Rhombohedral Perovskite Phase Research Articles

Optimization of dielectric response in BiFeO3–CoFe2O4 nanocomposites for high frequency energy storage devices

The rapid development of smart and sophisticated miniaturized electronic devices put a high demand for high permittivity material. In the current report, we analyze structural, morphological, and dielectric response of spinel-perovskite composites consisting of CoFe2O4 (CFO) as the spinel phase and BiFeO3 (BFO) as the perovskites phase. Here pristine BFO and CFO are fabricated using Sol—Gel auto-combustion route and their composites with a recipe (1-x) BiFeO3 - (x) CoFe2O4 (x = 0.0, 0.1, 0.2 and 0.3) using solid-state reaction technique. Structural investigation identifies presence of rhombohedral perovskite phase of BFO and cubic spinel phase of CFO and thus guarantees the formation of the composite. The crystallite size increases from 16 to 36 nm for BFO and 39.5–54 nm for CFO. The distribution of well-shaped particles with a reduction in grain size in range of 50–400 nm is witnessed in morphological analysis with the increment of CFO contents in composites. Elemental purity and the presence of various elements according to their stoichiometric ratio are witnessed during elemental investigation. A detailed analysis of the dielectric permittivity, electric modulus, and impedance of these compositions is carried out to investigate their suitability for electronic and energy storage devices. The nanocomposites under study exhibit a dielectric constant of 1126 at 100 Hz for x = 0.3, which decreases to 102 at 1 MHz. Concurrently, the tangent loss for x = 0.3 is observed to be 3.37 at 100 Hz, decreasing to 0.31 at 1 MHz. However, a decrease in dielectric loss and increase in impedance is noticed when the concentration of CFO in BFO nano-composite is increased which reflects the reduction in power losses and better control in electronic conductivity and thus highlights the role of these compositions for advanced energy storage electronic devices.

High energy storage performance induced by the introduction of BiScO3 into (Bi0.5Na0.5)TiO3–BaTiO3 lead-free ferroelectric ceramics

In this work, ternary 0.25(Bi0.5Na0.5)TiO3-(0.75-x)BaTiO3-xBiScO3(abbreviated as 0.25BNT-(0.75-x)BT-xBS, x = 0.19, 0.21, 0.23, 0.25, 0.27) lead-free ferroelectric ceramics were synthesized using the solid-state reaction method. The introduction of BiScO3 into (Bi0.5Na0.5)TiO3–BaTiO3 ceramics had a significant impact on changing the phase structures, and microstructures, as well as the dielectric and ferroelectric properties. All ceramics exhibited a coexistence of tetragonal(P4bm) and rhombohedral(R3c) perovskite phases, while the influence of the BiScO3(BS) content on the average grain size was not significant. Slim polarization-electric field hysteresis loops were recorded for the 0.25BNT-(0.75-x)BT-xBS ceramics, with low remnant polarization (Pr) and large maximum polarization(Pmax). 0.25BNT-0.50BT-0.25BS ceramic had the largest Pmax, which induced a high energy storage density of 2.93 J/cm3 and energy storage efficiency of 91 % under a low electric field of 230 kV/cm 0.25BNT-0.50BT-0.25BS ceramic not only yielded excellent fatigue resistance, but also maintained good energy storage performance at high temperature and high frequency, which are considered of great importance since they can be leveraged for the potential development of high temperature and frequency capacitors. In addition, an excellent pulse performance was measured, with a high discharge energy density of 3.42 J/cm3 and a fast discharging rate t0.9 of 130 ns. This good pulse performance was maintained at high temperatures, suggesting that the proposed material is also highly competitive for applications where high-temperature pulse devices are required.

