Titanium-supported Ce-, Zr-containing oxide coatings modified by platinum or nickel and copper oxides and their catalytic activity in CO oxidation

A combination of plasma electrolytic oxidation (PEO) and impregnation techniques followed by annealing in air has been used to obtain composites Pt/nZrO₂ + pTiO₂/Ti, Pt/nZrO₂ + pTiO₂ + zCeO_x/Ti, NiO + CuO/nZrO₂ + pTiO₂/Ti, NiO + CuO/nZrO₂ + pTiO₂ + zCeO_x/Ti with different zirconium and titanium contents and ZrO₂/TiO₂ phase ratio. The composites have been investigated by means of XRD, XPS and SEM/XSA methods. According to the XPS data, the platinum content on the coating surface is ~ 0.4 at.%, whereas the XSA measurements have shown that the nickel and copper contents in coatings attain 16 and 8 at.%, respectively, depending on the initial oxide coatings composition. Nickel and copper oxides form either extended islets or solid layers (“crusts”) on the coating surface. Both the composites promoted with platinum and those with the “crust” built from nickel and copper oxides are active in CO oxidation at the temperatures above 200 °C and 300 °C, respectively.     

Semiconductor TiO2–Ga2O3 thin film gas sensors derived from particulate sol–gel route

Nanostructured and mesoporous TiO₂–Ga₂O₃ thin films with various Ti:Ga atomic ratios were prepared by a new straightforward particulate sol–gel route. Titanium isopropoxide and gallium (III) nitrate hydrate were used as precursors, and hydroxypropyl cellulose (HPC) was used as a polymeric fugitive agent (PFA) in order to increase the specific surface area (SSA). XRD and TEM analysis of the powders revealed that the Ga₂O₃ formed from the nitrate precursor retarded anatase-to-rutile transformation, crystallization and crystal growth. The average crystallite size of pure TiO₂ powder annealed at 600–1000 °C were in the range 4–10 nm; the values that could be decreased to 2–6 nm for TiO₂–Ga₂O₃ powders. Furthermore, one of the highest SSA was obtained by introducing Ga₂O₃ into TiO₂, being 305 m² g⁻¹ for TG11 (Ti:Ga = 50:50 atomic ratio) binary oxide annealed at 600 °C. Thin films produced under optimized conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO and NO₂ gases at low operating temperature of 200 °C, resulting in increased thermal stability of sensing films as well as a decrease in their power consumption. TG11 sensor showed the highest response towards all CO and NO₂ concentrations operated at 200 °C. The response magnitude of 13.7 and 4.3 with response times of 30 s and 108 s were achieved for TG11 sensor towards 400 ppm CO and 10 ppm NO₂, respectively. Furthermore, calibration curves revealed that TiO₂–Ga₂O₃ sensors follow the power law (S = A[gas]^B) (where S is sensor response, coefficients A and B are constants and [gas] is gas concentration) for the two types of gases, and they have excellent capability for the detection of low gas concentrations (25 ppm CO and 0.5 ppm NO₂). The maximum response of TiO₂–Ga₂O₃ sensors towards CO and NO₂ was measured at 450 and 400 °C, respectively. The sensor response decreased with increasing film annealing temperature owing to sintering of the particles. The response magnitude and response time of the sensors obtained in this work is superior to TiO₂-based sensors reported in previous studies.     

