Si<Subscript>3</Subscript>N<Subscript>4</Subscript>/TiN composites produced from TiO<Subscript>2</Subscript>-Modified Si<Subscript>3</Subscript>N<Subscript>4</Subscript> powders

Si₃N₄/TiN composites have been produced by hot pressing at temperatures from 1600 to 1800°C in a nitrogen atmosphere, using silicon nitride powders prepared by self-propagating high-temperature synthesis and surface-modified with titanium dioxide nanoparticles. We examined the effect of TiO₂ content on the microstructure, phase composition, and mechanical strength of the ceramics. It is shown that titanium nitride can be formed by the reaction Si₃N₄ + TiO₂ → TiN + NO + N₂O + 3Si. The Si₃N₄/TiN composites containing 5–20% TiN have a low density, high porosity, and a bending strength of 60 MPa or lower. In Si₃N₄/TiN ceramics produced using calcium aluminates as sintering aids, the silicon nitride grains are densely packed, which ensures an increase in strength to 650 MPa.     

Catalytic effect of Ti<Subscript>5</Subscript>Si<Subscript>3</Subscript> on thermal decomposition of Li<Subscript>3</Subscript>AlH<Subscript>6</Subscript>

Fine Ti₅Si₃ powder has been mechanochemically synthesized from a mixture of elemental Ti and Si powders. When Ti₅Si₃ is added as a catalyst into Li₃AlH₆, it shows a good catalytic ability by reducing the decomposition temperature and improving the decomposition kinetics as well. Although its catalytic effect is not as good as well-known TiCl₃, the use of Ti₅Si₃ has a benefit of releasing more hydrogen than TiCl₃ during dehydrogenation. This can be explained by that Ti₅Si₃, unlike TiCl₃, does not incur any chemical reactions with Li₃AlH₆ and thus remains inert during milling for dispersion.     

Melting behavior of the Nowotny phase Mo<Subscript>4.8</Subscript>Si<Subscript>3</Subscript>C<Subscript>0.6</Subscript>

Mixtures of the Mo₅Si₃ silicide with 1.1–2.4 wt % carbon were melted after reaction sintering and the formation of the Nowotny phase (Mo_4.8Si₃C_0.6), and the effect of various heat treatments on the phase composition of the samples was studied. The crystallization of the melted samples leads to a reduction of the volume fraction of the Nowotny phase relative to that after reaction sintering, but subsequent annealing below the liquid phase formation temperature allows the volume fraction of Mo_4.8Si₃C_0.6 to be again raised. We discuss possible causes of the observed phase transformations.     

Formation of Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript> from Ti-Si-TiC powders by pulse discharge sintering (PDS) technique

Ti/Si/TiC powder mixture with molar ratios of 2:2:3 were sintered at various temperatures from 700–1300 °C for 15 min by PDS technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for the evaluation of phase composition in different samples for the understanding of the sintering mechanism for this system. Results showed that Ti₅Si₃ formed as the intermediate phase during sintering. The reaction between Ti₅Si₃ and TiC as well as Si induces the formation of Ti₃SiC₂, and TiSi₂ appears as the byproduct in this process. At temperature above 1000 °C, TiSi₂ reacts with TiC to form Ti₃SiC₂. High Ti₃SiC₂ phase content bulk material can be synthesized at 1300 °C for 15 min.     

Phase stability,microstructure and high-temperature properties of NbSi<Subscript>2</Subscript>- and TaSi<Subscript>2</Subscript>-oxide conducting ceramic composites

NbSi₂- and TaSi₂-based electroconductive ceramic composites with the addition of 40–70 vol% Al₂O₃ and ZrO₂ particles were fabricated by high-temperature sintering (1400–1600 °C) under argon. Their phase stability, microstructural evolution, oxidation kinetics and electrical properties were studied at high temperatures. The densification of the composites was improved by increasing the oxide phase content and sintering temperature. The interaction of the starting metal disilicides with residual oxygen sources resulted in the formation of the hexagonal-structured 5–3 metal silicide (Nb₅Si₃ and Ta₅Si₃) phases. The increasing sintering temperature and volume percentage of the oxide phase reduced the pest oxidation, particularly for the silicide–alumina composites, which exhibited lower oxidation-induced mass changes than their dense monolithic metal silicides. Depending on the silicide–oxide volume percentage, their electrical conductivities ranged from 5.3 to 111.3 S/cm at 900 °C. Their phase stability, reduced oxidation rates and high electrical conductivities at high temperatures show promise for future high-temperature applications in advanced sensing.     

