Bismuth Titanate Ceramics Research Articles

Formation kinetics and equilibrium thermodynamics study on the Bi2O3-TiO2 system for synthesis of the bismuth titanate ceramics

Formation kinetics and equilibrium thermodynamics are fundamental knowledge for predicting microstructure and properties during materials processing and utilization. This work prepared high purity Bi12TiO20, Bi4Ti3O12 and Bi2Ti4O11 compounds and characterized these compounds by in-suit X-ray diffraction, scanning electron microscope, energy dispersive spectrometer as well as calorimetry. Based on the experimental data obtained in this work and the literature, a thermodynamic description of the Bi2O3–TiO2 system was carried out, a thermodynamic database as well as the calculated phase diagram of the system was provided. The discrepancy between the present calculation with the experimental data were discussed, the formation kinetics of the compounds was explained and the bismuth titanate ceramics with tailored structure and specific physical properties were sintered.

Characterization of the Dielectric Parameters of Monophase Polycrystalline Bismuth Titanate Pyrochlore (Bi2Ti2O7) Ceramics and Glass-Ceramics

Pyrochlore compounds have a number of technological applications, such as dielectrics for high-frequency and magnetoelectric devices. In bulk materials, they exhibit stimulated cation arrangement and good long-distance order within the pyrochlore framework. Bismuth titanate ceramics containing SiO2 and Nd2O3 were synthesized in the Bi2O3-TiO2-SiO2-Nd2O3 system using the melt-quenching method. In a previous study, the phase composition of selected samples was determined by X-ray diffraction (XRD) analysis and the microstructure was studied by scanning electron microscopy (SEM). The preparation of monophase polycrystalline materials was concluded. Infrared Fourier-transformed spectroscopy (FTIR) was applied in order to identify the structure. The electrical conductivity, as well as the dielectric losses and dielectric constants of selected samples were determined, and the influence of the phase composition on the dielectric characteristics was evaluated. The combination of the pyrochlore phase with the amorphous phase represented by the structural groups Bi-O-Si and Si-O-Si exerts a grain boundary strengthening effect.

Achieving multiferroic properties in bismuth titanate ceramics via a tri-doping engineering mechanism with Co, Sm, and La at room temperature

Achieving multiferroic properties in bismuth titanate ceramics via a tri-doping engineering mechanism with Co, Sm, and La at room temperature

Effect of A-site excess on the shape memory effect of sodium bismuth titanate ceramics

The impact of A-site excess on the shape memory effect of Na0.5Bi0.5TiO3 ceramics was investigated. We found that the recoverable plastic-like strain was increased by more than 10 % by A-site excess. The enhancement is attributed to the change in crystal structure from a rhombohedral phase to a monoclinic one, which further changes the phase transition behavior between the ferroelectric and nonpolar phases. Suppression of grain size and the generation of defects after the addition of excess Bi and Na were proposed for the appearance of monoclinic phase. This investigation proposes a viable approach to modulate the shape memory effect of Na0.5Bi0.5TiO3-based ceramics through the manipulation of the crystal structure and the associated phase transition processes, ultimately influencing the shape memory characteristics.

Investigation of structural, dielectric, transport and optical characteristics of Sm/Ce modified bismuth titanate ceramics

Investigation of structural, dielectric, transport and optical characteristics of Sm/Ce modified bismuth titanate ceramics

BiFeO3-BaTiO3 ferroelectrics: Decrypting the mechanism of rare earth doping-induced electrical property discrepancy via scaling behavior and multi-level structure

