Mixed Oxide Method Research Articles

Grain engineering inducing high energy storage in CdCu3Ti4O12 ceramics

ACu3Ti4O12-type (ACTO) perovskite ceramics with colossal permittivity always display a low energy storage density since its low breakdown field strength (Eb). In this work, we designed an effective grain engineering strategy achieving a high energy storage density in CdCu3Ti4O12(CdCTO) ceramics via a mixed oxides method based on sol-gel technique. Al2O3 was selected as grain engineering dopant enhancing Eb for achieving the high energy storage density of CdCTO ceramics. Remarkably, at an Al2O3 doping level of 3.0 wt%, a decent dielectric energy storage performance with a high nonlinear coefficient (α) ~ 4.98 and energy storage density (η) ~ 1.52 mJ/cm3 was obtained in CdCTO-3.0 wt% Al2O3 ceramic. Besides, enhanced Eb is strongly associated with the decreased grain size that induced upon Al2O3 doping. This work not only proposes an effective strategy enhancing Eb but also provides new ideas for how to simultaneously achieve a high permittivity and high energy storage density in ACTO dielectric materials.

Electric field-induced strain in Sr(Hf0.5Zr0.5)O3-modified Bi0.5(Na0.8K0.2)0.5TiO3 piezoelectric ceramics

Lead-free Sr(Hf0.5Zr0.5)O3-modified Bi0.5(Na0.8K0.2)0.5TiO3 (SHZ-BNKT) ceramics were synthesized using a conventional solid-state, mixed-oxide method. In complex solid solutions such as BNKT, the role of a ternary additive is important because it can break up the long-range dipole order, which destabilizes the ferroelectric phase leading to relaxor behavior. In this system, as verified by x-ray diffraction, SHZ was incorporated into the BNKT perovskite lattice throughout the studied compositional range. The coexistence of tetragonal and rhombohedral phase was observed for x = 0.00 and with the addition of SHZ, a transition to pseudocubic symmetry was observed, which is indicative of the onset of relaxor behavior. To characterize the relaxor properties of the material, the polarization–electric field hysteresis, dielectric, and electric-field-induced strain behaviors were studied as a function of composition. The temperature-dependent dielectric spectra showed frequency dependence for all the SHZ-modified BNKT ceramics, which is a typical characteristic of relaxor ferroelectrics. Furthermore, constriction in polarization loops and an absence of negative strain in the bipolar strain measurement for SHZ-modified BNKT compositions confirms that the addition of SHZ significantly disrupts the ferroelectric order. The addition of 2 mol. % SHZ in BNKT markedly enhanced the electric field-induced strain from 0.10% (for pure BNKT) to 0.33% (for 2% SHZ-BNKT). The corresponding normalized strain coefficient (d33∗=Smax/Emax) increased from 196 pm/V to 663 pm/V at a moderate electric field of 50 kV/cm. These results indicate that BNKT–SHZ ceramics can be designed for an improved strain response via a cation substitution-induced relaxor state for electromechanical actuator applications.

Chemical and Physical Properties of the BLT4 Ultra Capacitor-A Suitable Material for Ultracapacitors.

This paper describes the properties of a lead-free ceramic material based on barium titanate, designed for the construction of ultracapacitors and sensors used in mechatronic systems. The admixture of lanthanum (La3+) served as a modifier. The ceramic powders were obtained by the solid phase reaction method (conventional method—mixed oxides method—MOM). Technological conditions of the synthesis process were determined on the basis of thermal analysis. The obtained samples are characterized, at room temperature (Tr < TC), by a single-phase tetragonal structure and a P4mm space group. Properly developed large grains (d = 5 µm) contributed to the increase in electric permittivity, the maximum value of which is at the level of εm ≈ 112,000, as well as to a strong decrease in specific resistance in the ferroelectric phase, whereas above the Curie temperature, by creating a potential barrier at their boundaries, there was a a rapid increase in resistivity. The temperature coefficient of resistance of the obtained posistor is 10.53%/K. The electrical properties of the obtained ceramics were examined using impedance spectroscopy. In order to analyze the obtained results, a method of comparing the behavior of the real object and its replacement system in a specific frequency region was used, whereas the Kramer–-Kroning (K–K) test was used to determine the consistency of the measured data. The proper selection of the stoichiometry and synthesis conditions resulted in the creation of an appropriate concentration of donor levels and oxygen gaps, which in turn resulted in a significant increase in the value of electrical permittivity, with small values of the angle of dielectric loss tangent. This fact predisposes the discussed material for certain applications (in the construction of ultracapacitors, among others).

