The ferroelectric (FE) to antiferroelectric (AFE) phase transition tuning the temperature range of electrocaloric (EC) effects was investigated using phenomenological Landau–Devonshire theory. Contrary to ferroelectric to paraelectric (PE) phase transitions for electrocaloric effects, the ferroelectric to antiferroelectric phase transition was adopted to obtain large entropy changes under an applied electric field in a Sm-doping BiFeO3 system. In addition, the doping composition and hydrostatic pressure was observed to tune the ferroelectricantiferroelectric–paraelectric phase transition temperatures and broaden the operating temperature range of electrocaloric effects. The optimal wide temperature range of ~78 K was observed at 3 GPa compressive hydrostatic pressures and 0.05 Sm-doping BiFeO3. The present study paves the way to designing high efficiency cooling devices with larger operating temperature spans.
AbstractMonte Carlo simulations of some typical order-disorder ferroelectrics such as TGS, NaNO2 and DKDP nanocrystals were studied using a Transverse Ising Model Hamiltonian with four-spins interactions. The microscopic parameters corresponding to this Hamiltonian were adjusted to fit the experimental polarization-temperature curves for each one of the materials in the bulk phase. Then the dependences of the ferroelectric-paraelectric phase transition temperatures, Tc, on the sizes of those crystals were studied with Monte Carlo simulations of the order-disorder system. We report a weak dependence of Tc on the size of the crystal (d) for these materials above d∼6nm. The addition of surface effects showed that the expected lowtemperature shift of Tc due to size effects, can be reverted.
Thermally- and pH-responsive microgels (MGs) and hydrogels are fascinating network systems that have been applied in biomedical engineering and sensing. The volume-swelling ratio (Q) and the volume-phase transition temperatures (VPTTs)...
In this work, the effect of thin films on the orientational, thermotropic and optical properties and on the peculiarities of the nematic–isotropic liquid phase transition has been carried out. The planar textures of MBBA+EBBA eutectic mixture on the surfaces coated with Al 2 O 3 and ZrO 2 thin films have been obtained. The optical and thermodynamical parameters of the obtained, oriented textures have been determined. The effect of thin films on the temperature width of heterophase region and on the nematic–isotropic liquid phase transition temperatures has been investigated. The shift of the phase transition temperatures and the change of the temperature width of the heterophase region have been revealed. For the analysis of peculiarities of the nematic–isotropic liquid phase transition and the heterophase regions of this transition, the mean field theory has been used.
Low-energy ferroelectric–paraelectric phase transitions of three-dimensional A(II)B(I)X3-type perovskite ferroelectrics: How to realize high phase transition temperatures
