BiFeO3 BaTiO3 Research Articles

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.

Significant enhancement in magnetization value of the K-doped 0.75 BiFeO3–0.25 BaTiO3 lead-free multiferroics

Effect of potassium doping on structure and magnetic properties of lead-free 0.75BiFeO3–0.25BaTiO3 multiferroics is investigated. The typical ferromagnetic hysteresis loop is observed with continuous increase in magnetization which is attributed to suppression of spin cycloid due to increase in distortion in rhombohedral structure. Remnant magnetization (Mr) of 5.55emu/g is achieved for x=0.10 sample, which is the highest among the Mr values reported in literature for doped BiFeO3–BaTiO3 (BFO-BT) systems. A significant enhancement in Mr (∼1100%) and a notable reduction in the coercive field (∼63%) suggest that K-doped 0.75BiFeO3–0.25BaTiO3 multiferroics could be a promising candidate for memory device applications.

Strong piezoelectricity and multiferroicity in BiFeO3–BaTiO3–NdCoO3 lead-free piezoelectric ceramics with high Curie temperature for current sensing application

Lead-free piezoelectric and multiferroic ceramics of BiFeO3–BaTiO3–NdCoO3 were synthesized by a conventional solid-state reaction method and the structural, piezoelectric, multiferroic and magnetoelectric properties of the materials were investigated. All the ceramics can be well sintered at a low sintering temperature of 980 °C for 2 h. The introduction of NdCoO3 into BiFeO3–BaTiO3 induces a dramatic enhancement in the piezoelectricity, multiferroicity and magnetoelectric effect of the materials. After the addition of 1.0–3.0 mol% NdCoO3, the ceramics possess a morphotropic phase boundary of rhombohedral and orthorhombic phases and exhibit high Curie temperature (~486–605 °C), strong piezoelectricity, good ferroelectricity and excellent temperature stability of piezoelectricity. The greatly enhanced magnetism with M r = 0.4229 emu/g and M s = 2.7186 emu/g is obtained in the ceramic with 8.0 mol% NdCoO3, almost six times larger than that of an undoped ceramic. The ceramic with 2.0 mol% NdCoO3 shows a strong magnetoelectric effect (α 33 = 750 mV cm−1 Oe−1). The practical application potential of the present materials has also been preliminarily demonstrated by mimicking current monitoring. Our results suggest that the present ceramics may have potential applications in advanced lead-free piezoelectric and/or multiferroic devices.

Impedance spectroscopy and conductivity analysis of multiferroic BFO–BT solid solutions

We report the investigations on the impedance and conductivity analysis of BiFeO3–BaTiO3 (BFO–BT) system prepared by solid state reaction route. The impedance studies reveal the presence of grain and grain boundary effects as confirmed from the single and double arc in the complex Cole–Cole plots. The impedance measurements confirm the temperature dependent electrical relaxation processes in the material for all compositions of BFO–BT attributing to the presence of immobile species at low temperature and defects/vacancies at higher temperatures. The BFO–BT systems exhibit non-Debye type of electric relaxation with concentration x=0.10, 0.15 and 0.30. The thermal variation of impedance parameters reflects a negative temperature coefficient of resistance behavior of the material analogous to semiconductor. The electrical conductivity studies obtained the activation energies related to grain contribution as 1.108, 0.795, 0.164 eV for (1−x)BFO–xBT (x=0.10, 0.15 and 0.30) and grain boundary as 0.708, 0.453 eV for (1−x)BFO–xBT (x=0.15 and 0.30) which is related to various factors including oxygen vacancies, mobility of defects, conduction via hopping and presence of same species responsible for conducting nature via grain and grain boundary.

Reduced dielectric loss and enhanced piezoelectric properties of Mn modified 0.71BiFeO3–0.29BaTiO3 ceramics sintered under oxygen atmosphere

0.71BiFeO3–0.29BaTiO3 piezoelectric ceramics with Mn modification (BF–BT–x %Mn) sintered in air and O2 atmospheres have been investigated to understand the effects of sintering atmosphere on structure, dielectric, ferroelectric and piezoelectric properties. All ceramics exhibited the pseudo-cubic phase, while the O2 sintered ceramics possessed larger grain sizes and more homogeneous distribution. Dielectric, ferroelectric and piezoelectric properties of BF–BT–xMn ceramics were improved obviously after O2 atmospheres sintering, especially for the compositions with Mn contents less than 1.2 mol%. The evidence of impedance spectroscopy indicated that the concentration of oxygen vacancies decreased significantly by the introduction of O2 atmosphere. The dielectric loss tanδ was decreased down to 1/2 and the resistivity ρ enhanced 11 times for BF–BT–0 %Mn ceramics by the introduction of O2 atmosphere. The strains of BF–BT–0.5 %Mn increased from 0.09 to 0.22 and the d33* increased from 119 to 284 pm/V after sintering in O2 atmosphere. The Curie temperature and piezoelectric constant of O2 sintered BF–BT–1.2 %Mn reached up to 500 °C and 353 pm/V, respectively. This work suggests that sintering in the O2 oxygen atmosphere is an effective way to improve the dielectric and piezoelectric properties of BiFeO3–BaTiO3 solid solutions.