Heat treatments for thermal sprayed lead-free piezoelectric ceramic coatings

[0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3]0.98-(LiNbO3)0.02 (BNBTLN) piezoelectric ceramic coating was fabricated by thermal spray process on stainless steel substrates with thermal barrier coating (TBC) as an intermediary layer. The morphology, structure, and electrical properties of the thermal-sprayed BNBTLN coatings after furnace heat treatment (F-HT) and plasma torch heat treatment (P-HT) were studied, respectively. The BNBTLN coatings after F-HT and P-HT both had the coexisting rhombohedral and tetragonal perovskite phases and exhibited excellent electrical properties, with an effective piezoelectric coefficient d33 of 68 p.m./V and 40 p.m./V, respectively. These results reveal that high quality piezoelectric coatings can be achieved by the P-HT method, which is promising for scaling up the fabrication of piezoelectric ceramic coatings.

Large electric field-induced strain and excellent photoluminescence properties of Pr-modified 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 lead-free ferroelectric ceramics

The 0.94Bi0.5-xPrxNa0.5TiO3-0.06BaTiO3 (BNT-6BT-xPr) lead-free ceramics with doping content of x = 0, 0.01, 0.025, 0.04, 0.05, 0.075, and 0.1 were synthesized by the conventional solid-state reaction method. After doping with the Pr element, a composition-induced phase transition took place, which from the rhombohedral perovskite (R3c) and tetragonal perovskite (P4bm) phases coexisting into the pseudo-cubic phase. At the same time, the introduction of the Pr element had a beneficial effect on grain growth, and the average size of the crystal particle increased from 299 to 742 nm. The Curie temperature Tm showed no obvious change with the increasing Pr content, but the temperature TF-R of the ferroelectric-relaxor phase transition was gradually shifted toward lower temperatures. In addition, the depolarization temperature Td gradually decreased from 125 to 53 °C. In the BNT-6BT-0.025Pr ceramics, giant electric field-induced strain (Smax) and normalized piezoelectric coefficient (d33*) were obtained (Smax = 0.58%, d33* = 723 pm/V). Furthermore, a significant photoluminescence emission intensity was achieved, exhibiting a bright red color. Due to significant enhancement of the piezoelectric and the photoluminescence properties, the BNT-6BT-0.025Pr ceramics exhibited strong competitiveness in actuators and multifunctional devices, which may broaden their application fields.

Dielectric and magnetic properties of (Pb, Ti) co-doped BiFeO3 multiferroic ceramics

In this study, Bi0.9Pb0.1Fe1-xTixO3 (0.05 ≤ x ≤ 0.20) multiferroic ceramics were prepared through solid-state reaction. The influence of Pb, Ti partial substitutions on the dielectric and magnetic properties of BiFeO3 multiferroic ceramics was investigated and discussed in detail. X-ray diffractions confirm rhombohedral perovskite phase formation (R3c space group). Scanning electron microscopy (SEM) was employed to investigate the morphology, revealing a cuboidal microstructure with bimodal distribution of grain sizes. Magnetic studies were carried out and the results reveal a slight enhancement of saturation magnetization with Ti concentration increasing. The present data indicates that Bi0.9Pb0.1Fe1-xTixO3 can be used as multifunctional material in different magnetoelectric applications.

DFT studies of BaTiO3

The structure of stable phases is investigated using first-principle calculations based on the functionals: LDA, GGA and newly developed general-purpose heavily constrained and appropriately normalized meta GGAfunctional (SCAN). The purpose of this study is to theoretically study the atomic displacements and band gap of the cubic, tetragonal, orthorhombic, rhombohedral perovskite phases for the comparison LDA, GGA-PBE and meta-GGA functionals using the density functional theory method. The obtained data of the density of states (DOS) showed that the values of the band gap energies are underestimated, and the DOS values show that the upper part (valence band) mainly consists of O 2p orbitals, the lower part (conduction band) consists of Ti 3d orbitals. The rhombohedral phase has a mixed composition of Ti states in the conduction band with a greater degree of 3dz2 than 3dxy. The values of the energies of the band gap (Egap) and the density of states show reasonable agreement with experimental and theoretical data. The LDA functional and, to a lesser extent, the GGA - PBE functional can also provide fairly accurate information about atomic displacements in these crystals. The values calculated by the SCAN functional do not differ much from the GGA and LDA functionals.

