Effects Of Fe2O3 Research Articles

Effects of Fe2O3-[BOx] reaction on sodium borosilicate glass structure doping with nano to macro sized α-Fe2O3 particles

Fe3+ is readily reacted with structural units to modify various properties of the borosilicate glasses and glass ceramics. However, there exists some controversies on Fe2O3 containing borosilicate glasses: (1) whether the Fe2O3 turned into the nanometer-sized polycrystalline structure or reacted with the glass matrix to form a new substance and (2) whether the role of Fe2O3 was depended on its concentration in the network of glass. Theoretical extinction spectra of α-Fe2O3 particles ranging from 1 to 180 nm in borosilicate glass align with UV–vis absorption spectra. Based on the Na2O-B2O3-Fe2O3 phase diagram, xFe2O3·(100-x) [41.6B2O3–20.7Na2O-19.2CaO-9.7Al2O3–7.0SiO2–0.6ZnO] (x=1.20∼1.95 mol%) were prepared for this study, analyzing from exterior characteristics to interior structure. Molecular vibrational spectroscopy and component structure measurement were applied to study the effect of doping α-Fe2O3 powders (particle sizes of 30 nm, 1 μm, 75 μm) on the sodium borosilicate glasses. Combination of experimental characterization and numerical simulation were also utilized to investigate the effects of iron oxide particle size on the color of dispersion systems. We discovered that (i) doping with either nanometer-sized or micron-sized particles of α-Fe2O3 can result in both the substitution for B3+ in tetra-coordination [BO4] and the bonding with [BO3] units within the amorphous network of sodium borosilicate glasses; (ii) Even at lower concentrations, α-Fe2O3 can still act as a network intermediate, combining both its former role and modifying properties. Based on these outcomes, for the reactive process, we formulated a constitutive model which offers valuable insights into understanding the behavior of iron oxide in sodium borosilicate glass. These findings are crucial for comprehending the processes involved in matrix preparation and are pivotal for progressing to the subsequent stage where designing and fabricating nanocomposite materials based on these matrices with spatial separation.

Reaction kinetics study in direct chemical looping process based on a multi-step reaction scheme

The investigation into reaction kinetics provides fundamental insights for reactor design in biomass thermochemical conversion. This work studied the kinetics of biomass chemical looping process based on a multi-step model. Cellulose, xylan, and lignin were employed as biomass representatives. The individual step in the multi-step scheme was formulated with a mass-balance equation form, requiring fewer parameters and thus less computational cost. In addition, the decomposition characteristics of different biomass samples in the presence of oxygen carrier (Fe2O3) were analyzed, and the effects of Fe2O3 on the kinetic parameters of reaction steps were investigated. The results revealed that volatiles pyrolyzed from cellulose and xylan were almost not involved with Fe2O3 reduction at high temperatures (∼1000 K) while playing a major role in terms of lignin (∼1050 K). Moreover, adding OC did not always positively affect the activation energy; in particular, it decreased the activation energy of xylan yet elevated the activation energies of cellulose (at low-temperature zone) and lignin to some extent.

Influence of Fe2O3 and bacterial biofilms on Cu(II) distribution in a simulated aqueous solution: A feasibility study to sediments in the Pearl River Estuary (PR China)

This study investigated physico-chemical interactions among Cu(II), biogenic materials, and Fe2O3 in a continuous-flow biofilm reactor system under a well-controlled environment. The effects of Fe2O3 and bacterial biofilms on the distribution of Cu(II) in a simulated aquatic environment were studied. To control biological and abiotic elements in the marine environment, a biofilm reactor was designed to understand the metal speciation of Cu(II) and its distribution. The reactor consisted of a biofilm chamber equipped with glass slides for biofilms attachment. Due to its ability to grow as biofilm in the medium, Pseudomonas atlantica was cultivated to adsorb trace Cu(II) to attached and suspended cells. It was found that biofilms with 170–285 mequiv chemical oxygen demand (COD) concentration/m2 of total oxidizable materials accelerated the Cu(II) adsorption to the surface of the reactor significantly by a factor of five. A significant inhibition to the bacterial growth took place (p ≤ 0.05; t-test) when Cu(II) concentration was higher than 0.5 mg/L. In the absence of Cu(II), bacterial cells grew normally to 0.075 of optical density (OD). However, at the Cu(II) concentration of 0.2 mg/L, the cells grew to a lower OD of 0.58. The presence of glycine and EDTA substantially reduced the toxicity of Cu(II) on bacterial growth (p ≤ 0.05; paired t-test). Their complexation with Cu(II) rendered the metal ions less available to bacterial cells. This implies that the Fe2O3 and bacterial biofilm affected Cu(II) distribution and speciation in the aquatic environment.