Rare earth doping has been widely used to modify electrical properties of piezo/ferroelectric materials. However, the physical mechanism behind property enhancement and the reason of property discrepancy induced by rare earth has been rarely solved in bismuth ferrite-barium titanate (BF-BT) ceramics. Here, two kinds of rare earth ions with different ion radii (La3+ and Sm3+) were separately introduced into Bi1-xRexFeO3-BaTiO3 (Re = La, Sm). As a result, doping an appropriate amount of rare earth ions (La3+x=0.05 and Sm3+x=0.04) can effectively improve the ferroelectricity and strain response. By combining ferroelectric scaling behavior and multi-level structure elucidation, the enhancement of electrical properties after La3+/Sm3+ doping can be attributed to the increase of total number of activated domains, the increased Bi ions off-centering and displacement of B-site ions coupled with the enhanced lattice deformation. Importantly, stronger lattice shrinkage and BO6 octahedral distortion can be achieved in Sm-doped ceramics, leading to a stronger intrinsic ferroelectric and strain response than that of La-doped ceramics, although a large enough electric field was required to release the intrinsic response because of the larger random field and dielectric relaxation induced by the larger ionic radius difference between Bi3+ and Sm3+. Oppositely, the decreased coercive field and promoted domain switching make the electrical response of La-doped ceramics can be released under a much lower electric field. The work highlights the role of rare earth doping and provides a paradigm for further designing high-performance BF-BT ferroelectrics.

Effect of gamma rays irradiation in the structure, optical, and electrical properties of samarium doped bismuth titanate ceramics

AbstractCeramics have enormous potential in several emerging technologies, including nuclear reactors. Materials with chemical inertness, high-temperature operation, and physical properties stability under applied radiation with high energy are all desired in this field of technology. Given these broad specifications, bismuth titanate ceramics may prove to be a valuable material. Regarding this task, the effect of gamma rays on the structural, optical, and ferroelectric properties of samarium-modified bismuth titanate ceramics was investigated. The Bi3.15Sm0.85Ti3O12(BSmT) compound was irradiated for 0, 50, 100, and 200 kGy using a60Co gamma source at a dose rate of 10 kGy h−1. The phase structure confirmed the orthorhombic, single-phase nature even after gamma irradiation. The results show that the unit cell volume decreases from 966.39 to 962.38 Å3with an increase in gamma dose from 0 to 200 kGy. The X-ray photoelectron spectroscopy study shows an irradiation-induced defect in the host matrix. The results show that the bandgap energy, dielectric constant, Curie temperatures, and remnant polarization slightly decreased with an increase in gamma irradiation. According to the findings of this study, the BSmT exhibits adequate stability against gamma irradiation, which offers tremendous promise in their utilization in nuclear reactor technology.

Effect of sintering time on electrical, ferroelectric, and piezoelectric performances of microwave synthesized sodium bismuth titanate ceramics

Herein, we report the synthesis of sodium bismuth titanate (Na0.5Bi0.5TiO3/NBT), a lead-free ceramic prepared via a cost and time-effective microwave synthesis route. This work presents the investigation of microstructural, electrical, and optical characteristics of NBT ceramics. The formation of a single-phase NBT sample sintered for 30 and 40 min (denoted as NBT 30 and NBT 40) is confirmed by Rietveld refinement and Raman measurement. FTIR spectroscopy is used to characterize the single-phase nature and to confirm the presence of desired vibrational spectra in the perovskite structure. Tightly packed micron-sized grains are observed from the field emission scanning electron microscopy. Due to the A-site disorder present in the lattice, two diffuse types of dielectric anomalies are present in the temperature-dependent dielectric plot for both samples. The maximum dielectric constant values of 1475 and 1628 are found for NBT 30 and NBT 40 samples at the transition temperature. From temperature-dependent AC conductivity measurement, NBT 40 samples show a higher value of conductivity in comparison to NBT 30. The PE hysteresis loops confirm the ferroelectric character present in both samples. An improved piezoelectric coefficient is observed with increasing sintering time and is found to be 80 pCN−1 for NBT 40. The optical bandgap of materials is 3.03 and 3.1 eV for NBT 30 and NBT 40, respectively.

