TiO2 Nb2O5 Research Articles

Effect of Li–B–Si glass on the low temperature sintering behaviors and microwave dielectric properties of the Li-modified ss-phase Li2O–Nb2O5–TiO2 ceramics

The effects of Li amount on the phase structures and microwave dielectric properties of the Li2.081Ti0.676Nb0.243O3 (LNT) ceramics were studied. And also the effects of the Li2O–B2O3–SiO2 (LBS) glass on the low temperature sintering behaviors, microstructures and microwave dielectric properties of the Li-modified LNT ceramics have been investigated. The results show that there is a phase boundary between cubic and monoclinic phase (so called ss-phase LNT) with different amount of Li. The LBS glass effectively lowered the sintering temperature and improving the microwave dielectric properties of the ss-phase LNT. The ss-phase LNT ceramic doped with 5 wt% LBS glass can be well sintered at 850 °C and has excellent microwave dielectric properties of e r = 19.16, Q × f = 41,413 GHz, and τ f = −1.62 ppm/°C.

Co-sensitization Promoted Light Harvesting for Dye-Sensitized Solar Cells

Co-sensitization of two sensitizers on core/shell TiO2–Nb2O5 with Ta2O5 scattering layer photoanode arranged in different sequences are investigated for application to dye sensitized solar cells (DSSCs). The co-sensitization of N719/Coumarin and CdS–CdSe quantum dots/Coumarin exhibited enhanced photovoltaic performances for the pertinent cells compared with the cell made from corresponding individual sensitizers. In the present investigation, co-sensitization by N719/Coumarin showed better photovoltaic performance and have the power conversion efficiency (PCE) of 9.9 % while the performances of cells with the individual sensitizers are 8.2 % (N719) and 6.9 % (Coumarin) respectively. The PCE of DSSC with CdS–CdSe/Coumarin co-sensitization is found to be 8.7 % whereas the performances of DSSCs with the individual sensitizers are 4.5 % (CdS–CdSe) and 6.9 % (Coumarin) respectively. These results indicated that the co-sensitization of sensitizers promoted the light harvesting efficiency of DSSCs as compared the cells with the consequent individual sensitizers.

New layer-by-layer Nb2O5–TiO2 film as an effective underlayer in dye-sensitised solar cells

All-inorganic layer-by-layer TiO2–Nb2O5 films were applied as underlayers in DSCs, leading to an expressive improvement on the conversion efficiency.

Femtosecond transient grating effect and stoichiometry of TeO2–Nb2O5–TiO2 glass

We observed efficient transient optical grating effect from the TiO2–Nb2O5–TeO2 glasses excited by femtosecond laser pulses. The glass samples were prepared via melt-quenching technique. The optical nonlinearities were calibrated by forward degenerate four wave mixing (DFWM) experiment with 50fs laser pulse at 800nm. The magnitude of the third order nonlinear susceptibility χ(3) was about 7–9×10−13esu, and its temporal response is up to the resolution limit of the laser 50fs pulse-width. It has been found that χ(3) is critically dependent on the stoichiometry of between TiO2 and TeO2. The results of Raman experiment have indicated that TiO2 dopant induces transformation from the [TeO4] unit into [TeO3] via [TeO3+1], and it results in reinforcement in the rigidity of the glass network so that the χ(3) was suppressed.

Effect of B2O3 on the aqueous tape casting and microwave properties of Li2O–Nb2O5–TiO2 ceramics

The effect of B2O3 addition on the aqueous tape casting, sintering, microstructure and microwave dielectric properties of Li2O–Nb2O5–TiO2 ceramics has been investigated. The tape casting slurries exhibit a typical shear-thinning behavior without thixotropy, but the addition of B2O3 increases the viscosity of the slurries significantly. It was found that doping of B2O3 can decrease the tensile strength, strain to failure and density of the green tapes. The sintering temperature could be lowed down to 900°C with the addition of 2wt% B2O3 due to the liquid phase effect. No secondary phase is observed. The addition of B2O3 does not induce much degradation on the microwave dielectric properties. Optimum microwave dielectric properties of εr=67, Q×f=6560GHz are obtained for Li2O–Nb2O5–TiO2 ceramics containing 2wt% B2O3 sintered at 900°C. It represents that the ceramics could be promising for multilayer low-temperature co-fired ceramics (LTCC) application.