Dielectric, ferroelectric, and piezoelectric properties of rare earth Sm-doped 0.94 Bi0.5Na0.5TiO3-0.06 BaTiO3 lead-free ceramics

Bi0.47-xSmxNa0.47Ba0.06TiO3 (BNT-6BT-xSm) ferroelectric ceramics with different doping contents of samarium (Sm) were prepared by solid-state reaction method. All ceramics lie in the coexistence region of the rhombohedral perovskite phase (R3c) and tetragonal perovskite phase (P4bm). When the Sm content increases, the grain growth is limited, and the average grain size is reduced from 1.69 µm (at the composition of x = 0.005) to 0.86 µm (at the composition of x = 0.05). When Sm is introduced into Bi0.5Na0.5TiO3-BaTiO3 binary system, the composition-induced local structure transition occurs, namely the transition from order to disorder. And after the introduction of Sm3+ ions, the depolarization temperature (Td) increases considerably. With the increase of the Sm content, the remnant polarization (Pr) decreases from 52 μC/cm2 to 8 μC/cm2, and the coercive field (Ec) gradually decreases from 37 kV/cm to 14 kV/cm, respectively. Under an electric field of 80 kV/cm, the maximum electric field-induced strain and corresponding normalized strain (d33*) reached 0.35% and 318 pm/V (at the composition of x = 0.03), respectively. The maximum piezoelectric coefficient (d33) is 158 pC/N (at the composition of x = 0.015), resulting from the structure transition between ferroelectric phase and anti-ferroelectric phase. Therefore, BNT-6BT-0.03Sm lead-free ferroelectric ceramic is a promising candidate of lead-based ferroelectric ceramics for piezoelectric actuators.

Tunability of magnetoelectric coupling in BiFeO3–PbZr0.52Ti0.48O3–CoFe2O4 tri-phase composites for ultra-fast switching applications

Magnetoelectric coupling an exquisite feature of multiferroics make them suitable for advanced technological applications like magnetic sensors, spintronic devices, and fast-switching devices, respectively. In the present work, a series of tri-phase composites (1-x)(0.7BiFeO3 +0.3PbZr0.52Ti0.48O3) + xCoFe2O4 (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10) is synthesized through sol–gel auto-combustion method followed by the solid-state ball milling route. The analysis of X-ray diffraction patterns confirms the development of the rhombohedral perovskite phase of BiFeO3, the tetragonal phase of PbZr0.52Ti0.48O3, and the cubic spinel structure of CoFe2O4. The micrographs clearly show an increase in the average grain size by enhancing the CoFe2O4 contents having sharp and distinct grain boundaries. The energy-dispersive X-ray study assures the exact formation of a composite recipe through elemental mapping. The ferroelectric analysis comprising bipolar polarization versus electric field loops exhibits a significant decrease in maximum polarization with an increase in remanent polarization by enhancing the CoFe2O4 contents in the composite. The positive up and negative down sequence validates the presence of leakage current in all the samples with precise measurement of remanent polarization with and without switching polarization. The gradual increase of CoFe2O4 contents causes an increase in the magnetic response of the composites. Meanwhile, the magnetoelectric coupling phenomenon for all the composition shows a linear response whereas for x = 0.1 there is a slight reversibility observed, making this tri-phase composite a robust candidate for fast-switching devices.

