Electrical and magnetic properties of ZrO2-doped lithium-titanium-zinc ferrite ceramics

This report documents the effect of 0–3 wt% ZrO₂ additive on the electrical and magnetic properties of LiTiZn ferrite. Ferrite powder of Li_0.65Fe_1.6Ti_0.5Zn_0.2Mn_0.05O₄ composition was synthesised at 900 °C for 4 h in air. Ferrite ceramics doped with ZrO₂ were sintered at 1010 °C for 2 h in air. A spreading resistance analysis showed that LiTiZn ferrites exhibited nonuniform distribution of depth DC resistivity, which varied in the range of (0.25–2.3) × 10⁹ Ω⋅cm depending on the amount of additive. Zirconia also affected the magnetic properties of ferrite so that the magnetisation increased and the initial permeability decreased as the ZrO₂ content increased. In addition, the Curie temperature varied. The permeability spectra measured in the frequency range from 10 MHz to 18 GHz changed depending on the zirconia content.     

Synthesis and characterization of zirconia toughened alumina ceramics prepared by co-precipitation method

Undoped and 3 mol% yttrium doped ZrO₂–Al₂O₃ composite powders with partially stabilized ZrO₂ (PSZ) content varying from 0 to 30 wt% were prepared by a co-precipitation route using inorganic precursors Al(NO₃)₃, ZrOCl₂ and Y(NO₃)₃. The precipitates were characterized by DTA and subsequently calcined at 1200 °C for 4 h to achieve fine grained composite powders. The calcined powders were characterized by FTIR and XRD. In order to enhance the sinterability, the calcined powders were wet milled in a high energy ball mill. Powders were uniaxially pressed to form pellets and sintered at 1600 °C for 5 h to achieve greater than 96% relative density. Microstructural analysis of the sintered compacts revealed the uniform distribution of the zirconia particles among the alumina matrix. It was also observed that the faceted intergranular zirconia grains were present at the grain boundaries and junctions in the alumina matrix. Vickers indentation was carried out at 1 kgf load for hardness and 2 kgf load for estimating the critical stress concentration factor (K_c). Microscopic studies of the indented samples showed that cracks were propagating around the grain boundaries. Highest K_c ∼8.40 ± 0.4 MPa√m and hardness ∼16.31 ± 0.58 GPa was obtained for the 30 wt% PSZ-Al₂O₃ composite. The sintered density and critical stress intensity factor (K_c) achieved were compararble to that achieved earlier by hot press and SPS.     

Magnetic properties and microstructures of a Ni-Zn ferrite ceramics co-doped with V2O5 and MnCO3

The present work investigated the effect of the addition of V₂O₅ and MnCO₃ on the microstructure and magnetic properties of Ni-Zn ferrite ceramic samples prepared by a conventional ceramic sintering method at different temperatures. With this aim, a series of samples were prepared by varying the loadings of V₂O₅-MnCO₃ (un-doped, 0.4–0.1?wt%, 0.1–0.4?wt%, 0.2–0.3?wt%, 0.3–0.2?wt%, and 0.5–0.1?wt%, denoted as sample 1, sample 2, sample 3, sample 4, sample 5, and sample 6, respectively). The initial permeability and power loss of the different Ni-Zn ferrites were investigated with respect to the sintering temperature. The V₂O₅ and MnCO₃ dopants significantly improved the initial permeability and power loss characteristics of the Ni-Zn ferrite at frequencies ≥0.5?MHz. When sintered at 1100?°C, sample 2 showed a maximum initial permeability of 931.23?H/m at a frequency of 1?MHz combined with a minimum power loss of 339.2?kW/m³. Co-doping with V₂O₅ and MnCO₃ also resulted in the sintered samples with larger average grain sizes and higher density, while the sintering temperature of Ni-Zn ferrites was significantly reduced.     

