Rapid Liquid Phase Sintering Research Articles

Room temperature multiferroic and magnetodielectric properties in Sm and Sc co-doped BiFeO3 ceramics

In this work, Sm and Sc co-doped Bi1−xSmxFe1−yScyO3 (x = 0.00–0.20; y = 0.03) ceramics are fabricated by a rapid liquid phase sintering method, in order to develop single-phase multiferroics with large magnetization and polarization. X-ray diffraction and Raman spectroscopic studies reveal that the ceramics are single-phase with a structural transition from rhombohedral to orthorhombic structures near x = 0.15. Electric and magnetic measurement results indicate that the transition significantly enhances the multiferroic properties, which stems from the Sm/Sc doping induced collapse of space-modulated spin structure and internal structural distortion. At an optimized composition of Bi0.85Sm0.15Fe0.97Sc0.03O3 (x = 0.15), a remanent polarization of 16.5 μC cm−2, a magnetization 0.2020 emu g−1, and a magnetodielectric effect of 0.46% can be obtained. These results clearly demonstrate a potential application for Sm/Sc doped BiFeO3 ceramics in the field of multiferroic devices.

Enhanced ferroelectric polarization and magnetization in BiFe1−xScxO3 ceramics

Multiferroic BiFe1−xScxO3 ceramics with x=0.00–0.10 were synthesized by rapid liquid phase sintering. The influences of Sc doping on the crystalline structures, dielectric, ferroelectric, and magnetic behaviors of BiFeO3 ceramics were explored. The X-ray diffraction and the Raman spectrometric analysis revealed that all the samples are nearly single phase of rhombohedral structure with the incorporation of Sc ions into BiFeO3. With increase doping concentration of x, the dielectric constant, dielectric loss, and remnant polarization for the doped BiFeO3 increase first and then drop down with further rise of x. A saturated ferroelectric polarization can be achieved at a small amount of Sc doping concentration (x<0.03), with a optimized remnant polarization of 17.6μC/cm2 at x=0.03. Meanwhile, the magnetization is also slightly increased by introducing Sc dopant, with a maximum remnant magnetization of 0.0105emu/g at x=0.01. These results indicate that BiFeO3 ceramics with small amounts of Sc-doping may be promising for applications in magnetoelectric devices.

Role of Mn Substitution in the Multiferroic Properties of BiFeO3 Ceramics

BiFe1-xMnxO3 (x=0.00, 0.10, 0.20 and 0.30) polycrystalline samples were prepared using solid-state reaction method followed by rapid liquid phase sintering in this paper. Subsequently, the effects of Mn substitution on structural, ferroelectric and magnetic properties of the BiFe1-xMnxO3 ceramic have been studied by changing Mn concentrations. And these characteristics are also compared with those of unsubstituted BiFeO3. The X-ray diffraction (XRD) analysis reveals that the Mn 4+ indeed entered into the crystal lattice of BiFeO3, and the crystal structure of BiFe 1-xMnxO3 system seems not altered due to Mn substitution. It is also observed that an increase in Mn doping concentration in BiFeO 3 can significantly improve the ferroelectric and magnetic properties while the average grain size of particles decreases by comparing with the original BiFeO 3.

Structural, dielectric, vibrational and magnetic properties of Sm doped BiFeO3 multiferroic ceramics prepared by a rapid liquid phase sintering method

Rare earth Sm substituted Bi1−xSmxFeO3 with x=0, 0.025, 0.05, 0.075 and 0.10 polycrystalline ceramics were synthesized by a rapid liquid phase sintering method. The effect of varying composition of Sm substitution on the structural, dielectric, vibrational, optical and magnetic properties of doped BiFeO3 (BFO) ceramics have been investigated. X-ray diffraction patterns of the synthesized rare earth substituted multiferroic ceramics showed the pure phase formation with distorted rhombohedral structure with space group R3c. Good agreement between the observed and calculated diffraction patterns of Sm doped BFO ceramics in Rietveld refinement analysis of the X-ray diffraction patterns and Raman spectroscopy also confirmed the distorted rhombohedral perovskite structure with R3c symmetry. Dielectric measurements showed improved dielectric properties and magnetoelectric coupling around Néel temperature in all the doped samples. FTIR analysis establishes O–Fe–O and Fe–O stretching vibrations in BiFeO3 and Sm-doped BiFeO3. Photoluminescence (PL) spectra showed visible range emissions in modified BiFeO3 ceramics. The magnetic hysteresis measurements at room temperature and 5K showed the increase in the magnetization with the increase in doping concentration of Sm which is due to the structural distortion and partial destruction of spin cycloid caused by Sm doping in BFO ceramics.