Synthesis,tunable luminescence and thermal stability of Mg<Subscript>2</Subscript>Al<Subscript>4</Subscript>Si<Subscript>5</Subscript>O<Subscript>18</Subscript>:Ce<Superscript>3+</Superscript>/Mn<Superscript>2+</Superscript> phosphors

Ce³⁺/Mn²⁺ singly doped and codoped Mg₂Al₄Si₅O₁₈ phosphors were synthesized by a solid state reaction. The phase, luminescent properties and thermal stability of the synthesized phosphors were investigated. Ce³⁺ and Mn²⁺ singly doped Mg₂Al₄Si₅O₁₈ phosphors show emission bands locating in blue and yellow–red regions, respectively. In Ce³⁺ and Mn²⁺ codoped Mg₂Al₄Si₅O₁₈, tunable luminescence was obtained because of the energy transfer from Ce³⁺ to Mn²⁺. In Mg₂Al₄Si₅O₁₈:Ce³⁺/Mn²⁺ phosphors with a fixed Ce³⁺ concentration, energy transfer efficiency increases with the increasing Mn²⁺ concentration, which is confirmed by the continually decreasing intensity and shortening decay time of Ce³⁺ emission. Moreover, the luminescent properties and thermal stability provide a great significance on the applications in the field of light emitting diodes.     

Electrochemical properties of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/C and Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/C/Ag nanomaterials

We have prepared and characterized lithium titanate-based anode materials, Li₄Ti₅O₁₂/C and Li₄Ti₅O₁₂/C/Ag, using polyvinylidene fluoride as a carbon source. The formation of such materials has been shown to be accompanied by fluorination of the lithium titanate surface and the formation of a highly conductive carbon coating. The highest electrochemical capacity (175 mAh/g at a current density of 20 mA/g) is offered by the Li₄Ti₅O₁₂-based anode materials prepared using 5% polyvinylidene fluoride. The addition of silver nanoparticles ensures a further increase in electrical conductivity and better cycling stability of the materials at high current densities.     

Preparation of Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript> through reduction of titanium dioxide with silicon carbide

This paper describes the reduction of titanium dioxide with a mixture of silicon carbide and silicon powders at a temperature of 1550°C under vacuum. It has been shown that the use of the combined reductant enables the preparation of the ternary phase Ti₃SiC₂ through concurrent carboand silicothermic processes. The optimal compositions for Ti₃SiC₂ formation are TiO₂ + (1.5–x)SiC + 2xSi with x = 0.4–0.5. The Ti₃SiC₂ yield then reaches 96 wt %.     

Diffusion bonding of Ti<Subscript>3</Subscript>AlC<Subscript>2</Subscript> ceramic via a Si interlayer

Based on the structure characteristic of Ti₃AlC₂ and the easy formation of Ti₃Al_{1 − x} Si _x C₂ solid solution, a Si interlayer was selected to join Ti₃AlC₂ layered ceramic by diffusion bonding method. Joining was performed at 1,300–1,400 °C for 120 min under 5 MPa load in an Ar atmosphere. The phase composition and interface microstructure of the joints were investigated by XRD, SEM and EPMA. The results revealed that Ti₃Al(Si)C₂ solid solution formed at the interface. The mechanism of bonding is attributed to silicon diffusing inward the Ti₃AlC₂. The strength of joints was evaluated by a 3-point bending test. The jointed specimens exhibit a high flexural strength of 285 ± 11 MPa, which is about 80% of that of the Ti₃AlC₂; and retain this strength up to 1,000 °C. The high mechanical performance of the joints indicates that diffusion bonding via a Si interlayer is effective to bond Ti₃AlC₂ ceramic.     

Synthesis and properties of AgTi<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>-based NASICON-type phosphates doped with Nb<Superscript>5+</Superscript>, Zr<Superscript>4+</Superscript>, and Ga<Superscript>3+</Superscript>

We have synthesized materials based on a silver titanium phosphate with partial substitution of tri-, tetra-, or pentavalent cations for titanium: Ag_1±x Ti_2−x M _x (PO₄)₃ (M = Nb⁵⁺, Ga³⁺) and AgTi_2−x Zr _x (PO₄)₃. The materials have been characterized by X-ray diffraction and impedance spectroscopy and have been shown to have small thermal expansion coefficients. Their ionic conductivity has been determined. Silver ions in these materials are difficult to replace with protons.     

Effect of Zn<Superscript>2+</Superscript>, Ti<Superscript>2+</Superscript> dopants on structural,optical and electrochemical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript> nanoparticles synthesized via non-aqueous sol–gel route

Transition divalent metal cations (Zn²⁺, Ti²⁺) doped V₂O₅ nanoparticles were synthesized via non-aqueous sol–gel route. The influence of dopant materials on the characteristics of V₂O₅ nanoparticles was studied. XRD studies ensure that all the prepared samples possess phase pure orthorhombic structure. From the FESEM images, it was noted that the products possess uniform particle size around 20–30 nm. The presence of functional groups and dopants was confirmed by FTIR, Raman, and elemental analysis respectively. From UV–Vis spectra, the significant blue shift was observed for doped samples compared to pure V₂O₅ nanoparticles, which is attributed to the quantum confinement effect. The high capacity retention of the intercalation compound was measured by using C–V study and implies that the prepared samples are very promising electrode materials for supercapacitor.     