Structural, electrical and optical properties of lanthanide-doped Na0·4K0·1Bi0·5TiO3 ceramics

Lead-free Sodium–Potassium Bismuth Titanate (Na0·4K0·1Bi0·5TiO3; NKBT) ceramics doped with rare earth elements (RE: Ho, Pr, Nd, Er, Dy) were synthesized using the solid-state reaction technique. The X-ray diffraction analysis showed that the RE-doped NKBT ceramics crystallize in a pure perovskite phase with R3c as the space group. Interestingly, the doped ceramics exhibited low dielectric losses compared to the undoped NKBT, especially in the high temperature region. The dielectric permittivity of the NKBT-Dy ceramic at high temperatures was treated using the temperature coefficient of capacitance (TCC ± 20% with εstable = 2451 in a wide temperature range of 150 °C–470 °C). In addition, all samples showed higher ferroelectric polarization comparing with pure NKBT. Furthermore, the incorporation of RE3+ ions into the NKBT host lattice led to the luminescence properties in the visible region under different excitation wavelengths. The simultaneous presence of ferroelectric/dielectric and photoluminescence properties makes NKBT-RE a promising candidate for optoelectronic applications.

Unveiling the high-temperature dielectric relaxation and conduction mechanisms in sol-gel derived LaFeO3 modified Sodium Bismuth Titanate ceramics

The lead-free NBT (Na0.5Bi0.5TiO3) ceramics doped with LaFeO3 having general chemical composition (1-x)Na0.5Bi0.5TiO3-(x)LaFeO3, where x = 0 and 0.05 (abbreviated as LFNBT0 and LFNBT5) were synthesized by sol-gel technique. These ceramics were characterized using X-Ray photoelectron spectroscopy to determine the elemental composition and chemical state of the samples whereas impedance spectroscopy was performed to investigate the electrical properties viz. dielectric constant, dielectric loss, impedance, modulus and conductivity over a wide temperature range (300–775 K) along with frequency (1 Hz - 1 MHz). XPS spectra at room temperature revealed the gradual reduction of valence states i.e., Fe3+ to Fe2+ and Ti4+ to Ti3+ resulting in the formation of oxygen vacancies in LFNBT system. A decrease in dielectric constant as well dielectric loss has been observed at room temperature i.e., from 898 to 541 and 0.75–0.25 respectively at 1 KHz frequency with the incorporation of LaFeO3 in the NBT. A phase transition from ferroelectric to para-electric phase is obtained at 583 K and 623 K for LFNBT0 and LFNBT5 respectively. The negative temperature coefficient of resistance (NTCR) behaviour is obtained from the analysis of impedance data. The Cole-Cole plots perceives the grain and grain boundary effect contribution of the materials with the non-Debye type of relaxation which is also confirmed by electric modulus data and aids in understanding of the transport phenomenon. The fitted conductivity data indicated that the conduction in the NBT system is governed by correlated barrier hopping (CBH). XPS analysis and activation energy values obtained from imaginary part of electrical impedance, modulus, and ac conductivity confirmed that the relaxation and conduction processes in LFNBT0 and LFNBT5 ceramics are attribute to the presence of oxygen vacancies.

Tailoring hardness behaviors of BIT-based piezoceramics via doping and annealing strategies

Bismuth titanate (BIT) piezoelectric ceramics are perceived as a strong competitor in high temperature applications. Currently, a mass of work has been done to optimize the electrical performance of the ceramic utilizing different strategies. However, little attention has been paid to the mechanical behaviors of BIT ceramics, especially the research on mechanical hardness behaviors under doping and annealing, limiting the deep understanding for ceramics and its further development of practical applications. In this work, the mechanical hardness behaviors of a type of bismuth titanate-based ceramics [Bi3.96Ce0.04Ti3-xWxNbxO12 (BCTWN)] at different doping contents and selectively annealing temperatures were investigated using nanoindentation and Vickers indentation techniques. The results show that the hardness is strongly dependent doping contents, wherein the samples with smaller grain size and higher density exhibit bigger hardness. For the poled samples, a higher annealing temperature could restore more domain walls and induce more oxygen vacancies in the samples, along with higher elastic recovery and less remanent strain, shedding extra deformation resistance to make sample harder. Moreover, a schematic of defect assistant domain wall pinning mechanism is proposed to further rationalize the enhanced deformation resistance by annealing strategy. This work helps us deep understand the deformation mechanism of BIT ceramics beneath indentation, and provides insight into tailoring mechanical hardness behaviors via doping and annealing strategies.

