Titanium diboride (TiB2) and its ceramic composites were prepared by hot pressing process. The sintering process, phase evolution, microstructure and mechanical properties of TiB2 ceramics prepared by using different milling media materials: tungsten carbide (WC/Co) or SiAlON was studied. It was found that the inclusion of WC/Co significantly improved the sinterability of the TiB2 ceramics. A core/rim structure with pure TiB2 as the core and W-rich TiB2, i.e. (Ti,W)B2 as the rim was identified. Microstructure analysis revealed that this core/rim structure was formed through a dissolution and re-precipitation process. In addition, silicon carbide (SiC) was also introduced to form TiB2–SiC composites. The addition of SiC as the secondary phase not only improved the sinterability but also led to greatly enhanced fracture toughness. The optimum mechanical properties with Vickers hardness ~22GPa, and fracture toughness ~6MPam1/2 were obtained on TiB2–SiC composites milled with WC/Co.

Dielectric properties of titanium oxide ceramics are strongly influenced by the microstructural features and concentration of dopants and impurity ions. Electrical conductivity (via insulation resistance) of vanadium doped nanostructured titanium dioxide (TiO 2 ) ceramics was measured as a function of donor concentration and temperature. In order to further clarify the effect of the dopants on the microstructural development and resultant dielectric properties of TiO 2 , electron paramagnetic resonance (EPR) spectroscopy was employed. Vanadium-doped TiO 2 exhibited well-defined hyperfine splitting characteristics of the 51 V nuclei indicating that the dopant ions are dispersed within the grains and not preferentially segregated at the grain boundaries.

We have successfully grown ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) films on base metal foils by chemical solution deposition using sol–gel solutions containing polyvinylpyrrolidone. Under zero-bias field, we measured a dielectric constant of ≈820 and dielectric loss of ≈0.06 at room temperature, and a dielectric constant of ≈1250 and dielectric loss of ≈0.03 at 150 °C. In addition, leakage current density of ≈1.5 × 10−8 A/cm2, remanent polarization of ≈11.2 μC/cm2, and coercive field of ≈40.6 kV/cm were measured at room temperature on a ≈3-μm-thick PLZT film grown on LaNiO3-buffered nickel substrate. Finally, energy density ≈25 J/cm3 was measured from the P–E hysteresis loop at an applied field of 2 × 106 V/cm.

High energy density and breakdown/operating voltages with lower dielectric film thickness and manufacturing cost are the necessary traits in futuristic capacitors for a variety of applications. Prior studies have reported the successful fabrication of high-k, thin-film ferroelectrics with aspect ratios (diameter/thickness) < 1000; however, devices with aspect ratios > 10(4)-10(5) are necessary to meet the large-capacitive requirements in pulsed-power applications such as the inverters in hybrid electric vehicles (HEVs). It is also widely accepted that the breakdown field of thin films decreases logarithmically with an increase in the aspect ratio (area) due to the increased probability of producing a defect spot. These observations raise an important question: can we fabricate ferroelectric high-k film capacitors that have large aspect ratio and can sustain high fields? Here we report the fabrication and characterization of Pb0.92La0.08Zr0.52Ti0.48O3 thin-film capacitors with aspect ratios > 10(4) that can be operated at similar to 1MV cm(-1) and are suitable for embedded passives in HEVs. Dielectric spectroscopy showed a low-frequency anomalous relaxation behaviour in large-aspect-ratio heterostructure, which was analysed and interpreted using an equivalent circuit model. The measured anomalous relaxation behaviour was de-convoluted using the model to obtain the actual material response. High capacitances (1-5 mu F) and energy densities of (similar to 9J cm(-3)) were routinely measured in these high-aspect-ratio films.

Nanostructured TiO2 has shown promise as a dielectric material for high energy density ceramic capacitors because of its high dielectric breakdown strength and dielectric constant. Strategies to increase the insulation resistance or to reduce the leakage current of TiO2 include doping with transition metal ions. It is shown that Mn doping followed by an appropriate thermal treatment increases the grain boundary resistivity significantly and lowers the dielectric loss. Electrical measurements along with electron paramagnetic resonance and scanning electron microscopy of Mn-doped nanoscopic TiO2 demonstrate that sintering at 900 degrees C leads to optimal electrical properties that are correlated with a non-uniform distribution of dopant ions, concentrated at the grain boundaries. Nanostructured TiO2 dielectrics with improved insulation resistance are promising for the development of higher energy density capacitors. (C) 2012 Elsevier B.V. All rights reserved.

Ba0.6Sr0.4TiO3 (BST) films were deposited by pulsed laser deposition on copper foils with low-temperature self-buffered layers. The deposition conditions included a low oxygen partial pressure and a temperature of 700 degrees C to crystallize the films without the formation of secondary phases and substrate oxidation. The results from x-ray diffraction and scanning electron microscopy indicated that the microstructure of the BST films strongly depended on the growth temperature. The use of the self-buffered layer improved the dielectric properties of the deposited BST films. The leakage current density of the BST films on the copper foil was 4.4 x 10(-9) A cm(-2) and 3.3 x 10(-6) A cm(-2) with and without the self-buffered layer, respectively. The ferroelectric hysteresis loop for the BST thin film with buffer layer was slim, in contrast to the distorted loop observed for the film without the buffer layer. The permittivity (700) and dielectric loss tangent (0.013) of the BST film on the copper foil with self-buffered layer at room temperature were comparable to those of the film on metal and single-crystal substrates.

