Electric conductivity and relaxation in ZnF2–AlF3–PbF2–LiF glasses

The electric conductivity of ZnF₂–AlF₃–PbF₂–LiF glasses has been studied in the frequency range 10 Hz–2 MHz and in the temperature range from 300 K to just below the glass transition temperature. The conductivity decreases with the increase in the LiF content in the composition, which results from the trapping of F⁻ ions by Li⁺ ions. Small values of the stretching exponent β are observed for the present glasses. The value of the decoupling index decreases with an increase in LiF content, consistent with the composition dependence of the conductivity.     

Optical and electrical properties of binary WO3–Pb3O4 glasses

A glass system of the composition xWO₃+(100−x)Pb₃O₄, with x=5, 10, 20 and 30 mol.% was prepared. The optical absorption, ac and dc conductivities are the subject of the present work. The optical absorption indicates that the electronic transition is indirect and is associated with phonon assisted transition. The exponential dependence of the absorption coefficient as a function of the incident photon energy suggests that the Urbach rule is obeyed, and indicates the formation of a band tail. On the other hand, ac conductivity measurements are performed in the frequency range 0.1–100 kHz, and in the temperature range 300–600 K. The results of the electrical conductivity are discussed on the basis of electronic glass conduction models. Correlated narrow-band limit for random sites and single polaron hopping model are found to describe the experimental results effectively. The dielectric constant was correlated to the optical band gap and a satisfactory relation was found. It was also possible to calculate the thermochromic properties from independent ac and dc measurements, and it was possible to evaluate the optical gap at 0 K by extrapolation.     

Anomalous behavior of ultrasonic properties near 50 K in Rb0.30MoO3 and Rb0.30(Mo1−xVx)O3

Depending on the temperature, the charge density wave (CDW) nonlinear conductivity of the blue bronzes A_0.30MoO₃ (A=K, Rb) shows two different regimes: a strongly damped motion above ∼50 K and motion with almost no damping below ∼50 K. In a search for an elastic signature of this CDW behaviour, we performed ultrasonic measurements on Rb_0.30MoO₃ and Rb_0.30(Mo_1−xV_x)O₃ single crystals between 4 K and 300 K. In Rb_0.30MoO₃, at T∼50 K, upon cooling, a large increase of the sound velocity is observed. The ultrasonic attenuation coefficient shows an increase down to 50 K followed by a plateau. In Rb_0.30(Mo_1−xV_x)O₃ (x=0.4 at%) the anomaly broadens and is shifted towards higher temperatures. The results are discussed in terms of CDW glass.     

Photo-operated two-photon absorption effects in the GeSe2–Ga2S3–PbI2 glasses

The possibility to operate the two-photon absorption (TPA) of newly synthesized GeSe₂–Ga₂S₃–PbI₂ glasses using the CO laser beam (λ=5.5 μm) as a photoinducing one has been demonstrated. As the fundamental laser beam we have used the illumination of 10.6 μm passively modulated 0.5 ns CO₂ laser with a rate repetition of about 10 Hz. We have established that the maximal photoinduced TPA is observed for the 8% doped samples (up to 14 cm/GW), which is achieved at a pump CO laser pump power density equal to about 0.6 GW/cm². The undoped PbI₂ samples show the TPA maximum at a pump power density of about 0.2 cm/GW. The minimal TPA values were observed for the samples with 5% of PbI₂. The obtained results show that these materials can be used as effective optically operated optical limiters.     

PbO–Bi2O3–Ga2O3–BaO glasses doped by Er as novel materials for IR emission

Infra-red luminescence (at wavelengths about 1600 and 2500 nm) from Er³⁺ ions embedded in PbO–Bi₂O₃–Ga₂O₃–BaO glass hosts is reported for room and helium liquid temperatures. The substantial influence of energy transfer processes between the host and Er³⁺ ions is shown experimentally through the dependences of photoluminescence on light polarization and excitation wavelength. Only the application of the polarized pumping YAG–Nd laser beam (λ=1060 nm) stimulates substantial luminescence with quantum efficiency up to 24%. The role of phonon-relaxation subsystem in the observed luminescence is discussed.     

Optical and acoustic properties of TeO2/WO3 glasses with small amount of additive ZrO2

The optical and acoustic properties of tellurite glasses in the system TeO₂/ZrO₂/WO₃ have been investigated. The refractive index at different wavelengths and the optical spectra of the glasses have been measured. From the refractive index and absorption edge studies for prepared glasses, the optical parameter viz; optical band gap (E_opt), Urbach energy, (ΔE), dispersion energy, E_d, and the average oscillator energy, E₀, have been calculated. Sound velocities were measured by pulse echo technique. From these velocities and densities values, various elastic moduli were calculated. The variations in the refractive index, optical energy gap and elastic moduli with WO₃ content have been discussed in terms of the glass structure. Quantitatively, we used the bond compression model for analyzing the room temperature elastic moduli data. By calculating the number of bonds per unit volume, the average stretching force constant, and the average ring size we can extract valuable information about the structure of the present glasses.     

Preparation and spectral characterization of new Er3+-doped TeO2－B2O3－WO3－ZnO－ZnS glasses

Erbium-doped TeO_2-based oxysulfide glasses have been prepared in argon atmosphere in graphite crucibles. The results of thermal analysis and spectroscopic properties of Er^{3+} have been studied in terms of sulfide influence. As a function of composition, we have measured principally the optical absorption, spontaneous emission, and lifetime of the materials. Judd－Ofelt theory was introduced to calculate bandwidth and emission cross-section of Er^{3+}. The results demonstrate that addition of sulfide in tellurite glasses results in broad emission spectra, with high emission cross-section, slightly low emission lifetime and a comparatively high thermal stability as pure oxide glasses.     