Structural, Dielectric Properties and Conduction Mechanism of SrBi4Ti4O15 Ceramics

Objectives: 1. To prepare SrBi4Ti4O15 ceramics via solid-state reaction method. 2. To make a systematic investigations on structural and dielectric properties of SBT ceramics. Methods: The structural information of Strontium Bismuth Titanate (SBT) ceramics is examined by X-ray diffraction and Raman spectroscopy techniques. The surface morphology and elemental analysis of SBT ceramic is employed by scanning electron microscope attached with energydispersive X-ray spectroscopy. The dielectric measurements of SBT ceramics were performed using the impedance analyzer HIOKI-3532 LCR meter. Findings: From the X-ray diffraction studies, SBT exhibits a strongest diffraction peak (1 1 9) with the lattice parameters a = 5.428 Å, b = 5.423 Å, and c = 42.146 Å. The diffraction patterns were indexed to the orthorhombic phase. The surface morphology of the samples shows plate-like morphology with a grain size of ~1mm. The temperature-dependent ac conductivity confirms the thermally activated conduction mechanism. The ac conductivity of SBT ceramic was increased from 2.25  10-5 to 7.16  10-4 Ω.m-1 with an increase of frequency from 10 kHz to 1 MHz. The high curie temperature at ~540 ◦C, and low dielectric loss of ~0.031 for SBT ceramics can be appropriate for high-temperature electronic applications. Novelty: SBT ceramic exhibits enhanced electrical conductivity value (7.16  10-4 Ω.m-1)and makes it suitable for electronic device applications. Keywords: Scanning electron microscope; Dielectric constant; Dielectric loss; Conduction mechanism 1; X-ray diffraction

Sintering characteristics of plate-like bismuth titanate ceramics with preferred c - axis orientation for memory storage devices

Bismuth titanate (Bi4Ti3O12) (BIT) has been an attractive material due to its high Curie temperature, large remnant polarization and relatively low processing temperature, making it suitable for piezoelectric, pyroelectric and non-volatile random access memory storage devices. In this present work, polycrystalline textured bismuth titanate ceramics were synthesised by the cost-effective molten salt synthesis method. The effect of sintering conditions on the structural, morphological and dielectric properties have been carried out in detail. The X-ray diffraction studies reveal the formation of the monophasic structure of BIT ceramics with a preferential orientation along the c-axis. It is also noticed that the orientation along the c-axis increases with an increase in sintering temperature. Interestingly, the parameters like crystallite size and micro-strain calculated from the Williamson - Hall method could be tailored as a function of sintering temperature. The microstructural studies carried out using FESEM technique suggested the presence of plate-like morphology of BIT ceramics and subsequently, the elemental mapping analysis used to confirm the uniform distribution of the elements Bi, Ti and O present in the ceramic sample. The Fourier transform infrared and X-ray photoelectron spectroscopic studies have been done to identify the constituent chemical bonds and oxidation states of BIT ceramics. Interestingly, it is noted that the value of the dielectric constant increases with the increase in sintering temperature of BIT ceramics. Furthermore, the high dielectric constant value of 200 obtained at 100 kHz for 950 °C sintered sample could establish this material for the embedded capacitor in memory storage devices.