Erbium and Ytterbium Codoped Titanoniobophosphate Glasses for Ion-Exchange-Based Planar Waveguides

This work presents the optical properties of erbium-doped and erbium/ytterbium codoped Na2O–Al2O3–TiO2–Nb2O5–P2O5 glass systems and also the characterization of planar waveguides obtained by typical thermally assisted Ag+↔Na+ ion-exchange process. The glass systems allow the preparation of single mode and multimode planar waveguides presenting a strong and relatively broad emission at 1536 nm. The emission signal in the infrared region is intensified for silver-containing samples when compared with free-silver samples. The emission signal intensification may be attributed to a nonplasmonic energy transfer from silver species to Er3+ ions as no bands related to surface plasmon resonance (SPR) of silver nanoparticles were observed.

A new microwave dielectric ceramic for LTCC applications

A new low-sintering temperature microwave dielectric ceramic was found and investigated in the Li2O–Nb2O5–TiO2 (Li2O:Nb2O5:TiO2 = 5.7:1:14.7, by mole, abbreviated as LNT) system. This new microwave dielectric ceramic shows a relatively high permittivity (47), high Q × f values up to 17,800 GHz, and low temperature coefficients (57 ppm/°C), which were obtained via sintering at 1,125 °C. With the low-level doping of B2O3–CuO (BCu) (below 2 wt%), the sintering temperature of the LNT ceramic could be effectively reduced to 900 °C. The addition of BCu does not induce apparent degradation in the microwave properties but lowers the τf value. Typically, the 2.0 wt% BCu-doped ceramics sintered at 900 °C have better microwave dielectric properties of er = 48.7, Q × f = 16,350 GHz, τf = 32 ppm/°C, which suggest that the ceramics could be applied in multilayer microwave devices requiring low sintering temperatures.

Ultralow dielectric losses in pyrochlore films of the PbO–MgO–Nb2O5–TiO2 system

( 1 − x ) Pb ( Mg 1 / 3 Nb 2 / 3 ) O 3 - x PbTiO 3 (PMNT) (with x=0.1) thin films were prepared on Pt-coated silicon substrates by radio-frequency magnetron sputtering and postdeposition annealing method. A well-crystallized pyrochlore phase structure, which started to nucleate and grow at 450–500 °C, was formed in the PMNT thin films. These pyrochlore-structured PMNT thin films show ultralow dielectric losses with a typical loss tangent as low as 0.001, accompanied by a relatively high dielectric constant (εr=176). Such an extremely low dielectric loss, having never been obtained in thin films of perovskite PMNT, is probably ascribed to the specific structural feature of pyrochlore phase, chemically different from its perovskite counterpart, and ascribed to the avoidance of the polar domain-related losses.

Nonlinear optical susceptibility of multicomponent tellurite thin film glasses

Tellurite (TeO2–TiO2–Nb2O5) thin film glasses have been produced by pulsed laser deposition. The dispersion of the real and imaginary parts of the linear refractive index has been measured in the range from 300 to 1700 nm. Films present high refractive index (n=2.01) and reduced absorption (k<10−4) at λ=1500 nm. The nonlinear third order optical susceptibility (|χ(3)|) has been determined at four different wavelengths (600, 800, 1200, and 1500 nm). The out-of-resonance |χ(3)| values (∼10−12 esu) are found to be ten times higher than those of the bulk glass and 102 times higher than that of silica. Compositional and structural analysis reveals an increase of both the Ti atomic content and the fraction of nonbridging oxygen bonds in the deposited films. Both factors lead to a higher hyperpolarizability of the film constituents that is proposed to be responsible for the high |χ(3)| value of the films.