Structural and dielectric properties of ultra-fast microwave-processed La0.3Ca0.7Fe0.7Cr0.3O3−δ ceramics

Perovskite La0.3Ca0.7Fe0.7Cr0.3O3-δ (LCFCr) is a mixed ionic and electronic conductor (MIEC) that can be employed as an electrode material in reversible solid oxide fuel cells (RSOFCs). In this work, an ultra-fast (15 ​min) one-step microwave (MW)-assisted combustion synthesis route has been developed to obtain phase pure and highly crystalline LCFCr powder. The synthesized powders exhibited a sponge-like microstructure with increased electrochemical reaction sites. Neutron thermodiffraction analysis revealed a structural transition above 500 ​°C from the room temperature (RT) orthorhombic Pnma to a rhombohedral R3c perovskite phase. The oxygen vacancy concentration was found to increase from δ ​= ​0.272(7) at RT to δ ​= ​0.333(5) at 900 ​°C. Furthermore, a 3-dimensional G-type antiferromagnetic structure was detected at RT. MW-sintering of pressed green ceramic pellets was carried out at 950 ​°C for 1 ​h, using a MW-transparent quartz fiber crucible or alternatively a SiC crucible acting as a MW-absorber. Impedance spectroscopy data on sintered ceramic pellets revealed electronic inhomogeneity as demonstrated by the occurrence of three dielectric relaxation processes associated with two grain boundary (GB)-like contributions and one bulk. The dielectric inhomogeneity encountered may be restricted to the extrinsic GB areas, which may be rather thin. More homogeneous dielectric properties of the GBs were found in the pellet that was sintered in the SiC crucible.

Self-Assembled Triple (H+/O2-/e-) Conducting Nanocomposite of Ba-Co-Ce-Y-O into an Electrolyte for Semiconductor Ionic Fuel Cells.

Triple (H+/O2−/e−) conducting oxides (TCOs) have been extensively investigated as the most promising cathode materials for solid oxide fuel cells (SOFCs) because of their excellent catalytic activity for oxygen reduction reaction (ORR) and fast proton transport. However, here we report a stable twin-perovskite nanocomposite Ba-Co-Ce-Y-O (BCCY) with triple conducting properties as a conducting accelerator in semiconductor ionic fuel cells (SIFCs) electrolytes. Self-assembled BCCY nanocomposite is prepared through a complexing sol–gel process. The composite consists of a cubic perovskite (Pm-3m) phase of BaCo0.9Ce0.01Y0.09O3-δ and a rhombohedral perovskite (R-3c) phase of BaCe0.78Y0.22O3-δ. A new semiconducting–ionic conducting composite electrolyte is prepared for SIFCs by the combination of BCCY and CeO2 (BCCY-CeO2). The fuel cell with the prepared electrolyte (400 μm in thickness) can deliver a remarkable peak power density of 1140 mW·cm−2 with a high open circuit voltage (OCV) of 1.15 V at 550 °C. The interface band energy alignment is employed to explain the suppression of electronic conduction in the electrolyte. The hybrid H+/O2− ions transport along the surfaces or grain boundaries is identified as a new way of ion conduction. The comprehensive analysis of the electrochemical properties indicates that BCCY can be applied in electrolyte, and has shown tremendous potential to improve ionic conductivity and electrochemical performance.

Ce and Fe doped LaNiO3 synthesized by micro-emulsion route: Effect of doping on visible light absorption for photocatalytic application

A series of La1−xCexNi1−yFeyO3 (x, y = 0.00–0.25) NPs was fabricated via micro-emulsion route and effect of doping was investigated on the basis of optical, photocatalytic and structural properties. The as-synthesized NPs were characterized via XRD, Raman analysis, SEM and UV–visible techniques. The XRD results confirmed the rhombohedral perovskite phase particles with particles of 60–80 nm range. UV–vis absorption edge showed significant red shift thereby tuning the band gap from 2.77 to 2.64 eV. The photocatalytic effectiveness of LaNiO3 and La0.80Ce0.20Ni0.80Fe0.20O3 catalysts was performed by degrading Congo red (CR) dye under visible light exposure. Substituted catalyst exhibited superior photodegradation by showing 97% degradation in comparison to pristine LaNiO3 (63% only) in 120 min. Degradation of CR followed the pseudo fist order kinetics. In addition, the catalyst dose effect, dye concentration and pH variation was studied for Cr dye degradation. Enhanced photocatalytic activity and narrow bandgap of Ce and Fe doped LaNiO3 introduce such materials as efficient visible active photocatalysts to be utilized in dye removal application from waste water and in photovoltaic applications, respectively.