Dielectric properties of undoped and manganese (Mn)-doped titanium dioxide (TiO2) ceramics were measured by various test methods including impedance spectroscopy techniques. It was found that direct current conductivity and dielectric loss were effectively suppressed by small amount (similar to 0.05 mol%) of Mn doping due to generation of possible electron traps. Further increase of Mn content led to formation of oxygen vacancies and increase of dielectric loss. Increased grain-boundary resistivity was observed as Mn-doping concentration increases, presumably due to segregation of Mn solutes at the grain boundaries. Larger difference between the grain and grain-boundary conductivity gave rise to space charge polarization. It was shown that TiO2 ceramics with optimum amount of Mn-doping concentration possess good dielectric properties that are suitable for energy storage applications.

Ceramic films of high permittivity and breakdown strength are critical to advanced power electronic devices. We have grown ferroelectric films of lead lanthanum zirconate titanate (PLZT) on base metal foils by chemical solution deposition. We measured a dielectric constant of ≈700 and dielectric loss of ≈0.07 at -50°C and a dielectric constant of ≈2200 and dielectric loss of ≈0.06 at 150°C. At room temperature, we measured a leakage current density of ≈6.6 × 10-9 A/cm2, mean breakdown strength of 2.6 MV/cm, and energy density >;85 J/cm3. Highly accelerated lifetime testing (HALT) was performed to determine the reliability of these PLZT film-on-foil capacitors under high temperature and high field stress conditions. Samples were exposed to temperatures ranging from 100 to 150°C and electric fields ranging from 8.7 × 105 V/cm to 1.3 × 106 V/cm during HALT. The breakdown behavior of the samples was evaluated by Weibull analysis. The mean time to failure, >;3000 h, was projected at 100°C with a dc electric field of ≈2.6 × 105 V/cm.

We have grown ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) films on platinized silicon and LaNiO3-buffered nickel substrates by chemical solution deposition using a sol–gel process based on acetic acid chemistry. The following measurements were obtained under zero-bias field: relative permittivity of ≈960 and dielectric loss of ≈0.04 on the PLZT film grown on Pt/Si substrates, and relative permittivity of ≈820 and dielectric loss of ≈0.06 on the PLZT film grown on LNO-buffered Ni substrates. In addition, a relative permittivity of 125 and dielectric loss of 0.02 were measured at room temperature under a high bias field of 1×106V/cm on PLZT deposited on LNO-buffered nickel substrate. Furthermore, a steady-state leakage current density of ≈8.1×10−9A/cm2 and mean breakdown field strength of 1.7×106V/cm were measured at room temperature. Finally, remanent polarization (Pr) of ≈2.0×10−5C/cm2, coercive electric field (Ec) of ≈3.4×104V/cm, and energy density of ≈45J/cm3 were determined from room-temperature hysteresis loop measurements on PLZT/LNO/Ni film-on-foil capacitors with 250-μm-diameter platinum top electrodes.

BaTiO3–SrTiO3 (BST) thick films (~250–390μm) with layered structures were fabricated by tape-casting and lamination process. Layered composites with various Ba/Sr ratios were obtained by lamination of BaTiO3 (BT) and SrTiO3 (ST) tapes in different spatial configurations (2–2). As-prepared BST ceramics showed much improved sinterability over the laminates of pure BT or pure ST tapes. Dielectric properties of materials were measured in the temperature range of 25°C to 200°C. The method of utilizing of layered structures offered flexibility to maximize the energy storage capability at specific operating conditions: (temperature and electric field) by tailoring the dielectric properties through varying the spatial configurations of BT and ST films.

Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) films were deposited on platinized silicon substrates (Pt/Si) using a polyvinylpyrrolidone (PVP) modified sol–gel method. Pyrolysis of the green films was conducted via two methods: rapid thermal annealing (RTA) and a step-wise preheat treatment (SPT). Microstructure analysis and dielectric property characterization were performed on samples treated by these two methods. Results showed that the SPT-pyrolyzed films exhibited much better dielectric properties when compared with the RTA-pyrolyzed films. The differences in dielectric properties were correlated to microstructural features caused by the different pyrolysis conditions. High-quality PLZT films with high dielectric constant (≈860 at zero bias) and high breakdown strength (≈2.1MV/cm) were fabricated under controlled pyrolysis conditions. This work demonstrated the potential application of this material for power electronics in electric drive vehicles.