Enhanced ferroelectric properties in Bi0.86Sm0.14FeO3–based ceramics

1 at. % Ti-doping on the B-site combined with a modified rapid liquid-phase sintering technique was conducted to improve the ferroelectric properties in Bi0.86Sm0.14FeO3 multiferroic ceramics. A tenfold increase of the remnant polarization was achieved in the present ceramics compared with the samples without Ti-doing and prepared by conventional solid state sintering, but the dielectric results and conductivities refuted the generally considered mechanism of suppression of leakage current or dielectric loss. Further investigation preferred an explanation of softening effects, which could be induced by donor doping and random orientation of defect dipoles during quenching process of the rapid liquid-phase sintering, and the ferroelectric data of the second heat-treated and polarized samples well supported such explanation.

Effects of trivalent gadolinium and cobalt co-substitution on the crystal structure, electronic transport, and ferromagnetic properties of bismuth ferrite

Multiferroic trivalent gadolinium and cobalt co-substituted bismuth ferrite Bi0.95Gd0.05Fe1−xCoxO3(x=0, 0.05, 0.1, 0.15, 0.2) ceramics were prepared by rapid liquid phase sintering method. The results showed that all the peaks of X-ray Diffraction (XRD) for Bi0.95Gd0.05Fe1−xCoxO3 samples can be indexed according to the crystal structure of pure BiFeO3. XRD analysis revealed a phase transition in Gd3+ and Co3+ co-doped BiFeO3 when x was larger than 0.1. The Scan Electron Microscope (SEM) images indicated that Gd3+ and Co3+ doping significantly decreased the grain sizes of BiFeO3 ceramic. Gd3+ and Co3+ co-doping BiFeO3 enhanced the electrical properties with lower leakage current. The magnetic hysteresis loops and the magnetization were greatly improved in co-substituted specimens at room temperature. The Mr of Bi0.95Gd0.05Fe1−xCoxO3 (x=0, 0.05, 0.1, 0.15, 0.2) was 34, 60, 105, 103 and 180 times of that of BiFeO3 at 30kOe, respectively. All the samples exhibited ferromagnetic behavior at 750K and paramagnetic behavior at 900K, indicating a high temperature magnetic phase transition of BiFeO3 at 870K, which shifted to 780K by Gd3+ and Co3+ doping. This can be attributed to the Fe3+–O2−–Fe3+ super-exchange strength and the relative stability of the magnetic structure.

Effect of Sr substitution on structural, dielectric, magnetic and magnetoelectric properties of rapid liquid sintered BiFe0.8Ti0.2O3 ceramics

Structural, dielectric, magnetic and magnetoelectric properties of polycrystalline Sr doped BiFe0.8Ti0.2O3 ceramics [Bi1−xSrx(Fe0.8Ti0.2)O3; x = 0.05, 0.10 and 0.15)] were studied. All the samples were prepared by rapid liquid phase sintering method. Rietveld refinement of X-ray diffraction patterns of all samples confirmed that the samples crystallize in a rhombohedral structure and showed change in Fe–O–Fe bond angle and Fe–O bond length which in turn enhanced magnetization from 0.33 to 0.73 emu/g with the increase in Sr concentration from x = 0.05 to 0.15. The dielectric constant and dielectric loss were observed to increase with the increase in temperature from 30 to 500 °C. An anomalous peak has been observed in dielectric constant versus temperature plot around 300 °C for all the samples, which is close to the magnetic transition temperature of BiFeO3. The composition-dependent magnetic properties with the expected Fe2+/Fe3+ ratio fluctuations were correlated by X-ray photoelectron spectroscopy. Magnetic and electric hysteresis loops showed a systematic increase in magnetization and polarization as a result of Sr doping in BiFe0.8Ti0.2O3 ceramics. The value of magnetocapacitance at 10 kHz was observed as 0.95, 1.23 and 1.73 for x = 0.05, 0.10, 0.15 respectively in Bi1−xSrxFe0.80Ti0.20O3 ceramics.