The effect of different forms of iron substances on the aging properties of carbon‐black filled natural rubber

AbstractThe effect of iron‐containing substances with different forms on the properties of carbon‐black filled natural rubber compound is discussed. The ionic iron substances (FeCl2, FeCl3, Fe(SA)3) have a detrimental effect on the rubber. Based on the oxidation induction temperature values, the relative deteriorating effects of ionic iron substances on the rubber are in the order: Fe(SA)3 > FeCl3 ≈ FeCl2. Not only are the metal ions (Fe2+, Fe3+) with adjacent stable oxidation states catalytically active in degrading rubber, but also the counterions have an influence on the effect of oxidation, particularly the stearic anion. Ionic iron materials can decrease the molecular weight, especially for the case of Fe(SA)3 as measured by gel permeation chromatography. Due to the degrading effect on the rubber molecules, Fe(SA)3 brings about a torque decrease in moving die rheometer and evident decrease of the Mooney viscosity at 100°C, which is different from the effects of Fe2O3 and 304L‐Fe. The insoluble iron substances behave more like hard fillers. Additionally, Fe(SA)3 remarkably alters the bound rubber content and the tensile properties after aging via two different process (scission and crosslinking). Overall, this work has a thorough comparison of effect of iron‐containing materials on rubber aging and provides useful inspiration to protect the rubber from deterioration by foreign reagents and regulating the rubber stability and degradation rate via introducing degradative metal ions.

Effect of Fe2O3 on the Crystallization Behavior of Glass-Ceramics Produced from Secondary Nickel Slag

In this paper, glass-ceramics were prepared from secondary nickel slag by the melting method. The effects of Fe2O3 on the crystallization behavior of glass-ceramics were investigated by differential thermal analysis, X-ray diffraction, and scanning electron microscopy. The properties of glass-ceramics such as Vickers hardness, bending strength, and acid and alkali resistance were systematically discussed. The results indicate that the crystallization temperature (Tc) and transition temperature (Tg) of the glass show a trend of decreasing and then increasing with the increase in Fe2O3 content. The precipitation and refinement of the crystalline phase were promoted significantly when the Fe2O3 content was lower (≤9.32 wt%), while the crystallinity decreased slightly when the Fe2O3 content increased to 12.42 wt%. The promotion of crystal precipitation led to the depolymerization of the glass network. When the Fe2O3 content was 9.32 wt%, the sample exhibited the best crystallization ability, consisting of uniformly distributed anorthite, ferrobustamite and glass phases, while the Vickers hardness and bending strength were 11.42 GPa and 121 MPa, respectively.

Effects of Fe2O3, MnO2, MgO and ZnO additives on lipid and biodiesel production from microalgae

At present, the major body of research is focused on weaning the world from fossil fuels. The problem is that the world is running out of fossil fuel. Therefore, an alternative source must be identified. The biofuels are promising alternatives. In the case of petrodiesel, a promising alternative is biodiesel production from algae. The ability of microalgae to generate large quantities of lipids with a fast growth rate made them superior biodiesel producers. An important factor of determining optimal microalgal activity is the bioresponse to changes in trace metal concentration and quantity. The effects of the addition of the following chemicals were investigated: ferric oxide (Fe2O3) with a concentration of 1.2 mg/L, manganese dioxide (MnO2) with a concentration of 1 mg/L, magnesium oxide (MgO) with a concentration of 7.3 mg/L, and zinc oxide (ZnO) with a concentration of 5 mg/L. Further treatment is a mixture of all additives with the same listed concentrations. According to the results of this study, it was found that iron, manganese, magnesium, and zinc concentration have great influence on the algal growth and lipid production. Furthermore, the mixture of all additives yielded the highest lipid and, therefore, the highest biodiesel production among all treatments.

