Rapid Liquid Phase Sintering Research Articles

Influence of substitution of different transition metal elements (Mn, Cr, Co) on the properties of Bi0.88Sm0.12FeO3-based ceramics

In this paper, the transition metal elements modified Bi0.88Sm0.12Fe0.97M0.03O3 (M = Mn, Cr, Co, Mn0.5Cr0.5, Mn0.5Co0.5, Cr0.5Co0.5) ceramics were synthesized by rapid liquid phase sintering. The effect of different transition metal elements on the structure and characteristics of BiFeO3-based ceramic were studied. Structural refinement revealed the coexistence of rhombohedral R3c phase, orthorhombic Pna21 phase and a small amount of Pbnm phase of all samples, and the element type had little effect on the phase composition. According to the XPS analysis, Co and Mn elements can be regarded as hard additives, and Cr element can be regarded as soft additives. Due to the different electronic structures of transition metal elements, different element substitutions have different effects on the electrical and magnetic properties of BiFeO3. The results show that the addition of Cr improved the electrical properties of BSF-based ceramics, and the best ferroelectric properties obtained in the BSF-Cr sample, where Pr = 18.30 μC/cm2. The magnetic properties of Co substituted samples were significantly improved, and the maximum remanent magnetization obtained in the BSF-Co sample, where Mr = 110.8 emu/mol, which may be attributed to the collinear magnetic structure induced by Co-substitution. Finally, the simultaneously enhanced ferroelectric and magnetic properties were obtained in the Cr and Co co-substituted composition, where Pr = 10.82 μC/cm2, Mr = 73.3 emu/mol. Multiple ion substitution is a very effective method to optimize the properties of BiFeO3.

Influence of Compacting Pressure on the Dielectric Properties of La-modified Bismuth Ferrite Multiferroics Prepared by Rapid Liquid-phase Sintering Method

Structure, perovskite phase formation, chemical and phase composition, microstructure, morphology and dielectric properties of the single-phase lanthanum-modified bismuth ferrite multiferroic ceramics obtained by the rapid liquid-phase sintering method under different compacting pressures have been investigated using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetry/differential thermal analysis and dielectric spectroscopy methods. The temperature and time for an express preparation of the single-phase Bi0.9La0.1FeO3 ceramics with formation of a perovskite structure have been found out. With an increase in the compacting pressure P from 100 to 1100 MPa, the dielectric constant ε′ changes by ∼25% and ∼80% in the low-frequency and ultra-high frequency ranges, respectively. In the low-frequency range, all samples depending on the pressure P demonstrate excellent dielectric behavior with a stable dielectric constant and quite low dielectric loss that make these samples perspective for their possible practical application in microelectronic and spintronic.

Sillenite phase stabilized ferromagnetic ordering in multiphasic magnetoelectric bismuth ferrite

This paper reports the synthesis of Sillenite phase stabilized multiphasic magnetoelectric Bismuth Ferrite. Five set of samples were prepared by employing different synthesis techniques namely soft chemical route and rapid liquid phase sintering. These samples were prepared by varying the stoichiometry of the precursors to identify the optimum conditions for the formation of the multiferroic phase of Bismuth Ferrite and characterized using X-ray diffraction, Scanning Electron Microscopy, SQUID VSM and Ferroelectric loop tracer. It is found that tartaric acid plays an important role in the stabilization of the Sillenite phase. The Sillenite phase imparts magnetic property to the already ferroelectric BiFeO3 and this material exhibits magnetoelectric characteristics. The details are discussed in this paper.

