O3 Bulk Ceramics Research Articles

Hybrid mechanism of electrical breakdown in ferroelectric materials under high-pressure shock loading

The unique ability of ferroelectrics to generate high voltage under shock loading is limited by electrical breakdown within the shock-compressed ferroelectric material. Breakdown is a hybrid process of initiation and growth. The possible mechanisms of electrical breakdown in ferroelectric films and bulk ceramics subjected to high-pressure shock loading are discussed and experiments designed to elucidate which mechanisms govern breakdown. Gigapascal shock loading experiments were performed on poled Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 ferroelectric film specimens in the range of 32–156 μm thickness to determine the dependence of the breakdown field on thickness and on film specimens in the range of 4–16 mm length to determine the dependence of the breakdown field on the duration of shock compression. The resulting breakdown-field vs thickness and breakdown-field vs shock transit time dependencies are consistent with a hybrid electron emission initiation and Joule heating microchannel growth mechanism. Further analysis of data previously obtained on shock-compressed 0.27Pb(In1/2Nb1/2)O3–0.47Pb(Mg1/3Nb2/3)O3–0.26PbTiO3 ferrvoelectric single crystals and Pb(Zr0.65Ti0.35)O3, Pb0.99(Zr0.52Ti0.48)0.99Nb0.01O3, Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 bulk ceramics is consistent with this dual mechanism. It appears that neither chemical composition nor microstructure (single crystal vs polycrystalline) of the ferroelectric material has a significant effect on the breakdown mechanism in shocked ferroelectrics.

High energy storage performance of (1-x)Ba0.9Ca0.1TiO3-xBaSn0.1Ti0.9O3 bulk ceramics

High energy storage performance of (1-x)Ba0.9Ca0.1TiO3-xBaSn0.1Ti0.9O3 bulk ceramics

Toward high-end lead-free ceramics for energy storage: Na0.5Bi0.5TiO3-based relaxor ferroelectrics with simultaneously enhanced energy density and efficiency

The utilization of relaxor ferroelectrics is thought to be a feasible approach to enhance energy storage performance due to the low remnant polarizations and slim hysteresis. Herein, environment-friendly (1-x)(Bi0.5Na0.5)TiO3-xSr(Ti0.5Zr0.5)O3 bulk ceramics have been developed, where the synergistic effect of enhanced relaxor-ferroelectricity and grain refinement with increasing x value boosts excellent energy storage performance, with impressive energy density (Wrec) of 4.2 J/cm3 accompanied by satisfactory energy efficiency (η) of 75.1%. Together with high thermal stability of the energy storage density of 2.0–2.1 J/cm3 (with minimal variation of ≤ ±5%) over 25–150 °C at 150.0 kV/cm due to the enhancement of thermal insensitivity, which is evidenced by simulation based on thermal conduction model. Additionally, an extraordinary fast discharge rate (t0.9) of 54.6 ns and a high power density (Pd) of 35.4 MW/cm3 can be achieved in the x = 0.20 ceramic sample. This discovery provides new opportunities to lead-free dielectric materials with a high energy density and efficiency for capacitive electrical energy storage.

Impact of annealing on electrocaloric response in Lanthanum-modified lead zirconate titanate ceramic

Over the past decades, there has been significant interest in new cooling technology based on the large electrocaloric effect observed in polymeric and inorganic ferroelectric materials. We report a dramatic impact of annealing on the electrocaloric effect observed by direct measurements in Pb0.88La0.12(Zr0.65Ti0.35)0.97O3 bulk ceramics (12/65/35 PLZT). In addition, the EC response was measured deep in a relaxor part of the PLZT composition phase diagram. After additional one-hour sample annealing at 600 °C, the EC response increased by about six times. Electrocaloric results confirm the existence of the significant electrocaloric response with the EC temperature change (ΔTEC) of 4.5 K at 360 K and 90 kV/cm in an annealed sample. This value exceeds previously obtained maximum ΔTEC values at the same field in perovskite relaxor ferroelectrics such as Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) and 8/65/35 PLZT ceramics. The electrocaloric responsivity ΔT/ΔE = 5.09 × 10−7 Km/V determined at 360 K is among the highest observed in bulk perovskite ferroelectrics at a relatively high electric field of 90 kV/cm.

