BiFeO3 xBaTiO3 Research Articles

High-efficiency energy storage in Nd-doped (1-x)BiFeO3–xBaTiO3 relaxor ferroelectric ceramics

Dielectric capacitors as energy storage electronics have drawn much attention due to ultrahigh power densities with quick charging and discharging rates. In this report, A-site Nd-doped (1-x)BiFeO3-xBaTiO3 (x = 0.2–0.45) relaxor ferroelectric ceramics with superior storage efficiencies were prepared with 0.1 wt% MnO2 additive. Energy-storage efficiency (η) increases from 63.7% to 89% at 190 kV/cm as BaTiO3 increases accompanied by recoverable energy densities (Wrec) in the range of 2.5–2.7 J/cm3. The energy-storage performance persists thermally stable up to 125 °C. The superior storage efficiency is associated with growth of the cubic Pm-3m symmetry and the core-shell structure with increasing BaTiO3 content. The formation of nanocluster/nanomosaic structure also plays an essential role as a barrier in suppressing the long-range polarization order. This work provides a design of binary rare-earth doped BiFeO3–BaTiO3 dielectric ceramics for thermally stable and high-efficiency electrical energy storage.

Local structure analysis of BiFeO3-BaTiO3 solid solutions

The average and local structures of solid solutions of (1 – x)BiFeO3–xBaTiO3 were investigated. At room temperature, pseudo-cubic phases appear in BaTiO3 compositions with x values ranging from 0.3 to 0.7. The ferroelectricity was not lost even in the cubic structure with the highest ferroelectricity observed at x = 0.3. We used a pair distribution function and an X-ray absorption fine structure to perform a structural analysis to determine the source of this ferroelectricity. These solid solutions’ local structures were consistent with the pure limits of BiFeO3 and BaTiO3, respectively, but when the composition of BaTiO3 was 0.3, a structure peculiar to the structural boundary in the solid solutions appeared. We discovered that the structure had the greatest randomness around this composition by performing a model fit of this local structure. Local structure changes to improve nanoscale dipole interactions while maintaining the ferroelectric long-range order structure. As a result, the domain size grows and the ferroelectricity improves.

The (1 − x)BiFeO3–xBaTiO3–Bi(Zn0.5Ti0.5)O3 high-temperature lead-free piezoelectric ceramics with strong piezoelectric properties

The structure, microstructure, piezoelectric properties, ferroelectric properties and Curie temperature of (1 − x)BiFeO3–xBaTiO3–Bi(Zn0.5Ti0.5)O3 + MnO2 + Li2CO3 ceramics were investigated experimentally. The samples were prepared by the improved solid-state reaction approach. The crystalline structures were examined by X-ray diffractometry. When x = 0.3, the rhombohedral and pseudocubic phases coexist in the ceramic structure. It is considered that the morphotropic phase boundary was formed here. At this composition, the piezoelectric performance d33, Curie temperature TC, and depolarization temperature are as high as 184 pC/N, 550 °C, 530 °C at x = 0.3, respectively. It is worth noting that, when x = 0.24, the ceramics have a high TC = 580 °C and low dielectric loss tanδ = 1.9%. The results show that the BFBT-BZT ceramics with high piezoelectric properties are applicable in high-temperature fields.

Improved Ferroelectric and Ferromagnetic Properties of 1 − xBiFeO3-xBaTiO3 Ceramics

This paper introduces the solid-phase preparation of bismuth ferrite-based multiferroic ceramics (1 − x BiFeO3-x BaTiO3). After the Ba and Ti doping, it can be observed from the XRD pattern that the crystal structure of the sample changes obviously. From the picture obtained from the SEM test, the grain size of the doped samples was significantly reduced. Pure BiFeO3 (BFO) showed a large leakage current, and in the leakage current test, we found that the leakage current of Ba, Ti-doped samples decreased significantly, which may be related to doping, leading to oxygen vacancy reduction. From the magnetization hysteresis loops, we can see that the ferromagnetism of the doped samples was significantly improved compared to pure BFO, because Ba, Ti doping destroys the G-type antiferromagnetic sequence of pure BFO, thereby enhancing the ferromagnetic properties.