Nanostructured (~200 nm grain size) titanium dioxide (TiO2) ceramics were densified at temperature as low as 800 °C by pressureless sintering in a pure oxygen atmosphere. Phase transition and microstructural development of sintered samples were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Dielectric properties including d.c. conductivity, dielectric constant, loss tangent, and dielectric breakdown strength (BDS) were determined for samples sintered at various temperatures. The influence of sintering temperature on the microstructural development, defect chemistry, and dielectric properties of TiO2 is discussed. Nanostructured TiO2 ceramics with high sintering density (>98%) lead to improved dielectric properties; high BDS (~1800 kV/cm), low electrical conductivity (~5 × 10−15 S/cm), high dielectric constant (~130), and low loss tangent (~0.09% at 1 kHz), which is promising for application in high energy density capacitors.

Nanosized titanium dioxide (TiO2) powders (similar to 40 nm) were used for preparation of tape-casting slurries. Effect of various solvents and dispersants on the dispersability of TiO2 slurries was studied by sedimentation tests and rheology measurements. TiO2 green tapes were prepared by tape-casting method and densified at 1000 degrees C with a sintered density > 95%. Dielectric properties of TiO2 tapes were studied by measuring of dielectric constant, loss factor and dielectric breakdown strength (BDS) with respect to their microstructural development. BDS values as high as similar to 1400 kV/cm were obtained for sintered tapes so that energy densities up to 14 J/cm3 could be achieved.

Titanium dioxide (TiO2) ceramics with various grain sizes were investigated by impedance spectroscopy techniques. Dielectric loss peak identified in coarse grain TiO2 was attributed to space charge polarization occurring at the grain boundaries. Electric modulus representation of the impedance data showed two types of relaxation processes in coarse grain TiO2, whereas only one type was observed in fine grain TiO2. Long-range migration of oxygen vacancies was found to be the dominant conduction mechanism for fine grain TiO2, while electron hopping between localized states was attributed to dielectric relaxation in coarse grain TiO2.

Effects of different solvent systems and dispersant on tape casting slurries of TiO2 nanopowders (similar to 40nm) were studied by rheological measurements. It was found that Xylenc/Ethanol with phosphate ester (PE) as dispersant gave the best dispersion quality which resulted in highly homogenous, dense. smooth and crack-free tapes. The presence of phosphate ester inhibited the sintering of TiO2 powders and refined the grain size. Sintered tapes with 200-300nm grain size and relative density over 90%, had dielectric constant similar to 100, dielectric loss less than 1% and dielectric breakdown strength (BDS) over 1000KV/cm.

High purity nanosized titanium dioxide (TiO2) powders were synthesized by precipitation method using Ti(IV)-isopropoxide as starting material. Well-crystallized and phase pure anatase TiO2 powders with a particle size about 10nm can be obtained by calcination of freeze-dried precipitates at 400 degrees C. The sinterability of powders calcined at 400 degrees C and 700 degrees C were compared with commercial TiO2 powders with similar particle size. The electrical and dielectric properties of the TiO2 bulk samples sintered at various temperatures were measured and correlated with the microstructural development.

Two kinds of ultra-fine Ti(C,N) based cermet cutter with different TiN content were manufactured by means of vacuum sintering technology.Under the condition of different cutting speed and feed rate in machining medium carbon steel 45,the endurance,wear mechanism and failure mode of cutters were analyzed.The results show that oxidation wear and diffusion wear are two principal wear mechanisms in high speed turning.Under the conditions of high speed and feed rate,the cutter with lower TiN content exhibits better performance.The cutting speed has a great influence on the cutting life.The feed rate also has influence on cutting life especially at low cutting speed.

A Ti(C, N)-based cermet with titanium carbide (TiC) additive was fabricated by the conventional powder metallurgy technique. The initial powder particle sizes of the main hard phase components [Ti(C, N), TiC and TiN] were nano/submicron-sized, in order to achieve an ultra-fine grain sizes microstructure. Through scanning electron microscopy observation, a new kind of bright core and grayish rim structure was detected, and its formation mechanism was proposed. In addition, quantitative information about the chemical composition of various phases was obtained by energy dispersive X-ray analysis. Phase identification was carried out by X-ray diffraction and the lattice parameter of each phase was calculated. The mechanical properties at room temperature were also tested, in order to correlate them with the cermet's starting composition and microstructural features.

Two series of Ti (C, N)-based cermets, one with TiC addition and the other with TiN addition, were fabricated by conventional powder metallurgy technique. The initial powder particle size of the main hard phase components (Ti (C, N), TiC and TiN) was nano/submicron-sized, in order to achieve an ultra-fine grade final microstructure. The TiC and TiN addition can improve the mechanical properties of Ti (C, N)-based cermets to some degree. Ultra-fine grade Ti (C, N)-based cermets present a typical core/rim (black core and grayish rim) as well as a new kind of bright core and grayish rim structure. The average metallic constituent of this bright core is determined to be 62 at% Ti, 25 at% Mo, and 13 at% W by SEM–EDX. The bright core structure is believed to be formed during the solid state sintering stage, as extremely small Ti (C, N)/TiC/TiN particles are completely consumed by surrounding large WC and Mo2C particles. Low carbon activity in the binder phase will result in the formation (Ni2Mo2W)Cx intermetallic phase, and the presence of this phase plays a very important role in determining the mechanical properties of TiN addition cermets.