Effect of Eu, Ti co-doping on the structural and multiferroic properties of BiFeO3 ceramics

Multiferroic ceramics Bi0.95Eu0.05Fe1−xTixO3 (x=0, 0.05, 0.10 and 0.15) were prepared by using the conventional solid-state reaction method followed by rapid liquid phase sintering. The structural, dielectric, ferroelectric and magnetic properties were investigated. The XRD and Raman results show that Eu–Ti co-doping induces a structure phase transition. The SEM investigation indicates that the Eu–Ti co-doping can hinder the grain growth. The dielectric and ferroelectric measurements reveal that enhancement in dielectric properties, frequency independence, and ferroelectric properties are observed in Eu–Ti co-doped samples due to the reduction of oxygen vacancies by co-doping. Room temperature magnetic measurements show that ferromagnetism exists in co-doped ceramics, and the remnant magnetization increases significantly with increasing Ti substitution concentration. The possible reasons may be the co-doping-induced collapse of cycloidal spin structure and internal structural distortion. These studies suggest that Eu–Ti co-doped BFO bulk is a promising candidate for magnetoelectric coupling studies.

Effect of Sintering Temperature on the Microstructure, Electrical, and Magnetic Properties of Bi 0 . 8 5 Eu 0 . 1 5 FeO 3 Ceramics

Polycrystalline Bi 0.85Eu 0.15FeO 3 ceramics were synthesized by solid-state reaction method with rapid liquid phase sintering process at various sintering temperatures. The dependence of structural, microstructural, electrical, and magnetic properties on sintering temperature was systematically investigated. X-ray diffraction measurements reveal that single perovskite phase is developed in Bi 0.85Eu 0.15FeO 3 ceramics sintered at 850 and 870∘ C, while secondary phases can be detected in the samples sintered at 890∘ C due to the volatilization of Bi 3+ ions, and the crystallinity increases with increasing sintering temperature from 850 to 890 °C. The scanning electron microscopy investigation has suggested that the grain size increases with increasing sintering temperature from 855 to 890∘ C; while the pore size decreases with increasing sintering temperature from 850 to 870∘ C and then increases with a further increase of sintering temperature. The electrical and magnetic measurements show that the leakage current, dielectric constant, dielectric loss, and magnetic properties are strongly dependent on the sintering temperature. The Bi 0.85Eu 0.15FeO 3 ceramics sintered at 870∘ C have the lower leakage current, higher dielectric constant, and lower dielectric loss. The room temperature magnetization increases with increasing sintering temperature from 850 to 890 °C. The possible reason for all the above observations was discussed.

Structural, dielectric and magnetic properties of La and Sc codoped BiFeO3

The La and Sc codoped ceramic Bi0·85La0·15Fe0·9Sc0·1O3 (BLFS) was prepared by a rapid liquid phase sintering method. For comparison, Bi0·85La0·15FeO3 (BLF) and BiFe0·9Sc0·1O3 (BFS) were also prepared using the same method. X-ray diffraction (XRD) patterns and Rietveld refinements indicate that samples crystallise in the rhombohedral structure with R3c symmetry, except for a small amount of secondary phase. The dielectric properties of the samples were affected by the codoping of La and Sc as well as the ferromagnetic property. The remarkable improved ferromagnetism of BLFS could be ascribed to the doping induced structural distortion and the destruction of the antimagnetic ordering.