Piezoelectric, ferroelectric and ferromagnetic properties of (1−x)BiFeO3–xBaTiO3 lead-free ceramics near morphotropic phase boundary

A series of solid solution of (1−x)BiFeO3–xBaTiO3 (abbreviated as BFO–xBT at 0.24 ≤ x ≤ 0.34) were prepared to reveal the relation between phase structure and multiferroic properties. A morphotropic phase boundary (MPB) separating R phase and T one was detected in BFO–xBT system at 0.26 ≤ x ≤ 0.34. Due to R and T two-phase coexistence, high piezoelectric properties of d 33 = 191 pC/N and k p = 34.68%, as well as excellent ferroelectric properties of 2P r = 56.13 μm/cm2 and 2E C = 75.35 kV/cm were achieved in the BFO–xBT ceramics at x = 0.30. Moreover, a low leakage current density (J) of 1.01 × 10−6–3.18 × 10−6 A/cm2 at an applied electric field of 30 kV/cm and a weak ferromagnetism with remanent magnetization M r of 0.014–0.054 emu/g and coercive fields H c of 946–2340 Oe were detected in BFO–xBT ceramics at 0.24 ≤ x ≤ 0.34, suggesting that the BFO–BT ceramics have promising prospects in magnetoelectric functional components.

Composition design and electrical properties in BiFeO3–BaTiO3–Bi(Zn0.5Ti0.5)O3 lead-free ceramics

Here we fabricated the (1−y)[(1−x)BiFeO3–xBaTiO3]–yBi(Zn0.5Ti0.5)O3 ceramics by the conventional solid-state method, and then a large piezoelectric constant (d 33) of ~195 pC/N together with a high Curie temperature (T C = 505 °C) could be attained in the ceramics by building the rhombohedral–cubic (R–C) phase boundary. The R–C phase coexistence can be shown in the ceramics with 0.25 ≤ x ≤ 0.35 and 0.01 ≤ y ≤ 0.05. In particular, both a high remnant polarization (P r = 18.5 μC/m2) and a relatively high strain of ~0.19% were also observed in the phase coexistence region. In addition, the thermal stability together with the effects of polarization temperature and cooling-down method was also explored.

Structure, microstructure, and dielectric responses of (1–х)BiFeO3–xBaTiO3 solid solutions

The structure, microstructure, and dielectric responses of (1–х)BiFeO3–xBaTiO3 (0.0 < x ≤ 0.5) solid solutions prepared as ceramics are studied. Patterns in their dielectric parameters and the formation of their crystal and grain structures are investigated in a wide range of temperatures and frequencies.

High piezoelectric performance of lead-free BiFeO3–BaTiO3 thin films grown by a pulsed laser deposition method

Lead-free (100 − x)BiFeO3–xBaTiO3 (BFBTx, x = 0, 30, 33, 40 and 50) piezoelectric thin films were deposited on platinized silicon substrates by using a pulsed laser deposition method.

Effect of poling on polarization alignment, dielectric behavior, and piezoelectricity development in polycrystalline BiFeO3–BaTiO3 ceramics

This study investigates the effect of poling electric field on polarization alignment, dielectric dispersion, relaxor feature, phase transition temperature (Tm), and piezoelectric properties evolution of (1–x)BiFeO3–xBaTiO3[(1–x)BF–xBT] ceramics with x = 0.26, 0.29, 0.32, and 0.35. The XRD pattern studies indicate that the application electric field induced the polarization alignment along with a significant change of the diffraction intensity of peaks, which gives rise to increasing piezoelectric properties. Simultaneously, the degree of dielectric dispersion and diffuse factor γ in the modified Curie–Weiss equation and Tm increase after applying the poling electric field. Moreover, the relaxor characteristics are more evident with increasing BT content. The dielectric behavior and relaxor feature may be attributed to the small random field domains resulting from local charge imbalance due to off‐valent substituents between A‐ and B‐site cation in (1–x)BF–xBT ceramics. Meanwhile, the application of the poling electric field probably increases the strength of the neighboring dipole–dipole interaction, giving the enhanced degree of dielectric dispersion and Tm.