Dielectric and Frequency Dependent Transport Properties of Gadolinium Doped Bismuth Ferrite

Ceramics of (Bi1−xGdxFeO3) [x = 0.5, 0.6 and 0.7] were synthesized through mixed oxide method. Structural studies of the ceramics were done using X-ray diffraction technique. At high frequency, nearly flat response in the dielectric constant and dielectric loss with temperature up to 200 °C were observed. Dielectric constant found to increase with decrease in Gadolinium concentration. Frequency dependent electrical data analysis at different temperatures suggested a temperature dependent non-Debye type relaxation process in the ceramics. Frequency dependence AC conductivity at different temperatures obeyed Jonscher’s universal power law. The temperature dependence of DC and AC conductivity was fitted with Arrhenius equation. The activation energies at different temperature ranges were calculated to understand the conduction process.

Synthesis and dielectric spectroscopic study of lead-free ferroelectric ceramic K0.5Bi0.5TiO3-NaNbO3

We report the synthesis and promising electrical properties of a new lead-free ferroelectric ceramic K0.5Bi0.5TiO3-NaNbO3 (KBT-NN), which can be a candidate of choice for future sensors, FeRAM etc. Mixed-oxide method has been employed to prepare the compound comprising of uniformly distributed grains. Detailed structural analysis revealed its orthorhombic structure with space group Pmc21. In-depth analysis of the electrical characterization data revealed a band-gap of 3.11 eV and presence of defects in the bands. Further, ferroelectric phase transition is observed to occur at 395 °C. The dielectric properties of the material, investigated over a wide range of frequencies and temperatures, indicate that its ac conductivity depends upon frequency according to Jonscher’s power law.

Influence of Al2O3nanoparticle doping on depolarization temperature, and electrical and energy harvesting properties of lead-free 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3ceramics

In this research article, the effects of Al2O3 nanoparticles (0–1.0 mol%) on the phase formation, microstructure, dielectric, ferroelectric, piezoelectric, electric field-induced strain and energy harvesting properties of the 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3 (BNT–6BT) ceramic were investigated. All ceramics have been synthesized by a conventional mixed oxide method. The XRD and Raman spectra showed coexisting rhombohedral and tetragonal phases throughout the entire compositional range. An increase of the grain size, TF–R, Tm, εmax and δA values was noticeable when Al2O3 was added. Depolarization temperature (Td), which was determined by the thermally stimulated depolarization current (TSDC), tended to increase with Al2O3 content. The good ferroelectric properties (Pr = 32.64 μC cm−2, Ec = 30.59 kV cm−1) and large low-field d33 (205 pC N−1) values were observed for the 0.1 mol% Al2O3 ceramic. The small Al2O3 additive improved the electric field-induced strain (Smax and ). The 1.0 mol% Al2O3 ceramic had a large piezoelectric voltage coefficient (g33 = 32.6 × 10−3 Vm N−1) and good dielectric properties (εr,max = 6542, Td = 93 °C, TF–R = 108 °C, Tm = 324 °C and δA = 164 K). The highest off-resonance figure of merit (FoM) for energy harvesting of 6.36 pm2 N−1 was also observed for the 1.0 mol% Al2O3 ceramic, which is suggesting that this ceramic has potential to be one of the promising lead-free piezoelectric candidates for further use in energy harvesting applications.