Control of dielectric properties in bismuth ferrite multiferroic by compacting pressure

Single-phase lanthanum-modified bismuth ferrite multiferroic ceramics have been synthesized by the rapid liquid-phase sintering (RLS) method. Phase composition, crystal structure, microstructure and dielectric properties of the Bi0·9La0·1FeO3 multiferroic have been studied using TG/DTA, XRD, SEM, capacitive and composite dielectric resonator methods. It has been established that the optimal conditions for formation of a perovskite Bi0·9La0·1FeO3 structure are 850 °C after 5 min in air. It has been found that the compacting pressure of the initial mixture of precursors from 90 to 1090 MPa can change the dielectric constant by ~25% in the low-frequency range and by ~80% in the microwave range up to complete elimination of the elastic polarization mechanism. The use of the RLS method under various compacting pressures opens additional possibilities for creating multifunctional multiferroics with controlled magnetoelectric coupling.

Effect of octahedron tilt on the structure and magnetic properties of bismuth ferrite

Multiferroic BiFeO3-based ceramics were synthesized using the rapid liquid-phase sintering method. The rare-earth ion (Sm3+, Gd3+, Y3+) doping causes structural distortion without changing the intrinsic rhombohedral perovskite structure. Raman analysis shows that the effect of doping on E modes is greater than A1 modes, and the microstructure of FeO6 octahedron can be regulated by ion doping. A-site trivalent ion doped ceramics exhibit improved magnetism compared with pure BiFeO3 ceramic, which originated from the suppressed spiral spin structure of Fe ions. The tilt of FeO6 octahedron as a typical structure instability causes the anomalous change of the imaginary part of permittivity at high frequency, and doped ceramics exhibit natural resonance around 16–17 GHz.

Bi volatilization and conduction mechanism of rapidly liquid phase sintering La-doped BiFeO3 perovskite ceramics

LaxBi1−xFeO3 (LBFO) materials were synthesized by sol–gel method with x = 0.0, 0.1, 0.2, and 0.3. LBFO ceramics were obtained by rapid liquid phase sintering and conventional sintering, respectively. X-ray diffraction (XRD) and Raman spectroscopy indicated that the phase transition from twisted diamond R3C to orthogonal Pbnm occurs in the course of the increase of La element doping. Scanning electron microscopy demonstrated that the grain size of LBFO ceramics decreased from 10 to 1 μm, with the increase of La ion doping, and the volatilization of Bi decreases from 6.48 to 1.43%. It was found that LBFO ceramics have the characteristic of negative temperature coefficient (NTC), the resistivity (100 °C) is from 4.32 × 106 to 2.71 × 108 Ω cm, the material constant (B100/700 value) is about 6000–9000 K, the activation energy of LBFO is around 0.56 to 0.82 eV, and the temperature range of LBFO is from 100 to 700 °C. The resistivity change of LBFO is less than 1% after 500 h of ageing at 300 °C.

The structural evolution and multiferroic properties of nonstoichiometric BiFe1−4x/3ZrxO3 ceramics with Fe vacancies

Nonstoichiometric BiFe1−4x/3ZrxO3 (0 ≤ x ≤ 15%) multiferroic ceramics with Fe vacancies were synthesized by using rapid liquid phase sintering process. It was found that nonstoichiometric Zr substitution induced structure distortion, and an appropriate amount of Zr could remove impurity phases. XPS and PAS studies indicated that there was no obvious change in Bi vacancies concentration, but the Fe vacancies concentration increased with increasing substitution amount of Zr. The Fe2+ concentration first decreased and then increased with the increase in substitution amount of Zr, while the oxygen vacancies concentration decreased with increasing substitution amount of Zr. Nonstoichiometric Zr substitution could effectively enhance the multiferroic behaviors of BiFeO3. The evolution of structure and properties induced by nonstoichiometric Zr substitution indicated that Fe2+ concentration was the main source of the leakage current, while Fe vacancies concentration was a key factor that modulated the magnetic performances of BiFeO3. Furthermore, the applied magnetic field dependence of dielectric constant suggested that the magnetodielectric effect increased with increasing Zr substitution amount. The results above imply that nonstoichiometric BiFeO3 composition with Fe vacancies has great potential for exploiting high quality BiFeO3-based ceramics.