Effect of mixing glass frits on electrical property and microstructure of sintered Cu conductive thick film

The resistivity of the sintered Cu thick film decreases with the weight percentage of the SiO₂–ZnO–B₂O₃ additive in the mixing glass frits up to 50 wt%. As the weight percentage of the SiO₂–ZnO–B₂O₃ additive in the mixing glass frits is over 50 wt%, the resistivity of the sintered Cu thick films is quite similar. The lowest resistivity (6.62 × 10⁻⁶ Ω-cm) of the sintered Cu thick films occurs at 75 wt% of the SiO₂–ZnO–B₂O₃ additive. Also, we observe the extensive glass phase framing around the large Cu grains in the Cu thick films sintered with low SiO₂–ZnO–B₂O₃ additives (less than 50 wt%) narrows the cross-section area of the electrical path. On the contrary, the round-shaped glass phase solidified among the small Cu grains allows a larger cross-section of the electrical path (a possible lower resistivity) for the Cu thick films sintered with higher SiO₂–ZnO–B₂O₃ additives (larger than 50 wt%). The above results imply that the resistivity of the sintered Cu thick film correlates well with the microstructure (Cu grain size and the glass/Cu composite structure) of the sintered Cu thick films. Twin grain boundaries can clearly be observed in the sintered Cu thick films, especially for the Cu thick film sintered with the higher SiO₂–ZnO–B₂O₃ additives. Owing to small Cu grains size and high density of Cu grain boundary, the probability of the grain boundaries with a high grain-boundary energy in the Cu thick film sintered with high SiO₂–ZnO–B₂O₃ additive would be much larger, comparing to that in the Cu thick film sintered with low SiO₂–ZnO–B₂O₃ additive. Thus, more annealing twin boundaries formed in the Cu thick film sintered with high SiO₂–ZnO–B₂O₃ additive. Hence, the formation of the twin boundary in the sintered Cu thick film helps reducing the resistivity of the sintered Cu films.     

Spark plasma sintering of ZrO2–Al2O3 nanocomposites at low temperatures aided by amorphous powders

In present work, ZrO₂-5 wt% Al₂O₃ and ZrO₂-10 wt% Al₂O₃ nanocomposites are fabricated through spark plasma sintering. Al₂O₃–ZrO₂ amorphous powders and polycrystal Al₂O₃ powders and are doped in the polycrystalline ZrO₂ powders, respectively. When doped with amorphous powders, the sintering of ZrO₂–Al₂O₃ nanocomposites is promoted, and ZrO₂-5 wt% Al₂O₃ and ZrO₂-10 wt% Al₂O₃ nanocomposites with relative densities of 99% are obtained after spark plasma sintering at 1200 °C; however, when sintering of polycrystalline ZrO₂ and polycrystalline Al₂O₃ powders, the relative densities are merely 93%. The enhanced sinterability is due to the metastability and phase transformation of the amorphous powders, which act as sintering aids. The nanocomposites with near-theoretical density show refined microstructure with homogenous mixture of ZrO₂ and Al₂O₃ grains, which further leads to excellent mechanical properties. This article provides new ideas for low-temperature sintering of nanocomposites via using doping amorphous powders.     

Effects of Bi2O3-Nb2O5 additives on microstructure and magnetic properties of low-temperature-fired NiCuZn ferrite ceramics

NiCuZn ferrite with superior magnetic performance is vital ceramic material in multilayer chip inductors (MLCI) applications. In this study, low-temperature-sintered Ni_0.22Cu_0.2Zn_0.58Fe₂O₄ ferrite ceramic doped with 1.0?wt% Bi₂O₃-x?wt% Nb₂O₅ (where x?=?0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) was synthesized via solid-state reaction method. Effects of Bi₂O₃-Nb₂O₅ additives on microstructures and magnetic properties of NiCuZn ferrite ceramics sintered at 900?°C were systematically investigated. Results indicate that an appropriate amount of Bi₂O₃-Nb₂O₅ composite additives can significantly promote grain growth and densification of NiCuZn ferrite ceramics when sintered at low temperatures. Specifically, samples doped with 1.0?wt% Bi₂O₃ and 0.4?wt% Nb₂O₅ additives exhibited excellent initial permeability (~ 410 @ 1?MHz), high cutoff frequency (~ 10?MHz), high saturation magnetization (~ 54.92?emu/g), and low coercive force (~ 20.32?Oe). These observations indicate that NiCuZn ferrite ceramics doped with appropriate amounts of Bi₂O₃-Nb₂O₅ additives are great candidate materials for MLCI applications.     