Effect of BaO–CaO–SiO2 addition on dielectric and electrocaloric properties of lead-free 0.2Ba(Ti0.9Sn0.1)O3-0.8Ba(Zr0.18Ti0.82)O3 bulk ceramics

In recent years, compared with traditional refrigeration technology, the electrocaloric refrigeration technology has been applied in variety of green cooling devices due to its high efficiency and environmentally friendly. Recent findings reveal that the ceramic system with additives (such as, LiBiO2, PbO) can create large ECE under low electric field. In this work, the ternary glass BaO–CaO–SiO2 (BCS) was used as a sintering aid to enhance the electrocaloric (EC) response of 0.2Ba(Ti0.9Sn0.1)O3-0.8Ba(Zr0.18Ti0.82)O3(BZSnT20) bulk ceramics. The EC properties of BZSnT20 could be also improved via controlling sintering temperature and the content of BCS sintering aid. It was found that BZSnT20 with 0.5 wt% BCS show the maximum EC response of 3.2 K under 7 MV/m with sintering temperature of 1262 °C. These results demonstrated that the ECE of BZSnT20 can be boosted by using appropriate additives, which provides an effective route to realize large ECE under low electric fields.

Modulating the energy storage performance of NaNbO3-based lead-free ceramics for pulsed power capacitors

Nb-containing antiferroelectric materials have recently attracted great research interest as energy storage materials for pulsed power capacitors due to their extraordinary energy storage performances. In this case, the optimization of the energy storage performance is obtained by a compositional modulation of NaNbO3-Bi(Zn2/3Nb1/3)O3 bulk ceramics. An optimal energy performance can be obtained with a composition of 0.85NaNbO3-0.15Bi(Zn2/3Nb1/3)O3, which is accompanied by a stable charge energy density in temperatures up to 150 °C owing to its relaxor characteristics and excellent cycling stability after 105 cycles. This work further broadens the scope of NaNbO3-based ceramic applications in the area of pulsed power sources.

Analysis of dielectric and magnetic phase transitions in Yb(Fe0.5Cr0.5)O3 bulk perovskite

A comprehensive investigation of dielectric and magnetic phase transitions in Yb(Fe0.5Cr0.5)O3 bulk ceramics has been presented. The co-existence of orthorhombic phase (Pbnm) along with minor hexagonal (P63cm) phase is detected through Rietveld refinement technique, whereas the presence of Fe3+/Fe2+ and Cr3+/Cr2+ species is also encountered under XPS study. The dielectric broad-band spectroscopic study (5–500 K) reveals that two dielectric transition peaks: (1) at 370 K, first order ferroelectric transition for induced local non-centrosymmetry, and (2) at 462 K, diffuse like relaxor transition because of formation of polar nano-regions and, Schottky barriers at sample-electrode interface, respectively. The complex impedance spectroscopic study exhibits the non-Debye type dielectric relaxation phenomena at lower temperatures, while at high temperatures, oxygen ion vacancies are found to contribute the conduction progression. Furthermore, dc-magnetization plot in FC-ZFC mode detects the strong interactions between Cr3+/Fe3+sublattices also with Yb3+ ions and Yb3+–Yb3+ ions. This results into an antiferromagnetic ordering at TN ~271 K for Cr3+–Cr3+/Fe3+–Fe3+ or Cr3+–Fe3+ spins followed by weak ferromagnetic ordering at 41 K for the occurrence of progressive spin reorientation and further at 11.2 K due to onset interactions of ferromagnetic Cr3+/Fe3+ sub-lattices with paramagnetic Yb3+ ions.

Improved pyroelectric figures of merit of Mn-doped Zr-rich lead zirconate titanate bulk ceramics near room temperature for energy harvesting applications

Pyroelectric energy harvesting has been attracting increasing attention due to its abundance and potential applications. In this work, we comparably investigated the pyroelectric properties of Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 bulk ceramics without (PNZT95/5) and with Mn doping (PNMZT95/5). Compared to PNZT95/5, PNMZT95/5 demonstrated a lower dielectric constant and low rhombohedral - high rhombohedral ferroelectric phase transition temperature (TLH from 37 °C to 27 °C). Moreover, the poling time displayed significant effects on the dielectric and pyroelectric properties of the ceramics. A giant pyroelectric response was obtained for the PNMZT95/5 ceramics, of which the maximum pyroelectric figure of merit FE was 16017 J/(m3K2) after 180 min of poling, which increased 62% compared with the FE for PNZT95/5 (9890 J/(m3K2), far higher than those of other pyroelectric materials as well. PNMZT95/5 ceramics is suggested to be a promising candidate for the thermal energy harvesting applications.