Liquid-phase sintered bismuth ferrite multiferroics and their giant dielectric constant

Abstract Rapid liquid-phase sintering method has been modified and used to synthesize Bi 1- x La x FeO 3- δ compositions (0 ≤ x ≤ 0.5). The temperature and sintering procedures to obtain stable single-phase samples have been defined. This provides a significant reduction in the synthesis time, which is especially important for mass production. Furthermore, giant dielectric constants have been observed in Bi 1- x La x FeO 3- δ compositions, the values of which are one order of magnitude larger than those of similar Bi-based multiferroics obtained by conventional methods. It potentially makes them one of the most promising materials for modern technological applications.

Controlling micro-porous size in TiO2 pellets processed by sol-gel and rapid liquid phase sintering

Abstract A fast and lower electric energy consumption process to synthesize TiO 2 pellets with interconnected micropores, is proposed. Pellets were prepared by rapid liquid-phase sintering (RLPS) at different temperatures (900, 1000 and 1100 °C) and times (2, 5, 7 and 10 min). The density of these samples increases when temperature rises and decreases for longer sintering times; the highest density, of 2.78 g/cm 3 was obtained when sintering at 1100 °C/2min. The addition of PEG and the annealing at 450 °C/2 min produced pores of 38.51 ± 27.51 μm and 48.98 ± 32.34 μm when PEG3350 and PEG8000 respectively, were used. An additional RLPS at 1100 °C/2 min gives rise to TiO 2 pellets in a rutile phase, with pores of 76.82 ± 34.23 μm and 173.04 ± 68.03 μm for PEG3350 and PEG8000, respectively. Interconnectivity of pores is obtained in all samples. The elastic module of these pellets was 39.22 ± 0.16 GPa, for the sample prepared with PEG3350; and 121.30 ± 0.04 GPa for the one made with PEG8000. The achieved pore size and interconnectivity at 1100 °C/2 min are a result of the optimized sintering conditions and the better control of PEG vapor pressure released when the intermediate annealing at 450 °C/2 min is introduced.

Structure, non-stoichiometry, valence of ions, dielectric and magnetic properties of single-phase Bi0.9La0.1FeO3−δ multiferroics

Abstract The structure, microstructure, valence states, non-stoichiometry, dielectric and magnetic properties of lanthanum-modified multiferroics have been studied by X-ray diffraction, thermogravimetric, iodometric titration, SEM, XPS, dielectric spectroscopy and magnetic methods. Multiferroics of bismuth ferrite have been obtained by a rapid liquid phase sintering method under different pressures, P, for compacting stoichiometric mixture of precursors. On the basis of the experimental data, the molar formulas of real BiFeO3−δ and Bi0.9La0.1FeO3−δ structures have been determined. The real structure contains Bi3+, La3+, Fe3+, Fe2+ and O2− ions as well as cation V(c) and anion V(a) vacancies. The optimal temperature regimes of the rapid liquid phase sintering method for obtaining the single-phase Bi0.9La0.1FeO3−δ, whose composition corresponds to the concentration region of destruction of a spin cycloid, have been defined. It has been established that oxygen non-stoichiometry δ and concentration of Fe2+ strongly depend on the pressure P. The initial dielectric permittivity of the Bi0.9La0.1FeO3−δ multiferroics can be controlled and changed by the pressure P more than 5000 times. The correlations between the composition, structure, non-stoichiometry, dielectric and magnetic properties in the BiFeO3−δ and Bi0.9La0.1FeO3−δ have been established. In the pure BiFeO3−δ at room temperature, rhombohedral distortions of a hexagonal structure with indications of a ferromagnetic double exchange have been detected. The magnetic structure of the single-phase Bi0.9La0.1FeO3−δ is homogeneous with a large value of coercivity, HC ≥ 10 kOe, at room temperature. An analysis of the magnetic properties indicates the appearance of a weak ferromagnetism due to the destruction of the spin cycloid by lanthanum ions.