Nickel-zinc ferrites with additives for use in magnetic heads

The effect of the addition of Na₂O, CaO and ZrO₂ on the properties of NiZn ferrite, manufactured by the classical method, was studied. Because the porosity, resistivity, permeability and saturation magnetisation are affected, it is possible to select the kind of additive needed to produce NiZn ferrites with electrical and magnetic properties suitable for magnetic heads.     

In-situ formation of Al2O3/Al core-shell from waste material: Production of porous composite improved by graphene

Aluminum dross produced from aluminum industry was used to fabricate Al₂O₃/Al porous composites. The dross was milled for 20?h to obtain nano powder. The milled material was examined by TEM and XRD. Graphene (up to 4?wt%) was mixed with the dross and utilized to reinforce sintered composites. The milled powders were compacted then fired at various temperatures up to 700?°C. Physical properties in terms of bulk density and apparent porosity for sintered composites were tested using Archimedes method. SEM attached by energy dispersive spectrometer (EDS) was used to inspect microstructure and elemental analysis of sintered composites. Microhardness and compressive strength were also measured. Ultrasonic nondestructive technique was utilized to examine the elastic moduli. Electrical conductivity of sintered composite was also studied. During milling up to 20?h, Al₂O₃/Al core-shell was in-situ formed with size of 65.9 and 23.8?nm, respectively. The apparent porosity of sintered composites was improved with rising graphene percent while it decreased with increasing sintering temperature. Increasing of graphene mass percent and firing temperature led to remarkable increase in all mechanical properties and electrical conductivity. The maximum compressive strength, hardness, elastic modulus and electrical conductivity were 200?MPa, 1200?MPa, 215?GPa and 1.42?×?10^?5 S/m, respectively, obtained for composite sintered at 700?°C having 4?wt% graphene.     

Effect of preparation method on sinterability and properties of nanocrystalline MgAl2O4 and ZrO2-MgAl2O4 materials

Abstract

Nanocrystalline MgAl₂O₄ and ZrO₂-MgAl₂O₄ powders were synthesised by combustion and conventional solid state reaction routes. The synthesised powders were processed, dry pressed, and sintered for 3 h at temperatures ranging from 1550 to 1625°C. The sintered pellets were then characterised in terms of phase (XRD), microstructure (SEM), relative density, apparent porosity, water absorption, hardness, three point bend strength, and fracture toughness. The XRD studies revealed that ZrO₂ was present in tetragonal form in the case of combustion synthesised powders (CSP), whereas in powders obtained by solid state reaction (SSP) it was present in the monoclinic form. This study also revealed that the addition of ZrO₂ improved the mechanical properties of sintered MgAl₂O₄ samples: 20 wt-%ZrO₂-MgAl₂O₄ composites prepared from CSPs and conventional SSPs and sintered at 1625°C for 3 h had fracture toughness of 5·96 and 4·33 MPa m^1/2 and three point bend strength of 269 and 98 MPa respectively. Higher sintered density, the presence of tetragonal zirconia as a major phase, and the finer microstructure are probably responsible for the superior mechanical properties exhibited by sintered CSP materials as compared with the sintered SSPs.     