Magnetoelectric dipole interaction in RF-magnetron sputtered (1 − x) BiFeO3–xBaTiO3 thin films

Optimum composition with improved ferroelectric polarization and magnetization of multiferroic thin films (1−x) BiFeO3–xBaTiO3 (x=0, 0.1, 0.2 and 0.3) prepared by RF-magnetron sputtering have been analyzed for their multi functionality. Composite film optimized for x=0.1, showed shift in dielectric loss peak toward lower frequency by 0.3MHz with applied magnetic field. It confirms electric dipoles are brought in equilibrium condition at lower frequency due to active magnetoelectric dipole interaction. The film showed remnant electric polarization (2Pr) of 11μC/cm2 and saturation magnetization of 3.75emu/g. Room temperature transverse magnetoelectric coupling coefficient (αME)∼124mV/cmOe has been observed for x=0.1 composite thin film. The observed properties are very useful to exploit room temperature functional spintronic devices.

Effect of BaTiO3 doping on the structural, electrical and magnetic properties of BiFeO3 ceramics

(1 − x)BiFeO3–xBaTiO3 (x = 0.00, 0.10, 0.20, 0.25 and 0.30) ceramics have been fabricated by the solid state reaction method. The effects of BaTiO3 (BTO) doping on the structural, electrical and magnetic properties of BiFeO3 (BFO) ceramics have been investigated. It is found that BTO doping can affect the structure of the BFO ceramics, and the multiferroic properties of BFO ceramics can hence be improved. The XRD measurements reveal that the structure of BFO was changed from rhombohedral to pseudo-cubic and the impurity phases were decreased both due to BTO doping. Analysis of microstructure indicates that the BTO doping can hinder the grain growth. Electrical measurements show that BFO doping improves the ferroelectric property due to the significantly decrease of the electric leakage density and the oxygen vacancy concentrations. Magnetic measurements indicate that the antiferromagnetism behavior of BFO is turned into a weak ferromagnetism state by addition of BTO. The related mechanism is also discussed in the paper.

Studies on magnetoelectric coupling and magnetic properties of (1 − x)BiFeO3–xBaTiO3 solid solutions

Structure, magnetization and magnetoelectric coupling of (1 − x)BiFeO3–xBaTiO3 (BFO–BT) solid solutions have been studied as a function of BT content (x = 0.10, 0.15, 0.20, 0.25 and 0.30).The phase purity and crystal lattice symmetry were estimated from X-ray diffraction studies, which undergo gradual, well-controlled structural transformations from rhombohedral to cubic structure with morphotropic phase boundary (MPB). The micro-structural features, observed by scanning electron microscopy, demonstrate that the ceramic has highly compact and uniform microstructure having average grain size ~(3 ± 1) μm. The room-temperature magnetization studies exhibit hysteretic behavior with remnant magnetization values of m r ≤ 0.407 emu/gm and low coercivity H c ≈ (196 − 1,989) Oe indicating that the latent magnetization locked within the toroidal spin structure of BFO has been released and low loss is achieved. An observation on low coercivity, magnetoelectric (ME) coupling coefficient α ≈ 11.6 mV/cm/Oe at 5,000 Oe, effective high magnetic susceptibility χ eff ≈ 1.18 × 10−4 or 1.47 × 10−5 emu/gm Oe and pronounced anomaly in the dielectric constant near the magnetic transition temperature suggests quantitative as well as qualitative magnetoelectric coupling in BFO–BT solid solutions.

Conduction mechanism and dielectric properties of BiFeO3–BaTiO3 solid solutions

The first measurements are reported for the frequency-dependent conductivity of (1−x)BiFeO3–xBaTiO3 (x = 0.10, 0.15 and 0.30) solid solutions in the frequency range of 100–106 Hz and in the temperature range of 50–300 °C. Powder X-ray diffraction confirms the formation of solid solutions. The dielectric properties were seen to improve with increasing BaTiO3 (BT) content. The conductivity (AC and DC) measurements reveal an inverse variation of the frequency exponent ‘s’ with temperature, high density of states and thermally activated process. The calculated density of states was found to be N(Ef) = 80.2 × 1032 eV−1 cm−1 at 1 kHz and 50 °C for BiFeO3–10 % BaTiO3 (BFO–10 % BT) solid solution. The impedance spectroscopy analysis confirms the presence of grain and grain boundary affecting the conductivity. Our results provide the first unambiguous evidence of conduction in crystallite BFO–BT solid solutions through correlated-barrier-hopping model.