Effects of treatment process and nano-additives on the microstructure and properties of Al2O3-TiO2 nanocomposite powders used for plasma spraying

ABSTRACT Al2O3-TiO2 nanocomposite powders with or without nano-additives used for plasma spraying were successfully prepared by spray drying, heat treatment and plasma treatment. The effects of treatment process and nano-additives on the microstructure and properties of Al2O3-TiO2 nanocomposite powders were investigated. Al2O3-TiO2 composite powders prepared by spray drying and heat treatment were nanostructured composite powders with high sphericity and nanosized grains. Spherical and dense particles with smooth surface were formed due to the extremely rapid liquid phase sintering during plasma treatment. The formation of different microstructures after plasma treatment was mainly determined by two key factors: the density and heating temperature of powder particles. The three-dimensional network structure was the typical microstructure in the plasma treated Al2O3-TiO2 composite powder with nano-additives. The nanocomposite powder with three-dimensional network structure was composed of amorphous intergranular network thin film rich in Ti, Zr and Ce surrounding the α-Al2O3 colonies. Spherical powders with smooth surface and dense microstructure were formed due to the rapid melting and solidifying of plasma treatment. Therefore, the flowability and density of the plasma treated powders was significantly improved. The plasma treated composite powders were good spraying material with excellent performance, which can be used to prepare high performance nanostructured coatings.

The effect of ion doping at different sites on the structure, defects and multiferroic properties of BiFeO3 ceramics

The polycrystalline samples of undoped BiFeO3, Ce doped BiFeO3 (Bi0.9Ce0.1FeO3) and Zr dpoped BiFeO3 (BiFe0.9Zr0.1O3) were prepared by rapid liquid phase sintering technique. The effects of A-site substitution with Ce and B-site substitution with Zr on the structure, defects and multiferroic properties of BiFeO3 ceramics were comparative investigated. Undoped and doped BiFeO3 samples are well crystallized in perovskite structure, whilst Ce and Zr doping results in slight distortion in the lattice structure. With Ce and Zr doping, the average grain sizes decrease. Positron annihilation lifetime measurements reveal that there are vacancy-type defects in the three samples, and Bi0.9Ce0.1FeO3 sample has the maximum open volume and concentration of the vacancy defect among those three samples. Both Ce and Zr doping can improve the leakage current, ferroelectric and magnetic properties, whereas Zr doping exhibited better ability. The better electric properties in BiFe0.9Zr0.1O3 may be due to the effective reduction of oxygen vacancies, Fe2+ and impurity phases by Zr doping. The cause for better magnetic properties in BiFe0.9Zr0.1O3 sample may be that the insertion of Fe vacancies and nonmagnetically active Zr4+ ions in antiferromagnetic Fe sublattice can effectively suppress the spiral spin modulation structure.

The structure, defects, electrical and magnetic properties of BiFe1−x Zr x O3 multiferroic ceramics

BiFe1−x Zr x O3 (x = 0.00–0.30) ceramics were synthesized using solid state reaction method followed by rapid liquid phase sintering, and the microstructure, electrical and magnetic properties of the synthesized ceramics were systematically investigated. The XRD patterns show that no impurity phases exist in Zr doped samples; Zr doping induces the crystal structure distortion when x ≤ 0.10, and a structural phase transition occurs when the content of Zr varies from 0.10 to 0.20. SEM observations indicate that the average grain size is remarkably decreased by Zr doping. Positron annihilation lifetime spectra results indicate that cation vacancy-type defects exist in all samples, the cation vacancy concentration increases with increasing Zr content from 0.00 to 0.20, and then decreases with further increase of Zr content. Electrical and magnetic measurements show that enhanced leakage, ferroelectric and magnetic properties are observed in Zr doped ceramics. The analysis of microstructure and properties show that the cation vacancy defect plays an important role in modulating the electrical and magnetic properties of BiFeO3.