Phase formation and dielectric properties of ceramics in the BiFeO3–BaTiO3–Bi(Mg0.5Ti0.5)O3 system

We have studied the effect of Bi(Mg0.5Ti0.5)O3 additions on the phase formation, structural parameters, microstructure, and dielectric properties of solid solutions in the region of a morphotropic phase boundary in the BiFeO3–BaTiO3 system. Single-phase samples with the perovskite structure have been obtained and the addition of Bi(Mg0.5Ti0.5)O3 has been shown to raise the Curie temperature of the ceramics and improve their dielectric properties.

Dielectric and impedance spectroscopy of Ni doped BiFeO3-BaTiO3 electronic system

A nickel modified BiFeO3–BaTiO3 electronic system has been fabricated by using a high-temperature solid-state reaction process. Preliminary X-ray structural analysis has confirmed the formation of a single-phase material in the orthorhombic crystal system. The dielectric and impedance characteristics of the prepared material have been studied in a wide range of frequency (1 kHz-1 MHz) at different temperatures (25–500 °C) for the better understanding of the frequency-temperature dependence of its capacitive and resistive behavior respectively. A significant effect of grains and grain boundaries of the resistive characteristics of the material is observed at high temperatures. The electrical conductivity of the material increases with increase in frequency in the low-temperature region. Preliminary study of a small amount of Ni doping in the above binary system (i.e., BiFeO3–BaTiO3) has provided many interesting results which may be useful for the fabrication of an electronic device.

Multiferroic and conduction characteristics of (Bi0.5Ba0.5) (Fe0.5Ti0.5) O3 solid solution

A solid solution of multiferroic BiFeO3 and ferroelectric BaTiO3 in equal molar ratio (i.e., (Bi0.5Ba0.5) (Fe0.5Ti0.5) O3 (BF–BT)) was synthesized by using solid state reaction route. By adding BaTiO3 in BiFeO3, the crystalline structure and ferroelectric properties of the system was improved. The significantly reduced leakage current results to get regular ferroelectric hysteresis loop of the parent compound. The dielectric relaxation observed at 365 °C may be related to the anti-ferromagnetism transition suggesting the coupling between the ferroelectric and magnetic orders essential for the multiferroic materials. Moreover, the remnant magnetization (2Mr) of 0.00014 emu/g and coercive field (2Hc) of 6.94 kOe were observed in the system. The ac conductivity study confirmed transport phenomena in the material are due to hopping of polarons.

Enhanced ferroelectric and ferromagnetic properties of Er-modified BiFeO3–BaTiO3 lead-free multiferroic ceramics

Lead-free multiferroic ceramics of 0.75Bi1−xErxFeO3–0.25BaTiO3 + 1 mol% MnO2 were synthesized by a conventional ceramic technique, and their structure, piezoelectric, ferroelectric and ferromagnetic properties were investigated. All the ceramics possess a perovskite structure. The crystal structure of the ceramics is transformed from rhombohedral to orthorhombic phase with increasing x. The ceramics with x = 0.125–0.15 exhibit good electric insulation (R = 2.75–2.83 × 1010 Ω cm) and strong ferroelectricity (Pr = 13.4–14.2 µC cm−2). The remanent magnetism Mr and saturated magnetization Ms of the ceramics are greatly improved by 380 and 722 % with increasing x from 0 to 0.15, respectively. The present materials exhibit strong ferroelectricity, considerable improved ferromagnetism and relatively good piezoelectricity, suggesting potential applications in advanced multiferroic devices.

Enhanced piezoelectric properties of Bi(Mg1/2Ti1/2)O3 modified BiFeO3–BaTiO3 ceramics near the morphotropic phase boundary

(0.7-x)BiFeO3−0.3BaTiO3–xBi(Mg1/2Ti1/2)O3 system was designed to obtain morphotropic phase boundary (MPB) between rhombohedral (R) phase and pseudocubic (PC) one to enhance the piezoelectric property. Their phase structures were investigated by the X-ray diffraction, temperature dependence of dielectric constant εr and Raman spectrum, which revealed that the phase transition exists from R–PC two-phase coexistence at 0.00 ≤ x ≤ 0.04 to PC-phase at 0.06 ≤ x ≤ 0.08 at room temperature. Due to coexisting R–PC two phases near MPB region and the improvement of polarization property, high d33 = 154 pC/N, kp = 28.5% and Pr = 16.2 μm/cm2 were achieved as x = 0.04. This research revealed the potential of BiFeO3–BaTiO3–Bi(Mg1/2Ti1/2)O3 system as promising lead-free piezoelectric ceramics with relatively high Curie temperature TC = 482 °C.