The effects of Fe2O3 and MoS2 on the catalytic activation pathway of hydrogen sources during direct coal liquefaction

Direct coal liquefaction (DCL) can be highly promoted by catalysts due to the acceleration of hydrogen activation. There are two pathways of activation for H2 during the process of DCL. One is that H2 dissolves in the liquid phase and then transfers to coal after splitting (molecular hydrogen), and the other is dissolved H2 is hydrogenated with solvent and then transferred from solvent to coal (transfer hydrogen). In addition, hydrogen in the solvent molecules can be supplied to coal (solvent hydrogen). The effects of two catalysts, Fe2O3 and MoS2, on the activation of molecular hydrogen, transfer hydrogen, and solvent hydrogen during DCL were investigated. Herein, we conducted a series of experiments, including DCL with H2-decalin, DCL with N2-tetralin, tetralin dehydrogenation, naphthalene hydrogenation, and DCL with H2-tetralin. The catalyst and products were characterized by XRD, GC, GC-MS, 1H NMR and TG. Quantum chemistry reveals the catalyst effect on hydrogen activation. The catalytic performance and different hydrogen consumption reveal that the Fe2O3 catalyst primarily activates molecular hydrogen, and MoS2 activates all three kinds of hydrogen. This work not only reveals the catalyst effect on hydrogen activation but also gives light to the design of an appropriate and effective catalyst for DCLs.

Preparation and characterization of corundum-based ceramics for thermal storage

Corundum-based ceramics were prepared by two methods. The first used Fe2O3 and TiO2 as additives to react with α-Al2O3. The second made full use of Al2O3, SiO2 and TiO2 in calcined bauxite, and Fe2O3 was used as an additive. The SiO2-TiO2-Fe2O3 system was designed to influence corundum. The effects of Fe2O3, TiO2 and SiO2 on physical properties, phase transformation, microstructure, thermophysical properties and thermal shock resistance were investigated. Results showed that Fe2O3 and TiO2 realized densification sintering through entering in the lattice of corundum, and the solubility of Fe2O3 was higher than that of TiO2. In addition, the excess TiO2 tend to synthesize iron aluminum titanate in the grain boundaries, which could refine the grains and improve the mechanical properties. The SiO2-TiO2-Fe2O3 system reduced significantly the sintering temperature, but the imperfect microstructure impaired the properties. Corundum-based ceramics prepared by Fe2O3, TiO2 and α-Al2O3 had the optimal properties. The thermal conductivity and thermal storage density were 14.81 W/(m·K) (25 °C), 837 kJ/kg (25–800 °C), respectively. No cracks were formed after 30 thermal shock cycles (1100 °C-room, air cooling), and the bending strength increased by 2.59%. This study supports the application of corundum-based ceramics as a promising thermal storage candidate.

Characterization of Fe2O3 doping on structure, optical and luminescence properties of magnesium aluminosilicate-based glasses

The Fe2O3-doped magnesium aluminosilicate-based glasses were prepared by the traditional melt quenching method. The effects of Fe2O3 on the structure and properties of the prepared glasses were analyzed. DSC results indicate that the crystallization peak temperature is increasing first and then decreasing with Fe2O3 doping, and the thermal stability gradually decreases. Infrared spectrum curve illustrates that with increasing Fe2O3 content, the glass network is destroyed, and the number of non-bridging oxygen increases, resulting in a decrease of the optical band gap energy and an increase of the Urbach energy. In ultraviolet-visible absorption spectra, two bands observed around 540 and 1035 nm are corresponded to the electronic transitions of Fe3+ from 6A1g to 4T2g and Fe2+ from 5T2g to 5Eg, respectively. The obtained chromaticity coordinate parameters indicate that the prepared Fe2O3-doped magnesium aluminosilicate-based glasses can be applied to the fluorescent material of the light conversion layer of blue light-emitting diode device.

