Jinghan Gao

Coexistence of multiple positive and negative electrocaloric responses in (Pb, La)(Zr, Sn, Ti)O3 single crystal

The electrocaloric effect has been investigated in antiferroelectric (Pb, La)(Zr, Sn, Ti)O3 (PLZST) single crystals grown by the flux method. The measurements of polarization versus electric field loops on unpoled crystals revealed that at room temperature, a critical electric field of 1.8 kV/mm is needed to induce a ferroelectric phase from an antiferroelectric phase. The dielectric properties demonstrated that the induced ferroelectric phase recovers to antiferroelectric phase when temperature is above the depolarization temperature (70 °C–100 °C). Coexistence of the negative and positive electrocaloric effect has been achieved in ⟨001⟩-oriented PLZST single crystals. Multiple electrocaloric response values of −0.054 °C at room temperature, 0.17 °C near the depolarization temperature, −0.14 °C at 125 °C, and 0.75 °C around Curie temperature have been observed under an electric field of 3 kV/mm. The coexistence of multiple negative and positive electrocaloric effects in one material provides a possibilit...

Electric field induced metastable ferroelectric phase and its behavior in (Pb, La)(Zr, Sn, Ti)O3 antiferroelectric single crystal near morphotropic phase boundary

Antiferroelectric (AFE) (Pb, La)(Zr, Sn, Ti)O3 (PLZST) single crystal with composition near morphotropic phase boundary has been grown and studied. X-ray diffraction analysis and electrical properties reveal coexistence of antiferroelectric/ferroelectric (FE) phases, with the AFE phase dominated at room temperature. Temperature-dependent polarization and strain measurements indicate that the AFE phase can be induced into a metastable FE phase by electric field. The FE phase can be maintained in a wide temperature range above room temperature and recovers to AFE phase around a critical temperature of 90 °C, accompanied with remarkable change in field-induced strain. The strain at 90 °C (∼0.50%) is ten times larger than that at room temperature (∼0.04%), which makes the PLZST single crystal a promising candidate for thermal switch and actuator application.

Electric field induced phase transition and domain structure evolution in (Pb, La)(Zr, Sn, Ti)O3 single crystal

Antiferroelectric (Pb, La)(Zr, Sn, Ti)O3 (PLZST) single crystals with composition in the vicinity of morphotropic phase boundary have been grown and studied. From electric measurements, Raman study, and observation of domain structures, we found an electric field induced antiferroelectric to ferroelectric phase transition accompanied with fifteen times of strain difference. After this phase transition, the metastable ferroelectric phase (FEin) is preserved with soften of A1(TO1) mode and increase of long-range force. Coexistence of tetragonal (T) and rhombohedral (R) domains has been observed in virgin sample. Electric field induced T to R phase transition is verified by both extinction angle and domain morphology changes. Clamping “polar” structure formed by the embedded R phase would contribute to increase of long-range force. The remarkable strain difference accompany with induced phase transition makes the PLZST single crystal a promising candidate for electric switch and actuator applications.

Effect of A-site La3+ modified on dielectric and energy storage properties in lead zironate stannate titanate ceramics

(Pb1-1.5xLax)(Zr0.66Sn0.23Ti0.11)O3 (PLZST) ceramics with different lanthanum (La3+) content (x = 0–6%) were prepared by conventional solid state reaction process, and exhibited excellent electrical properties with high switching field from AFE to FE phase and electric breakdown strength. The maximum dielectric constant (em) and its corresponding temperature (Tm) decreased with La3+ doping and a phase transition from rhombohedral ferroelectric (FE) to tetragonal antiferroelectric (AFE) state was found at 2% La3+ doping. At room temperature, a maximum energy density of 1.47 J cm−3 was obtained for x = 4%. In addition, electric-field-dependent energy storage properties of PLZST (x = 4%) ceramics have been investigated, which could be ascribed to the AFE–FE phase transition associated with the increase of strain.

Field induced phase transitions and energy harvesting performance of (Pb,La)(Zr,Sn,Ti)O3 single crystal

(Pb,La)(Zr,Sn,Ti)O3 (PLZST) single crystals with composition close to the morphotropic phase boundary had been grown by the flux method. The antiferroelectric-ferroelectric phase switching electric field was 0.8 kV/mm. Temperature-dependent dielectric and polarization versus electric field hysteresis loops revealed that the electric field induced ferroelectric phase could transform back into the antiferroelectric phase at depolarization temperature (145 °C). An enhanced pyroelectric coefficient value of 1.46 μC/cm2/K was obtained at 145 °C, which is several times larger than that of conventional pyroelectric materials. Furthermore, multiple peak pyroelectric responses and an enhanced harvested energy density value of 0.4 J/cm3 were achieved in the PLZST crystal. The enhanced harvested energy density and multiple peak pyroelectric responses make the PLZST crystal a promising candidate for high sensitive temperature sensors and energy conversion technologies.

Structural phase transition, depolarization and enhanced pyroelectric properties of (Pb1−1.5xLax)(Zr0.66Sn0.23Ti0.11)O3 solid solution

(Pb1−1.5xLax)(Zr0.66Sn0.23Ti0.11)O3 (PLZST) (x = 0–0.024) ceramics were designed based on chemical composition modification and fabricated using the conventional solid-state method. Structural phase transition, thermal depolarization and pyroelectric properties of the PLZST system were investigated systematically. Phase structures of various chemical compositions in the PLZST system were discussed based on the electronegativity difference versus tolerance factor relationship phase diagram. Enhanced pyroelectric response with a value of 14.01 μC cm−2 K−1 was realized for the ceramics with x = 0.018, which is far larger than the previously reported values. The results indicated that there was a quadratic function relationship between the pyroelectric peak temperature (Tpeak) and composition (x): Tpeak = 182 + 404x − 3.0 × 105x2. The composition dependence of the wide range pyroelectric response over 19–185 °C was obtained by changing x from 0 to 0.024. Our results also reveal that the enhanced and wide temperature range pyroelectric properties of the composition-optimized PLZST system are of great significance to pyroelectric technology.

Giant Negative Electrocaloric Effect in (Pb,La)(Zr,Sn,Ti)O3 Antiferroelectrics Near Room Temperature

(Pb0.97La0.02)(Zr xSn0.94- xTi0.06)O3 (PLZST) antiferroelectric ceramics with x = 0.75-0.90 have been fabricated and found to be a novel electrocaloric material system with a giant negative electrocaloric effect (Δ T = -11.5 K) and a large electrocaloric strength (|Δ T/Δ E| = 0.105 K cm kV-1) near room temperature. Additionally, the PLZST antiferroelectric ceramic also exhibits a large positive electrocaloric effect around the Curie temperature. The giant negative effect and the coexistence of both positive and negative electrocaloric effects in one material indicate a promising possibility to develop mid- to large-scale solid-state cooling devices with high efficiency.