Impedance spectroscopy and ferromagnetic properties of Bi0.8Gd0.2FeO3 multiferroics

Multiferroic Bi0.8Gd0.2FeO3 (BGFO) ceramics were prepared by a rapid-liquid phase sintering process. BGFO ceramics can be sintered at a sintering temperature range of 875°C–940°C and shown a pure orthorhombic (space group, Pnma) structure. The crystal symmetry and lattice parameters were determined from the Rietveld analysis for the experimental data. BGFO ceramics sintered at 900°C exhibited high theoretical relative density (∼98%), strong ferroelectricity and good magnetism. BGFO ceramics exhibited the similar dielectric relaxation properties to the typical relaxor ferroelectrics. The role of oxygen vacancies at high temperature in dielectric and ac conductivity behavior was also discussed. The diffusing of structure defects between the grain and grain boundary was established using Impedance Spectroscopy (IS).

Effect of Zr substitution on structural, magnetic, and optical properties of Bi0.9Dy0.1Fe1−xZrxO3 multiferroic ceramics prepared by rapid liquid phase sintering method

Zr substituted Bi0.9Dy0.1Fe1−xZrxO3 (x=0.03, 0.06 and 0.10) multiferroic ceramics were synthesized by rapid liquid phase sintering technique to improve its multiferroic properties. Rietveld structural refinement of XRD patterns and Raman spectra revealed a partial structural phase transition from rhombohedral (R3c) to biphasic structure (R3c+P4mm) on codoping. The substitution of larger ionic radii and higher valence Zr4+ ions at Fe-site leads to decrease in the grain size as a result of charge compensation at Fe site. The weak ferromagnetic behavior were observed in all samples along with maximum Mr value of 0.159emu/g for x=0.03 concentration, which is also endorsed by second order Raman modes. The distortion in FeO6 octahedra due to Zr substitution leads to splitting of electronic bands of 3.2eV into multiplets, which in turn reduced the optical band gap value in the range of 2.06–2.10eV for all samples.

Effect of CaCu3Ti4O12 modification on the structural, electrical and magnetic properties of BiFeO3 ceramics

ABSTRACTThe polycrystalline samples of (1−x)BiFeO3-xCaCu3Ti4O12 (x = 0, 0.05, 0.10 and 0.15) were synthesized by solid state reaction method followed by rapid liquid phase sintering. The effects of CaCu3Ti4O12 (CCTO) doping on the microstructure, dielectric and magnetic properties of BiFeO3 (BFO) ceramics were studied by changing CCTO concentrations. The XRD analysis reveals that that a little amount of CCTO as a solid solution in the BFO phase leads to expanding the lattice, no phase transition has occurred in the doping content range, but CCTO doping induces the crystal structure distortion. Impedance spectroscopy results show that the doped BFO ceramics have a broadband stability of the dielectric constant and dielectric loss on frequency, the CCTO doping can improve the dielectric constant and reduce dielectric loss of BFO. It is also observed that an increase in CCTO doping concentration in BFO can improve the magnetic properties of BFO.

Crystal structure refinement, ferroelectric and ferromagnetic properties of Ho3+ modified BiFeO3 multiferroic material

Multiferroic Bi1-xHoxFeO3 (x = 0, 0.05, 0.1) ceramics have been prepared by rapid liquid phase sintering method. The effect of Ho3+ doping on the crystal structure, dielectric, ferroelectric properties, TN and TM 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 and the grain size from 1 to 5 μm is observed for BiFeO3 samples with Ho3+ doped. The dielectric behavior of Bi1-xHoxFeO3 ceramics varies with frequency and temperature, which might be understood in terms of an oxygen vacancy, the displacement of Fe3+ ions and lattice phase transition. There is a perfect dielectric hysteresis phenomenon in the ɛr-V curves of Bi1-xHoxFeO3 samples at bias voltage with 10 V. Under the action of the bias voltage, more and more dipoles are“frozen”in the bias voltage direction and quit polarization gradually, resulting in lower dielectric constant. The unsaturated P-E hysteresis loop of Bi1-xHoxFeO3 (x = 0.05, 0.1) samples is obtained with a large 2Pr of 3.08 μC/cm2. The Pr, Mr of Bi0.9Ho0.1FeO3 sample is nearly 23, 35 times as large as that of BiFeO3, respectively. It can be inferred that Ho3+ doping in BiFeO3 ceramics is proved to be an effective way to modulate the ferroelectric and the magnetic properties. It shows that the TN of BiFeO3 changes slightly from 644 K to 638 K and the TM of Bi1-xHoxFeO3 will reduce from 878 K to 860 K with increasing Ho3+ content. It can be attributed to the Fe3+–O2+–Fe3+ super-exchange strength and the relative stability of the magnetic structure.

