Effect In Ba0 Research Articles

Role of Density and Grain Size on the Electrocaloric Effect in Ba0.90Ca0.10TiO3 Ceramics.

Pure perovskite Ba0.90Ca0.10TiO3 ceramics, with a relative density of between 79 and 98% and grain sizes larger than 1 µm, were prepared by solid-state reaction. The dielectric and electrocaloric properties were investigated and discussed considering the density and grain size of the samples. Room temperature impedance measurements show good dielectric properties for all ceramics with relative permittivity between 800 and 1100 and losses of <5%. Polarization vs. E loops indicates regular variation with increasing sintering temperature (grain size and density), an increase in loop area, and remanent and saturation polarization (from Psat = 7.2 µC/cm2 to Psat = 16 µC/cm2). The largest electrocaloric effect was 1.67 K for ceramic with GS = 3 µm at 363 K and electrocaloric responsivity (ζ) was 0.56 K mm/kV. These values are larger than in the case of other similar materials; thus, Ba0.90Ca0.10TiO3 ceramics with a density larger than 90% and grain sizes of a few µms are suitable materials for electrocaloric devices.

Emergence of reentrant relaxor behavior with enhanced electromechanical and electrocaloric effect in Ba0.95Ca0.05Sn0.09Ti0.91O3 ceramic

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.

Effects of Swift-Particle Irradiations on Critical Current Density in CaKFe4As4

Introduction of columnar defects to superconductors through swift-particle irradiation enhances their critical current density (Jc). Iron-based superconductors (IBSs) have been investigated as promising materials for practical applications because of their large Jc at high magnetic fields and temperatures. Recently, another promising IBS CaKFe4As4 (1144-type IBS) was found, and attracts much interest due to its high Jc in the pristine sample. We compare effects of 800 MeV Xe, 3 MeV proton, and 320 MeV Au irradiations on the critical temperature (Tc) and Jc of CaKFe4As4 single crystals, and compare them with irradiation effects in Ba0.6K0.4Fe2As2.

Spin glassy behavior and large exchange bias effect in cubic perovskite Ba0.8Sr0.2FeO3-δ**Project supported by the National Key Research and Development Program of China (Grant Nos. 2018YFA0305700 and 2018YFGH000095), the National Natural Science Foundation of China (Grant Nos. 51772324 and 11574378), and the Fund from the Chinese Academy of Sciences (Grant No. QYZDB-SSW-SLH013, GJHZ1773).

A single-phase iron oxide Ba0.8Sr0.2FeO3-δ with a simple cubic perovskite structure in Pm-3m symmetry is successfully synthesized by a solid-state reaction method in O2 flow. The oxygen content is determined to be about 2.81, indicating the formation of mixed Fe3+ and Fe4+ charge states with a disorder fashion. As a result, the compound shows small-polaron conductivity behavior, as well as spin glassy features arising from the competition between the ferromagnetic interaction and the antiferromagnetic interaction. Moreover, the competing interactions also give rise to a remarkable exchange bias effect in Ba0.8Sr0.2FeO2.81, providing an opportunity to use it in spin devices.

Tribological behaviour of Fe3Al-Ba0.25Sr0.75SO4 self-lubricating composites in vacuum and air

The effect of Ba0.25Sr0.75SO4 on tribological properties of the Fe3Al-based composites were evaluated both in vacuum and air. The tribological properties of the composites were significantly improved by the addition of Ba0.25Sr0.75SO4, especially in vacuum. The Fe3Al alloy shows relative poor tribological performance in vacuum than in air. The main reason was the severe adhesion wear and deleterious contact surfaces in vacuum, but in air, the formation of the oxides film on the friction surface protected the Fe3Al alloy materials from wear. It is worth noting that the wear rate of the 30% self-lubricating composite reduced almost 3–7 times than that of Fe3Al alloy in vacuum, and the COF also lowered to about 2 times. The improvement of tribological properties of Fe3Al-based composites was attributed to that the Ba0.25Sr0.75SO4 was easily softened and formed lubricating film on the worn surfaces to effectively reduce friction and wear in vacuum. The dominant wear mechanism for Fe3Al alloy was surface fatigue wear and oxidative wear in air, but in vacuum was adhesive wear and plastic deformation. For Fe3Al-Ba0.25Sr0.75SO4 composites, mainly wear mechanism was adhesive wear and surface fatigue wear in air, while in vacuum that was abrasive wear and adhesive wear.

