Articles you may be interested inElectro-caloric effect in (Ba1−xCax)(Zr0.05Ti0.95)O3: A lead-free ferroelectric material

Artificial superlattices (SLs) consisting of ferroelectric BaTiO3 (BT) and paraelectric BaZrO3 (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 La1/2Sr1/2CoO3. 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 Ti4+ ions due to the epitaxial strain. This strain is responsible for the upward frequency shift in the soft modes, especially, the E(1TO) 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 (32 Å≤Λ≤256 Å) while a weak ferroelectricity is observed for the large periods (Λ=500 Å and 1056 Å). This is attributed to the strain-induced ferroelectricity in BZ layers for the constrained SLs.

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Lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) ceramic exhibits excellent dielectric, ferroelectric and piezoelectric properties at the Morphotropic Phase Boundary (MPB). Previously, we demonstrated that the use of the anionic surfactant Sodium Dodecyl Sulfate (SDS, NaC12H25SO4) could enhance the dielectric properties of BCZT ceramic using surfactant-assisted solvothermal processing [1]. In the present study, structural, dielectric, ferroelectric properties, as well as electrocaloric effect and energy storage performances of this BCZT ceramic were thoroughly investigated. X-ray diffraction (XRD) measurements revealed the presence of single perovskite phase at room temperature with the coexistence of orthorhombic and tetragonal symmetries. In-situ Raman spectroscopy results confirmed the existence of all phase transitions from rhombohedral through orthorhombic and tetragonal to cubic symmetries when the temperature varies as reported in undoped-BaTiO3. Evolution of energy storage performances with temperature have been investigated. BCZT ceramic exhibits a high energy storage efficiency of ~80% at 120 °C. In addition, the electrocaloric responsivity was found to be 0.164×10 -6 K.m/V at 360 K.

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