Improving dielectric properties of Zn2(Ti0.88Sn0.12)O4 ceramics by using molten-salt method to optimize the microstructure

Zn2(Ti0.88Sn0.12)O4 samples were synthesized by a mixed-oxide reaction method (abbreviated as MO) and a molten-salt method (abbreviated as MS), respectively. The effects of preparing method on the phase-structures, microstructure, and the dielectric properties were systematically discussed. The results show that the MS ceramics have a cubic spinel structure and the MO ceramics have a tetragonal crystal structure. The MS ceramics are composed of more angular and homogeneous grains compared with that of the MO samples. Grain growth of two kinds of ceramic was studied. The results show that the grain growth of MO ceramics exhibits grain boundary diffusion and surface diffusion mechanisms, while MS ceramics exhibits lattice diffusion or evaporation/condensation mechanisms. The MS ceramics are found to have lower apparent activation energy. Densification and homogeneous microstructure play a more important role in controlling the dielectric properties. Therefore, the MS ceramics exhibit better dielectric properties by optimizing the microstructure.

Properties of NaCu3Ti3NbO12 based-ceramics doped with nanopowders

In this work, the properties of NaCu3Ti3NbO12 based ceramics preparing by mixed oxide method were studied. The starting materials including Na2CO3, CuO, TiO2 and Nb2O5 were mixed by ball milling for 24 hours with stoichiometry, calcined at 950 °C for 24 hours and were doped with (0–2.0 vol%) MgO, Al2O3 and ZrO2 nanopowders. Then, the mixed powder was pressed into a disc shape. The green bodies were sintered at 975–1025 °C for 10 hours. Phase formation was investigated by XRD and microstructure by SEM. The body-centered cubic perovskite-related structure of space group Im-3 and small amount of second phase were detected. The normal grain growth is observed and shown rectangular grain shape. Density of the sintered samples was measured by Archimedes’s method using distilled water as the fluid medium. The highest density of NCTNO and NCTNO/Al2O3 ceramics were found at 1025 °C sintered temperature and 1000 °C for NCTNO/MgO and NCTNO/ZrO2 samples. Dielectric constant of the samples was examined using an LCR meter and the mechanical properties of samples were investigated by Vickers microhardness tester. The addition of nanopowders can be improved the mechanical property and 1.0 vol%ZrO2 doping sample showed the highest the dielectric constant.

Local structure and evolution of phase transformation in Bi0.4871Na0.4871La0.0172TiO3–BaTiO3 materials

Lead-free bismuth sodium lanthanum titanate and barium titanate (Bi0.4871Na0.4871La0.0172TiO3–BaTiO3; ((1-x)BNLT-xBT) ceramic system, where x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10, were synthesized by a modified two-step mixed oxide method. The global structure was investigated by X-ray diffraction (XRD), while the local structure was elucidated by X-ray absorption near edge structure (XANES). The XRD results indicated a rhombohedral perovskite crystal structure for x < 0.04 and a tetragonal perovskite crystal structure for x ≥ 0.04. The Ti K-edge XANES spectra indicated a change in local structure around the Ti atom, which corresponds to an evolution of phase transition from rhombohedral to tetragonal structure in BNLT-BT system with increasing BaTiO3 content. A comparison between the measured and simulated spectra was obtained and discussed in details.

Structural, dielectric, impedance, and modulus spectroscopy of BaSnO3-Modified BiFeO3

A BaSnO3-modified BiFeO3 compound (i.e., Bi0.95Ba0.05Fe0.95Sn0.05O3) was synthesized by a cost-effective mixed-oxide reaction method at 850 °C. The solubility of 5% BaSnO3 in BiFeO3 (BFO) and the formation of a single-phase compound in the rhombohedral structure was checked by the Rietveld refinement method using the X-ray diffraction data. The analysis of Fourier transform infrared (FTIR) spectra reconfirmed the formation of the compound. The temperature-dependent dielectric spectrum for the sample exhibits a broad anomaly at 190 °C, which seems to be the superposition of three Gaussian peaks corresponding to the Maxwell–Wagner effect, as well as the oxygen-vacancy-induced Fe2+/Fe3+ and Sn2+/Sn4+ redox mechanism. A sharp peak at 350 °C corresponds to the magnetic reordering around the Néel temperature. Complex impedance spectroscopy along with modulus analysis confirmed the deviation from Debye-type behavior. The Cole–Cole model was used to resolve the components contributing to the loss tangent. Different models of electrical conduction were used to explain the conduction mechanism in the material. The existence of ferroelectricity in the sample was confirmed from the study of the room-temperature P–E loop. The addition of 5% BaSnO3 to BFO resulted in a 10-fold increase in the dielectric constant and the polarization accompanied by reduced tangent loss, making it attractive for device applications.

