The electrocaloric properties of PbZr0.52Ti0.48O3 (PZT) epitaxial films and 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (0.7PMN-0.3PT) single crystals are measured and demonstrated enhanced low temperature refrigeration at morphotropic phase boundary compositions. The results reveal large adiabatic cooling figures in ∼260 nm PZT films (11 K in 15 V) and 200 μm thick 0.7PMN-0.3PT single crystals (2.7 K in 240 V) at Curie transition temperatures and secondary cooling peaks at lower temperatures, near critical points. This is a very useful aspect of ferroelectric cooling elements to attain effective cooling over wide range of working temperatures in solid-state devices.

Truncated nanocubes of barium titanate (BT) were synthesized using a rapid, facile microwave-assisted hydrothermal route. Stoichiometric composition of pellets of nanocube BT powders was prepared by two-stage microwave process. Characterization by powder XRD, Rietveld refinement, SEM, TEM, and dielectric and polarization measurements was performed. X-ray diffraction revealed a polymorphic transformation from cubic Pm3̅m to tetragonal P4mm after 15 min of microwave irradiation, arising from titanium displacement along the c-axis. Secondary electron images were examined for nanocube BT synthesis and annealed at different timings. Transmission electron microscopy showed a narrow particle size distribution with an average size of 70 ± 9 nm. The remanence and saturation polarization were 15.5 ± 1.6 and 19.3 ± 1.2 μC/cm(2), respectively. A charge storage density of 925 ± 47 nF/cm(2) was obtained; Pt/BT/Pt multilayer ceramic capacitor stack had an average leakage current density of 5.78 ± 0.46 × 10(-8) A/cm(2) at ±2 V. The significance of this study shows an inexpensive and facile processing platform for synthesis of high-k dielectric for charge storage applications.

The strain dependent magnetocaloric properties of La0.67Sr0.33MnO3 thin films deposited on three different substrates (001) LaAlO3 (LAO), (001) SrTiO3 (STO), and (001) La0.3Sr0.7Al0.65Ta0.35O9 (LSAT) have been investigated under low magnetic fields and around magnetic phase transition temperatures. Compared to bulk samples, we observe a remarkable decrease in the ferromagnetic transition temperature that is close to room temperature, closely matched isothermal magnetic entropy change and relative cooling power values in tensile strained La0.67Sr0.33MnO3 films. The epitaxial strain plays a significant role in tuning the peak position of isothermal magnetic entropy change towards room temperature with improved cooling capacity

Electrocaloric effects of (001), (011) and (111) oriented single crystals have been thoroughly investigated to study the ferroelectric-ferroelectric (FE-FE) phase transition induced isothermal entropy changes in 0.94Pb(Zn1/3Nb2/3)O3–0.06PbTiO3 (PZN-PT) material. The results showed that the PZN-PT crystals oriented in (111) direction exhibit ∼ 38% higher electrocaloric cooling values near lower critical phase transitions from rhombohedral (R) to tetragonal (T) phases in PZN-PT crystals, compared to those oriented in (011) direction. Though (111) samples display higher cooling values, (011) samples showed broader cooling curves due to their easily switchable characteristics between R and T phases

A prototype device was designed to demonstrate electrocaloric cooling of Pb(Mg 1/3 Nb 2/3 )O3-PbTiO3 70/30 single crystals as active cooling elements. The test section was devised to investigate potential bulk cooling effects of the single-crystal materials under repeated electric-field cycles. Despite the low electrocaloric temperature changes measured by indirect method (ΔTmax = 2.7 K in 240 V), the test materials showed significant cooling rates under optimized device parameters compared to those of natural cooling conditions. It was emphasized that the pulse duration and frequency of the applied electric field play an important role in achieving high cooling rates in electrocaloric cooling devices besides high electrocaloric effects of test materials.