Wang Xiuqin

Composition Dependence of Electrocaloric Effect in (1 − x)Pb(Mg1/3Nb2/3)O3 −xPbTiO3 Single Crystals*

Composition dependence of electrocaloric effect is investigated in(1- x)Pb(Mg1/3Nb2/3)O3- xP b Ti O3 single crystals by using an eighth-order Landau–Devonshire theory. The applied electric field along [001] direction reduces the ferroelectric-ferroelectric phase transition temperatures, but increases the Curie temperatures. The electrocaloric coefficients of tetragonal phase are much larger than that of rhombohedral and monoclinic phase. A negative electrocaloric effect is observed near the MC-T phase transition in 0.69Pb(Mg1/3Nb2/3)O3-0.31 Pb Ti O3 single crystal. The application of a strong enough electric field results in a high adiabatic temperature change over a broad range of temperature.Therefore, it would be useful to construct a solid state cooling cycle over a broad temperature range for practical applications.

Effect of misfit strain on the electrocaloric effect of polydomain epitaxial ferroelectric thin films

The effect of misfit strain on the electrocaloric effect in polydomain epitaxial BaTiO3 thin films at room temperature is investigated using the Ginzburg—Landau—Devonshire thermodynamic theory. Numerical calculations indicate that the misfit strain has a large impact on the ferroelectric polarization states and the electrocaloric effect. Most importantly, the electrocaloric effect in the polydomain ca1/ca2/ca1/ca2 phase is much larger than that in the monodomain c phase and the other polydomain phases. Consequently, a large electrocaloric effect can be obtained by carefully controlling the misfit strain, which may provide potential applications in refrigeration devices.

Piezoelectric and electro optic properties of tetragonal (1 ? x)Pb(Mg1/3Nb2/3)O3?xPbTiO3 single crystals by phenomenological theory

An eighth-order Landau–Devonshire theory is constructed to investigate the piezoelectric and electro–optic properties of tetragonal (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals (x = 0.38 and x = 0.4). The dielectric stiffness coefficients of the Landau potential are obtained by fitting to the dielectric properties and the phase transition temperature between cubic phase and tetragonal phase. It is indicated that tetragonal (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals have the first-order cubic-tetragonal phase transitions. The dielectric constants are in great agreement with the experimental results. The piezoelectric coefficients d33 and d31 at room temperature are about 145 pC/N and −62 pC/N respectively which are smaller than that of (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals around the morphotropic phase boundary. Moreover, tetragonal (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals have the linear electro–optic coefficients rc = 33.7 pm/V and rc = 28.8 pm/V for x = 0.38 and x = 0.4, respectively which are in accordance with the measurements.

Electrocaloric Effect of P(VDF-TrFE)/SrTiO3 Bilayer Thin Films

A phenomenological thermodynamic theory is applied to investigate the effect of misfit strain and electric field on the electrocaloric effect of P(VDF-TrFE)/SrTiO3 bilayer thin films. Theoretical results indicate that the low electric field results in the decrease of the average polarization with the increase of the relative thickness of SrTiO3 layer, and the high electric field has an opposite effect on it. Moreover, the electrocaloric effect strongly depends on the electric field. The low electric field and the small field change can lead to a maximum of the electrocaloric effect, meanwhile the high electric field or the large field change results in the opposite trend.