The electrocaloric effect was investigated in lead-free Zr doped Ba_0.8Ca_0.2(Zr_xTi_1−x)O₃ (BCTZ) ceramics synthesized by a conventional sintering process. Room-temperature x-ray diffraction analysis showed that the tetragonal structure is obtained in BCTZ for x $\le$ 0.08 and a pseudo cubic phase for x > 0.08. The dielectric spectroscopy and calorimetry revealed that the Curie temperature decreases as a consequence of Zr doping and that the BCTZ exhibits a first order ferroelectric phase transition. The electrocaloric effect was determined by the calculation of the electrocaloric change of temperature (ΔT) using the Maxwell relation based on the P–E hysteresis loops measured at different temperatures. A large electrocaloric responsivity ΔT/ΔE = 0.34 × 10⁻⁶Km/V was found for x = 0.04, which significantly exceeds of values found so far in other lead-free electrocaloric materials.

Phase transitions in gadolinium potassium niobate GdK₂Nb₅O₁₅ (GKN) ceramics have been investigated by x-ray diffraction, dielectric susceptibility, differential scanning calorimetry, and Raman scattering. The results of our complementary studies show that GKN exhibits two phase transitions at T_c1 = 238 °C and T_c2 = 375 °C attributed to the ferroelectric-antiferroelectric-paraelectric (FE-AFE-PE) phase transitions. According to the x-ray diffraction analysis, the FE and PE phases were refined in the polar P4bm and centrosymmetric P4/mbm space groups. For the intermediate phase, the structure is refined in the space group P4nc with doubling of the c unit cell parameter, which is compatible with an AFE phase. This result was confirmed by Raman spectroscopy since new low-frequency lines are activated in the AFE phase due to the Brillouin zone-folding effect, typical for the modulated phases. The presence of the AFE phase between the FE and PE phases and the complex nature of tetragonal tungsten bronze crystal structure can explain the large thermal hysteresis observed at the FE-AFE transition between heating and cooling cycle and the strong depression of the Curie-Weiss temperature T₀. The semi-phenomenological Ising-like model based on the obtained experimental data is proposed to account for the observed FE-AFE-PE transition sequence.

FePO₄ is a quartz analogue that presents also an α−β phase transition from a P622 to a P32 phase. We describe in this paper the works done in view of obtaining single crystals, and discuss results showing that an incommensurate phase takes place in between α and β phases in a range of 17 C. The main α−β transition appears to be closer to the tricritical point than in quartz and berlinite.

Artificial superlattices (SLs) consisting of ferroelectric ${\text{BaTiO}}_3$ (BT) and paraelectric ${\text{BaZrO}}_3$ (BZ) have been growth by a pulsed laser deposition technique. The epitaxial BT and BZ layers with a periodicity from 16 Å to 1056 Å were sequentially deposited on (001) MgO substrate buffered with an oxide conducting layer of ${\text{La}}_{1/2}{\text{Sr}}_{1/2}{\text{CoO}}_3$ . The out-of-plane lattice parameters of the SLs constituents were determined by modeling of the x-ray diffractograms. The results indicate that the polar $c$ -axis of the BT layers lies in the plane of the substrate and BZ layers exhibit enhanced tetragonal distortion which is induced by the mismatch between the alternating BZ and BT layers. The Raman data reinforces this interpretation and suggest a monoclinic phase in BT layers and polar phase in BZ layers. The Raman spectra give evidence of coupling between the constituent layers and a narrowing of the Raman peaks is attributed to a reduction in the disorder of the ${\text{Ti}}^{4+}$ ions due to the epitaxial strain. This strain is responsible for the upward frequency shift in the soft modes, especially, the $E\left(1\text{TO}\right)$ mode, which is markedly altered with respect to its analogs in BT-bulk crystal and BT thin film. Ferroelectric hysteresis loops measurements, confirmed the x-ray diffraction and Raman results, and revealed a clear ferroelectric behavior for the constrained SLs $\left(32\text{Å}\le \Lambda \le 256\text{Å}\right)$ while a weak ferroelectricity is observed for the large periods ($\Lambda =500\text{Å}$ and 1056 Å). This is attributed to the strain-induced ferroelectricity in BZ layers for the constrained SLs.