Comparative study of room temperature and low temperature magnetization and magnetoelectric coupling behavior of Ti and Pr doped BiFeO3

Four different compositions of Ti and Pr doped BiFeO3 samples were synthesized by conventional rapid liquid phase sintering method and their magnetic and magnetoelectric properties were studied. XRD pattern confirms the single phase formation of BiFeO3 for all samples without any impurity. Room temperature magnetic (M–H) curve shows slight increment in the value of magnetization from 0.070 to 0.078emu/gm for pristine BiFeO3 to Pr and Ti co-doped (Bi0.9Pr0.1Fe0.9Ti0.1O3), respectively. The M–H curve at 80K also shows that the value of magnetization increases from 0.08 to 0.10emu/g for pure BiFeO3 to Pr and Ti co-doped (Bi0.9Pr0.1Fe0.9Ti0.1O3). Ferroelectric behavior observed through P–E loop shows enhancement in the value of maximum polarization Pmax from 0.185 to 0.859μC/cm2 for pure BiFeO3 to Pr doped (Bi0.9Pr0.1FeO3), respectively. Room temperature magnetoelectric effect was studied through dynamic method and second order quadratic magneto-electric coefficient (β) was calculated for all the samples. The value of β is found to be maximum 34.72×10−5mV/cmOe2 for Pr, Ti co-doped BiFeO3 (Bi0.9Pr0.1Fe0.9Ti0.1O3) and minimum 12.25×10−5mV/cmOe2 for pristine BiFeO3 (BiFe0.9Ti0.1O3).

Effect of Ho3+doping on the electric, dielectric, ferromagnetic properties and TC of BiFeO3 ceramics

Multiferroic Bi1−xHoxFeO3 (x=0, 0.05, 0.1, 0.15, 0.2) ceramics have been prepared by rapid liquid phase sintering method. The effect of Ho doping on the structure, electrical, dielectric, ferromagnetism properties and TC of BiFeO3 ceramics is studied. The result shows that all the peaks for Bi1−xHoxFeO3 samples can be indexed according to the crystal structure of pure BiFeO3 by XRD. When x=0.15 and 0.2, the samples consist of two phases including rhombohedral and orthorhombic. Ho doping BiFeO3 enhanced the electrical properties with lower leakage current density. This dielectric behavior of Bi1−xHoxFeO3 ceramics varies with content x and frequency, which might be understood in terms of oxygen vacancy, the displacement of Fe3+ ions and lattice phase transition. The magnetic moment of Bi1−xHoxFeO3 ceramics varies with temperature from 300 to 1000K at 5kOe. It shows that the TN of BiFeO3 changes slightly from 638K to 632K with Ho3+ doping. The magnetic Curie temperature of Bi1−xHoxFeO3 will reduce from 970K to 890K with increasing Ho3+ content, depending mainly on the Fe–O–Fe super-exchange and magnetic structure of relative stability. By measuring the magnetic hysteresis loops, all the samples exhibit weak ferromagnetic behavior under 890K and paramagnetism above 890K. It evidences that the ferromagnetic phase transition of Bi1−xHoxFeO3 samples occurs at 890K.

High temperature dielectric and magnetic response of Ti and Pr doped BiFeO3 ceramics

Abstract In the present study, four different compositions of Ti and Pr doped BiFeO3 samples were synthesized by conventional rapid liquid phase sintering and their structural, dielectric, ferroelectric and magnetic properties were investigated. High temperature dielectric study shows different anomalous response for all compositions. A major peak in dielectric constant versus temperature curve is observed at 640 K for pristine BiFeO3 which shifts to 545 K for Ti doped (BiFe0.9Ti0.1O3) sample. Moreover, multiple peaks are observed for Pr doped (Bi0.9Pr0.1FeO3) sample in temperature range of 400–800 K. The room temperature P–E loop study shows that the value of maximum polarization increases from 0.185 to 0.859 µC/cm2 for Pr doped (Bi0.9Pr0.1FeO3) sample and also increases the ability of BiFeO3 to withstand higher electric field. Room temperature magnetic (M–H) curve shows a slight increment in the value of magnetization from 0.071 to 0.078 emu/gm for pristine BiFeO3 to Pr and Ti co-doped Bi0.9Pr0.1Fe0.9Ti0.1O3, respectively.

