Conventional Mixed Oxide Method Research Articles

Effect of WO3 loading on structural, electrical and dielectric properties of CaCu3Ti4O12 ceramic composites

CaCu3Ti4O12–xWO3 (CCTO–xWO3) (x = 5, 10, 15, 20 wt%) ceramic composites were synthesized using conventional mixed oxide method. The effect of various amounts of WO3 loading on its microstructure, electrical and dielectric properties of CCTO ceramic composites were studied using XRD, FESEM-EDAX, Hall effect and dielectric measurement. XRD analysis revealed that the CCTO–xWO3 ceramic composites have cubic structure and WO3 loading had no effect on its crystal phase structure. The FESEM analyses showed that the samples had a porous structure. It is noted that the porosity of CCTO films increased from 2.97% to 6.11% with 20% wt. WO3 loading. Also, the electrical resistivity and dielectric permittivity of CCTO ceramics was reduced with increasing WO3 loading. Particularly, the CCTO–20 wt% WO3 ceramic composites exhibited the lowest electrical resistivity (81 Ω cm) and dielectric permittivity (486 measured at 1 kHz) but the highest dielectric loss (0.6 measured at 1 kHz). These results have practical implication for fabrication and optimizing of CCTO ceramics for low power loss microelectronics.

Giant dielectric response, electrical properties and nonlinear current-voltage characteristic of Al2O3-CaCu3Ti4O12 nanocomposites

In this work, xAl2O3-(1 − x)CaCu3Ti4O12, where x = 0, 2, and 10 vol%, nanocomposites were prepared by a conventional mixed oxide method using Al2O3 nanopowders with particle sizes of ≈20–40 nm. The giant dielectric properties, electrical responses and nonlinear characteristics of Al2O3-CaCu3Ti4O12 nanocomposites were investigated. Interestingly, the (2 vol%)Al2O3-CaCu3Ti4O12 ceramic exhibited significantly improved dielectric properties with large dielectric constant and low loss tangent values of about of 2.0 × 104 and 0.038, respectively. The nonlinear current-voltage properties of CaCu3Ti4O12 ceramics were also enhanced by the addition of Al2O3. X-ray photoelectron spectroscopy technique was used to confirm the existence of Cu+, Cu3+ and Ti3+ ions in the composite ceramics, indicating the primary cause of the conduction mechanism inside the grains. The first principle calculation was performed to predict the most possibility of site preference of Al ion in CCTO lattice structure. The improved dielectric and nonlinear electrical properties can be well explained based on the internal barrier layer capacitor effect, resulting from the improved electrical properties of internal interfaces.

Effect of Nb, Ta and Sb Addition on Structure and Electrical Properties of PZT Ceramics

Abstract In this study, the effect of Nb, Ta and Sb addition on the structure, dielectric and ferroelectric properties of the Pb(Zr0.5Ti0.5)O3 ceramics in the morphotropic phase boundary (MPB) region were investigated. Powders of pure PZT, PZT + 0.1 mol% Nb, PZT + 0.1mol% Ta and PZT + 0.1mol% Sb were synthesized by conventional mixed oxide method via a vibro-milling technique. All compositions of powders were uniaxially pressed in pellets and sintered at the temperature of 1275°C for 2h. Phase formation, dielectric and ferroelectric properties of ceramics were characterized by XRD, LCR meter and modified Sawyer–Tower Circuit respectively.

The role of TiO2 on the microstructure and the electrochemical behavior of Ce0.8Gd0.2O2-δ for solid oxide fuel cell electrolyte

Ce0.8Gd0.2O2-δ (GDC) with various TiO2 contents was prepared by a conventional mixed oxide method. The effects of doping the ceramic solid electrolyte (GDC) with titanium oxide were investigated with regard to crystal structure, microstructure, electrical property and fuel cell performance. The XRD analysis revealed the existence of a phase comprising a cubic fluorite structure. Above 2 mol% TiO2 a second phase as Gd2Ti2O7 was found. TiO2 promoted grain growth of the ceria ceramics. The grain boundary (GB) conductivity of GDC-TiO2 composite was increased by a small addition of TiO2. The maximum power density was achieved by the cell with GDC-1mol%TiO2 as electrolyte.