The effect of TiO2 additive on sinterability and properties of SiC-Al2O3-Y2O3 composite system

In the current research, the effects of TiO₂ additive on mechanical and physical properties of SiC bodies, sintered by liquid phase methods were investigated. Al₂O₃ and Y₂O₃ were used as sintering-aids (10?wt% in total) with an Al₂O₃/Y₂O₃ ratio of 43/57 to provide liquid phase during Sintering. TiO₂ was also used as the oxide additive with an amount ranging from 0 to 10?wt%. After scaling and mixing the starting materials by a planetary mill, the obtained slurry was dried at 100?℃ for four hours. The derived powders were finally pressed under a pressure of 90?MPa. The samples were then pyrolyzed and sintered at 600?℃ and 1900?℃, respectively under argon atmosphere for 1.5?h. Phase analysis showed no trace of TiO₂ after the sintering process, demonstrating the complete TiO₂ to TiC transformation. The results showed that an increase in TiO₂ content up to 5?wt%, led an improvement in all the measured properties including the relative density, hardness, Young's modulus, bending strength, indentation fracture resistance and the brittleness factor, reaching to 96.2%, 24.4?GPa, 395.8?GPa, 521?MPa, 5.8?MPa?m^1/2 and 286.5?×?10^?6 m^?1, respectively. However more than 5?wt% additive resulted in a decrease in all the above-mentioned properties. Microstructural studies demonstrated that crack deflection and crack bridging were the major mechanisms responsible for an increase in the indentation fracture resistance.     

Electrical and mechanical properties of pressureless sintered SiC-Ti2CN composites

Highly conductive SiC-Ti₂CN composites were fabricated from β-SiC and TiN powders with 10?vol% Y₂O₃-AlN additives via pressureless sintering. The effect of initial TiN content on the microstructure, and electrical and mechanical properties of the SiC-Ti₂CN composites was investigated. It was found that all specimens could be sintered to ≥98% of the theoretical density. The electrical resistivity of the SiC-Ti₂CN composites decreased with increasing initial TiN content. The SiC-Ti₂CN composites prepared from 25?vol% TiN showed the highest electrical conductivity (～1163 (Ω?cm)^?1) for any pressureless sintered SiC ceramics thus far. The high electrical conductivity of the composites was attributed to the in situ-synthesis of an electrically conductive Ti₂CN phase and the growth of N-doped SiC grains during pressureless sintering. The flexural strength, fracture toughness, and Vickers hardness of the composite fabricated with 25?vol% TiN were 430?MPa, 4.9?MPa?m^1/2, and 23.1?GPa, respectively, at room temperature.     

Physical and electrical properties of yttria stabilised zirconia prepared from nanosized powders

Abstract

Nanosized powders of ZrO₂-10 mol-%Y₂O₃ were prepared by a wet chemical process, with the main purpose of verifying changes in the physical properties of powders, and to study their influence on the electrical resistivity of the sintered ceramic. Optimisation of some parameters involved in the synthesis process resulted in a powder with high specific surface area (> 150 m² g^-1) and with monomodal pore size distribution. The rate of shrinkage was a maximum at 1040°C and high density was obtained on optimising the firing schedule. Impedance spectroscopy results show that the intragrain resistivity was approximately equal to that of a single crystal of the same chemical composition.     

AC Impedance Spectroscopy of CaF2‐doped AlN Ceramics

The electrical conductivity of CaF₂‐doped aluminum nitride (AlN) ceramics was characterized at high temperatures, up to 500°C, by AC impedance spectroscopy. High thermal conductive CaF₂‐doped AlN ceramics were sintered with a second additive, Al₂O₃, added to control the electrical conductivity. The effects of calcium fluoride (CaF₂) on microstructure and related electrical conductivity of AlN ceramics were examined. Investigation into the microstructure of specimens by TEM analysis showed that AlN ceramics sintered with only CaF₂ additive have no secondary phases at grain boundaries. Addition of Al₂O₃ caused the formation of amorphous phases at grain boundaries. Addition of Al₂O₃ to CaF₂‐doped AlN ceramics at temperatures 200°C–500°C revealed a variation in electrical resistivity that was four orders of magnitude larger than for the specimen without Al₂O_3. The amorphous phase at the grain boundary greatly increases the electrical resistivity of AlN ceramics without causing a significant deterioration of thermal conductivity.     

