Peculiarities of the electrocaloric effect in relaxors

A comprehensive study and detailed analysis of pyroelectric and electrocaloric effects in relaxor ferroelectrics based on lead magnesium niobate as a promising object for such investigations have been carried out.It was found that even at the maximum values of pyroelectric coefficients the electrocaloric response inextricably linked with the pyroelectric effect does not exceed 1°C in the temperature range from 10 to 60°C under DC electric field up to 60 kV/cm.These conditions are the most demanded for the operation of electrocaloric cooling devices.Vision for the future as to increasing the efficiency of the main elements for such devices is discussed.

Effective multi-field properties of electro-magneto-thermoelastic composites estimated by finite element method approach

A finite element approach based on the micromechanics was performed to estimate the multi-field properties of electro-magneto-thermoelastic composites. The thermal field and the involved pyroelectric and pyromagnetic effect of the multi-phase composite materials were taken into account in the investigation and implemented in the finite element modeling. The multi- fields related to the electric field, magnetic field, deformation and temperature field, as well as their coupling effects of the smart composites under periodic boundary conditions were obtained numerically. Especially, by means of the homogenization approximation, the effective thermal ex- pansion coefficients, pyroelectric coefficients, pyromagnetic coefficients and other elastic, electric, and magnetic properties for the piezoelectric material, piezomagnetic material and magnetoelec- tric material were calculated, respectively. Some results are compared to the theoretical predictions by the well-known Mori-Tanaka method to show good agreements.

Piezoelectric constant temperature dependence in strained [111]-oriented zinc-blende MQW-SOAs

Here,we present a study of the effective piezoelectric constant(e_(14_(e)))temperature dependence in strained[111]-oriented zinc-blende quantum wells(QWs)embedded within a semiconductor optical amplifier(SOA).We determined e_(14_(e)) using a method that was insensitive to the segregation phenomenon and to the temperature dependence of the bandgap energy,which required neither fitting parameters nor temperature-dependent expressions for energy and out-of-plane effective masses of electrons and heavy holes.An e_(14_(e))=−0.0534±0.0040 C·m^(−2) at 23°C was obtained for an SOA with 1.2 nm[111]-oriented strained In0.687Ga0.313As/In0.807Ga0.193As0.304P0.696 QWs.Unlike previously published research,where e_(14_(e)) magnitude increased as temperature rised,we extracted an e_(14_(e)) magnitude that decreased as temperature increased.

A thermally flexible and multi-site tactile sensor for remote 3D dynamic sensing imaging

A flexible,multi-site tactile and thermal sensor(MTTS)based on polyvinylidene fluoride(resolution 50×50)is reported.It can be used to implement spatial mapping caused by tactile and thermal events and record the two-dimensional motion trajectory of a tracked target object.The output voltage and current signal are recorded as amapping by sensing the external pressure and thermal radiation stimulus,and the response distribution is dynamically observed on the three-dimensional interface.Through the mapping relationship between the established piezoelectric and pyroelectric signals,the piezoelectric component and the pyroelectric component are effectively extracted from the composite signals.The MTTS has a good sensitivity for tactile and thermal detection,and the electrodes have good synchronism.In addition,the signal interference is less than 9.5%and decreases as the pressure decreases after the distance between adjacent sites exceeds 200μm.The integration of MTTS and signal processing units has potential applications in human-machine interaction systems,health status detection and smart assistive devices.

Possibilities of the practical use of a stationary strain gradient in the interelectrode volume of unpolarized ferroceramic plates

It has been established that in plates made of hot-pressed ferroelectric ceramics PZT-19(Tc=300℃),after metal electrodes from Ag are burned into opposite surfaces with different depths of mechanical damage,counter-directional stationary deformation gradients and,accordingly,internal electric displacement fields create a stationary flexoelectric effect.As a result,unpolarized ceramics below the Curie temperature become a pyroelectric,and above it become a pyroelectric bolometer.After polishing the less damaged surface and replacing the Ag(valency v=3)electrode with Cr(v=6)by thermal evaporation in vacuum from the intact surface,a new thermally stable polarization is created,directed from the damaged surface in the interelectrode volume.Such plates have an asymmetric dielectric hysteresis loop,retain the values of the pyroelectric effect and piezoelectric effect in the ferroelectric phase,as well as the bolometric effect in the paraelectric phase after repeated heating cycles to 400℃ and cooling to T_(norm).