Effects of preparation method on the microstructure and electrical properties of tungsten bronze structure Sr2NaNb5O15 ceramics

Herein, Sr2NaNb5O15 (SNN) ceramics with a filled tungsten bronze structure were synthesized by the various methods of conventional mixed-oxide (CMO), two-step sintering (TSS), reactive sintering (RS) and molten salt synthesis (MSS). It was found that varying the preparation method could result in significant differences in the ceramic morphology, relative density, and electrical properties. The TSS, RS and MSS methods all produced a pure tungsten bronze phase SNN ceramic, though the CMO method could not. Further characterization revealed a sharp drop in the Curie temperature and significant deterioration of the dielectric properties in the ceramics prepared by MSS compared to the other methods, likely owing to residual K+ from the molten salt. Systematic comparison of the electrical properties of the ceramics produced by the RS and TSS method found that the RS method was the most suitable preparation method for SNN ceramics. The superior ferroelectric and piezoelectric properties in the sample produced by the RS method were attributed to the highly distorted NbO6 octahedron, as suggested by Raman spectroscopy.

Pyroelectric and Piezoelectric Properties of (1-x)Na0.5K0.5NbO₃-xBiScO₃ Lead-Free Ceramics.

In this research, the pyroelectric and piezoelectric properties of (1 - x)Na0.5K0.5NbO3-xBiScO3 ceramics were investigated and analyzed. (Na, K)NbO3 based (1 - x)Na0.5K0.5NbO3-xBiScO3 ceramics were prepared by a conventional mixed oxide method. As the substituent, BiScO3 material enhanced the sintering mechanism of NKN ceramic, which improved the density, pyroelectric and piezoelectric properties, without any structural distortion. In this study, the structural dependent improved piezoelectric properties of (1 - x)Na0.5K0.5NbO3-xBiScO3 ceramics were investigated with various sintering temperatures. Also, the pyroelectric properties of (1 - x)Na0.5K0.5NbO3-xBiScO3 ceramics were observed up to 200 °C for the devices applications. The crystalline structures of the (1-x)Na0.5K0.5NbO3-x BiScO3 ceramics were measured by X-ray diffraction (XRD). The microstructure was examined by field emission scanning electron microscopy (FE-SEM). In addition, piezo-electric charge coefficient d33 and pyroelectric coefficient will be discussed.

Excellent piezoelectric properties and high Tc in Fe2O3-doped PMW-PNN-PZT ceramics

In this work, in order to develop piezoelectric ceramics sintered at low temperature with high piezoelectric d31 coefficient, Pb(Mg1/2W1/2)0.03(Ni1/3Nb2/3)0.09(Zr0.5Ti0.5)0.88O3 ceramics were fabricated as a function of the amount of Fe2O3 addition using a conventional mixed oxide method. The microstructure, dielectric and piezoelectric properties were systematically investigated as a function of amount of Fe2O3 addition. At the sintering temperature of 920 °C, the excellent values of density = 7.94 (g/cm3), piezoelectric coefficient (d31) = 246 pC/N, planar electromechanical coupling coefficient (kp) = 0.69, mechanical quality factor (Qm) = 213, dielectric constant (εr) = 2,682 and high Curie temperature =366 °C were obtained from the ceramics doped with 0.3 wt% Fe2O3, respectively.

Dielectric, conductivity and piezoelectric properties in (0.67-x)BiFeO3-0.33BaTiO3-xSrZrO3 ceramics

A new type of (0.67-x)BiFeO3-0.33BaTiO3-xSrZrO3 (x = 0.00, 0.02, 0.04, 0.06, 0.08 wt%, abbreviated as SZ100x) ternary lead-free relaxation ceramic was prepared by a conventional mixed-oxide sintering method. The surface texture, dielectric, impedance, electrical conductivity and piezoelectric were studied in detail. It was found that three kinds of compounds are completely dissolved into a single structure with a pseudo-cubic (Pc) phase. Besides, scanning electron microscopy figures indicated that proper doping can make the ceramic system more compact while excessive SrZrO3 content would cause abnormal growth of the grain. In addition, the analysis of dielectric temperature spectra shown that the dielectric peaks gradually widen with an increase in x and the x = 0.04 sample has the strongest relaxation characteristics. Importantly, doping of SrZrO3 can greatly improve the impendence and electrical insulation characteristics. Besides, high strain value of 0.24% with the normalized strain value of 400 pm/V was obtained at x = 0.04, which was related to the relaxation response of the polar nanoregion under electric field.