Influence of excess bismuth oxide on the structural and dielectric characteristics of textured Bi4Ti3O12 ceramics

Bismuth titanate (Bi4Ti3O12), an Aurivillius family of ferroelectric oxide, has been widely investigated due to its large remnant polarization, high Curie temperature, high dielectric constant and relatively low tangent for the application in information memory storage devices. In this work, polycrystalline bismuth titanate ceramics samples with different amounts of excess Bi2O3 (3 and 5 wt%) were prepared using a low temperature, cost-effective molten salt synthesis method. The structural, microstructural and dielectric properties depend on the addition of excess Bi2O3 and the sintering duration of Bi4Ti3O12 ceramics. Moreover, the X-ray diffraction studies revealed the effect of excess bismuth oxide on the formation of preferential orientation along the c-axis. It is also observed that the orientation factor along the c-axis increases with an increase in the sintering duration for different content of bismuth oxide. The morphological studies revealed the oriented plate-like structure of bismuth titanate ceramics associated with the enhanced growth of grains. It is noticed from the EDAX analysis that the addition of excess bismuth oxide compensated the volatilization of bismuth ions in the crystal lattice of Bi4Ti3O12 ceramics. The dielectric property studies have exhibited a high value of dielectric constant (εr ~ 190), and low tangent loss factor (tanδ ~ 0.08) for the optimum bismuth oxide content of 5 wt% added Bi4Ti3O12 ceramics. Hence, we suggest that these materials could be utilized for the high energy storage capacity of non-volatile memory devices.

In-depth understanding of {110}-type domain walls in bismuth titanate ceramics

Bismuth titanate(BIT) ceramics have been widely studied for high temperature applications thanks to their high Curie temperature and large spontaneous polarization. The underlying domain structures play significant roles in regulating the macroscopic properties of ferroelectric materials, while there is only limited knowledge of the domain structures for BIT ceramics until now, substantially bad for the development of BIT-based new materials. In this study, the intriguing domain walls(DWs) in BIT ceramics were investigated in detail. The atomic-scale observation reveals that there primarily exist energetically favorable {110}-type 90° DWs in BIT ceramics. Combined with the theoretical analysis, these DWs are not only elaborated under multiple piezoelectric response modes, but also further corroborated by the quantitative reconstruction of spatial polarization distributions of twin-related ferroelectric variants. This work sheds insight into domain structure and piezoelectric response mechanism in BIT ceramics, and contributes to promoting their more applications in advanced electron devices.

Distorted Lattice Structure of La and Nd Co-Doped Bismuth Titanate Bi3-XTi4O12 Nano-Grained Ceramics for High Quality Energy Storage Application

Capacitive energy storage technology becomes more popular due to the fast charging facilities. Bismuth titanate (BIT) is a lead-free ferroelectric material used as a dielectric medium in the capacitive energy storage system. La and Nd co-doped BIT has been synthesized through a solid-state reaction process to obtain improved dielectric properties. Various characterization technologies such as Fourier Transform Infrared (FTIR) and X ray diffraction (XRD) have been done to sure the reaction completion and absence of the impurity phase of BIT. Rietveld refinement of XRD has been carried out to investigate the crystal structural properties of La and Nd-doped BIT. Capacitive energy storage performances have been tested by measuring the parallel plate capacitance and quality factor of BIT ceramics. Co-doped BIT possesses the highest crystal density, which results in a high Q factor. The unit cell of the TiO6 octahedral of BIT becomes highly distorted as a consequence of La and Nd co-doping, which increases surface polarization, and the capacitance of BIT increases.