Architecture,optical absorption,and photocurrent response of oxygen-deficient mixed-phase titania nanostructures

The optical absorption and photoelectric properties of oxygen-deficient titania (TiO₂) nanostructures consisting of anatase nanotubes and rutile film layer were investigated. The nanostructures were prepared by electrochemical anodization followed by long-time annealing at four temperatures – 450, 550, 650 and 750 °C. Various characterization techniques, including X-ray photoelectron spectroscopy depth profiling, revealed that elemental stable zones (structural regions in which the concentrations of O and Ti are stable) formed within the TiO₂ nanostructures at high annealing temperatures (650 and 750 °C) have O/Ti atomic ratios significantly less than 2. A direct relationship between oxygen vacancy concentration and annealing temperature was established on the basis of this finding. Measurement of the optical absorption spectra of the TiO₂ nanostructures revealed a blue-shift in the absorption edge along with a notable increase in the long-wavelength absorption due to the presence of oxygen vacancies. This observation is in agreement with the first-principles calculations of the absorption coefficients of anatase Ti_nO_2n?1 and Ti_nO_2n?2 structures, in which the oxygen vacancy concentration can be adjusted by varying the supercell size. The contrary photocurrent responses of the TiO₂ nanostructures under ultraviolet and visible light were measured. A strong photocurrent response under filtered visible light (λ > 500 nm) was found for the TiO₂ nanostructures annealed at 650 and 750 °C, which suggests that the dominant positive effect of oxygen vacancies exceeds the adverse impact of other features associated with thickening of the rutile film layer at high annealing temperatures, such as a reduction in the specific surface area and an increased charge recombination rate.     

Stability and dewetting kinetics of thin gold films on Ti,TiOx and ZnO adhesion layers

We present an in situ high-temperature confocal laser microscopy study on the thermal stability of 40 nm thick gold thin films grown on 40 nm Ti, TiO_x and ZnO adhesion layers on (0 0 1) Si. In situ observation of the dewetting process was performed over a wide range of set temperatures (400–800 °C) and ramp rates (10–50 °C min^?1) for each gold/adhesion layer combination. We found that significant dewetting and subsequent formation of gold islands occurs only at and above 700 °C for all adhesion layers. The dewetting is driven to equilibrium for gold/ZnO compared to gold/Ti and gold/TiO_x as confirmed by ex situ X-ray diffraction and scanning electron microscopy characterization. Quantification of the in situ data through stretched exponential kinetic models reveals an underlying apparent activation energy of the dewetting process. This energy barrier for dewetting is higher for gold/Ti and gold/TiO_x compared to gold/ZnO, thus confirming the ex situ observations. We rationalize that these apparent activation energies correspond to the underlying thermal stability of each gold/adhesion layer system.     

The interdependence of structural and electrical properties in TiO2/TiO/Ti periodic multilayers

Multilayered structures with 14–50 nm periods composed of titanium and two different titanium oxides, TiO and TiO₂, were accurately produced by DC magnetron sputtering using the reactive gas pulsing process. The structure and composition of these periodic TiO₂/TiO/Ti stacks were investigated by X-ray diffraction and transmission electronic microscopy techniques. Two crystalline phases, hexagonal close packed Ti and face centred cubic TiO, were identified in the metallic-rich sub-layers, whereas the oxygen-rich ones comprised a mixture of amorphous TiO₂ and rutile phase. DC electrical resistivity ρ measured for temperatures ranging from 300 to 500 K exhibited a metallic-like behaviour (ρ_473K = 1.05 × 10^?5 to 1.45 × 10^?6 Ω m) with a temperature coefficient of resistance ranging from 1.20 × 10^?3 K^?1 for the highest period (Λ = 50.0 nm) down to negative values close to ?4.97 × 10^?4 K^?1 for the smallest one (Λ = 14.0 nm). A relationship between the dimensions of periodic layers and their collective electrical resistivity is proposed where the resistivity does not solely depend on the total thickness of the film, but also depends on the chemical composition and thickness of each sub-layer. Charge carrier mobility and concentration measured by the Hall effect were both influenced by the dimension of TiO₂/TiO/Ti periods and the density of ionized scattering centres connected to the titanium concentration in the metallic sub-layers.     