Quasi-adiabatic calorimeter for direct electrocaloric measurements.

The electrocaloric effect (ECE) in ferroelectric materials is a promising candidate for small, effective, low cost, and environmentally friendly solid state cooling applications. Instead of the commonly used indirect estimates based on Maxwell's relations, direct measurements of the ECE are required to obtain reliable values. In this work, we report on a custom-made quasi-adiabatic calorimeter for direct ECE measurements. The ECE is measured for two promising lead-free materials: Ba(Zr0.12Ti0.88)O3 and Ba(Zr0.2Ti0.8)O3 bulk ceramics. Adiabatic temperature changes of ΔTEC = 0.5 K at 355 K and ΔTEC = 0.3 K at 314 K were achieved under the application of an electric field of 2 kV/mm for the Ba(Zr0.12Ti0.88)O3 and Ba(Zr0.2Ti0.8)O3 samples, respectively. The quasi-adiabatic ECE measurements reliably match other direct EC measurements using a differential scanning calorimeter or an infrared camera. The data are compared to indirect EC estimations based on Maxwell's relations and show that the indirect measurements typically underestimate the effect to a certain degree.

Effect of Ti content on energy storage properties of (Pb0.87Ba0.10La0.02)(Zr0.60Sn0.40-xTix)O3 bulk ceramics

ABSTRACT(Pb0.87Ba0.10La0.02)(Zr0.60Sn0.40-xTix)O3(PLBZST) (x = 0–0.20) bulk ceramics were prepared by the conventional solid state method, and the dependence of phase transformation, ferroelectric properties and energy storage properties on x values has been investigated. When x = 0.12, the unit cell volume significant change indicted the phase transformation of the ceramics. As x = 0.04–0.10, the PLBZST ceramics possess anti-ferroelectric phase with high recoverable energy storage density 0.8–1.3 j/cm3 and when x = 0.12–0.20, the ceramics with ferroelectric phase have lower density values about 0.2–0.3 j/cm3. The phase switching electric field, saturation polarization and test temperature have an important influence on energy storage density and efficiency. As a result, the PLBZST bulk ceramics exhibit the largest recoverable energy density of 1.3 j/cm3 with efficiency of 77.4% at 20°C.

Modified Differential Scanning Calorimeter for Direct Electrocaloric Measurements

Solid-state refrigeration using the electrocaloric effect (ECE) in ferroelectric materials is a promising alternative to the conventional vapor-compression technology. In spite of growing interest to the investigation of the ECE, direct measurements of the effect are still rare. In this paper, we report on a modification of a differential scanning calorimeter for direct ECE measurements. The importance of proper estimation of the thermal correction factor and use of proper values of the heat capacitance for correct ECE measurements is discussed. The ECE measurements were performed for Ba(Zr0.2Ti0.8)O3 and Ba(Zr0.12Ti0.88)O3 bulk ceramics. Large electrocaloric temperature changes of 0.54 and 0.34 K are achieved under the application of an electric field of 2 kV/mm for the Ba(Zr0.12Ti0.88)O3 and Ba(Zr0.2Ti0.8)O3 samples, respectively. The relation between the directly measured ECE values and frequently used indirect estimation based on Maxwell's relations is discussed.

Hydroxyl defect effect on the resistance degradation behavior in Y-doped (Ba,Ca)(Ti,Zr)O3 bulk ceramics

Degradation behavior of acceptor (Y)-doped (Ba,Ca)(Ti,Zr)O3 ceramics sintered in moist reducing atmosphere and subsequently re-oxidized in dry or wet atmospheres was contrasted. The degradation behavior critically depends on the water vapor incorporation, the time to degradation systematically decreased with the incorporation of hydroxyl defects (OH)O•. The electrical conductivity was investigated by means of impedance spectroscopy (IS) to determine properties, such as grain and grain boundary conductivity, grain boundary potential barrier height, and space charge layer thickness. Furthermore, transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) were applied to consider microstructure, microchemistry, and oxygen stoichiometry changes.