Effect of Titania Doping on Structural and Mechanical Properties of NiO/YSZ Anode Materials Sintered by Using Microwave Energy

The current article presents first-hand work on the synthesis of nickel oxide–titania-doped yttria-stabilized zirconia (NiO-YZT) composites of composition 0.40NiO-0.60{[(ZrO2)0.92(Y2O3)0.08]1−x(TiO2)x} with x = 0.00, 0.03, 0.06, 0.09, 0.12 and 0.15 using microwave processing. The composites are prepared by mixed oxide method by taking yttria (Y2O3), titania (TiO2) and monoclinic zirconia (ZrO2) in their stoichiometric ratio and sintered by using conventional and microwave processing techniques. The investigation of prepared composites has been carried out by x-ray diffractometer, scanning electron microscope and Vickers hardness technique to probe the crystal structure, microstructure and mechanical properties. Also, the results obtained are compared for both the conventionally and microwave-sintering routes. It was inferred that the microwave-sintered NiO-YZT showed better results than the conventional samples in terms of greater density, uniform microstructure and better microhardness.

Comparison of microwave and conventionally sintered manganese and niobium doped lanthanum germanate based apatites by micro Raman Spectroscopy

In this paper, the effect of microwave and conventional sintering on doping behaviour of Mn2+ and Nb5+ in lanthanum germanate based apatite have been compared. The precursor of apatite has been prepared by mixed oxide method and conventionally calcined at 1100 °C for 6 h. The resulting powders have been sintered by microwave energy at 1400 °C for 30 min and by conventional heating 1400 °C for 4 h. The products prepared have been characterized by X-ray diffraction, scanning electron microscope, Micro Raman spectroscopy, and Vicker's hardness and the results are compared. The apatites of similar compositions sintered by microwave energy have higher density and hardness than the apatites sintered by electric heating.

Synergistic effect of terbium and calcium ions on the temperature stability and dielectric loss of BaTiO3-based ceramics

To improve permittivity-temperature stability for BaTiO3 ceramics containing terbium dopant, a new dielectric system (Ba1–xTbx)(Ti1–x/2Cax/2)O3 (x = 0.01–0.20) (BTTC) was prepared at 1400 °C using the conventional mixed-oxide method. The solubility limit of Tb/Ca in BTTC was determined by XRD to be x = 0.12 and BTTC exhibited tetragonal perovskite structures. An abnormal phenomenon was discovered that with increasing x from 0.01 to 0.04 the dielectric peak associated with the orthorhombic-tetragonal phase transition point shifted to low temperatures. The mixed valence states of Tb3+/Tb4+ and mixed A and B occupancy of Tb/Ca2+ in the perovskite lattice were confirmed. BTTC with x = 0.03 and 0.04 satisfied X5R and X4P specifications, respectively, and exhibited some advantageous properties such as higher relative density (ρr = 91 and 93%), lower loss (tan δ = 0.016 and 0.014), higher permittivity (ε′RT = 1820 and 1360), and frequency stability in the range of 1–107 Hz. The point defect chemistry is discussed and the real formula of BTTC is suggested. By comparing BaTiO3 ceramics containing Tb or co-doped with Tb and other rare-earth ions (La, Dy) in many existed works in the dielectric field, the synergistic effect of Tb and Ca in BaTiO3 is more significant and helpful to improve the temperature stability of Tb-related BaTiO3 ceramics or to reduce the dielectric loss in the working temperature region. A small number of B-site Tb4+ in BTTC played a decisive role in the low dielectric loss.