Morphology-dependent catalytic activity of Fe2O3 and its graphene-based nanocomposites on the thermal decomposition of AP

The spherical, hollow and tubular Fe2O3 (s, h and t) and their graphene-based nanocomposites rGO-Fe2O3 (s, h and t) were fabricated using the facile solvothermal methods. The morphologies and compositions of the as-synthesized Fe2O3 (s, h and t) and rGO-Fe2O3 (s, h and t) nanocomposites were systematically characterized by SEM, TEM, XRD, FTIR and XPS methods. Then, the effect of the catalytic performance of Fe2O3 (s, h and t) and rGO-Fe2O3 (s, h and t) nanocomposites on the thermal decomposition of ammonium perchlorate (AP) were studied by DSC method. The DSC results showed that all of the Fe2O3 (s, h and t) and rGO-Fe2O3 (s, h and t) nanocomposites can effectively promote the thermal decomposition of AP. Besides, rGO-Fe2O3(s) nanocomposite has the best catalytic performance, and the high-temperature decomposition exothermic peak of AP was significantly reduced after its mixing with rGO-Fe2O3 (s) nanocomposite. It can be seen that the effects of Fe2O3 on AP decomposition is mainly reflected in the high temperature process, while the effects of rGO-Fe2O3 (s) on AP decomposition is reflected in both high and low temperature stages, and the effect on the high temperature stage is more significant. The excellent catalytic performance of rGO-Fe2O3 (s) nanocomposite can be attributed to the in-situ growth of Fe2O3 on the surface of rGO, which contributes to the low temperature decomposition process of AP.

Phase formation, microstructure development, and mechanical properties of kaolin‐based mullite ceramics added with Fe2O3

AbstractThe effects of Fe2O3 on phase evolution, density, microstructural development, and mechanical properties of mullite ceramics from kaolin and alumina were systematically studied. X‐ray diffraction results suggested that the ceramics consisted of mullite, sillimanite, and corundum, in the sintering range of 1450°C–1580°C. However, as the sintering was raised to 1580°C, mullite is the main phase with a content of 94%, and the corundum phase content is 5.9%. Simultaneously, high‐temperature sintering had a positive effect on the densification of the mullite ceramics, where both the bulk density and flexural strength could be optimized by adjusting the content of Fe2O3. It was found that 6 wt% Fe2O3 was optimal for the formation of rod‐shaped mullite after sintering at 1550°C for 3 h. The sample's maximum bulk density was 2.84 g/cm3, with a flexural strength of 112 MPa. Meanwhile, rod‐shaped mullite grains with an aspect ratio of ~9 were formed. As a result, a dense network structure was developed, thus leading to mullite ceramics with excellent mechanical properties. The effect of Fe2O3 on the properties might be attributed to the fact that Al3+ ions in the [AlO6] octahedron were replaced by Fe3+ ions, resulting in lattice distortion.

A novel recycling approach for efficient extraction of titanium from high-titanium-bearing blast furnace slag

The recycling of high-titanium-bearing blast furnace slag (TiO2 > 23 wt.%) is an urgent problem that has attracted global research attention. To achieve high-efficiency, low-consumption, clean, and high value-added recycling utilization, a new process is proposed herein, which entails reacting a CH4-H2-N2 gas mixture with the titanium-bearing blast furnace slag to initially produce Ti(C, N, O) at a low temperature, whereafter the product is purified and chlorinated. The effects of Fe2O3, urea, and sawdust on the reduction and carbonitriding characteristics are also investigated. The results indicate that the Fe2O3 additive can promote the formation of Ti(C, N, O), while urea and sawdust are instrumental for enhancing gas diffusion in solid powders. The proposed novel recycling process was assessed and it evinced many advantages and great feasibility.

Effects of Fe2O3 and B4C Addition on the Mechanical Properties and Corrosion Resistance of Al–Mg–Si Alloy in 3.5% Brine Solution

In this present investigation aluminum Al6061 alloy and 5 wt% of Fe2O3 in addition to 2%, 4%, 6% weight of B4C reinforced matrix composites (AMCs) is fabricated by stir casting method. Upon increasing the amount of weight percentage to the composites, the mechanical properties also increased. The AC impedance spectra and polarization studies have been utilized to investigate the resistance towards corrosion of the Fe2O3 and B4C reinforced Al6061 metal matrix composites (AMCs). Corrosion current (Icorr), Linear Polarization Resistance (LPR), corrosion potential (Ecorr), capacitance (C), charge transfer resistance (Rct) parameters were considered by the materials submerged in 3.5% of Brine solution and the resistance towards corrosion of the material is determined. Scanning Electron Microscopy (SEM) is utilized to identify the before and after corrosion of the prepared composites. The resistance towards the corrosion is significantly increased with increasing the wt% of reinforced composites.