Magnetoelectric composites of nickel ferrite and lead zirconnate titanate prepared by spark plasma sintering

Magnetoelectric (ME) bulk composites of ferrite and lead zirconnate titanate (PZT) were prepared by spark plasma sintering (SPS) of mechanically mixed ferrites, BaFe₂O₄ or NiFe₂O₄ and a soft lead zirconnate titanate, PZT-5A, powders. The feasibility of retarding possible reactions occurring between the ferrite and lead zirconnate titanate was approved by applying such a dynamic process as SPS. It was further revealed that nickel ferrite and PZT-5A is a more favorable combination that underwent no obvious reactions up to 1050 °C. Efforts were made to optimize the SPS processing parameters in order to produce immiscible composites with high electrical resistivity, low dielectric loss and better magnetoelectric response.     

Electrical resistivity of silicon nitride produced by various methods

It has been shown that the grain growth and amount of the glass phase influence the electrical resistivity of pressureless sintered and spark plasma sintered silicon nitride. Sintering additives strongly affect the impurity conductivity of pressureless sintered silicon nitride and slightly influence the intrinsic conductivity due to the longer sintering process as compared with the spark plasma sintering. It was demonstrated that Al₂O₃-Y₂O₃ lead to decrease in the electrical resistivity of SPSed silicon nitride due to increase in the band gap width as opposed to Al₂O₃-MgO. Effect of the sintering additive on the impurity conductivity is practically absent but there is a strong dependence of the sintering temperature for reported spark plasma sintered silicon nitride. However, intrinsic conductivity of SPSed silicon nitride is affected by both sintering temperature and sintering additive. It was also shown that electrical resistivity of produced ceramics is linearly depends on the content of β-Si₃N₄ and microhardness. Electrical resistivity of manufactured silicon nitride varied from 3.16·10⁹ to 1.73·10¹¹ Ω?m. It has been observed strong influence of the sintering additive and sintering temperature on the electrical properties of SPSed and pressureless sintered silicon nitride.     

Electrical resistivity of silicon carbide ceramics sintered with 1 wt% aluminum nitride and rare earth oxide

The influence of additive composition on the electrical resistivity of hot-pressed liquid-phase sintered (LPS)-SiC was investigated using AlN–RE₂O₃ (RE = Sc, Nd, Eu, Gd, Ho, Er, Lu) mixtures at a molar ratio of 60:40. It was found that all specimens could be sintered to densities >95% of the theoretical density by adding 5 wt% in situ-synthesized nano-sized SiC and 1 wt% AlN–RE₂O₃ additives. Six out of seven SiC ceramics showed very low electrical resistivity on the order of 10^?4 Ω m. This low electrical resistivity was attributed to the growth of nitrogen-doped SiC grains and the confinement of non-conducting RE-containing phases in the junction areas. The SiC ceramics sintered with AlN–Lu₂O₃ showed a relatively high electrical resistivity (～10^?2 Ω m) due to its lower carrier density (～10¹⁷ cm^?3), which was caused by the growth of faceted grains and the resulting weak interface between SiC grains.     

Sol-gel synthesis and characterization of ZnAl2O4 powders for transparent ceramics

The sol-gel synthesis of ZnAl₂O₄ ceramic powders from alkoxide and acetate sources of metals, as well as the microstucture and the hardness of the hot-pressed ZnAl₂O₄ specimens were considered. ZnAl₂O₄ powders were prepared by the hydrolysis of an alcohol solution of aluminium isopropoxide using an aqueous solution of zinc acetate followed by heat treatment. The thermal evolution of the ZnAl₂O₄ precursor was investigated. The effect of calcination temperature on the morphology and the specific surface area of ZnAl₂O₄ powders were also studied. The sintering of the resultant powders to the high transparent ceramic using a hot pressing with 1?wt% ZnF₂, as a sintering additive was successfully demonstrated. The in-line transmittance of ZnAl₂O₄ ceramics (1?mm thickness) achieved 80% in the visible region and 85% at 5?µm; Vickers hardness was 11.6?GPa.     

