Enhancement of thermal stability of energy storage performances and electrocaloric effect in lead-free Ba0.65Sr0.35TiO3 ceramic

Structural, dielectric, ferroelectric, energy storage properties, and electrocaloric effect were studied in lead-free ceramic Ba0.95Ca0.05Ti0.89Sn0.11O3 (BCTSn) elaborated by the sol–gel method. Phase purity structure was confirmed from X-ray data using the Rietveld refinement analysis which revealed the coexistence of tetragonal (P4mm) and orthorhombic (Amm2) symmetries at room temperature. Phase transitions were detected by dielectric and differential scanning calorimetry measurements. The energy storage properties were determined from P-E hysteresis, and the electrocaloric properties were calculated indirectly via the Maxwell approach. The large value of electrocaloric temperature change of ΔT = 0.807 K obtained at a relatively small electric field of 30 kV cm−1, and the high energy storage efficiency can make BCTSn ceramic a promising candidate for environmentally friendly refrigeration and energy storage applications.

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 {\deg}C. In addition, the electrocaloric responsivity was found to be 0.164.10-6 K.m/V at 360 K.

The structural, dielectric, electrocaloric, and energy storage properties of lead-free Ba0·90Ca0·10Zr0·15Ti0·85O3

The electrocaloric effect was investigated in lead-free Zr doped Ba0.8Ca0.2(ZrxTi1−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 ≤ 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 × 10−6 Km/V was found for x = 0.04, which significantly exceeds of values found so far in other lead-free electrocaloric materials.

Microstructure induced ultra-high energy storage density coupled with rapid discharge properties in lead-free Ba0.9Ca0.1Ti0.9Zr0.1O3–SrNb2O6 ceramics

Low field assisted electrocaloric effect and energy storage responses through optimization of morphotropic phase boundary by sintering temperature for lead-free Ba0.95Ca0.05Sn0.09Ti0.91O3 ceramics

Stress-induced tailoring of energy storage properties in lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 ferroelectric bulk ceramics

The 1 wt % Li-doped (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT-Li) ceramics prepared by the citrate method exhibit improved phase purity, densification and electrical properties, which provide prospective possibility to develop high-performance electrocaloric materials. The electrocaloric effect was evaluated by phenomenological method, and the BCZT-Li ceramics present large electrocaloric temperature change ∆T, especially large electrocaloric responsibility ξ = ∆Tmax/∆Emax, which can be comparable to the largest values reported in the lead-free piezoelectric ceramics. The excellent electrocaloric effect is considered as correlating with the coexistence of polymorphic ferroelectric phases, which are detected by the Raman spectroscopy. The large ξ value accompanied by decreased Curie temperature (around 73 °C) of the BCZT-Li ceramics prepared by the citrate method presents potential applications as the next-generation solid-state cooling devices.

Electrocaloric effect in lead-free Ba0.94Ca0.06Ti1−xSnxO3 ceramics is studied using an indirect method. The Ba0.94Ca0.06Ti0.875Sn0.125O3 ceramic located near a multi-phase point shows best electrocaloric performance, which provides further experimental evidence for optimizing electrocaloric properties through constructing multiphase coexistence. Giant electrocaloric efficiency (∼0.4 K mm/kV) is achieved in this ceramic at about room temperature at a low electric field of 6 kV/cm. While large electrocaloric temperature (∼0.63 K) is obtained by further enhancing electric field (20 kV/cm), a decrease in electrocaloric efficiency (0.32 K mm/kV) is simultaneously observed, which is attributed to phase transition from first-order to more diffusive second-order under higher electric field.

Both A- and B-site-substituted BaTiO3 ceramics are promising alternative relaxor materials to replace lead zirconium titanate as an actuator. With a motivation to improve electromechanical properties, a lead-free Ba0.95Ca0.05Sn0.09Ti0.91O3 (BCST) ceramic close to the polymorphic phase boundary composition is synthesized by solid-state reaction. X-ray diffraction and Raman spectroscopy confirm the coexistence of orthorhombic (Amm2) and tetragonal (P4 mm) phases at room temperature. Our low-temperature dielectric study reveals the appearance of a reentrant relaxor state from the ferroelectric state near ∼150 K and is attributed to the coexistence of short and long ferroelectric ordered regions and slowing down of domain dynamics in the smaller regions, similar to the reentrant spin glass state observed in the system Fe-xAu. This feature is confirmed through glass model fitting parameters [ωo = 2.66(±0.28) × 108 Hz, Tg = 110(±1) K, zv = 4.5(±0.3)], and Mydosh parameter (“K” ∼ 0.05). The field-induced polarization (P–E) and strain (S–E) curves show well-defined slim ferroelectric and “butterfly-like” loops with a large value of maximum strain of ∼0.12%, an electromechanical coefficient of d*33 ∼ 1113 pm/V, and an electrostrictive coefficient of Q11 ∼ 0.048 m4/C2 at room temperature.