Structure and microwave dielectric properties of Zn0.9Mg0.1TiO3–Zn0.15Nb0.3Ti0.55O2 ceramics with ZnO–B2O3–SiO2 glass

(1 − x)Zn0.9Mg0.1TiO3–xZn0.15Nb0.3Ti0.55O2 ((1 − x)ZMT–xZNT) (x = 0.100, 0.125, 0.150, 0.175, 0.200) ceramics were prepared at 900 °C by conventional mixed-oxide method. The phase content, microstructure and microwave dielectric properties had been investigated in detail. Rietveld refinement shows the coexistence of Zn0.9Mg0.1TiO3, Zn0.15Nb0.3Ti0.55O2, Zn(BO2)2 and Zn2TiO4 phases. With ZnO–B2O3–SiO2 (ZBS) glass added, the ceramics can be sintered well at 900 °C with a smaller grain size of 0.12 µm and a higher relative density (> 95%). The microwave dielectric properties are largely influenced by the phase composition according to mixture rule. A typical sample of 0.825ZMT–0.175ZNT ceramic with optimal dielectric properties (e r = 26.14, Q × ƒ = 27184 GHz, τ ƒ = − 3.46 ppm °C−1) was sintered at 900 °C for 4 h.

High Dielectric and Piezoelectric Properties of Low-Temperature Sintering PNN-PMN-PZT Ceramics for Low-Loss Piezoelectric Actuator Application

Piezoelectric actuators have been utilized in piezoelectric speakers. In this study, in order to develop a piezoelectric actuator capable of being used in piezoelectric speakers, Pb(Mn1/3Nb2/3)0.07(Ni1/3Nb2/3)0.10(Zr0.5Ti0.5)0.83O3 composition ceramics were fabricated by the conventional mixed oxide method. The effects of ZnO and Nb2O5 on their microstructure and piezoelectric properties were systematically investigated. The tetragonality has been increased in the ceramics with the increase of the Nb2O5 addition. When Nb2O5 content and sintering temperatures were 0.2 wt%, 940 °C, respectively, the excellent physical properties of d33 = 386 pC/N, er = 1667, kp = 0.661, Qm = 1285 and FOM = 935 103 were obtained for low loss piezoelectric actuator application.

Anelastic and optical properties of Bi0.5Na0.5TiO3 and (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramic systems doped with donor Sm3+

The effect of Sm3+ substitution in (Bi0.5Na0.5)(1−x)SmxTiO3 (BNT-100xSm) and [(Bi0.5Na0.5)0.94Ba0.06](1−x)SmxTiO3 (BNT6-100xSm) has been studied by conventional X-ray diffraction (XRD), mechanical spectroscopy and photoluminescence (PL) measures. Ceramic samples of BNT-100xSm (x = 0 and 0.02) and BNT6-100xSm (x = 0, 0.01, 0.02 and 0.04) were prepared via the conventional mixed-oxide method. X-ray diffraction patterns obtained for all the sintered samples at room temperature (RT) confirm the formation of perovskite structure without spurious phases. The BNT-0Sm and BNT-2Sm compositions have the same rhombohedral (R3c) crystalline structure at RT. The BNT6-0Sm composition is confirmed to be at the morphotropic phase boundary of the BNT-BT system, and when samarium is added, a clear evolution towards the tetragonal phase was observed, with corresponding disappearance of the rhombohedral peaks in XRD patterns. The analysis of the anelastic spectra indicate higher compositional disorder, reduction of tendency of the octahedra to tilt (in agreement with the stabilization of the tetragonal phase) and preferential substitution of Sm3+ in the position of Bi3+. New anomalies (induced by addition of Sm3+) are observed on the anelastic spectra. From the PL results we can confirm the presence of emissions corresponding to Sm3+ with small contribution of Sm2+, evidencing the different mechanisms for the charge balance needed in the donor doping.

Technology and electrophysical properties of Mn4+, Sb3+, Dy3+ and W6+ -doped Pb(Zr0.49Ti0.51)O3 ceramics

In paper three multicomponent PZT-type ceramics doped by Mn4+, Sb3+, Dy3+, W6+ have been prepared by the conventional mixed oxide method. The multicomponent PZT-type ceramic powders were synthetized by calcining route, while densification was carried out by pressureless sintering method. The paper presents XRD, SEM, EDS, dielectric and DC electric conductivity measurements of the multicomponent PZT-type ceramic samples. Conducted tests indicate obtained multicomponent PZT-type exhibit good dielectric properties giving the possibility for their use as actuators and piezoelectric transducers in modern micromechatronic and microelectronic applications.

Electric and dielectric properties of (Ba0.6Pb0.4)TiO3 ceramics modified with special glass in the range of phase transition

Perovskite ceramics (Ba0.6Pb0.4)TiO3 modified with PbO-B2O3-Al2O3-WO3 special glass was prepared with the conventional mixed oxide method. X-ray diffraction analysis (XRD) of the obtained materials confirmed singlephase and pure tetragonal structure. The Rietveld method was used to determine unit cell parameters. Uniform deformation of the tetragonal parameter was observed with addition of the glass. Dielectric measurements revealed the remarkable influence of special glass admixture on the value of dielectric permittivity and dielectric losses, as well as the Curie temperature. However, the most important achievement of the investigations is obtaining a significant PTCR effect in the sample containing 6 wt.% of special glass admixture.