High-temperature oxidation behaviour of Ti<Subscript>3</Subscript>Si<Subscript>(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript>Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>C<Subscript>2</Subscript> in air

The oxidation behaviours of bulk Ti₃Si_(1−x)Al _x C₂ prepared by hot pressing were investigated. The results showed that the isothermal oxidation behaviour of Ti₃SiC₂ obeyed a parabolic law between 900 and 1100°C, and followed a two-step parabolic rate law between 1200°C and 1300°C. The cyclic oxidation behaviour of material is assumed to obey a three-step parabolic rate law at 1100°C and 1200°C. The calculated activation energy of isothermal oxidation is 101·43 kJ·mol⁻¹. The oxide layers consisted of a mass of α-Al₂O₃ and little TiO₂ and SiO₂ are observed on Ti₃SiC₂ as a dense and adhesive protect scale. The oxidation mechanism varies with the additive aluminum that greatly improves the oxidation resistance of Ti₃SiC₂.     

Structural,Magnetic, and Optoelectronic Properties of TbNi<Subscript>5</Subscript>, TbNi<Subscript>3</Subscript>Ti<Subscript>2</Subscript> and TbNi<Subscript>3</Subscript>V<Subscript>2</Subscript> Compounds

The spin-polarized, electronic, magnetic, and optical properties of TbNi₅, TbNi₃Ti₂, and TbNi₃V₂ intermetallic compounds have been calculated by employing the full-potential linear augmented plane waves (FP-LAPW) within the density functional theory (DFT) and implemented in the WIEN2k package. In this approach, the generalized gradient approximation with Hubbard U-correction (GGA + U) was chosen as exchange-correlation potential. The electronic structure such as band structure and density of states have been investigated and compared among them. The frequency dependences of dielectric function, optical absorption, reflectivity, and optical conductivity are determined. The optical spectra are changed due to the substitution of nickel with titanium and vanadium. Total and local magnetic moments of Tb, Ni, Ti, and V are also estimated; it is shown that the total magnetic moment of the three alloys is vigorously contributed by the local magnetic moment of terbium.     

Structure of a HAp/TiO<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Nanocomposite Studied by Vibrational Spectroscopy Techniques

A hydroxyapatite/TiO_y nanocomposite material has been studied by X-ray diffraction, infrared spectroscopy, and Raman spectroscopy. The results demonstrate that annealing at 400°C changes the valence state of the titanium and leads to the formation of [Ti(OH)₂]²⁺ and [TiHPO₄]²⁺ surface groups and terminal carbonyls and partial heterovalent cation substitutions of Ti³⁺ and Ti⁴⁺ for Ca²⁺. As the annealing temperature is raised to 600°C, surface groups disappear. The amount of inflowing oxygen is insufficient for the complete oxidation of TiO_0.92 to TiO₂ in hydroxyapatite/TiO_0.92. The result is the formation of an intermediate nanophase with the composition Ti_4.5O₅.     

Structural and optical characterization of RE (Eu<Superscript>2+</Superscript>, Ce<Superscript>3+</Superscript>) doped SrMg<Subscript>2</Subscript>Al<Subscript>6</Subscript>Si<Subscript>9</Subscript>O<Subscript>30</Subscript> nanocrystalline phosphor

This article present the reports on optical study of Eu²⁺ and Ce³⁺ doped SrMg₂Al₆Si₉O₃₀ phosphors, which has been synthesized by combustion method at 550 °C. Here SrMg₂Al₆Si₉O₃₀:Eu²⁺ emission band observed at 425 nm by keeping the excitation wavelength constant at 342 nm, whereas SrMg₂Al₆Si₉O₃₀:Ce³⁺ ions shows the broad emission band at 383 nm, under 321 nm excitation wavelength, both the emission bands are assigned due to 5d–4f transition respectively. Further, phase purity, morphology and crystallite size are confirmed by XRD, SEM and TEM analysis. However, the TGA analysis is carried out to know the amount of weight lost during the thermal processing. The CIE coordinates of SrMg₂Al₆Si₉O₃₀:Eu²⁺ phosphor is observed at x?=?0.160, y?=?0.102 respectively, which may be used as a blue component for NUV-WLEDs. The critical distance of energy transfer between Ce³⁺ ions and host lattice is found to be 10.65 Å.     