Microwave dielectric properties of the 5.5Li2O–Nb2O5–7TiO2 ceramics

A new Li2O–Nb2O5–TiO2 (LNT) ceramic with the Li2O:Nb2O5:TiO2 mole ratio of 5.5:1:7 was prepared by solid state reaction route. The phase and structure of the ceramic were characterized by X-ray diffraction and scanning electron microscopy (SEM). The microwave dielectric properties of the ceramics were studied using a network analyzer. The microwave dielectric ceramic has low sintering temperature (∼1075°C) and good microwave dielectric properties of er=42, Q×f=16900 GHz (5.75 GHz), and τf=63.7 ppm/°C. The addition of B2O3 can effectively lower the sintering temperature from 1075 to 875°C and does not induce degradation of the microwave dielectric properties. Obviously, the LNT ceramics can be applied to microwave low temperature-cofired ceramics (LTCC) devices.

Fluorescence line narrowing spectroscopy of Eu3+ in TeO2–TiO2–Nb2O5 glass

In this work we report time-resolved line-narrowed fluorescence spectra of the 5D0→7F0–6 transitions of Eu3+-doped 80TeO2–5TiO2–15Nb2O5 glass obtained at 10K by using different resonant excitation wavelengths along the 7F0→5D0 transition. The wavelength dependence of the 7F1 splitting suggests the existence of a broad distribution of Eu3+ centres possessing a variety of local field environments. The influence of the local coordination ions on the optical properties of Eu3+ has been studied by analysing the dependence of the crystal field (CF) parameters on the excitation energy along the 7F0→5D0 transition.

Microwave dielectric properties of 3Li2O–Nb2O5–3TiO2 ceramics with Li2O–V2O5 additions

A new Li2O–Nb2O5–TiO2 (LNT) ceramic with the Li2O:Nb2O5:TiO2 mole ratio of 3:1:3 has been investigated. The compound is composed of two phases, the Li2TiO3 and “M-phase” solid solution phase. The microwave dielectric ceramic has low sintering temperature (∼1100 °C) and good microwave dielectric properties of a relatively high permittivity (∼51), high Q × f value up to 8700, and small temperature coefficient (∼37 ppm/°C). The low-amount doping of 0.83Li2O–0.17V2O5 (LV) can effectively lower the sintering temperature from 1100 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 1 wt.% LV-doped ceramic sintered at 900 °C has better microwave dielectric properties of er = 51.3, Q × f = 7235 GHz, τf = 22 ppm/°C, which suggests that the ceramics can be applied in microwave LTCC devices.

Laser action and upconversion of Nd3+ in tellurite bulk glass

Laser action together with upconversion processes that produce green, orange, and red emissions in Nd3+-doped tellurite glass (TeO2–TiO2–Nb2O5) have been investigated. The upconversion processes were conducted in such a way that the dynamics of the visible fluorescence was analyzed under lasing and nonlasing conditions. The features observed in the time resolved upconverted emission show the existence of excited state absorption of both pump radiation and laser emission.

Spectroscopy and frequency upconversion inNd3+-dopedTeO2–TiO2–Nb2O5 glass

In this work, we report the optical properties ofNd3+ ions in telluriteglasses (TeO2–TiO2–Nb2O5) fortwo different Nd3+ concentrations. Judd–Ofelt intensity parameters were derived from the absorptionspectrum and used to calculate the radiative lifetime and stimulated emissioncross section of the transition. The non-exponential character of the decays from the4F3/2 level and the reduction of the lifetime even at low temperature asNd3+ concentration increases reveal the presence of nonradiative processes. The time evolution of the decaysfrom the 4F3/2 level is consistent with a dipole–dipole direct energy transfer mechanism. Upconversionprocesses that produce green, orange, and red emissions after infrared excitation in the4F3/2 and 4F5/2 levels have been investigated by using steady-state and time-resolved laser spectroscopy.The characteristics of the excitation spectra together with the temporal behaviour of thedecays from the upconverted luminescence suggest that energy transfer upconversionprocesses are the dominant mechanisms in such emissions.

Tungsten Bronze‐Structured Temperature‐Stable Dielectrics

Dielectrics with exceptional temperature stability suitable for multilayer capacitor applications have been fabricated based on compositions in the tungsten bronze‐structured BaO–M2O3–TiO2–Nb2O5 (BMTN, M=La3+, Nd3+, Sm3+) system. Heterogeneous mixtures of BLTN, BNTN, and BSTN end members groups have been used to manufacture a ceramic capacitor stable to −15% of the room temperature capacitance (ɛr>300) between −50° and + 200°C, with a room temperature dielectric loss of <0.02 at 1 MHz.