Porous hierarchical TiO2 nanostructures: Processing and microstructure relationships

A dual porous hierarchical coating of TiO₂ nanotubes (～50 nm diameter) on the nanoscale and large (～1 to 20 μm) pores on the micro-scale can be fabricated on the surface of Ti by anodic oxidation. This unique coating may have potential applications as bioactive coatings for Ti bone implants. This paper details several important aspects of the coating microstructure. TiO₂ coatings were fabricated by anodic oxidation in 1 M H₂SO₄ + 0.1 M NaF solution. Microstructure characterization was carried out using scanning electron microscopy. We also report on the observation of precipitates which form as both a continuous surface layer and of a conical geometry. The mechanism for nanotube formation, precipitate layer formation, and microscopic pitting was discussed. The effect of processing variables (i.e. time, temperature, pH) on the TiO₂ microstructure was studied. Anodization time was found to affect nanotube length and also pit size and density. Lowering the electrolyte pH decreased the nanotube length and microscopic pit density. Increasing electrolyte temperature decreased nanotube length and increased pit/pore and precipitate density. Microscopic pitting, in the nanotube coating was found to occur above grain boundaries in the Ti substrate and above Ti grains with (0 0 0 1) orientation.     

In situ synchrotron diffraction of the electrochemical reduction pathway of TiO2

Despite over ten years of work into the low-cost electrowinning of Ti direct from the oxide, the reduction sequence of TiO₂ pellets in molten CaCl₂ has been the subject of debate, particularly as the reduction pathway has been inferred from ex situ studies. Here, for the first time white beam synchrotron X-ray diffraction is used to characterize the phases that form in situ during reduction and with ～100 μm resolution. It is found that TiO₂ becomes sub-stoichiometric very early in reduction, facilitating the ionic conduction of O ions, that CaTiO₃ persists to nearly the end of the process and that, finally, CaO forms just before completion of the process. The method is quite generally applicable to the in situ study of industrial chemical processes. Implications for the industrial scale-up of this method for the low-cost production of Ti are drawn.     

New dielectric material system of Nd(Mg1/2Ti1/2)O3–CaTiO3 with V2O5 addition for microwave applications

The effects of sintering aids additives on the microstructures and microwave dielectric properties of (1 ? x)CaTiO₃–xNd(Mg_1/2Ti_1/2)O₃ ceramics were investigated. The effects of V₂O₅ additions on the microwave dielectric properties and the microstructures of (1 ? x)CaTiO₃–xNd(Mg_1/2Ti_1/2)O₃ ceramics have been investigated. Doping with 0.5 wt% V₂O₅ can effectively promote the densification and the microwave dielectric properties of (1 ? x)CaTiO₃–xNd(Mg_1/2Ti_1/2)O₃. It is found that CaTiO₃–Nd(Mg_1/2Ti_1/2)O₃ ceramics can be sintered at 1325 °C due to the liquid phase effect of a V₂O₅ additions. The dielectric constant decreases from 140 to 28 as x varies from 0.1 to 1.0. The microwave dielectric properties indicate the possibility of a phase transformation for x between 0.3 and 0.5. A low-pass filter is designed and simulated using the proposed dielectric to study its performance.     

Surface modeling and chemical solution deposition of SrO(SrTiO3)n Ruddlesden–Popper phases

Strontium titanate (STO) is a preferred substrate material for functional oxide growth, whose surface properties can be adjusted through the presence of Ruddlesden–Popper (RP) phases. Here, density functional theory (DFT) is used to model the (1 0 0) and (0 0 1) surfaces of SrO(SrTiO₃)_n RP phases. Relaxed surface structures, electronic properties and stability relations have been determined. In contrast to pure STO, the near-surface SrO–OSr stacking fault can be employed to control surface roughness by adjusting SrO and TiO₂ surface rumpling, to stabilize SrO termination in an SrO-rich surrounding or to increase the band gap in the case of TiO₂ termination. RP thin films have been epitaxially grown on (0 0 1) STO substrates by chemical solution deposition. In agreement with DFT results, the fraction of particular RP phases n = 1–3 changes with varying heating rate and molar ratio Sr:Ti. This is discussed in terms of bulk formation energy.     