Correlation between temperature-dependent permittivity dispersion and depolarization behaviours in Zr4+-modified BiFeO3–BaTiO3 piezoelectric ceramics

The correlation between permittivity frequency dispersion and depoling process upon heating was investigated in Zr4+-modified 0.75BiFeO3–0.25BaTiO3 (BF–BZT) ceramics. The temperature-dependent permittivity ε r(T) and the piezoelectric coefficient d 33 for poled samples were measured under heating conditions to clarify the depolarization mechanism. The results indicate that the poling temperature plays a crucial role in the domains’ alignment process, as expected. The temperature-dependent permittivity frequency dispersion and depolarization behaviours may have same origin. The aligned domains’ break up into random state/nanodomains at depoling temperature (T d), which causes strong frequency dependence of the permittivity, simultaneously, induces the loss of piezoelectricity. It suggests that the temperature-dependent permittivity measurements method is a simple way to determine the depolarization temperature.

Manganese‐Doped BiFeO3–BaTiO3 High‐Temperature Piezoelectric Ceramics: Phase Structures and Defect Mechanism

The bulk BiFeO3–BaTiO3 system has been studied as a potential lead‐free high‐temperature piezoelectric material. It is found that the multivalency manganese‐doped 0.8BiFeO3–0.2BaTiO3 ceramics exhibit the coexistence of tetragonal and rhombohedral phases, whereas Mn doping improves the resistivity and exhibits hard characteristic. The optimal properties were obtained at 0.12 wt% Mn addition exhibiting Tc ˜ 637°C. The increase of Tc in Mn‐modified compositions can be ascribed to the appearance of internal electric bias field by acceptor doping. The combination of good electrical properties and high Tc makes these ceramics suitable for elevated temperature piezoelectric devices.

Improved ferroelectricity and ferromagnetism of Eu-modified BiFeO3–BaTiO3 lead-free multiferroic ceramics

Multiferroic ceramics of 0.75Bi1−xEuxFeO3–0.25BaTiO3 + 1 mol% MnO2 were synthesized by a conventional solid state reaction method and the effects of Eu doping on microstructure, ferroelectric, ferromagnetic and piezoelectric properties of the ceramics were investigated. All the ceramics exhibit a pure perovskite structure without any secondary phases. After the addition of Eu3+ ions, the crystal structure of the ceramics is transformed from rhombohedral to tetragonal phase at x = 0.025. The ferroelectricity and ferromagnetism of the ceramics are improved. For the ceramic with x = 0.025, the optimum remanent polarization of 18.3 μC/cm2 and good piezoelectricity of 82 pC/N are obtained. The saturated magnetization Ms and remanent magnetism Mr of the ceramics are improved by 165 and 141 % with x increasing from 0 to 0.175, respectively.

Structure, piezoelectric and multiferroic properties of Bi(Ni0.5Mn0.5)O3-modified BiFeO3–BaTiO3 ceramics

(0.725 − x)BiFeO3–0.275BaTiO3−xBi(Ni0.5Mn0.5)O3 + 1 mol% MnO2 lead-free multiferroic ceramics have been fabricated by a conventional ceramic technique and the structure, multiferroic and piezoelectric properties of the ceramics have been investigated. All the ceramics sintered at 950 °C for 2 h possess a pure perovskite structure. XRD patterns show that a coexistence of rhombohedral and pseudocubic phases are formed at x = 0.05−0.07. The average grain size decreases and the range of the grain size distribution greatly becomes narrow after the addition of Bi(Ni0.5Mn0.5)O3. The dielectric peak becomes gradually diffusive with increasing x. A small amount of Bi(Ni0.5Mn0.5)O3 doping (x ≤ 0.02) maintain the ferroelectric (P r = 16.7−19.3 μC/cm2), piezoelectric properties (d 33 = 124−145 pC/N) and ME coefficient performance (α 33 = 444.45–553.65 mV cm−1 Oe−1).

Temperature stability of sodium-doped BiFeO3–BaTiO3 piezoelectric ceramics

An enhancement in piezoelectric properties of lead-free ceramic materials by compositional engineering is often accompanied by a sacrifice in the temperature-stability of properties. Here we demonstrate that high piezoelectric properties and excellent high-temperature stability are obtained simultaneously in 0.72BiFeO3–0.28Ba1−x Na x TiO3 (BF–BTNx, x = 0–0.035) ceramics. Our results show that the high temperature-stable piezoelectric properties from 26 to 470 °C, combined with room temperature high piezoelectric constant d 33 = 165pC/N and electromechanical coupling factor k p = 0.35 are achieved for x = 0.015 BF–BTNx ceramics. The results suggest Na-doped BF–BT system ceramic is a potential candidate for high temperature harsh environments actuators and sensors applications.