Structural, optical and impedance spectroscopic studies of lead-free 0.2(K0.5Bi0.5TiO3)–0.8(NaNbO3) solid solution

Polycrystalline, lead free ceramic, 0.2(K0.5Bi0.5TiO3)–0.8(NaNbO3) is prepared by high temperature mixed oxide method. Experimental studies reveal the structural and vibrational and ferroelectric properties of the ceramic. The micro structural study exhibits that small grains are distributed uniformly throughout the surface with well-defined grain boundaries and few pores. The structural analysis illustrates that the compound is formed exhibiting the structure as orthorhombic at room temperature with space group Pmc21. While adding the NaNbO3(NN) on K0.5Bi0.5TiO3 (KBT), the vibrational phonon modes undergoes a notable change, as envisaged from the FTIR spectra. From the diffuse absorbance spectra, the optical band gap is found as 3.14 eV and useful for photo catalytic application. Raman spectra exhibit different vibrational modes in the frequency ranging from 130 to 900 cm−1. Polarization study confirms the presence of ferroelectricity. Dielectric analysis infers that phase transition temperature from ferroelectric to paraelectric is observed around 500 °C. The electrical parameters related to microstructure are reflected from impedance analysis. The frequency dependent ac conductivity depends upon frequency validating Jonscher’s power law. While increasing temperature, ac conductivity increases which represents the semiconducting nature of the sample. The bulk conductivity is found to be driven by thermally activated process following Arrhenius relation.

Excellent electric field-induced strain with high electrostrictive and energy storage performance properties observed in lead-free Bi0.5(Na0.84K0.16)0.5TiO3-Ba(Nb0.01Ti0.99)O3-BiFeO3 ceramics

In this research, ceramics with a high electromechanical strain based on the composition (1-x)[0.97Bi0.5(Na0.84K0.16)0.5TiO3-0.03Ba(Ti0.99Nb0.01)O3]-xBiFeO3 or (1-x)[BNKT-0.03BNbT]-xBFO (with x = 0, 0.03, 0.05, 0.07, and 0.09 mol fraction) were investigated. All compositions were synthesized via a conventional solid-state mixed oxide method. The effects of the addition of BFO on the phase structure, dielectric, ferroelectric, and piezoelectric properties and electric field-induced strains behavior of BNKT-0.03BNbT ceramics were systematically studied in this work. X-ray diffraction (XRD) analysis revealed that all ceramics exhibited a pure perovskite structure. The coexistence of rhombohedral (R) and tetragonal (T) phases was observed for all compositions. The electric field-induced strain increased with increasing BFO content and attained a maximum value of Smax = 0.65% and d*33 = 1161 pm/V (@40 kV) for the composition x = 0.05 at room temperature (RT). The bipolar strain behavior exhibited minimal asymmetry and a low driving electric field. The composition also exhibited a high electrostrictive response (Q33 ∼ 0.039 m4/C2). In addition, the x = 0.09 composition showed excellent energy storage properties, with an energy storage density of 0.91 J/cm3 at 125 °C, high normalized energy storage density (∼0.14 μC/mm2), thermal stability (7% for 75-150 °C) and energy storage efficiency (η = 87% @125 °C). These results suggest that the (1-x)[BNKT-0.03BNbT]-xBFO ceramics are promising as lead-free piezoelectric material candidates, and are also suitable for both actuator and high temperature energy storage applications.

The influence of in situ thermal treatment on electric properties of BaBi2Nb2O9 ceramics

The chemical composition as well as impedance spectroscopy were investigated for BaBi2Nb2O9 ceramics obtained by conventional mixed oxides method, before and after the sample was thermally treated (for 1 h) in an ultra-high vacuum (5 × 10−11 bar) at the temperature of 900 °C. The obtained results indicate the loss of stoichiometry as a result of applied thermal treatment, and lead to conclusion, that the chemical formula of the obtained material should be determined as BaBiNb2O9-x. The suggested formula emphasises the oxygen deficiency due to Bi–O saturated precipitate, along with lack of barium ions at the surface of the sample, and has major influence on material's electric properties.

Dielectric, impedance and modulus spectroscopy of Ta-based layered perovskite

ABSTRACTPbBi2Ta2O9 ceramic samples were fabricated by high-temperature mixed oxide method. X-ray diffraction determines the structure as orthorhombic. The scanning electron microscopy confirms the formation of densely packed grains in the sample. The dielectric measurements, complex impedance and complex modulus study were carried out in a frequency range of 1 kHz–1 MHz and a temperature rangeof 25–500°C. The conduction mechanism of the material is discussed in details using variable range hoping, nearest neighbor hopping relaxation model and dc activation energy at two different temperature regimes. From the J-E characteristics studies, the occurrence of non-linear curves endorses the non-Ohmic nature of the material.