An empirical model for B-site cation ordering in Ba(Mg1/3Ta2/3)O3

Processing-structure models are needed in both the lab and industry; however, few exist for cation ordering in perovskites. The perovskite Ba(Mg1/3Ta2/3)O3 in its ordered form is one of the best known high-Q dielectric materials but requires extended high-temperature annealing to achieve high degrees of order; so an empirical model which describes the ordering as a function of an easily obtainable processing parameter would be useful. In this work, powders of Ba(Mg1/3Ta2/3)O3 were synthesized using a conventional solid-state mixed-oxide method. The as-calcined compound had a cubic (lacking long-range B-site cation order) structure but contained short-range-ordered nanodomains. Upon annealing at 1500 °C for up to 40 h an increasingly ordered arrangement of Mg2+ and Ta5+ on the B site was generated, with the ordering causing a trigonal distortion. Empirical modeling as well as first-principles calculations via density functional theory showed that this ordering process was accompanied by a volume decrease despite the fact that ordered planes stack less efficiently. An empirical model was developed to describe the ordering parameter as a function of either annealing time or effective B-site contraction. The implication of this modeling method is that it may be possible to predict the degree of cation ordering in complex perovskite systems from ionic-radii data and experimentally-derived pseudocubic lattice constants alone. Conversely, it may also be possible to predict the degree of volume expansion/contraction upon ordering, which has implications for functional properties like ionic conduction.

Multiferroic properties of (1−x)BiFeO3-xBa(Fe1/2Nb1/2)O3 ceramics

Multiferroic ceramics, (1−x)BiFeO3-xBa(Fe1/2Nb1/2)O3 (BF-xBaFN), with x ranging from 0.1 to 0.6, were prepared by conventional mixed oxide method. X-ray diffraction analyses indicates a rhombohedral distorted perovskite structure (R3c space group) of BiFeO3 for x=0.1 and cubic-like perovskite structure for x=0.2–0.6. Significant magnetic enhancements were discovered in the BF-xBaFN ceramics. Ferromagnetic loops revealed the maximum remanent magnetization of 1.61emu/g of BF-xBaFN with x=0.25.

Effects of LiNbO3-doping on properties of (Na0.535K0.48)NbO3 piezoelectric ceramics with high electromechanical coupling coefficient for application in surface acoustic wave devices

Abstract In this study, lead-free LiNbO3-doped (Na0.535K0.48)NbO3 (NKN) ceramics (NKLxN, x = 0–0.09) were prepared using a conventional mixed oxide method to investigate the effects of LiNbO3 additives on the microstructure and electrical properties. The addition of LiNbO3 reduced the optimal sintering temperature from 1100 to 950 ℃ and increased the bulk relative density to 99.61% (g/cm3) at x = 0.05 through the formation of a homogeneous microstructure. The electrical properties remained highly stable, even when the ambient temperature was increased from room temperature to 140 ℃. NKLxN ceramics sintered at 950 ℃ with x = 0.05 exhibited the following excellent piezoelectric properties: kp：50% (34%); kt：53% (40%); Qm：168 (112); d33：150 pC/N (80 pC/N); and tan δ ：4% (8%). These values far exceed those of pure NKN ceramics sintered at 1100 ℃. Surface acoustic wave (SAW) devices fabricated using the proposed NKLxN (x = 0.05) ceramics presented high phase velocity of 3210 m/s, k2 of 6.7%, and TCF of approximately −282 ppm/℃. Our results clearly demonstrate the effectiveness of adding LiNbO3 to prevent deliquescence and thereby enhance resistance to the effects of humidity. The resulting devices are highly sensitive to changes in temperature, making them ideally suited to electromechanical transducers as well as SAW temperature sensors.