Crystal structure,morphology and physical properties of LaCo1−xTixO3±δ perovskites prepared by a citric acid assisted soft chemistry synthesis

The influence of the partial substitution of Co by Ti in the LaCoO₃ perovskite system is studied by evaluating the electrical conductivity, the Seebeck coefficient and the thermal conductivity of the compounds up to T = 1273 K. The X-ray diffraction patterns of the LaCo_1?xTi_xO_3±δ (0.01 ? x ? 0.5) phases show two structural modifications depending on the Ti content. Compounds with x < 0.3 crystallize in the rhombohedrally distorted perovskite structure while samples with x ? 0.3 possess an orthorhombic unit cell. The oxidation state of the Co ions is studied by X-ray absorption near edge structure (XANES) spectroscopy. A negative thermoelectric power is found in the LaCoO₃ system for low level Ti substitution (x = 0.01). In contrast, samples with higher Ti content show a large positive Seebeck coefficient, indicating positive majority charge carriers in the system. The electrical resistivity of the studied materials reveals a semiconducting-like behaviour. The lattice thermal conductivity was found to be low and nearly temperature-independent. The samples exhibit very small crystallite sizes in the range of few nanometres. Therefore, the low thermal conductivity can be assigned to an enhanced phonon scattering on grain boundaries.     

Properties of composite films of titania nanofibers and Safranin O dye

Titania (TiO₂) nanofibers and composite thin films of titania nanofibers and Safranin O dye (SAF) were studied. TiO₂ nanofibers were prepared by electrospinning technique from titanium tetra-isopropoxide precursor solution in ethanol. Surface topology of the nanofibers was observed using scanning electron microscopy (SEM), their crystal structure was studied by X-ray diffraction (XRD) and the chemical composition by X-ray photoelectron spectroscopy (XPS). Properties of the TiO₂ nanofibers were studied in dependence on the values of relative air humidity in the range from 15% to 55%. It was necessary to maintain the relative humidity lower than 30% during electrospinning in order to obtain high quality nanofiber films. The average minimum diameter of the as-prepared TiO₂ nanofibers was found to be around 100 nm. Nanofiber diameter diminishes to about 50 nm after annealing at 420 °C for 1 h. The as-prepared titania nanofiber films were completely amorphous while anatase crystal phase was detected in the films after annealing. In order to prepare the composite films, solution of SAF dye with poly(vinylpyrrolidone) in ethanol/water was dropped off on the prepared titania nanofibers surface. Opto-electrical properties of SAF dye and the resulting nanocomposite films were studied by UV–Vis spectroscopy and current–voltage characteristics. Safranin O is characterized by two strong absorption peaks; one at 274 nm and a wide band with splitting between 420 nm and 600 nm. The optical energy band gap of titania nanofibers was estimated from the UV–Vis measurements to be 3.4 eV. The charge transport in the composite films is influenced by the space charge limited currents due to the very high resistance of the materials.     

Structural response of A2TiO5 (A = La,Nd, Sm,Gd) to swift heavy ion irradiation

Different compositions of orthorhombic A₂TiO₅ (A = La, Nd, Sm, Gd) have been irradiated with swift Xe ions (1.47 GeV). Systematic analysis of the structural modifications induced by ion track formation was completed using transmission electron microscopy, synchrotron X-ray diffraction, and Raman spectroscopy. Significant radiation-induced amorphization occurred, but the size of the amorphous regions within the tracks decreased as smaller cations (higher Z) occupied the A-site. This decrease in the amorphous domain size is attributed primarily to epitaxial recrystallization of a disordered phase at the outer edge of the tracks, the stability of which is related to the ratio of the ionic radii of the A- and B-site (B = Ti) cations. While similar ion track recrystallization phenomena have been observed in pyrochlores of varying composition, A₂TiO₅ is unique in that the disordered phase is not a high-temperature polymorph, suggesting kinetic control of the radiation-induced transformation.     

