High-resolution electrocaloric and heat capacity measurements in barium titanate

Abstract

The electrocaloric (EC) effect in a BaTiO3 single crystal oriented along the [001] direction has been studied by direct high-resolution EC measurements in the vicinity of the fieldinduced critical point. It is shown that the observed behavior of the EC temperature change ΔT , as well as the heat capacity anomalies are in good agreement with the predictions of the Landau theory. We also present the electric field-temperature phase diagram for the field-induced paraelectric-to-ferroelectric phase transition line, derived from the calculated latent heat.

Towards multicaloric effect with ferroelectrics

“…37). This dependence is in contrast to the trend under electric field (0.75 K cm/kV, which agrees with the experimental value [12] of ~0.78 K cm/kV) and tensile stress (266 K/GPa). Therefore, the sign of the barocaloric effect under positive (compressive) hydrostatic pressure is negative, [31] which is consistent with experimental results.…”

“…[11,31] By carrying out these kinds of calculations we could at least obtain qualitative information about the multicaloric effect, which acts as an important guide to future experimental studies. Moreover, previous results [11,12,24,31] based on this model appear to be compatible with the recent developments from both first-principles predictions and experimental data. [21,22,26,30] Considering simultaneous application of electric field E and uniaxial stress 3 σ (denoted as σ in the following) along polarization z-direction or hydrostatic pressure p adiabatically on BaTiO 3 single crystals, the multicaloric temperature change 2 1 T T T Δ = − can be obtained through the following relation…”

“…On the basis of previous phenomenological efforts [11,12,24,31] we can deduce the caloric behavior in normal ferroelectric simply in terms of its order parameter, i.e., polarization. The principle idea is to "transform" the lattice entropy change due to structural transition into polar contributions.…”

“…[6] Among the ferroic materials ferroelectrics can be good potential candidates for developing multicaloric effect, due to the fact that the phase transition in ferroelectrics can be triggered by electric field, uniaxial stress and hydrostatic pressure. [7] According to the literature, individual caloric effects such as electrocaloric, [8][9][10][11][12][13][14][15][16][17][18][19][20] elastocaloric [21][22][23][24][25][26][27][28] and barocaloric [28][29][30][31][32][33] scenarios have all been reported in ferroelectric materials. In this context only a few theoretical studies have been published to understand the multicaloric effect in ferroelectric bulk and thin films driven by simultaneous application of electric and mechanical fields.…”

Some strategies for improving caloric responses with ferroelectrics

“…While first-principles calculations predicted that the electrocaloric effect could continuously increase with electric field until this critical point, 35 experimental results in BaTiO 3 single crystals showed rather a continuous decrease in electrocaloric response, attributed to smooth evolution of the polarization when being close to this critical point. 36 In addition, largest electrocaloric strength, i.e., ∆T E /∆E is expected near the field value where the first-order type transforms into second-order one. 37 Regarding the second-order transition, it should also disappear as long as the field is high enough.…”