High H2/CO ratio syngas production from chemical looping co-gasification of biomass and polyethylene with CaO/Fe2O3 oxygen carrier

Chemical looping co-gasification of pine wood and polyethylene with CaO/Fe2O3 oxygen carrier was preliminarily conducted in a fixed bed reactor and thermogravimetric analyzer (TGA). The effects of Fe2O3 /biomass mass ratio, temperature and steam/biomass mass ratio on the product distribution (syngas yield, H2/CO ratio and cold gas efficiency) during the pine wood chemical looping gasification were investigated. Results showed that the optimal product distribution was obtained at the gasification temperature of 850 °C with the Fe2O3/feedstock ratio of 0.25 and steam/biomass mass ratio of 0.25. The interactions of pine wood and polyethylene were further studied. It was found that the positive or even the synergetic effects existed, which resulted in the enhancement of syngas and hydrogen yield. The optimal addition of 75% polyethylene increased H2 yield from 0.62 Nm3/kg to 1.59 Nm3/kg compared to the pine wood chemical looping mono-gasification. Chemical looping co-gasification also improved the cold gas efficiency from 77.22% to 89.30% and H2/CO ratio from 1.54 to 1.88. The CaO/Fe2O3 mass ratio of 1.0 was sufficient to elevate the H2/CO ratio above 2. The maximum H2 yield of 1.73 Nm3/kg, cold gas efficiency of 92.23% and H2/CO ratio of 2.09 were finally obtained to meet the demand for the Fischer-Tropsch synthesis. The presence of synergetic effects on syngas and hydrogen yield from the fixed bed data but their absence from the TGA data revealed the interaction mechanism could be attributed to gas phase reformation and cracking reactions.

Biomechanical Response of Lung Epithelial Cells to Iron Oxide and Titanium Dioxide Nanoparticles.

Increasing evidence shows that lungs can be damaged by inhalation of nanoparticles (NPs) at environmental and occupational settings. Recent findings have associated the exposure to iron oxide (Fe2O3) and titanium dioxide (TiO2) – NPs widely used in biomedical and clinical research – with pulmonary oxidative stress and inflammation. Although changes on cellular mechanics could contribute to pulmonary inflammation, there is no information regarding the effects of Fe2O3 and TiO2 on alveolar epithelial cell biomechanics. The aim was to investigate the NPs-induced biomechanical effects in terms of cell stiffness and traction forces exerted by human alveolar epithelial cells. Cell Young’s modulus (E) measured by atomic force microscopy in alveolar epithelial cells significantly decreased after exposure to Fe2O3 and TiO2 (∼28 and ∼25%, respectively) compared to control conditions. Moreover, both NPs induced a similar reduction in the traction forces exerted by the alveolar epithelial cells in comparison to the control conditions. Accordingly, immunofluorescence images revealed a reduction of actomyosin stress fibers in response to the exposure to NPs. However, no inflammatory response was detected. In conclusion, an acute exposure of epithelial pulmonary cells to Fe2O3 and TiO2 NPs, which was mild since it was non-cytotoxic and did not induce inflammation, modified cell biomechanical properties which could be translated into damage of the epithelial barrier integrity, suggesting that mild environmental inhalation of Fe2O3 and TiO2 NPs could not be innocuous.

Improvements in heterogeneous cation exchange membranes by incorporation of Fe2O3 nanoparticles

Ion exchange membranes are the heart of the electrodialysis process which is a well-known water treatment technology. Herein, a heterogeneous cation exchange membrane (CEM) is synthesized by using a polymeric blend and the effects of Fe2O3 and sulfate-functionalized (s-Fe2O3) nanoparticles incorporation on the properties of the membranes were investigated. The addition of Fe2O3 nanoparticles caused a reduction in electrical resistance up to 53%. Moreover, the ion exchanged capacity (IEC) and permselectivity were improved by 34% and 42%, respectively. Meanwhile, by sulfonation of the Fe2O3 nanoparticles, further cation exchange groups were introduced to the nanoparticles structure which significantly improved the membrane properties. Through addition of 0.5 wt% s-Fe2O3 nanoparticles to the CEM matrix, a 45% reduction in the electrical resistance, and 45% and 43% enhancement in the IEC and permselectivity were obtained, respectively.