Magnetoelectric coupling-induced anisotropy in multiferroic nanocomposite (1 − x)BiFeO3–xBaTiO3

Nanocomposite (1 − x)BiFeO3–xBaTiO3 for x = 0.1, 0.2 and 0.3 compositions were prepared by sol–gel technique. X-ray diffractograms confirmed the formation of desired crystallographic phase of the composite. The average particle size was determined 75, 128 and 150 nm for x = 0.1, 0.2 and 0.3 samples by HRTEM measurement. Magnetic, dielectric and magnetoelectric response has been investigated to find out the magnetoelectric (ME) coupling at atomic scale mixing of the two phases. For effective ME coupling nanoscale synthesis provided large surface area and subsequently induced magnetic anisotropy in the sample. The computed value of magnetic anisotropy constant 4.8 × 103 erg/cm3 was found to be maximum for x = 0.1 composition. It is believed that the anisotropy is being induced by ME coupling which changes with the composition. Correlated magnetic and dielectric transition temperatures were determined as an evidence of ME coupling in the material. To confirm the ME coupling room-temperature ME coupling coefficient (α) was calculated using dynamic method which was observed to have a maximum value of 2.74 mV/cmOe for x = 0.1 confirming the presence of room-temperature ME coupling in the nanocomposite. Spin flipping behaviour has been confirmed by ZFC–FC measurements at low temperature while the coercivity was found to be almost constant. Significantly, controlled coercivity behaviour has been correlated to the presence of ME coupling in the composite material, which can be very useful in memory device and spintronic application.

Compositional dependence of dielectric and ferroelectric properties in BiFeO3–BaTiO3 solid solutions

Polycrystalline (1−x)BiFeO3–xBaTiO3 (0.11≤x≤0.5) ceramics have been prepared by the solid-state reaction method to investigate their phase structure, dielectric, ferroelectric, and field-induced strain behaviors. The phase was found to change from rhombohedral in BiFeO3-rich compositions to pseudocubic at a BaTiO3 content of x=0.33. The room-temperature dielectric permittivity increased with increasing BaTiO3 content regardless of phase structure, except for a small dielectric permittivity peak additionally observed at x=0.33. The (1−x)BiFeO3–xBaTiO3 solid solutions displayed a maximum in permittivity at temperatures (Tm) above 300°C in the compositional range of 0.2≤x≤0.5. The frequency dependence of high-temperature dielectric properties suggests that BiFeO3–BaTiO3 is a relaxor ferroelectric. Normal ferroelectric loops and large electric field-induced strains were observed for the BiFeO3–BaTiO3 ceramics. The BiFeO3–BaTiO3 shows a promising candidate for high temperature ferroelectric applications.

Dielectric, Ferroelectric, and Piezoelectric Properties of BiFeO3–BaTiO3 Ceramics

Perovskite solid solution ceramics of (1 − x)BiFeO3–xBaTiO3 (1 − x)BF–xBT, 0.2 ≤ x ≤ 0.45) with high electrical resistivity were prepared by solid‐state reaction method. Actual ferroelectric hysteresis loops and temperature dependence of dielectric constant of the ceramics were obtained. Ceramics of 0.7BF–0.3BT with small rhombohedral distortion show highest remnant polarization (Pr = 26.0 μC/cm2) and piezoelectric coefficient (d33 = 134 pC/N). Compositions with pseudo‐cubic symmetry (intermediate phases) show relaxor‐like dielectric anomaly. The values of Pr and d33 decrease with increasing BT content, from 24.8 μC/cm2 and 104 pC/N for 0.65BF–0.35BT to 8.2 μC/cm2 and 5 pC/N for 0.55BF–0.45BT.