Development and excitation performance of lead free electronic material: Eu and Fe doped Bi0.5Na0.5TiO3 for filter application

The polycrystalline samples with chemical formula Bi0.49Na0.49Eu0.02Ti0.98Fe0.02O3 (BENFTO-2 abbreviated ahead), Bi0.48Na0.48Eu0.04Ti0.96Fe0.04O3 (BENFTO-4 abbreviated ahead) and Bi0.47Na0.47Eu0.06Ti0.94Fe0.06O3 (BENFTO-6 abbreviated ahead) have been processed using a mixed oxide method. The refinement of XRD data suggests that all prepared materials exhibit tetragonal crystal system with perovskite structure. The surface morphology denotes a high density of grain growth without any cracks. This finding can contribute to grain and grain boundary associated with resistive and capacitive characteristics. The impedance and modulus are performed at various temperatures and frequencies in order to discern the relaxation as well conduction mechanism in these samples. The non-Debye dielectric relaxation is confirmed by the complex impedance formalism in all the composition. The activation energies are estimated from the AC conductivity versus inverse temperature according to the Arrhenius equation. The excitation of materials is investigated by application of a generated electric waveform. The application of series RC filter highlights Eu and Fe doped Bi0.5Na0.5TiO3 as a base for device engineering.

The dielectric property and phase transition of Sr‐doping effect of Ba1−xSrxTi0.9Mn0.1O3‐δ ceramic

AbstractIn this work, we prepare Ba1−xSrxTi0.9Mn.01O3‐δ (x = 0.00, 0.01, 0.03, 0.05, and 0.07) ceramics by the mixed oxide method and study the relationship between phase transition and dielectric property of the ceramics. The phase of the samples transformed from a hexagonal phase to mixed phases due to the increase in Sr doping amount. The X‐ray diffraction (XRD) profiles and Raman spectra of the samples also show the same phase transformation due to increasing Sr doping amount. The XRD pattern of the undoped sample indicates a single h‐BaTiO3 phase with P63/mmc symmetric space group, while the samples with high Sr doping amounts have a mixed phase with t‐BaTiO3 with P4mm symmetric space group. The scanning electron microscopy images show two types of BaTiO3 grains, which grew with increasing sintering temperature. With increasing Sr concentration, the K‐values (relative dielectric constant) of the ceramics increased, while the Qxf values (the quality factor multiplied by frequency) decreased, which indicate that the microwave dielectric property is related to phase transformation.

The Influence of Various Dopants and Sintering Techniques on the Properties of the Yttria-Ceria-Zirconia System As an Electrolyte for Solid Oxide Fuel Cells

Zirconia-based ceramic oxides Zr0.90Y0.06Ce0.02X0.02O2−δ (X = Ca, Fe, La, Sr, and Mg) were prepared by conventional and microwave processing. The precursors of Zr0.90Y0.06Ce0.02X0.02O2−δ (X = Ca, Fe, La, Sr, and Mg) were prepared by a mixed oxide method and were calcined at 600°C in an electric furnace. The powders were consolidated in pellet form and sintered in a conventional electric furnace at 1400°C for 6 h and compared using microwave energy at 1400°C for 20 min. The structure and microstructure of sintered products obtained by both methods were studied by x-ray diffraction and scanning electron microscopy. Their density and microhardness were also compared. The electrical conductivities of these samples were studied using alternating current impedance spectroscopy. The analysis of the products obtained by microwave aand conventional methods shows that the microwave sintered samples have uniform grain growth, higher density, higher microhardness and higher electrical conductivity than the corresponding conventionally sintered products. The microwave sintered sample of composition Zr0.90Y0.06Ce0.02Ca0.02O2−δ was found to have the highest density and microhardness, as well as the highest electrical conductivity among all of the microwave and conventionally sintered products.