Low-temperature sintering of K0.5Na0.5NbO3 lead free ceramics using nano CuO sintering aid

Lead free piezoelectric ceramic K0.5Na0.5NbO3 (KNN) was synthesized by conventional mixed oxide method. The effect of nano CuO additive as the sintering aid, on microstructure and electrical properties of pure KNN ceramics was investigated. Sintering process has a great impact on the piezoelectric properties of lead free piezoelectric ceramics. The results indicated that adding small amount of nano CuO sintering aid reduces the sintering temperature of lead free piezoelectric KNN ceramic to 900 °C, and also leads to excellent densification and proper microstructure. Samples characterization by X-ray diffraction represented that there are no secondary phases for KNN ceramics with CuO additive in the range of 0–2 mol%. The dielectric and piezoelectric properties are strongly modified by the amount of nano CuO additive. A high piezoelectric coefficient (d33) up to 130 pC/N and a dielectric loss <0.008 achieved for the sample with 0.5 mol% nano CuO, sintered at 900 °C for 4 h.

Dielectric spectroscopy and magnetometry investigation of Gd-doped strontium titanate ceramics

Structural, dielectric and magnetic properties of dense Gd-doped strontium titanate ceramics prepared by the conventional mixed oxide method are studied. Lattice parameter is found to decrease linearly in the Sr1-1.5xGd xTiO3 system, confirming the incorporation of Gd onto the Sr site of the perovskite lattice of strontium titanate up to x=0.05. Real and imaginary parts of the dielectric permittivity of Sr1-1.5xGd xTiO3 ceramics exhibit a relaxation between 100Hz and 1MHz in the temperature range of 17–26K, slightly shifting to higher temperatures with increasing Gd content. Such dielectric behaviour is attributed to the relaxation of individual dipoles formed by off-centre displacement of Gd3+ ions on Sr sites in a highly polarizable lattice of strontium titanate. Other dielectric relaxations observed in Sr1-1.5xGd xTiO3 from 125 to 300K are attributed to the oxygen vacancy related mechanisms. No magnetic anomaly but paramagnetic behaviour is observed for Sr1-1.5xGd xTiO3 ceramics, indicating an absence of the magnetic order and hence magnetoelectric coupling.

Synthesis and Characterisation of Nanocomposites of TiO₂ and MgAl₂O₄ for Gas Sensing Applications.

In this study, a conventional mixed oxide method was used to prepare nanocomposites of titanium dioxide and magnesium aluminate samples. The synthesis process of a low concentration of posttransition metal oxide like TiO2 with pre-transition metal oxides like MgO and Al₂O3 and its gas sensing behaviour were investigated. The present work focuses on applying different nanocomposite samples of (TiO2) x and MgAl₂O₄ (at x = 0 magnesium aluminate namely MA; x = 0°25 and 0.75 N namely MAT0.25 and MAT0.75 at 4 and 10 wt% of TiO2 in MgAl₂O₄ respectively and TiO₂ namely T) for gas sensing applications (O₂, CO and H₂ gases). The composite samples were characterized by their X-ray diffraction pattern, Fourier transform infrared spectroscopy, a particle size analyzer, X-ray fluorescent spectroscopy, scanning electron microscopy, ultraviolet visible spectroscopy, and Brunauer–Emmett–Teller methods. The response to changes in gas pressure (from 0.5 to 2 bar) was quantitatively studied in all samples (MA, MAT0.25, MAT0.75 and T) at different operating temperatures from 300 to 600 K. All samples showed a fast and improved gas response at different operating temperatures. Moreover, it was observed that the gas response of the composite sample, MAT0.75 increased by 11% more than the pure titanium sample at an operating temperature of 360 K, on the passage of O₂ gas.

Piezoelectric and ferroelectric properties of lead-free Bi0.5(Na0.80K0.20)0.5TiO3-(Ba0.98Nd0.20)TiO3 binary system

ABSTRACTThis research was conducted to investigate the effect of (Ba0.98Nd0.20)TiO3 addition on properties of Bi0.5(Na0.80K0.20)0.5TiO3 ceramic. The binary system having composition of(1-x)Bi0.5(Na0.80K0.20)0.5TiO3-x(Ba0.98Nd0.20)TiO3 or (1-x)BNKT-xBNdT (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06 mol fraction) was prepared by a conventional mixed oxide and sintering method. From the characterization results, the ceramics sintered at 1125°C had relative density of more than 98% of their theoretical values regardless of BNdT content. X-ray diffraction pattern of the ceramics showed a single perovskite structure with mixed rhombohedral and tetragonal phases (i.e. within MPB region). Scanning electron micrographs showed a cubic-like grain shape and the grain size decreased with increasing BNdT content. The ceramic with x = 0.04 showed relatively high room temperature dielectric constant with low loss (ϵr = 1670, tanδ = 0.0532), high piezoelectric coefficient (d33 = 192 pC/N) and good ferroelectric properties (Pr = 19.12 µC/cm2, Ec = 13.54 kV/cm and Rsq = 1.52) which may be suitable for transducer and actuator applications.