The Influence of Pressure on Structural, Elastic, Piezoelectric and Dielectric Properties of R3c‐BiAlO3 Based on Ab Initio Calculations

AbstractIn this paper, we deal with a theoretical and predictive study of the influence of the applied pressures on the structural, elastic and piezoelectric properties of the rhombohedral BiAlO3 perovskite (R3c space group) phase by combining both the density functional theory (DFT) and the density functional perturbation theory (DFPT) included in the ABINIT code. The results indicate a decrease in structural cell volume and the elastic constants appear to be more intense as the applied pressure increases. Due to the increase in the direct piezoelectric coefficient (e33) and the decrease of the elastic constant (c33), the converse piezoelectric coefficients (d33) tend to improve with increased pressure applied. At a pressure of 10 GPa, the value of the direct piezoelectric constant reached 6.23 C/m2 which becomes an indirect competitor to lead zirconate titanate (PZT). The dielectric constants and born effective charge at high pressure have been calculated. Our results agree well with the available experimental and theoretical results. Our findings, especially piezoelectricity, can help in various applications of high‐pressure devices such ultrasonic transducer.

Effect of sintering temperature on the microstructure and conductivity of Na0.54Bi0.46Ti0.99Mg0.01O3-δ

The present work examines the effect of sintering temperature on the phase formation and the conductivity of Na0.54Bi0.46Ti0.99Mg0.01O3-δ. The formation of the secondary phase and the poor grain boundary conductivity are a few major concerns in this recently developed material. Polycrystalline bulk specimens are fabricated through conventional pressureless sintering at different temperatures of 930 °C, 950 °C, 1000 °C, and 1050 °C for 2 h. A single rhombohedral perovskite phase is detected in the XRD profiles collected on all the sintered samples. However, the SEM micrographs reveal the existence of impurity phase in all the tested samples with the amount increasing considerably with the increase in temperature. The local elemental analysis of the impurity phase suggests the presence of non-stoichiometric Na2xTi2-xMgxO4 compound. However, the chemical composition of this compound varies across different specimens. The samples sintered at 950 °C exhibit the maximum bulk and grain boundary conductivities of 13.3 mS.cm−1 and 3.6 mS.cm−1, respectively, at 600 °C. A lower magnitude of both the conductivities is observed on sintering the samples at higher temperatures. The activation energy for bulk ionic conduction also decreases from 0.67 eV to 0.48 eV with the sintering temperature supporting the conjecture that higher Mg2+ amount is dissolved in the perovskite phase present in the samples sintered at 950 °C. The higher total conductivity in the samples sintered at 950 °C is attributed to the formation of comparatively less amount of Mg-rich impurity phase. Even though 950 °C appears to be an optimum sintering temperature, the grain boundaries of the samples continue to be resistive. At 600 °C, the grain boundary conductivity is less than one-third of the bulk conductivity. As a result, grain boundaries contribute a significant portion of the total resistivity offered by the Na0.54Bi0.46Ti0.99Mg0.01O3-δ samples.

Effect of Zr/Ti Ratio on Piezoelectric and Dielectric Propertiesof 0.1Pb[Fe1/2Nb1/2]O3-0.9Pb[ZrxTi(1–x)]O30 Ceramics

This study describes the microstructure, crystal structure, dielectric and piezoelectric behavior of 0.1Pb[Fe1/2Nb1/2]O3-0.9Pb[ZrxTi(1–x)]O3 (x = 0.49-0.55) ceramics synthesized by solid-state reaction. Compositions were sintered at 1180oC for 120 min. Dense and uniform microstructure was seen through microstructural analysis. XRD pattern confirmed the co-existence of tetragonal and rhombohedral perovskite phases in these compositions where 0.51 ≤ x ≤ 0.53. Compositions with 0.51 ≤ x ≤ 0.53 resulted in the optimum values of properties, viz. dielectric constant (ϵrr) of 1150, piezoelectric coefficient (d31 ) of 95x10–12 C/N, piezoelectric voltage constant (g31 ) of 70x10–3 mV/N and the coupling factor (kp ) value of 0.67. Results indicated that this material composition could be suitable for power harvesting and sensor applications.