Structural and Electrical Properties of Bismuth Ferrite Ceramics Sintered in Different Atmospheres

Bismuth ferrite (BiFeO3) ceramics were synthesized by the solid-state reaction method followed by rapid liquid phase sintering. The effect of sintering atmosphere (N2, air and O2) on the structure and electrical properties of BiFeO3 multiferroic ceramics were investigated. XRD analysis revealed that N2 sintering was effective in reducing impurity phases and improving the crystallization behavior. XPS analysis showed that fewer Fe2+ ions but more oxygen vacancies were involved in the N2 sintered ceramics. The SEM investigations suggested that the grain size of the BiFeO3 ceramics sintered in nitrogen are larger than those sintered in air and O2. Electrical measurements revealed that the ceramics sintered in N2 showed lower leakage current, superior dielectric and ferroelectric properties.

Correlation of microstructural and physical properties in bulk BiFeO3 prepared by rapid liquid-phase sintering

BiFeO3 sample prepared by rapid liquid phase sintering (RLPS) technique is found to posses better dielectric properties than the subsequently annealed sample. These samples also show ferromagnetism at room temperature. Detailed X-ray diffraction and Rietveld refinement of the data show that oxygen–iron–oxygen (O–Fe–O) bond angle is considerably more distorted in samples prepared by rapid liquid-phase sintering technique than in the annealed sample. In addition, synchrotron X-ray diffraction as well as high resolution transmission electron microscopy studies show higher concentration of impurity phases in the annealed samples, which is the likely reason for inferior dielectric properties. Further transmission electron microscopy results indicate that high crystalline order is not necessary for better dielectric properties. However weak ferromagnetism is observed in all these samples and appears to be the intrinsic property of samples prepared by rapid liquid phase sintering technique.

Effects of Dy and Co co-substitution on the magnetic properties and TC of BiFeO3 ceramics

Multiferroic Bi0.95Dy0.05Fe1-xCoxO3 (x=0, 0.05, 0.1, 0.15) ceramics were prepared by rapid liquid phase sintering method. We studied the effect of (Dy+Co) doping on the structure, electrical and ferromagnetism properties of BiFeO3 ceramics. The structure and morphology of BiFeO3 ceramics were characterized by X-ray diffraction (XRD) and scanning electron microscopey (SEM). The results showed that all the peaks for Bi0.95Dy0.05Fe1-xCoxO3 samples can be indexed based on the crystal structure of pure BiFeO3. And XRD analysis revealed a phase transition in (Dy+Co) co-doped BiFeO3 when x was larger than 0.1 and grain sizes changed from 1 to 5 μm. Magnetic hysteresis loops were clearly observed in co-substituted specimens and magnetization was greatly improved. Magnetic measurements showed that all samples possess strong ferromagnetism at room temperature expect BiFeO3 and Bi0.95Dy0.05FeO3, which are weakly ferromagnetic. The M'rs, of Bi0.95Dy0.05Fe1-xCoxO3 with x=0.05, 0.01 and 0.15 are 0.43, 0.489, 0.973 emu/g and the M'rs of them are 0.77, 1.65, 3.08 emu/g, respectively. The magnetic moment of BiFeO3 and B0.95Dy0.05Fe1-xCoxO3 ceramics varies with temperature from 300 to 900 K at an applied field of 5 kOe. It shows that the TN of BiFeO3 from 644 to 648 K with different content of Dy3+ can be changed by crystal structures and exchanges between Dy3+-Fe3+. The phase transition temperature of Bi0.95Dy0.05Fe1-xCoxO3 shifted to lower temperatures from 870 K to 780 K demonstrate that Co3+ doping causes a drop of TC as compared with BiFeO3. The change of TC of Bi0.95Dy0.05Fe1-xCoxO3 depends mainly on the Fe-O-Fe super-exchange strength and the relative stability of magnetic structure.