The ferroelectric, dielectric and energy storage properties of Pb-free 0.6Na0.5Bi0.5TiO3-0.4SrTiO3 bulk ceramics modified by Fe2O3

Lead-free 0.6Na0.5Bi0.5TiO3-0.4SrTiO3-xFe2O3 ceramics (x = 0, 0.25, 1 and 2, mol%) were fabricated by solid-state reaction processing. By means of XRD, SEM and Ferroelectric station, the effects of Fe2O3 on the phase, microstructure, dielectric properties and energy storage performances of NBT-ST ceramics were investigated systematically. The samples modified by Fe2O3 do not remarkable affect its perovskite crystal structure, but beneficial to its density and grain size. With introduction of Fe2O3, the dielectric properties enhanced, meanwhile, the P-E hysteresis loops were slim in appearance, presenting a typical relaxor ferroelectric characteristic. The sample with Fe2O3 doping amount of 0.25 mol% exhibits high η and the optimum energy storage performance with excellent stability of temperature, frequency and fatigue circle. These results of the Fe2O3 doped Pb-free NBT-BT based ceramics are attractive features for applications in energy storage capacitor and power electronics.

Effects of Fe2O3 on the Properties of Glass Foams Prepared by Iron-Containing Solid Waste

Increasing attention has been paid nowadays to glass foams that were prepared by recycling solid waste. Fe2O3, as a main compound in solid waste, plays an important role in glass-foam preparation process. This work investigates the influence of Fe2O3 existing in solid waste on the properties of glass foams. The results revealed that Fe2O3 in glass matrix would increase the viscosity of glass on one hand. On the other hand, appropriate content of Fe2O3 could increase the oxygen supply to carbon and delay the redox reaction, leading to a better compromise between the glass viscosity and the gas generating, so as to a lower density. Adding 1 wt % Fe2O3 as oxidants could further promote foaming to achieve a better property. Therefore, in glass-foam preparation with the solid waste containing Fe2O3, proper utilization of the Fe3+ ions in parent glass is beneficial to reduce cost, improve utilization ratio and obtain glass foams with better properties.

Structure and properties of in situ synthesized FeSi2-diopside glass ceramic composites from Bayan Obo tailings, blast furnace slag, and fly ash

FeSi2 -glass ceramic composites are successfully synthesized in situ from Bayan Obo tailings, blast furnace slag, and fly ash by a melting method. The effects of Fe2O3 on the crystallization behavior, microstructure, and performance of the composites have been investigated by differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, transmission electron microscopy, and mechanical performance tests. The results show that the glass ceramics are composed of a diopside dendritic crystal matrix (primary phase) in which FeSi2 metal particles with diameter ∼5 μm are dispersed (dispersed phase). With increase in the amount of Fe2O3, the crystallization activation energy of the composites decreases from 343.20 to 309.71 kJ/mol and the Avrami parameter increases from 2.12 to 3.17. The composites exhibit the maximum density of 3.04 g/cm3, microhardness of 8.37 GPa, bending strength of 210.27 MPa, impact toughness of 3.68 kJ/m2, acid resistance of 97.91%, and alkali resistance of 98.85%, proving their high potential for various industrial applications.

Low temperature sintering of Pb(Ni, Nb)O3-Pb(Hf, Ti)O3 piezoceramics with Fe2O3 and Bi2O3 addition

The effects of Fe2O3 and Bi2O3 addition on the microstructures and the piezoelectric and dielectric properties of 0.49Pb(Ni1/3Nb2/3)O3-0.51Pb(Hf0.3Ti0.7)O3 ceramics were investigated in detail. Results showed that 0.49Pb(Ni1/3Nb2/3)O3-0.51Pb(Hf0.3Ti0.7)O3 ceramics with better performance were prepared at a sintering temperature as low as 1050 °C via the addition of Fe2O3 and Bi2O3. In the case of 2% Fe2O3 and 2% Bi2O3, the optimal properties, i.e. d33 = 865 pC/N, kp = 0.60, εr = 6500 and tanδ = 2.5%, were achieved for the sample. The d33 revealed the greatest value among the ever reported piezoceramics sintered at the temperature below 1100 °C. The results suggest Fe2O3 and Bi2O3 addition to be an effective approach to lower the sintering temperature and simultaneously improve the performance of Pb(Ni, Nb)O3-Pb(Hf, Ti)O3 ceramics.