Effect of synthesis route on the structural and electrical properties of sodium bismuth titanate: A comparative study of solid-state and polyol mediated synthesis

Sodium bismuth titanate (NBT) was synthesized through two different synthesis methods: solid-state reaction (SS) and polyol mediated synthesis (PM). The effect of synthesis route on the structural and electrical properties of NBT system has been investigated. Polyol mediated synthesize NBT sample result in single-phase at relatively lower temperature than of prepared via the solid-state reaction method. The Rietveld refinement of the XRD data confirms that both the sample crystallizes in the rhombohedral perovskite phase with R3c space group. The morphological properties indicate that the grain size of the polyol method processed sample is smaller and slightly agglomerated than the one prepared via solid-state route. Impedance results reveal enhanced bulk conductivity for PM synthesized samples as compared to SS route. Thus, the polyol mediated synthesis may be a better approach for the synthesis of NBT samples. Furthermore, a correlation between the structural and electrical properties for both methods synthesized samples have been discussed to explain the conductivity behaviour.

Microstructure correlated ion transport mechanism of sol-gel derived sodium bismuth titanate oxide ion conductors

In this work, we report the structural, optical, electrical conductivity and relaxation dynamics study of Sodium Bismuth Titanate (Na0.5Bi0.5TiO3) (NBT) materials prepared through sol-gel citrate auto-ignition method and sintered at different temperatures ranging from 700 °C to 900 °C. A primary rhombohedral perovskite phase with space group R3c was confirmed from X-ray diffraction analysis. Lattice parameters, particle size, and lattice strain values were obtained using Rietveld Analysis of the XRD profiles. The analysis of impedance spectroscopy data indicated the presence of non-Debye type relaxation for all the samples. The electrical study, conducted under the air atmosphere, showed the dc conductivity to be thermally activated. It increased with an increase in measuring temperature while decreased with an increase in sintering temperature. The nature of impedance spectra revealed the presence of both grain and grain boundary contribution.

Influence of spinel ferrites in the modification of magneto-electric coupling effect in BiFeO3

Magnetoelectric nanocomposites (1−x)BiFeO3-xAFe2O4 (A = Zn, Ni, Mn), x = 0.3 have been prepared using citrate sol-gel precursor method and investigated to understand the effect of spinel ferrites on magnetoelectric coupling properties of BiFeO3. The X-ray diffraction (XRD) analysis confirms the formation of di-phase compounds having rhombohedral perovskite and spinel phase for BiFeO3 and ZnFe2O4, NiFe2O4, MnFe2O4, respectively. Field Emission Scanning Electron Microscopy (FESEM) study shows the agglomerated granular particle shape in the samples. Energy Dispersive X-ray Atomic Spectroscopy (EDAX) was used to find the elemental composition of the nanocomposites. The frequency dependence of dielectric properties at room temperature has been investigated. The perovskite-spinel composite system modified the dielectric behaviour of BiFeO3. Furthermore, the linear magnetoelectric coupling coefficient study gives the strong coupling effect in BiFeO3. The study shows that the spinel ferrites bring significant changes in the magnetoelectric coupling coefficient of BiFeO3, which is useful for technological applications.

Novel defect-fluorite pyrochlore sodium niobate nanoparticles: solution-phase synthesis and radiation tolerance analysis.