Enhancement in multiferroic and piezoelectric properties of BiFeO3–BaTiO3–Bi0.5Na0.5TiO3 lead-free ceramics with MnO2 addition by optimizing sintering temperature and dwell time

Multiferroic ceramics of 0.705BiFeO3−0.275BaTiO3−0.02Bi0.5Na0.5TiO3+1mol% MnO2 were prepared by a conventional ceramic technique and the effects of sintering temperature (Ts) and dwell time (ts) on the phase structure, piezoelectric and multiferroic properties of the ceramics were investigated. As Ts increases from 880°C to 1040°C, the ceramics are transformed from rhombohedral to tetragonal structure and a MPB is formed at Ts=1000°C and ts=2h. The increase in Ts greatly improves the densification, electric insulation, ferroelectricity and piezoelectricity of the ceramics, while relatively weak dependences on ts are observed. As Ts increases from 880°C to 1000°C, the magnetism of the ceramics is significantly enhanced and the values of Mr are increased by ∼400%. The optimum sintering conditions of the ceramic is 1000°C/2h, in which high density, good electric insulation and enhanced ferroelectricity (Pr=18.4μC/cm2), piezoelectricity (d33=140 pC/N, kp=31.4%) and ferromagnetism (Mr=0.099emu/g) are simultaneously obtained.

Unusual relaxor–normal ferroelectric crossover in Cu-doped BiFeO3–BaTiO3 ceramics

The structural origin of relaxor behavior in perovskite ferroelectrics has remained elusive for decades. In this study, we observed a unique thermally driven normal to ferroelectric phase transition and Cu-doping induced relaxor to normal ferroelectric transition in 0.70BiFeO3–0.30BaTiO3 + x wt%CuO (x = 0.1, 0.2, 0.4, 0.6 and 0.8) ceramics. The XRD results show that Cu-doping induces a structural transition from pseudo-cubic phase to rhombohedral phase, associated with the domain switch from nanodomains to macrodomains, might be the origin of the relaxor–normal ferroelectric phase transition.

Investigation of multiferroic properties of doped BiFeO3–BaTiO3 composite ceramics

The 0.85Bi0.95Dy0.05Fe0.98Cu0.02O3–0.15BaTiO3 and 0.85Bi0.95Dy0.05FeO3–0.15BaTiO3 multiferroic composites were prepared by a solid state reaction method. The XRD patterns of the composites confirmed the presence of BiFeO3 and BaTiO3. The ME coupling of the composites shows conspicuous enhancement compared to that of undoped BiFeO3. Among the composites, Bi0.95Dy0.05Fe0.98Cu0.02O3–BaTiO3 composite shows multiferroic properties better than that of Bi0.95Dy0.05FeO3–BaTiO3 composite. The results are attractive for the applications in memory devices.

Local structure investigation and properties of Mn-doped BiFeO3–BaTiO3 ceramics

Bi0.75Ba0.25(Fe,Ti)1−xMnxO3 with x=0, 3 and 5mol% Mn ceramics were prepared by a solid state reaction method. The relationships between site substitution of Mn in Mn-doped 0.75BF–0.25BT ceramics, phase formation and their properties were investigated. The addition of Mn was shown to improve densification, electrical and magnetic properties, especially ME coefficient. The Synchrotron X-Ray Absorption Near Edge Structure (XANES) spectra showed that Mn substituted for Fe/Ti atom and did not affect the oxidation state of Ti and Bi. However, a significant change of oxidation state was observed in Fe, Mn and Ba atoms.

Phase transition, dielectric, ferroelectric and ferromagnetic properties of La-doped BiFeO3–BaTiO3 multiferroic ceramics

0.70Bi1−xLaxFeO3–0.30BaTiO3 + 1 mol% MnO2 multiferroic ceramics were prepared by using the solid state reaction and their phase structure, dielectric, ferroelectric and ferromagnetic properties were studied. All the ceramics possess perovskite structure and exhibit good insulation and densification. A morphotropic phase boundary of rhombohedral and tetragonal phases is formed at x = 0.02. As the concentration of La3+ is increased, the ferroelectric–paraelectric phase transition of the ceramics at Curie temperature becomes gradually more diffusive. A small amount of the substitution of La3+ for Bi3+ improves effectively the ferroelectricity of the ceramics and the optimum remanent polarization of 27.2 μm/cm2 reaches at x = 0.04. After the addition of La3+, the ferromagnetism of the ceramics is greatly enhanced and the remanent magnetization M r monotonously increases from 0.0321 to 0.147 emu/g with x increasing from 0 to 0.10. Our results show that the ceramics possess simultaneously improved ferroelectric and ferromagnetic properties and may a promising candidate for room-temperature multiferroic materials.