Investigations on the structure, defects, electrical and magnetic properties of Ni-substituted BiFeO3 ceramics

Polycrystalline BiFe1−xNixO3 (x = 0.00–0.30) ceramics were synthesized by solid state reaction method followed by rapid liquid phase sintering. The effect of Ni substitution on the structure, defects, electrical and magnetic properties of BiFeO3 ceramics was investigated. X-ray diffraction measurements reveal that Ni-substituted samples exhibit distorted rhombohedral perovskite structure as that of unsubstituted BiFeO3, and the impurity phases such as Bi2Fe4O9 decrease due to Ni substitution. The changes in the phonon frequencies in Raman spectra reveal the lattice distortion in Ni-substituted samples which are in agreement with the XRD analysis. Positron annihilation lifetime measurements reveal that cation vacancy-type defects exist in all samples, the vacancy concentration increases with increasing Ni content from 0.00 to 0.30. The enhancement in leakage current and dielectric properties is observed in Ni-substituted samples due to the suppression of impurity phases and Fe2+. Magnetic measurements indicate that the Ni-substituted BiFeO3 samples exhibit weak ferromagnetism. The magnetic properties are found to increase with increasing Ni concentration due to the internal structural distortion, cation vacancy, the ferromagnetic exchange between the neighboring Fe3+ and Ni2+ ions and the change in Fe–O–Fe bond angle.

Rare earth and transition metal doped BiFeO3 ceramics: structural, magnetic and dielectric characterization

Here we studied the effect of rare earth (Y) and transition metal (Co, Ni) substitution on the structure, magnetic and dielectric properties of the BiFeO3 (BFO) multiferroic ceramic. The samples were synthesized by modified rapid liquid phase sintering method. The phase purity and structural characteristics of the ceramics were investigated by X-ray diffraction and scanning electron microscope. The results revealed the uniform micro-structure with reduced grain size due to the rare earth doping in the BFO. Compared to the pure BFO, enhanced coercivity and resistivity were observed for the co-doped ceramics with Y and Co. The improvement of temperature stability of magnetism and electrical conductivity was found for ceramic co-doped with Y+3 and Ni+2 ions. The possible origin of the improvement in these properties has been discussed on the basis of the size effect and nature of the dopants.

Studies on the structural, electrical and magnetic properties of Ce-doped BiFeO3 ceramics

Bi1-xCexFeO3 (x = 0, 0.05, 0.10, 0.15 and 0.20) ceramics were synthesized using solid state reaction method followed by rapid liquid phase sintering. The influences of Ce doping on the microstructure, electrical and magnetic properties of BiFeO3 (BFO) ceramics have been investigated. The XRD results indicate that Ce doing induce a structural transition from rhombohedral to cubic in Bi1-xCexFeO3, and the impurity phases decrease and almost vanish when the Ce doping content above 0.15. SEM analysis shows the decrease of grain size in Bi1-xCexFeO3 with increasing Ce content. Positron annihilation lifetime measurements reveal that cation vacancy-type defects exist in all samples, the open volume of vacancy-type defect increases with increasing Ce content. The vacancy concentration increases with increasing Ce content from 0.00 to 0.15, while decreases with increasing Ce content from 0.15 to 0.20. Electrical and magnetic measurements show that the dielectric, ferroelectric and magnetic properties of BFO can be improved by doping with an appropriate amount of Ce. These results are interpreted by means of the subtle change in the structure, reduction of oxygen vacancies and the level of cation vacancy concentration in the doped samples.