Structural, dielectric and magnetoelectric properties of (BSPT–LSMO) composites

The paper discuses mainly P-E and M-H hysteresis loops and magnetoelectric effect in Ba0.8−xSrxPb0.2TiO3 (BSPTx)–La0.7Sr0.3MnO3 (LSMO) composites. BSPTx powder is synthesized using solid state reaction method while, LSMO is synthesized using hydroxide co-precipitation route. The (BSPTx–LSMO) composites are prepared by mixing the respective powder in their weight proportion and sintering at 1100 °C. The resulting composites are investigated for crystal structure, microstructure, dielectric properties and magnetoelectric coupling. The results are understood employing qualitative approach.

Enhanced structural, dielectric, ferroelectric, and piezoelectric properties of (1−x)Ba0.9Sr0.1TiO3–(x)Ba0.7Ca0.3TiO3 ceramics derived using mechano‐chemical activation technique

AbstractThe effect of Ba0.7Ca0.3TiO3 (BCT) substitution on the structural, dielectric, ferroelectric, and piezoelectric properties of mechano‐chemically synthesized lead‐free (1−x)Ba0.9Sr0.1TiO3‐(x)Ba0.7Ca0.3TiO3 (x=0.0, 0.10, 0.20, 0.35, and 0.50) ceramics have been investigated. XRD patterns confirms the formation of tetragonal phase with P4mm space group. The results indicate a strong influence of BCT substitution on the structural and electrical properties of Ba0.9Sr0.1TiO3 (BST) ceramic. BST–BCT ceramic for x=0.35 have shown high dielectric constant εm~21 800, high remnant polarization Pr~10.16 μC/cm2, large piezoelectric charge constant D33~293 pC/N, large piezoelectric voltage constant g33~5.80 mV·m/N, and highest dielectric breakdown strength Ebd~224 kV/cm among the five synthesized samples. The correlation between structural, dielectric, ferroelectric, and piezoelectric properties of the BST ceramic with increasing BCT content have been systematically described on the basis of domain wall motion and grain size effect.

Preparation, microstructure and relaxor ferroelectric characteristics of BLNT–BCT lead-free piezoceramics

In the present study, lead-free piezoelectric (1-x)[(Bi0.96La0.04)0.5Na0.5TiO3]-(x)[Ba0.90Ca0.10TiO3] ceramics with x ≤ 0.20 have been prepared at optimum temperature (950°C–1050 °C) by employing semi-wet technique. The effect of Ba0.90Ca0.10TiO3 (BCT) content on the phase formation, surface morphology, dielectric and piezoelectric properties is systematically investigated and characterized by X-ray diffraction (XRD), Raman Spectroscopy, Field emission Scanning electron micrographs (FE-SEM), Impedance analyzer. XRD analysis shows phase transformation from rhombhohedral to tetragonal with the addition of BCT and the average grain size decreases with BCT content, x. Temperature dependent dielectric behavior exhibits two phase transitions, i.e. depolarization temperature; Td and phase transition temperature; Tm. The phase transitions; Tm tends to diffuse with increasing x and exhibited a broad frequency dependent maximum upto x ≤ 12. Optimum piezoelectric and dielectric properties (i.e., d33 = 165 pC/N, kp = 39%, kt = 47% and k33 = 57%, εr = 1585, tan δ = 0.07) in the studied system have been obtained.

Large electrocaloric strength and broad electrocaloric temperature span in lead-free Ba0.85Ca0.15Ti1−xHfxO3ceramics

The electrocaloric (EC) effect of Ba0.85Ca0.15Ti1−xHfxO3 (abbreviated as: BCTHx) ceramics has been systematically investigated using an indirect method.

Enhanced electrocaloric effect in Ba0.85Ca0.15Zr0.1Ti0.9–xSnxO3 ferroelectric ceramics

ABSTRACTThe present work deals with the study of effect of Sn addition (0%–6% by mole) on the electrocaloric (EC) performance of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramics. Maxwell's relations in conjunction with data from experimental observations were used for the indirect caloric measurements. Small percentage change with Sn addition is found to increase the EC performance of BCZT ceramics. A peak adiabatic temperature change of 0.84 K (353 K) was predicted for 0–32 kV/cm electric field, significantly higher than pristine BCZT ceramics. A simultaneous increase in specific entropy change was also observed.