TiO2–Nb2O5 Nanotubes with Electrochemically Tunable Morphologies

Made to measure: TiO2–Nb2O5 nanotubes are grown on a Ti–Nb alloy (Ti45Nb) by anodization in a fluoride-containing electrolyte (see micrograph), and their lengths and diameters can be controlled by adjusting the potential. The low rate of chemical dissolution of Nb2O5 in the electrolyte allows the formation of long nanotubes with regular morphology.

A new Li2O–Nb2O5–TiO2 microwave dielectric ceramic composite

AbstractIn the Li2O–Nb2O5–TiO2 (LNT) system, a new dielectric ceramic composite with special structure has been found and investigated. The compound is composed of two phases, the “M‐phase” and Li2TiO3 solid solution phase. This ceramic composite has a low sintering temperature (∼1100 °C) and good microwave dielectric properties of high permittivity (∼49), high Q × f value up to 9500 GHz, and small tempe‐ rature coefficient (∼22 ppm/°C). Furthermore, by adding 1 wt% B2O3, the ceramic could be densified at very low sintering temperatures (≯900 °C) and also have good microwave dielectric properties of ϵ r = 49.2, Q × f = 8839 GHz, which suggests that the ceramic could be a promising candidate for multilayer low‐temperature co‐fired ceramics applications. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A New Microwave Dielectric Ceramic for LTCC Applications

A new low‐sintering temperature microwave dielectric ceramic, the Li2TiO3 solid solution, was found and investigated in the Li2O–Nb2O5–TiO2 system. The compound with the composition of Li2.081Ti0.676Nb0.243O3 crystallizes as a monoclinic structure. This new microwave dielectric ceramic shows a relatively low permittivity (∼20), high Q×f values up to 50 000 (7.8 GHz), and near‐zero temperature coefficients (13 ppm/°C), which were obtained via sintering at 1100°C. The addition of ≤2 wt% B2O3 was very effective in lowering the sintering temperature (Ts), and dense ceramics could be obtained at Ts≤900°C. The addition of B2O3 does not induce apparent degradation in the microwave properties but lowers the τf value to near zero. It is obvious that the ceramics could be promising candidates for multilayer low‐temperature co‐fired ceramics applications.

High‐Temperature Phase Equilibria of the Magnesium–Niobium–Titanate System

The high‐temperature phase equilibria for the MgO–Nb2O5–TiO2 system have been determined in air and at 1 atm O2. Three isothermal sections, namely 1450°, 1350°, and 1250°C, were determined experimentally. From this, the 1000°C isothermal section was deduced by extrapolation. Throughout each diagram, most compounds were found to have an extended range of solubility, each exhibiting the same substitutional pattern of the combination 1/3(MgNb2)4+ replacing Ti4+. Furthermore, entropic stabilization because of cation mixing is evident for all phases except for the columbite solid solution, in which case the solid solution range decreased with increasing temperature.

Crystal structure and microwave dielectric properties of a new A6B5O18-type cation-deficient perovskite Ba3La3Ti4NbO18

A new microwave dielectric ceramic Ba3La3Ti4NbO18 has been synthesized and characterized. Through Rietveld refinement of X-ray powder diffraction data, Ba3La3Ti4NbO18 is identified as the A6B5O18 type cation-deficient perovskites with space group R3¯m and lattice constants a=b=5.6198(1)Å, and c=41.6402(4)Å, V=1138.90(1)Å3 and Z=3. The crystal structure can be described as consisting of identical perovskite-like blocks, five corner-sharing (Ba, La)O6 octahedra thick, separated by layers of vacant octahedral. The (Ba, La)O bond lengths range from 2.526(5) to 3.262(7)Å and the (Ti, Nb)O bond lengths range from 1.784(5) to 2.227(6)Å. Further, the effects of ionic polarizability and crystal structure on the microwave dielectric properties of A6B5O18 ceramics in the BaO–La2O3–TiO2–Nb2O5 system are discussed.