Electric-field-induced phase-change behavior in (Bi0.5Na0.5)TiO3–BaTiO3–(K0.5Na0.5)NbO3: A combinatorial investigation

The electric-field-induced strain behavior in (1 ? x ? y)(Bi_0.5Na_0.5)TiO₃–xBaTiO₃–y(K_0.5Na_0.5)NbO₃ electroceramics has been studied using a combinatorial technique. A stoichiometrically graded sample was produced to contain compositions across the ternary phase diagram between the two end-member components of 0.93(Bi_0.5Na_0.5)TiO₃–0.07BaTiO₃ and 0.86(Bi_0.5Na_0.5)TiO₃–0.14(K_0.5Na_0.5)NbO₃. Both composition and structural information were measured simultaneously during the application of electric fields using secondary X-ray fluorescence and high-energy X-ray microdiffraction, respectively. An initial electric-field-induced distortion from the pseudo-cubic structure is seen across all compositions, while those with a greater concentration of BaTiO₃ also undergo an electric-field-induced phase transformation. The microstructural contribution to the macroscopic strain within the 0.93(Bi_0.5Na_0.5)TiO₃–0.07BaTiO₃ end member is quantified at a field strength of 5.5 kV mm^?1; 0.08% and 0.11% of the measured macroscopic strain of 0.4% is contributed by the induced ferroelastic domain texture and the volumetric strain associated with the electric-field-induced phase transformation, respectively.     

A thermo-gravimetric and microstructural study of the oxidation of Nbss/Nb5Si3-based in situ composites with Sn addition

The effect of Sn addition on the oxidation of the Nb–24Ti–18Si–5Al–5Cr–2Mo–5Hf–5Sn (at.%) alloy (JG6) in the as cast (AC) and heat treated (HT) conditions was studied at 800 °C and 1200 °C in static air using thermo-gravimetry and microstructural analysis. The oxidation kinetics, morphology and microstructure of the oxide scale and the microstructure of the bulk of the oxidised alloy were investigated. Oxidation occurred by inward oxygen anion diffusion. The oxidation of JG6 at 800 °C and 1200 °C is compared with the oxidation of Sn-free Nb–Ti–Si–Cr–Al–Mo–Hf alloys and is found to have been improved by the addition of Sn. At 800 °C pest oxidation, which was exhibited by the heat treated Nb–24Ti–18Si–5Al–5Cr–2Mo–5Hf alloy (JG4-HT), was eliminated by alloying with 5 at.% Sn. The elimination of pesting at 800 °C is attributed to the nature of the Nb solid solution in the alloy which consists of Sn-rich, Si-rich and Ti lean solid solution usually surrounded by Sn-poor, Si-poor and Ti-rich solid solution. The oxide scales that formed at 1200 °C on JG6 did not separate from the base metal and consisted of Nb₂O₅, TiO₂, SiO₂, HfO₂ and TiNb₂O₇. TiN, instead of TiO₂, and the (Nb,Ti)₅(Sn_1−xSi_x)₃ phase, which is considered as a ternary phase based on Nb₅Sn₂Si, are formed in the diffusion zone of the alloys JG6-AC and JG6-HT after oxidation at 1200 °C. The formation of these phases in the oxidised alloys JG6-AC and JG6-HT controlled the penetration of oxygen into the base material. The better oxidation performance of JG6-AC compared to JG6-HT at 1200 °C is attributed to the formation of Nb₃Sn in the former. It is suggested that the presence of the Sn-poor, Si-poor and Ti-rich Nb_ss in the microstructure is a key to the formation of the Nb₃Sn phase at the scale/diffusion zone interface in the JG6-AC oxidised at 1200 °C.     