Effect of Nano-ZrO2 on the Properties of Al-Al2O3 Nanocomposites Prepared by Mechanical Alloying

In the present work, mechanical alloying was used to prepare Al-20wt.% Al₂O₃ metal-matrix nanocomposites having up to 4wt.% ZrO₂ at the expense of Al₂O₃. The powders were milled for different time intervals. To characterize the powders after milling, x-ray diffraction and transmission electron microscopy were used to identify the phase composition, crystallite size and morphology. In order to study the sinterability, the milled powders were cold pressed and sintered in argon atmosphere at different firing temperatures up to 470 °C for 1 h. The relative density and apparent porosity of the sintered composites were determined according to Archimedes principle. Moreover, the microstructure was examined by a scanning electron microscope attached with an energy dispersive spectrometer (EDS). Microhardness and AC conductivity of sintered composites were also measured. The results pointed out that the increasing of milling time is responsible for uniform distribution of Al₂O₃-ZrO₂ particles in the Al matrix as well as remarkable increases in relative density, microhardness and AC conductivity of the sintered specimens. Also, the relative density was affected considerably by the increasing of sintering temperature. Moreover, increasing of ZrO₂ content led to a significant decrease in the crystal size of the milled powders and increase in the microhardness of the sintered compacts. No changes were observed on the conductivity after addition of ZrO₂.

     

Improvement of wetability,sinterability, mechanical and electrical properties of Al2O3-Ni nanocomposites prepared by mechanical alloying

The wetability improvement and particle size reduction of alumina/Ni composites through mechanical alloying were addressed. Their effect on the sinterability (at high temperature), mechanical and electrical properties were studied. Al₂O₃ matrix nanocomposites reinforced with different volume fractions of Ni up to 10 vol% were prepared by mechanical alloying. The milled powders were cold pressed and sintered at different firing temperatures up to 1600 °C. The morphology of powders and the microstructure of sintered bodies were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), respectively. Furthermore, relative density, apparent porosity, mechanical properties and electrical resistivity of the sintered composites were investigated. The results revealed that Al₂O₃ matrix was successfully coated with Ni thin film through mechanical alloying; the thickness of coat was increased with increasing the Ni content. Moreover, the increasing of both Ni content and sintering temperature up 1600 °C, led to a remarkable increase in the relative density and facture toughness of the sintered specimen. On the other hand, microhardness and elastic modulus were decreased with increasing of Ni content, while they increased significantly with the increase of sintering temperature. The electrical resistivity was decreased with increasing Ni content and sintering temperature.     

Enhanced electromagnetic properties of low-temperature sintered NiCuZn ferrites by doping with Bi2O3

NiCuZn ferrite is a material suitable for low-temperature co-fired ceramic (LTCC) technology due to its high permeability and relatively low sintering temperature. The main research questions regarding NiCuZn ferrites are focused on reducing the sintering temperature of the NiCuZn ferrites to achieve compatibility with the Ag electrodes and improve their electromagnetic properties. In this study, the electromagnetic properties of NiCuZn (Ni_0.29Cu_0.14Zn_0.60Fe_1.94O_3.94) ferrites were enhanced by doping with Bi₂O₃, resulting in a reduction of the sintering temperature to 925 °C. The findings show that a suitable concentration of Bi₂O₃ doping could promote the growth of grains and result in NiCuZn ferrites with denser microstructures sintered at a low temperature. Furthermore, adding 0.30 wt% Bi₂O₃ to NiCuZn ferrite enhances its electromagnetic properties, such as a high real part of permeability (～937.6 @ 1 MHz), high saturation magnetization (～60.353 emu/g), low coercivity (～0.265 kA/m), and excellent dielectric constant (～14.71 @ 1 MHz). In addition, the chemically compatible Ag electrodes suggest that the NiCuZn +0.30 wt% Bi₂O₃ ceramics may be acceptable for LTCC technology.