We report a large electrocaloric efficiency of 0.029 K cm kV−1 at 303 K and in a wide operating temperature range of 293 K to 313 K in a lead-free Ba0.9Sr0.1(Ti0.9Zr0.1)0.95Sn0.05O3 ceramic by using direct electrocaloric effect (ECE) measurements. Sn4+ doping in Ba0.9Sr0.1Ti0.9Zr0.1O3 not only tunes the rhombohedral-to-paraelectric phase transition temperature to room temperature but also slightly widens the phase transition region, by slightly strengthening the diffuse character and maintaining its good ferroelectricity. Also, polar nanoregions embedded in the matrix facilitate polarization rotation because of a flat energy landscape associated with the relaxor-to-ferroelectric phase transition, inducing enhanced entropy changes and consequently excellent ECE performance.

Recently, considerable focus has been on exploring the electrocaloric effect in environmentally friendly, lead-free ferroelectric materials. In this study, lead-free (Ba0.95Ca0.05)(Ti0.95Zr0.05)1-x (Zn1/3Nb2/3) x O3 (BCTZ-xZN) ceramics were investigated. X-ray diffraction (XRD) analysis confirmed the formation of a pure perovskite structure with a structural phase transition depending on ZN substitution. Dielectric measurements revealed a diffuse phase transition and a shift in Curie temperature with increasing x. The electrical energy storage density (W rec) was found to be 150 mJ cm-3 with an efficiency of η = 83% for BCTZ-2.5ZN. At an electric field strength of 25 kV cm-1, a peak electrocaloric response of 0.68 K at 340 K was attained, with a corresponding electrocaloric responsivity of 0.27 K mm kV-1 observed at 340 K for BCTZ-2.5ZN. The electrocaloric effect, combined with a calculated coefficient of performance (COP) of 2, demonstrates the material's potential for both cooling and energy storage. These findings underscore BCTZ-xZN as a promising material for applications in cooling systems and energy storage for electronic devices, offering versatile properties conducive to cooling operations via an external electric field across various operating temperatures.

Synergistic effects of Zn B-site substitution in lead-free Ba0.95Ca0.05Ti0.92Sn0.08O3 ferroelectric ceramics for enhancing piezoelectric properties in energy harvesting applications

Perovskite ferroelectric ceramics with large energy storage density and electrocaloric (EC) effect at a low-electric field are very attractive in modern electronic devices such as capacitors and solid refrigerators. In this work, it is demonstrated that the energy storage and EC performances of the BiFeO3 (BFO)-doped Bi[Formula: see text]Na[Formula: see text]TiO3-BaTiO3 (BNT-BT)-based ceramics near the MPB (0.89Bi[Formula: see text]Na[Formula: see text]TiO3–0.11BaTiO[Formula: see text] can be regulated by using the strain-modified calcined powders as sintering precursor. The 0.89Bi[Formula: see text]Na[Formula: see text]TiO3–0.11BaTiO3 ceramic prepared from the strain-modified calcined powder with a nanoscaled size (abbreviated as nanoceramic) simultaneously obsesses a large energy density ([Formula: see text] 0.847 J/cm[Formula: see text] and a high-energy storage efficiency ([Formula: see text] 80%) in a broad temperature range (333–453 K) at a very low-electric field ([Formula: see text] 80 kV/cm). The high-energy storage performance maybe is related to the breaking of the ferroelectric long-range order inherited from the strain-modified calcined powder with an ultra-fine size ([Formula: see text] 110 nm). Moreover, a large negative EC effect ([Formula: see text]−1.1 K) at a very low-electric field ([Formula: see text] 29.8 kV/cm) was also achieved for the ceramic prepared by using the submicro-sized calcined powder with a BFO doping amount of 6% (mole ratio). It is concluded that using strain-modified calcined powder as a sintering precursor for ceramic preparing can be used as an alternative candidate strategy to improve and optimize the energy storage and EC performances.

Enhanced electrocaloric and energy-storage properties of environment-friendly ferroelectric Ba0.9Sr0.1Ti1−xSnxO3 ceramics