Effect of crystal structure and cationic order on phonon modes across ferroelectric phase transformation in Pb(Fe0.5-xScxNb0.5)O3 bulk ceramics

Pb(Fe0.5-xScxNb0.5)O3 [(PFSN) (0 ≤ x ≤ 0.5)] multiferroic relaxors were synthesized and the temperature dependence of phonon modes across ferroelectric to paraelectric transition was studied. With varying Sc content from x = 0 to 0.25 the structure remains monoclinic and with further addition (x = 0.3 - 0.5) the structure transforms into rhombohedral symmetry. Structural refinement studies showed that the change in crystal structure from monoclinic to rhombohedral symmetry involves a volume increment of 34-36%. Associated changes in the tolerance factor (1.024 ≤ t ≤ 0.976) and bond angles were observed. Structure assisted B′-B″ cation ordering was confirmed through the superlattice reflections in selected area electron diffraction (SAED) pattern of Pb(Sc0.5Nb0.5)O3 (x = 0.5). Cation ordering is also evident from the evolution of Pb-O phonon mode in Raman spectra of compositions with rhombohedral symmetry (x ≥ 0.3). The high temperature Raman scattering studies show that the B-localized mode [F1u, ∼250 cm−1] and BO6 octahedral rotational mode [F1g, ∼200 cm−1], both originating from polar nano regions (PNRs) behave like coupled phonon modes in rhombohedral symmetry. However, in monoclinic symmetry they behave independently across the transition. Softening of B localized mode across the transition followed by the hardening for all compositions confirms the diffusive nature of the ferroelectric transformation. The presence of correlation between the B localized and BO6 rotational modes introduces a weak relaxor feature for systems with rhombohedral symmetry in PFSN ceramics, which was confirmed from the macroscopic dielectric studies.

Dielectric and temperature stable energy storage properties of 0.88BaTiO3–0.12Bi(Mg1/2Ti1/2)O3 bulk ceramics

The 0.88BaTiO3–0.12Bi(Mg1/2Ti1/2)O3 ceramics were prepared via the solid state reaction route. The temperature dependence of permittivity in 0.88BaTiO3–0.12Bi(Mg1/2Ti1/2)O3 (0.88BT–0.12BMT) ceramics shows relaxor-like behavior and weak temperature-dependence over a temperature range from −50°C to 100°C at 100Hz. The polarization–electric field hysteresis (P–E) loops display a linear behavior at low fields, and slight saturated nonlinear behaviors at higher fields. It can be inferred from the polarization behavior at high fields that a field-induced phase transition from relaxor state to ferroelectric state can be detected. Energy storage performance at different temperatures was also studied. The maximum energy storage density of 1.81J/cm2 was obtained at room temperature. And, a temperature stable energy storage property of the 0.88BT–0.12BMT over a temperature range from −50°C to 120°C suggests its potential application in energy storage capacitors.

Large electrocaloric effect in Ba(Ti1−xSnx)O3 ceramics over a broad temperature region

A large electrocaloric effect (ECE) near room temperature is reported in Sn doped BaTiO3 ceramics. By tuning Ba(Ti1−xSnx)O3 compositions which also exhibit relaxor ferroelectric response to near the invariant critical point, the Ba(Ti1−xSnx)O3 bulk ceramics at x ∼ 0.12 exhibit a large EC coefficient (ΔT/ΔE =0.27*10−6K⋅mV−1) over a 50 K temperature range. In addition to that, the diffuse phase transition is successfully applied to broaden the EC peaks under low electric field. These properties added together indicate a general solution of the electrocaloric materials with high performance for practical cooling applications.