Modelling of Dielectric Studies on Rare-Earth Substituted Strontium Bismuth Titanate Using Modified Lorentz Equation

Samarium, Sodium modified Strontium Bismuth Titanate ceramics were prepared using solid-state sintering approach. Calcined powders obtained after treatment at 800 °C for 120 min were pressed into1 cm diameter and 1 mm thick pellets using uniaxial hydraulic press. These pellets were sintered at 1160 °C for 120 min in a programmable furnace. XRD studies confirmed single-phase Orthorhombic structure and SEM micrographs identified the sheet-like grain formation with no preferred alignment. Dielectric data was matched with modified Lorentz equation to ensure the reliability of the obtained experimental results. The activation energies (Ea) of samples were found to be in the range 70–85 μeV.

Effect of neodymium and zirconium substitution on electrical properties of SrBi4Ti4O15

Neodymium and zirconium modified strontium bismuth titanate ceramics with content changing from 2.5 to 10 at% Nd and a 2.5 at% Zr of SrBi4Ti4O15 (SrNdxBi4-xZryTi4-yO15, (x = 0.00, 0.025, 0.05, 0.075, and 0.1, y = 0.00 and 0.025) have been prepared by solid state reaction method and analyzed by X-ray diffraction (XRD), dielectric response, ferroelectric hysteresis, electromechanical coupling coefficient, and piezoelectric charge coefficient. From hysteresis loop, the remnant polarization and coercive field were calculated and explained. Dielectric analysis explained the sample behavior. Piezoelectric charge and electromechanical coupling coefficients were found to be increased with the addition of Zr and Nd.

Enhanced electrical and photocatalytic activities in Na0.5Bi0.5TiO3 through structural modulation by using anatase and rutile phases of TiO2

This paper deals with an in-depth analysis on the role of the microstructure phase of titanium dioxide (TiO2) precursor in sodium bismuth titanate (Na0.5Bi0.5TiO3, hereafter represented as NBT) ceramics prepared through the hydrothermal method. The comparison of the grain size, microstructure, crystal structure, and electrical properties of the NBT ceramics is carried out using anatase and rutile TiO2. NBT ceramics with anatase TiO2 (denoted by NBTA) displayed superior dielectric and ferro/piezoelectric properties along with the additional functionality in terms of photocatalysis. Systematic studies of functional properties such as piezoelectric, ferroelectric, and dielectric stressed the far-reaching influence of effects on grain size. The mechanisms and functional properties of grain quantitative effects are also discussed. Grain boundaries volume fraction increment has decreased the dielectric peak but increased the diffusiveness in the case of the NBT with rutile TiO2 precursor (denoted as NBTR). Similarly, elastic stiffness increment restricts the movement of the domain wall and led to a decrement in remnant polarization along with an increase in the values of the corresponding piezoelectric coefficient in fine-grain NBTR samples.

Bismuth titanate based piezoceramics: Structural evolutions and electrical behaviors at different sintering temperatures

Bismuth titanate piezoceramics are considered as the most promising candidate for high temperature applications, and its multi-functional properties such as dielectricity, piezoelectricity, ferroelectricity, and so forth have been widely studied for several decades. Nevertheless, it still lacks of the systematically research on sintering temperature dependent electrical behaviors of bismuth titanate ceramics, and more importantly, to date there is no report on lattice distortion and domain evolution at different sintering temperatures for the ceramics as well, substantially bad for deep understanding the ceramics and limiting its further applications. Here, a type of bismuth titanate based ceramics (Bi3.96Ce0.04Ti2.97W0.015Nb0.015O12, abbreviated as BCTWN) was prepared by traditional solid-phase reaction technology, and the effects of sintering temperature on the multiple microstructures and electrical properties for BCTWN ceramics were investigated in details. The results show that oxygen octahedral rotation primarily determines the lattice distortion of pseudo-perovskite layer, and domain structures are composed of 90° and 180° domains. The higher sintering temperature generates more distorted crystal structure and induces larger domain size and fewer domain wall density. The grain features and defect dipole distribution are also significantly affected by sintering temperature, thus yielding the distinct electrical behaviors. This research sheds insight in micro-mechanism of optimizing electrical properties, and contributes to expanding more applications for bismuth titanate ferroelectrics.