. The X-ray intensity had a local maximum in the pressure range of approximately 3.9 to 5.4 Pa and it decreased with increasing inner diameter of the case in low vacuums. The X-ray intensity had a local maximum at an inner diameter of 21 mm. The X-ray intensity increased with decreasing pressure in high vacuums.

A nonlinear thermodynamic formalism is developed to calculate the pyroelectric property of epitaxial single domain ${\mathrm{\text{SrTiO}}}_3∕\mathrm{\text{Si}}$ heterojunctions by taking into account the thermal expansion misfit strain at different temperatures. It has been demonstrated that the crucial role was played by the contribution associated with the structure order parameter arising from the rotations of oxygen octahedral on pyroelectricity. A dramatic decrease in the pyroelectric coefficient due to the strong coupling between the polarization and the structure order parameter is found at ferroelectric ${\mathbf{\text{T}}}_{\mathrm{\text{F1}}}$–${\mathbf{\text{T}}}_{\mathrm{\text{F2}}}$ phase transition. At the same time, the thermal expansion mismatch between film and substrate is also found to provide an additional weak decrease of pyroelectricity. The analytic relationship of the out-of-plane pyroelectric coefficient and dielectric constant of ferroelectric phases by considering the thermal expansion of thin films and substrates has been determined for the first time. Our research provides another avenue for the investigation of the pyroelectric effects of ferroic thin films, especially, such as antiferroelectric and multiferroic materials having two or more order parameters.

Ferroelectricity in biological system has been anticipated both theoretically and experimentally over the past few decades. Claims of ferroelectricity in biological systems have given rise to confusion and methodological controversy. Over the years, a “loop” of induced polarization in response to a varying applied electrical field and a consequent polarization reversal has prompted many researchers to claim ferroelectricity in biological structures and their building blocks. Other observers were skeptical about the methodology adopted in generating the data and questioned the validity of the claimed ferroelectricity as such, “loop” can also be obtained from linear capacitors. In a paper with somewhat tongue-in-cheek title, Jim Scott showed that ordinary banana peels could exhibit closed loops of electrical charge which closely resemble and thus could be misinterpreted as ferroelectric hysteresis loops in barium sodium niobate, BNN paraphrasing it as “banana”. In this paper, we critically review ferroelectricity in biological system and argue that knowing the molecular and crystalline structure of biological building blocks and experimenting on such building blocks may be the way forward in revealing the “true” nature of ferroelectricity in biological systems.