Multifunctional polyconjugated molecules with carbazolyl and pyrazolyl moieties for optoelectronic applications

Diethylene derivative possessing carbazolyl and pyrazolyl moieties and its analogue containing additional cyano groups were synthesized and investigated as potential multifunctional materials for organic light emitting diodes. The influence of the electron affinitive cyano groups on the ionization potential (I_p) of the films as well as on the photoluminescence (PL) spectrum, PL quantum yield (η) and PL decay time of the dilute solutions and thin films of the diethylene derivatives was studied. PL measurements revealed that highly luminescent (η = 0.80) cyano-free pyrazole–carbazole derivative in solution became weakly emissive (η = 0.04) by attaching cyano groups as a result of these groups-induced torsional deactivation. However in the solid state, the steric and electrostatic effects of the bulky and polar cyano groups prevented close packing of the molecules, thus significantly reducing migration-induced quenching of the excitons at the defects. Incorporation of the cyano groups resulted in the 3-fold enhancement of the PL quantum yield in the neat film of the polyconjugated derivative as compared to that of the cyano-free film. The I_p of 5.50 eV estimated for the cyano groups-containing compound was found to be higher as compared to the I_p of 5.35 eV for the cyano-free analogue, which in conjunction with the PL data for the films indicated increased electron affinity (by 0.40 eV) in the cyano groups-containing diethylene derivative.     

Ion-irradiation-induced structural transitions in orthorhombic Ln2TiO5

The response of a material to a high radiation field is important when selecting materials for nuclear applications, such as structural materials, nuclear waste forms and inert matrix fuels. In the present study, the radiation response of orthorhombic, rare-earth titanates, Ln₂TiO₅ (Ln = La, Nd, Sm, Gd, Dy and Y), was investigated by 1 MeV Kr²⁺ ion bombardment at temperatures ranging from 50 to 1073 K. In situ transmission electron microscopy revealed that the radiation tolerance and irradiation-induced structural transitions vary largely with composition. Y₂TiO₅ exhibits the lowest critical amorphization temperature (T_c = 623 K), above which crystals cannot be amorphized, which is consistent with its use in the form of nanoclusters in radiation-resistant oxide-dispersion-strengthened steels. The disordered fluorite structure type of Ln₂TiO₅, with smaller Ln cations, formed as an intermediate phase prior to becoming fully amorphous. The fluorite structure type of Ln₂TiO₅, containing more vacancies as compared with that of Ln₂Ti₂O₇, may exhibit enhanced ionic conductivity, which highlights an effective way of using ion beams to modify the properties of materials.     

Surface modification of NiTi/PZT heterostructure thin films using various protective layers for potential MEMS applications

The present study explored the in-situ deposition of hard and adherent nanocrystalline protective coatings on NiTi/PZT/TiO_x thin film heterostructure prepared by dc/rf magnetron sputtering. Protective layers (AlN, CrN and TiCrN) of approximate thickness (~ 200 nm) were used to improve the surface, mechanical and corrosion properties of NiTi/PZT/TiO_x heterostructure without sacrificing the shape memory effect and ferroelectricity of the NiTi and PZT layers, respectively. The influence of the protective layer on structural, electrical and mechanical properties of NiTi/PZT/TiO_x heterostructure was systematically investigated and the results were compared. Nanoindentation studies were performed at room temperature to determine the hardness and reduced modulus. The surface modified NiTi/PZT/TiO_x heterostructures were found to exhibit high hardness, high elastic modulus and thereby better wear resistance as compared to pure NiTi/PZT/TiO_x films. From the results of potentiodynamic polarization test conducted in 1 M NaCl solution, the CrTiN coated NiTi/PZT/TiO_x heterostructure showed the best corrosion resistance with the lowest corrosion current density (1.52 × 10^? 8 A cm^? 2) and the highest protective efficiency (96.8%). The results presented here prove the potential of a surface modified NiTi/PZT/TiO_x heterostructure to be used in various microelectromechanical (MEMS) applications.     