Fabrication and mechanical properties of WC particulate reinforced Cu<Subscript>47</Subscript>Ti<Subscript>33</Subscript>Zr<Subscript>11</Subscript>Ni<Subscript>6</Subscript>Sn<Subscript>2</Subscript>Si<Subscript>1</Subscript> bulk metallic glass matrix composites

The mechanical behavior of the WC particulate (WC_p) reinforced Cu₄₇Ti₃₃Zr₁₁Ni₆Sn₂Si₁ bulk metallic glass (BMG) matrix composites has been examined. The mechanical properties are improved with increasing WC_p content up to 20 wt%. The ultimate compression strength and plastic strain of the composite containing 20 wt% WC_p are 2.4 GPa and 2.4%, while those of the monolithic BMG are 1.6 GPa and ∼0%, respectively. The multiple shear band formation and crack deflections through WC particles have been identified as the main mechanism for the improved toughness.     

Ba<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>TiO<Subscript>3</Subscript> ferroelectric nanofilms on silicon buffered with a TiO<Subscript>2</Subscript> layer

Polycrystalline, 50- to 70-nm-thick barium strontium titanate films of composition Ba_0.8Sr_0.2TiO₃ have been grown on single-crystal silicon substrates by rf ion-beam sputtering. We have determined their structure and composition and detected impurities at the film/substrate interface in the form of titanium silicide islands. The deposition of a 4- to 6-nm-thick TiO₂ buffer layer onto Si by ion-beam sputtering before ferroelectric film growth is shown to prevent uncontrolled formation of impurities near the interface. The buffered heterostructures possess high thermal stability.     

A facile method to enhance electrochemical performance of high-nickel cathode material Li(Ni<Subscript>0.8</Subscript>Co<Subscript>0.1</Subscript>Mn<Subscript>0.1</Subscript>)O<Subscript>2</Subscript> via Ti doping

The cycle stability of Li(Ni_0.8Co_0.1Mn_0.1)O₂ is enhanced obviously by titanium doping via a facile solid-state method. The property of crystal structure is evaluated by XRD, which illustrates the samples possessed a layered α-NaFeO₂ structure with R-3m space group. According to the charge/discharge studies, the capacity retention of pristine sample is around 51% after 125 cycles at 5 C, and the sample with Ti dopant displays a good cyclic stability, after 125 cycles, the capacity retention increases to 75% under 5 C, suggesting it could be possibly applied in fast charge Lithium-ion battery area. The superb electrochemical performance might be attributed to the Ti⁴⁺ occupy the layer structure to broaden the Lithium-ion channel, which is benefit to lithium intercalation and deintercalation during cycling.     

Giant dielectric and electrical properties of sodium yttrium copper titanate: Na<Subscript>1/2</Subscript>Y<Subscript>1/2</Subscript>Cu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript>

The electrical properties and dielectric response in Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramic prepared by conventional solid-state reaction method and sintered at 1,090 °C for 5 h were investigated as functions of frequency and temperature. Main phase of Na_1/2Y_1/2Cu₃Ti₄O₁₂ with CaCu₃Ti₄O₁₂-like crystallographic structure and CuO secondary phase were observed in the X-ray diffraction pattern. Abnormal grain growth was observed just as observed in CaCu₃Ti₄O₁₂ ceramics. The Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramic exhibits a high ε′ of ~2.04 × 10⁴ at 20 °C and 1 kHz and low tan δ (with the minimum 0.080 at 5 kHz). Impedance spectroscopy analysis reveals that Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramic is electrically heterogeneous, consisting of semiconducting grains and insulating grain boundaries. Giant ε′ response in Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramic is therefore attributed to an internal barrier layer capacitor effect.     

Enhanced red-emitting phosphor Na<Subscript>2</Subscript>Ca<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>8</Subscript>:Eu<Superscript>3+</Superscript> by charge compensation

A series of novel red-emitting Na₂Ca_3???x Si₂O₈:xEu³⁺ phosphors were synthesized by solid state reactions. The phosphors can strongly absorb 395 nm light, and show red emission with a good color purity. The excitation and emission spectra properties of Na₂Ca₃Si₂O₈:Eu³⁺ were characterized. Na₂Ca₃Si₂O₈:Eu³⁺ with self-compensated and alkali metal ions charge compensated approaches (2Ca²⁺→Eu³⁺ + M⁺, M?=?Li⁺, Na⁺, K⁺) have investigated, which found that the red emission of luminescent intensity can be greatly enhanced, and shows superior luminescent property to the commercial Y₂0₃S:Eu³⁺. The present work implies that the efficient charge compensated phosphors are promising candidates as red-emitting phosphor for w-LEDs.