Effect of Ba0.5Bi0.5Fe0.9Sn0.1O3 addition on electrical properties of thick-film thermistors

Thick-film thermistor with negative temperature coefficient (NTC), low room-temperature resistivity and modest thermistor constant was screen-printed on the alumina substrate by the combination of with Ba0.5Bi0.5Fe0.9Sn0.1O3. The electrical properties of the thick films were characterized by a digital multimeter, a Keithley 2400 and an impedance analyzer. The results show that with the Ba0.5Bi0.5Fe0.9Sn0.1O3 content increasing from 0.05 to 0.25, the values of room-temperature resistivity, thermistor constant and peak voltage of the thick films increases and are in the ranges of 1.47-26.5 O-cm, 678-1345 K and 18.9-47.0 V, respectively. The corresponding current at the peak voltage of the thick films decreases and is in the range of 40-240 mA. The impedance spectroscopy measurement demonstrates that the as-prepared thick films show the abnormal electrical heterogeneous microstructure, consisting of high-resistive grains and less resistive grain boundary regions. It can be concluded that the addition of Ba0.5Bi0.5Fe0.9Sn0.1O3 into improves the thermistor behavior and but also deteriorates the current characteristics.

Change of the charge modulation during superconducting transition in SmFeAsO0.91F0.09 seen by 57Fe Mössbauer spectroscopy

Iron-based superconductor SmFeAsO0.91F0.09 has been investigated by the 57Fe Mössbauer spectroscopy versus temperature with the special attention paid to the region of the superconducting transition at about 47 K. Modulation of the electron charge density was found. It leads to the development of the charge density wave (CDW) and electric field gradient wave (EFGW). The modulation of CDW is enhanced in the temperature region of the superconducting gap opening, while the amplitude of EFGW is partly suppressed within this temperature region. This effect is exactly opposite to the similar effect in Ba0.6K0.4Fe2As2 superconductor. Hence, it seems that d electrons contribute significantly to the Cooper pair formation in both compounds as EFGW is perturbed within the temperature region of the superconducting gap formation.

Electrocaloric effect in Ba0.2Ca0.8Ti0.95Ge0.05O3 determined by a new pyroelectric method

The present letter explores the electrocaloric effect (ECE) in the lead-free oxide Ba0.8Ca0.2Ti0.95Ge0.05O3 ceramics (BCTG). The electrocaloric responsivity was determined by two different methods using the Maxwell relationship . In a first well-known indirect method, hysteresis loops were measured in a wide temperature range from which the pyroelectric coefficient and thus ξ were determined by derivation of data. In the second novel method the pyroelectric coefficient pE and consequently the electrocaloric responsivity ξ were determined by direct measurements of the pyroelectric currents under different applied electric fields. Within the experimental error, good agreement was obtained between two methods with at about 410 K.

Increased saturation field as the origin of the giant electrocaloric effect in Ba0.8Sr0.2TiO3 thin films

We investigated the electrocaloric (EC) effects in epitaxial Ba0.8Sr0.2TiO3 (BSTO) thin films grown on LaAlO3 and MgO substrates and in BSTO sol-gel thin films grown on Si substrates. We compared the EC effects in two forms of BSTO to confirm whether the giant EC effect recently observed in the polycrystalline thin film is an intrinsic effect or an extrinsic effect exclusively occurring in polycrystalline thin films with nano-sized grains. The EC effect in our BSTO single crystals exhibited a moderate EC temperature change over a broad temperature range. On the other hand, the EC effect in the BSTO sol-gel film was observed over a narrow temperature range with a giant ΔT of about 14 °C. We claim that this giant EC effect is due to the increased saturation field related to the small grain size in the sol-gel thin film.

Electrocaloric Behavior and Temperature‐Dependent Scaling of Dynamic Hysteresis of Ba0.85Ca0.15Ti0.9Zr0.1O3 Ceramics

This article presents electrocaloric effect in Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCTZO) using an indirect approach based on Maxwell's relations. The peak electrocaloric performance is found to be an adiabatic temperature change of 0.41 K with electrocaloric strength of 19 mK cm/kV and a heat carrying capacity of ~0.17 J/g under an electric field of 0–21.5 kV/cm. The ferroelectric hysteresis scaling relations for coercive field (EC), remnant polarization (Pr), and hysteresis area (<A>) as a function of temperature (T) are also systematically investigated. The power‐law temperature exponents are obtained for all the hysteresis parameters. The scaling relations are established as Ec ∝ T−0.6584, Pr ∝ T−1.59, and <A> ∝ T−1.01623. The presented scaling relations are compared with those reported in the literature for other ferroelectric materials.