Electronic and luminescence properties of sputter-deposited TiO2 nanostructures

TiO₂ nanostructures are synthesized here by a radiofrequency magnetron sputter deposition technique using tin as a catalyst. The catalyst seeding and the sputter deposition are performed at ambient temperature. The growth of TiO₂ is carried out in a mixed Ar + O₂ and Ar + N₂ atmosphere and is found to comprise pure anatase. The morphologies of the obtained TiO₂ nanostructures are characterized using scanning electron microscopy. The electronic structures are investigated by X-ray absorption near-edge structure spectroscopy. The chemical compositions are analyzed using X-ray photoelectron spectra analysis, which indicates the presence of Ti³⁺. The luminescence properties are examined using cathodoluminescence spectroscopy. Five peaks are resolved from the luminescence data, indicating emissions of oxygen vacancies, F, F⁺, band-to-band emission and self-trapped excitons on TiO₆.     

Precipitation in 18 wt% Ni maraging steel of grade 350

The evolution of precipitates in maraging steel of grade 350 was studied using the complementary techniques of small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). These investigations revealed that ageing the steel at 703 K involved a rhombohedral distortion of the supersaturated b.c.c. martensite accompanied by the appearance of diffuse ω-like structures. This was followed by the appearance of well-defined ω particles containing chemical order. At the ageing temperature of 783 K, Ni₃(Ti, Mo) precipitates were the first to appear with a growth exponent of 1/3. The values of the Porod exponent obtained from the SAXS profiles indicated that the ω particles, formed below 723 K, had diffuse interfaces up to an ageing time of 48 h. On the other hand, Ni₃(Ti, Mo) precipitates, formed above 723 K, developed sharp interfaces in just about an hour. Also, the steel exhibited scaling in phase separation both at 703 and 783 K, but only during the early stages. Through this study it was established that, at temperatures of ageing less than 723 K, evolution of ω particles takes place through the collapse of the unstable b.c.c. lattice and, at temperatures above 723 K, precipitation of A₃B type of phases through the mechanism of clustering and ordering of atomic species. Sharp interfaces develop rather quickly when the mechanism of precipitation involves development and amplification of a concentration wave alone as in the nucleation of Ni₃(Ti, Mo) at 783 K than when an interplay of both the displacement and concentration waves is required as in the evolution of ω at 703 K. These results indicate towards the possibility of existence of two separate time–temperature–transformation (TTT) curves, one for the evolution of ω-phase and another for nucleation and growth of Ni₃(Ti, Mo).     

Characterization and dielectric behavior of V2O5-doped 0.9Mg0.95Co0.05TiO3–0.1Ca0.6La0.8/3TiO3 ceramic system at microwave frequency

The microwave dielectric properties and the microstructures of Mg_0.95Co_0.05TiO₃–Ca_0.6La_0.8/3TiO₃ ceramics, prepared by a mixed oxide route, have been investigated. With small amount of V₂O₅ additions, the sintering temperatures of 0.9Mg_0.95Co_0.05TiO₃–0.1Ca_0.6La_0.8/3TiO₃ ceramics can be lowered to 1250 °C. The microwave dielectric properties are found strongly correlated with the sintering temperature as well as the amount of V₂O₅ additions. The Q × f value of 0.9Mg_0.95Co_0.05TiO₃–0.1Ca_0.6La_0.8/3TiO₃ increased with increasing temperature to 1250 °C and decreased thereafter. The decrease in Q × f value was coincident with the abnormal grain growth. A maximum Q × f value of 58,000 (GHz) associated with a dielectric constant (?_r) of 21.7 and a temperature coefficient (τ_f) of ?10 ppm/°C, was achieved for 0.25 wt.% V₂O₅-doped samples at 1250 °C. Moreover, a cross-coupled compact hairpin filter with designed center frequency of 2.0 GHz is designed and fabricated using the proposed dielectric ceramic to study its performance. It also showed a substantial reduction in both insertion loss and size in comparison with other dielectrics FR4 and alumina.