Structural and electric properties of polycrystalline Bi1−xErxFeO3 ceramics

Polycrystalline Bi1−xErxFeO3 ceramics were synthesized by the solid state reaction method followed by rapid liquid phase sintering. The effects of Er substitution on the structure, morphology and electrical properties of the BiFeO3 multiferroic ceramics were investigated. X-ray diffraction and Raman studies reveal that the structure of BiFeO3 is changed from rhombohedral to orthorhombic in the Er concentration range of 0.10–0.15, and the impurity phases decrease both due to Er substitution. The X-ray photoelectron spectroscopy shows that Fe2+ could be suppressed by Er substitution. The SEM investigations suggest that the Er substitution could significantly reduce the grain sizes and increase the density of the samples. The leakage current is found to be decreased with increasing Er concentration. The dielectric and ferroelectric measurements show that dielectric constant, dielectric loss and ferroelectric properties are strongly dependent on the Er concentration. Er substitution can significantly improve the dielectric constant and remnant polarization, and decrease the dielectric loss by reducing the leakage current.

Enhanced Sintering Behavior and Electrical Properties of Single Phase BiFeO3Prepared by Attrition Milling and Conventional Sintering

Dense and single phase BiFeO₃ (BFO) ceramics were prepared using attrition milled calcined (coarse) powders of an average particle size of 3 μm by conventional sintering process. A relative density of 96% with average grain size 7.3 μm was obtained when the powder compacts were sintered at 850℃ even for a shorter duration of 10 min. In contrast, densification barely occurred at 800℃ for up to 12 h rather the microstruce showed the growth of abnormal grains. The grain growth behavior at different temperatures is discussed in terms of nonlinear growth rates with respect to the driving force. The sample sintered at 850℃ for 12 h showed enhanced electrical properties with leakage current density of 4 × 10 ?7 A/㎠ at 1 kV/cm, remnant polarization 2Pr of 8 μC/㎠ at 20 kV/cm, and minimal dissipation factor (tan δ) of ~0.025 at 106 Hz. These values are comparable to the previously reported values obtained using unconventional sintering techniques such as spark plasma sintering and rapid liquid phase sintering.

Anomalous dielectric response with suppression in Neel temperature of Bi0.9Y0.1Fe1−xMnxO3 (0 ⩽ x ⩽ 0.07) ceramics

In this study, we have prepared Bi0.9Y0.1Fe1−xMnxO3 (0⩽x⩽0.07) samples by rapid liquid phase sintering method. XRD confirms the pure phase formation without any impurity for all samples. An anomaly near the Neel temperature in dielectric measurement has been observed in the sample with x=0, which suppressed towards lower temperature as Mn concentration increases from x=0 to 0.07. This indicates the suppression in Neel temperature, which is further confirmed by magnetization versus temperature results. Magnetization versus field (M–H) curves recorded at room temperature reveal that the value of magnetization increases from 0.046 to 0.62emu/g by increasing the Mn concentration from x=0 to 0.07 and samples starts to show the saturated ferromagnetic behavior. Polarization versus electric field (P–E) studies demonstrate that the value of polarization decreases from 0.73 to 0.37μC/cm2 as Mn concentration increases from x=0 to 0.07.

Microstructure and properties of Sm-substituted BiFeO3 ceramics

Bi1−xSmxFeO3 (x=0.00−0.15) ceramics were synthesized by sol-gel technique with rapid liquid phase sintering process to study the effects of samarium (Sm) substitution on their microstructure and properties. X-ray diffraction (XRD) and Raman studies showed that the structure of BiFeO3 was changed from rhombohedral to orthorhombic at the samarium substitution concentration about x=0.10. The SEM investigation suggested that the Sm substitution hindered the grain growth. Magnetic measurements showed that all the samples studied had a weak ferromagnetism, and the ferromagnetic property of BiFeO3 was improved by Sm substitution due to the suppressed or broken cycloid spin structure caused by the changes in the crystalline structure and size effect. The leakage current was found to be reduced with increasing Sm concentration. The dielectric and ferroelectric measurements showed that dielectric constant, dielectric loss and ferroelectric properties were strongly dependent on the Sm content, Sm substitution could significantly improve the dielectric constant, remnant polarization and decrease the dielectric loss due to the significant decrease of the electric leakage of the samples.