Materials possessing a defect-fluorite pyrochlore structure can have a range of useful properties that are sought after, which include their radiation tolerance, nuclear waste immobilization, and phase stability at elevated temperatures. In this study, we demonstrate for the first time the synthesis and a detailed analysis of defect-fluorite pyrochlore sodium niobate (NaNbO3) nanoparticles. This analysis included an investigation into their stability to elevated temperatures and neutron irradiation. A surfactant-assisted solvothermal method is used to prepare nanoparticles of NaNbO3. This solution-phase approach results in the formation of crystalline nanoparticles of a defect-fluorite pyrochlore NaNbO3 at relatively low temperatures. The products had an average diameter of ∼74 ± 11 nm. The nanoparticles adopted a defect-fluorite pyrochlore phase and matched the cubic Fm3[combining macron]m space group. This pyrochlore form of NaNbO3 was found to be stable up to 500 °C. The nanoparticles transformed into the orthorhombic and rhombohedral perovskite phases of NaNbO3 along with the introduction of a pseudo-hexagonal Nb2O5 at higher temperatures. These defect-fluorite pyrochlore nanoparticles of NaNbO3 also exhibited a resistance to radiation induced amorphization. The dimensions, phase, and crystallinity of the defect-fluorite pyrochlore nanoparticles after exposure to a flux of neutrons were comparable to those of the as-synthesized product. The thermal stability and radiation tolerance of these pyrochlore nanoparticles could be useful in the design of thermally resilient materials, high temperature catalysts, and durable materials for the handling and storage of radioactive waste.

Microstructure and piezoelectric properties of thermal sprayed Bi0.5(Na0.70K0.20Li0.10)0.5TiO3 ceramic coatings

The microstructure of Bi0.5(Na0.70K0.20Li0.10)0.5TiO3 (BNKLT) coatings fabricated by thermal spray method was closely examined by TEM, revealing the coexistence of rhombohedral and tetragonal perovskite main phases, and very minor secondary phases, while all amorphous phase was crystallized after heat treatment. Obtaining coexisting rhombohedral and tetragonal perovskite phases after the thermal spray process involving the melting-recrystallization and heat treatment process resulted in piezoelectric ceramic coating with excellent electrical and electromechanical properties. The effective piezoelectric coefficient d33 of the heat-treated BNKLT coating reached 86 pm/V with substrate clamping, measured over macroscale by laser scanning vibrometer.

Microstructure, enhanced electric and magnetic properties of Bi0.9La0.1FeO3 ceramics prepared by microwave sintering

Bi0.9La0.1FeO3 (short for BLFO) ceramics was fabricated by conventional solid-state reaction and microwave sintering. Effects of microwave sintering temperature on microstructure, electric and magnetic properties have been systematically investigated. The XRD results indicate that BLFO ceramics sintered at 800 °C and 820 °C are single rhombohedral distortion perovskite phase, and there is small amount of secondary phase (Bi2Fe4O9) in the ceramic sample sintered at 780 °C. As microwave sintering temperature rises, the densification of BLFO ceramics enhances and the grain size increases, but the homogeneity of grain becomes worse. Microwave sintering temperature has little effect on room-temperature dielectric constant. The leakage current density decreases with the rise of sintering temperature, which is closely related to enhanced densification. The leakage mechanism of BLFO ceramics changes from bulk-limited Poole-Frenkel emission to space-charge-limited bulk conduction as sintering temperature rises. The remnant polarization of BLFO ceramics sintered at 820 °C is much higher than that of the samples sintered at 800 °C and 780 °C, and the coercive electric field changes little with sintering temperature. The results indicate the higher sintering temperature is benefit for the ferroelectricity of BLFO ceramics. The magnetic hysteresis loops of BLFO ceramics indicate that the ceramic samples sintered at 800 °C and 820 °C show a typical ferromagnetic behavior at room temperature. Compared with BLFO ceramics sintered at 800 °C, the spontaneous magnetization and saturation magnetization of BLFO ceramics sintered at 820 °C are higher, and its remnant magnetization and coercive magnetic field are lower.