Strong visible‐light photovoltaic effect in multiferroic Pb(Fe1/2V1/2)O3 bulk ceramics

AbstractThe multiferroic Pb(Fe1/2V1/2)O3 (PFV) bulk ceramic was fabricated by a conventional ceramic sintering method. The strong visible‐light photovoltaic effect in Sn‐doped‐In2O3(ITO)/PFV/ITO structure capacitor was observed. The open‐circuit voltage was up to ∼0.7 V, which was much higher than the value (∼0.3 V) in BiFeO3 film. The photo‐excited electric current is almost proportional to the incident light illumination intensity. The good visible‐light photovoltaic makes PFV ceramic a potential candidate for practical application in solar cell devices.magnified imageVisible‐light photovoltaic effect in multiferroic Pb(Fe1/2V1/2)O3 bulk ceramics. The open‐circuit voltage and zero‐bias photocurrent are ∼0.7 V and 0.02 μA, respectively.(© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Giant Electrocaloric Response Over A Broad Temperature Range in Modified BaTiO3 Ceramics

A giant electrocaloric effect (ECE) near room temperature is reported in a lead‐free bulk inorganic material. By tuning Ba(ZrxTi1–x)O3 compositions which also exhibit relaxor ferroelectric response to near the invariant critical point, the Ba(ZrxTi1–x)O3 bulk ceramics at x ∼ 0.2 exhibit a large adiabatic temperature drop of 4.5 K, a large isothermal entropy change of 8 J kg−1 K−1, and a large EC coefficient (|ΔTc/ΔE| = 0.52 × 10−6 KmV−1 and ΔS/ΔE = 0.93 × 10−6 J m kg−1 K−1 V−1) over a 30 K temperature range. These properties added together indicate a general solution of the electrocaloric materials with high performance for practical cooling applications.

Structural and Magnetic Properties of Bi(Fe1−xMnx)O3

Bi(Fe1−xMnx)O3 bulk ceramics with Mn concentration x up to 0.3 were prepared by rapid sintering using sol-gel derived fine powders. Structure transformation is found to depend on the Mn doping concentration by X-ray diffraction and Raman spectroscopy. Bi(Fe1−xMnx)O3 maintains the rhombohedral structure of BiFeO3 with x=0.05 and 0.1, but changes to the orthorhombic structure with x=0.3. Weak ferromagnetism is observed for Bi(Fe1−xMnx)O3 with x=0.05 and 0.1, but stronger paramagnetism is observed for Bi(Fe1−xMnx)O3 with x=0.3 indicating a magnetic phase change from antiferromagnetic to paramagnetic with the structure changing from R3c to C222. Two anomalies at 30 and 140 K are observed for Bi(Fe1−xMnx)O3 with x=0.05 and 0.1. The anomaly at 30 K is concluded to be related to the freezing of cluster spin glass from dc magnetic memory and relaxation measurements.

First order reversal curves diagrams for describing ferroelectric switching characteristics

First Order Reversal Curves (FORC) are polarization-field dependences described between saturation field Esat and a variable reversal field E,?(-Esat, Esat). The FORC diagrams were proposed to describe some characteristics of the switching process in ferroelectrics. The approach is related to the Preisach model which considers the distribution of the elementary switchable units over their coercive and bias fields. The influence of the anisotropic porosity in Pb(Zr,Ti)O3 bulk ceramics on the FORC distributions demonstrated the existence of a positive/negative bias as a result of the confinement induced by anisotropy. The reducing of grain size in Ba(Zr,Ti)O3 ceramics causes an increase of the ratio of the reversible/irreversible components of the polarization on the FORC distribution indicating the tendency of system towards the superparaelectric state. The FORC method demonstrates to provide a kind of 'fingerprinting' of various types of switching characteristics in ferroic systems. .

Dielectric tunability of (Ba0.90Ca0.10)(Ti0.75Zr0.25)O3 ceramics

We have performed a study on the dielectric properties of (Ba0.90Ca0.10)(Ti0.75Zr0.25)O3 bulk ceramics prepared by a sol–gel technique in the cooling temperature range from 400to213K. The ceramics are found to exhibit an interesting dielectric response under the presence of a dc bias field. The field dependence of dielectric constant is stronger at T≈Tm (Tm is the temperature of dielectric maximum) and the field-induced variation of dielectric constant Δε is nonzero for T−Tm<150K. One striking feature of these ceramics is that they possess a broad optimum value of figure of merit (as high as 200 at 30kV∕cm) between the temperature range from 295 and 330K. At room temperature, the high tunability (K=60%), low-loss tangent (≈0.003), and large figure of merit (200), clearly indicate that these ceramics are suitable candidates for microwave applications.