Evidences of magneto-electric coupling in BFO–BT solid solutions

Abstract Multiferroic properties viz antiferromagnetism and ferroelectricity of BiFeO3 (BFO) has been reported to be enhanced by forming solid solution with BaTiO3 (BT) designated by BFO–BT. In the present investigations a few compositions in the solid solution (1−x)BiFeO3–xBaTiO3 (x = 0.10, 0.15 and 0.30) have been synthesized by solid state ceramic route. Structural, magnetic and electrical properties of single phase solid solution compositions of BFO–BT have been studied in detail to understand their multiferroic properties. Powder X-ray diffraction confirms the formation of solid solution. All the samples show ferromagnetic behavior at room temperature having low coercivity and high saturation magnetization. Substitution of BaTiO3 into BiFeO3 enhances dielectric and ferromagnetic responses and reduces electrical leakage. It suggests a coupling between ferroelectric and magnetic parameters near the antiferromagnetic–paramagnetic transition, which is responsible for the broad frequency dependent dielectric maxima. The impedance spectroscopy also confirms the origin of the structure.

Dielectric response and origin in antiferromagnetic/ferroelectric (1 − x)BiFeO3-(x)BaTiO3 ceramics

Dielectric permittivity (ε) and conductivity (σ) have been measured in (1 − x)BiFeO3-(x)BaTiO3 (BFO-xBT) multiferroic ceramics for x = 0.0, 0.05, and 0.10 as functions of temperature and frequency. A one-dimensional across-barrier model with intrinsic barriers B every lattice constant a and extrinsic barriers B + Δ every distance d is introduced to describe the dielectric response and conductivity. The across-barrier hopping is responsible for the high-temperature conductivity and dielectric relaxation in the lower temperature region. Good qualitative fits of dielectric permittivity and conductivity are obtained as functions of temperature and frequency. BaTiO3 substitution can enhance the intrinsic barrier and reduce the hopping conductivity.

Effect of sintering temperature on microstructure and piezoelectric properties of Pb-free BiFeO3–BaTiO3 ceramics in the composition range of large BiFeO3 concentrations

Lead-free (1-x)BiFeO3–xBaTiO3 [(1-x)BF-xBT] piezoelectric ceramics in the range of large BF concentrations were prepared by conventional oxide-mixed method at various sintering temperatures. The sintering temperatures have a significant effect on the microstructure of the ceramics, and the composition has a remarkable effect on optimal sintering temperature of the ceramics, which are closely related with piezoelectric properties. The grain size increased with increasing sintering temperature and the optimal sintering temperature increased with increasing BT content. The ceramics with x = 0.275 sintered at 990 °C exhibit enhanced electrical properties of d 33 = 136pC/N and k p = 0.312 due to the polarization rotation mechanisms at MPB and desired microstructure. These results show that the ceramic with x = 0.275 is a promising lead-free high-temperature piezoelectric material.

Structural, dielectric, magnetic, magnetodielectric and impedance spectroscopic studies of multiferroic BiFeO3–BaTiO3 ceramics

Abstract Polycrystalline (1−x)BiFeO3–xBaTiO3 (x = 0.00, 0.10, 0.20 and 0.30) ceramics have been prepared via mixed oxide route. The effect of BaTiO3 substitution on the dielectric, ferroelectric and magnetic properties of the BiFeO3 multiferroic perovskite was studied. From XRD analysis it revealed that BaTiO3 substitution does not affect the crystal structure of the (1−x)BiFeO3–xBaTiO3 system up to x = 0.30. Improved dielectric properties were observed in the prepared system. An anomaly in the dielectric constant (ɛ) was observed in the vicinity of the antiferromagnetic transition temperature. Experimental results suggest that in the (1−x)BiFeO3–xBaTiO3 system, the increase of BaTiO3 concentration leads to the effective suppression of the spiral spin structure of BiFeO3, resulting in the appearance of net magnetization. The dependence of dielectric constant and loss tangent on the magnetic field is a evidence of magnetoelectric coupling in (1−x)BiFeO3–xBaTiO3 system. The impedance analysis suggests the presence of a temperature dependent electrical relaxation process in the material, which is almost similar for all the concentrations in the present studies. The electrical conductivity has been observed to increase with rise in temperature showing a typical negative temperature coefficient of the resistance (NTCR) behaviors analogous to a semiconductor and suggests a non-Debye type of electrical relaxation.