Observation of weak coupling effects in Ba0.6 K0.4 Fe2 As2 junctions patterned across a naturally formed grain boundary

We have fabricated intergrain nanobridge junctions from a Ba0.6K0.4Fe2As2 film and observed their weak coupling effects. We prepared the junction by patterning a nanobridge across a natural grain boundary by using a focused ion beam etching technique and studied their superconducting transition properties. The resistive transition showed three steps: the transitions of the bulk, the microbridge, and the junction grain boundary. Current–voltage curves showed typical Josephson junction characteristics, well-matched with the model of a resistively shunted junction incorporated with thermal fluctuations. Fitting data to theory revealed much larger current fluctuations than expected from the Johnson–Nyquist theorem. The junction showed a linear temperature dependence of the critical current and a constant normal-state resistance, indicating that the grain boundary played a role as a tunnel barrier with a very poor conductance.

Magnetoelectric Effect in Ba0.5Sr0.5TiO3/CoFe2O4 Thin Film Prepared by Pulsed Laser Deposition Method

Magnetoelectric materials have attracted considerable attention for several decades owing to their both magnetic and electric properties. The magnetoelectric multilayer, Ba0.5Sr0.5TiO3/CoFe2O4, has been fabricated by the aid of pulsed laser deposition technique and after fabrication characterized by X-ray diffraction pattern and magnetoelectric effect. Sufficient magnetoelectric coefficient has been observed in samples with increasing biased magnetic field. Our results suggest that magnetoelectric coupling effect may be tuned by interlayer properties and biased magnetic field which show the capability of use in nonvolatile memory, phase shifter, and sensor applications.

Field- and temperature-induced evolution of the magnetocaloric effect in Ba0.3Sr1.7Co2Fe12O22 single crystals with heliconical magnetism

The magnetocaloric effect (MCE) associated with the spin transitions of alternating longitudinal conical (ALC)–mixed conical (MC) and MC–ferrimagnetic (FIM) states in a Ba0.3Sr1.7Co2Fe12O22 single crystal has been investigated. For magnetic field directions applied along either the [120] or [001] directions, the crystal is found to exhibit the conventional and inverse MCE near the ALC–MC (TN1 = 235 K) and MC–FIM (TN2 = 348 K) states, respectively. The dependence of the magnetic entropy on the magnetic field also exhibits such sign change behaviors in the MCE, which is attributed to the magnetic field induced gradual collapse of heliconical magnetic order.

Preparation and characterization of (1 – y)BiFeO3/y(Ba0.7Na0.3Ti0.7Nb0.3)O3multiferroic ceramics

We present in this work a contribution to the study of the solid solution (1 – y)BiFeO3/y(Ba0.7Na0.3Ti0.7Nb0.3)O3. Room temperature X-ray diffraction patterns for some prepared compositions confirmed the formation of perovskite structure. The study of the evolution of dielectric properties as a function of sintering temperature allowed us to determine the optimum conditions that minimize the presence of defects and oxygen stoichiometric limit fluctuations due to the volatility of bismuth. The variation of permittivity as a function of temperature and frequency for the (1 – y)BiFeO3/y(Ba0.7Na0.3Ti0.7Nb0.3)O3 solid solution was measured. The effect of Ba0.7Na0.3Ti0.7Nb0.3O3 addition content on crystal structure, dielectric and magnetic properties of BiFeO3 was investigated. Raman measurements reveal resonant enhancement of two-phonon excitation for (1 – y)BiFeO3/y(Ba0.7Na0.3Ti0.7Nb0.3)O3 samples. We also expect that the solid solution shows weak ferromagnetic behavior for low Ba0.7Na0.3Ti0.7Nb0.3O3 levels of substitution.

Effect of Ba0.85Ca0.15Ti0.90Zr0.10O3 content on the microstructure and electrical properties of Bi0.51(Na0.82K0.18) 0.50TiO3 ceramics

(1−x)Bi0.51(Na0.82K0.18)0.50TiO3–xBa0.85Ca0.15Ti0.90Zr0.10O3 [(1−x)BNKT–xBCTZ] ceramics were prepared by the conventional solid-state method, and the effect of BCTZ content on their microstructure and electrical properties was investigated. A stable solid solution with a pure perovskite phase is formed between BNKT and BCTZ, and these ceramics have a coexistence of rhombohedral and tetragonal phases in the range of 0≤x<0.15. Their Tm and Td values are strongly independent on the BCTZ content. Moreover, the sintering temperature strongly affects the ferroelectric and piezoelectric properties of these ceramics with x=0.02. These ceramics with x=0.02 exhibit an optimum electrical behavior of d33∼205, kp∼0.25, Pr∼31.8μC/cm2, and Ec∼19.1kV/cm together with a high Td value of ∼91°C when sintered at 1180°C and poled at an optimum condition. As a result, the (1−x)BNKT–xBCTZ ceramic is a promising candidate material for lead-free piezoelectric ceramics.