Ultrasonic Study on Jahn-Teller Distortions in La1=3Sr2=3CoO3

系统研究了La1=3Sr2=3CoO3单相多晶样品在低温下的电磁输运性质和超声特性．电阻率测量表明,La1=3Sr2=3CoO3在整个温区内都表现出金属特性,并且在235 K处电阻率-温度曲线的斜率发生了变化,同时伴随着铁磁相变．超声声速在铁磁相变温度以下出现软化,并在120 K附近达到最小,之后,随着温度的进一步降低,声速开始硬化,同时出现了一个宽大的超声衰减峰．分析认为,该超声异常可能起源于中等自旋态Co3+的Jahn-Teller效应．     

Nature of intrinsic luminescence in the glasses of CaO–Ga2O3–GeO2 system

The intrinsic luminescence of glasses of the CaO–Ga₂O₃–GeO₂ system has been investigated. High chemical purity and optical quality glasses, both undoped and doped with transition and rare-earth ions with different compositions, were obtained by high-temperature synthesis. The influences of the basic glass composition, impurities (Cr³⁺, Mn²⁺, Eu²⁺, Nd³⁺, Ho³⁺, Er³⁺, and Ce³⁺) and different kinds of excitation, on the intrinsic luminescence of the CaO–Ga₂O₃–GeO₂ glasses were investigated. The nature and possible mechanisms of the intrinsic luminescence in glasses of this system are discussed. The proposed models of intrinsic luminescence are supported by electron spin resonance spectroscopy.     

Annealing effect on the superconductivity of In2O3–ZnO thin films

We have investigated the relation among ρ–T characteristics, superconductivity, annealing conditions and the crystallinity of polycrystalline (In₂O₃)_1−x–(ZnO)_x films. We annealed as-grown amorphous films in air by changing annealing temperature and time. It is found that the films annealed at 200 °C or 300 °C for a time over 0.5 h shows the superconductivity. Transition temperature T_c and the carrier density n are T_c < 3.3 K and n ≈ 10²⁵–10²⁶ m⁻³, respectively. Investigations for films with x = 0.01 annealed at 200 °C have revealed that the T_c, n and crystallinity depend systematically on annealing time. Further, we consider that there is a suitable annealing time for sharp resistive transition because the transition width becomes wider with longer annealing times. We studied the upper critical magnetic field H_c2(T) for the film with different annealing time. From the slope of dH_c2/dT for all films, we have obtained the resistivity ρ dependence of the coherence length ξ(0) at T = 0 K.     

Lithium insertion to ReO3-type metastable phase in the Nb2O5–WO3 system

Lithium insertion to distorted ReO₃-type metastable solid solution Nb_xW_1−xO_3−x/2 (0≤x<0.25) has been studied by chemical and electrochemical methods. In the course of lithium insertion into tetragonal compounds, transition to a cubic phase was found to occur in the region where values of y (in Li_yNb_xW_1−xO_3−x/2) fall between 0.2 and 0.3, and the phase transition was found to depend on the conditions of the reaction. Changes in OCV and lattice parameters in tetragonal region (y<0.2) were discussed from the viewpoint of the ordering of lithium ions. Also, the component diffusion coefficient of lithium in tetragonal compounds Li_0.1Nb_xW_1−xO_3−x/2 (0≤x≤0.23) was found to increase with niobium content when x≤0.10, and to saturate at 4×10⁻⁹ cm²/s.     

Ab-initio density functional theory study of a WO3 NH3-sensing mechanism

WO 3 bulk and various surfaces are studied by an ab-initio density functional theory technique.The band structures and electronic density states of WO 3 bulk are investigated.The surface energies of different WO 3 surfaces are compared and then the (002) surface with minimum energy is computed for its NH 3 sensing mechanism which explains the results in the experiments.Three adsorption sites are considered.According to the comparisons of the energy and the charge change between before and after adsorption in the optimal adsorption site O 1c,the NH 3 sensing mechanism is obtained.     

Correlation among electronic polarizability, optical basicity and interaction parameter of Bi2O3–B2O3 glasses

For optical basicity and electronic polarizability, the previous studies basically concentrate on the wavelength range of the visible light region. However, heavy metal oxides glasses have a reputation of being good materials for infrared region. In this study, new data of the average electronic polarizability of the oxide ion _O^2-, optical basicity Λ and Yamashita–Kurosawa's interaction parameter A of Bi₂O₃–B₂O₃ glasses have been calculated in a wavelength range from 404.66 to 1083.03 nm. The present investigation suggests that both _O^2- and Λ increase gradually with increasing wave number, and A decreases with increasing wave number. Furthermore, close correlations are studied among _O^2-, Λ, A and refractive index n in this paper. Particularly, it has been found that a quantitative relationship between electronic polarizability and optical basicity is observed in a wavelength range from 404.66 to 1083.03 nm. Our present study extends over a wide range of _O^2-, Λ and A values.     

Study on the structure dependent ultrafast third-order optical nonlinearity of GeS2–In2S3 chalcogenide glasses

The results of the femtosecond time-resolved optical Kerr at 820 nm in GeS₂–In₂S₃ chalcogenide glasses indicate that the response time in GeS₂–In₂S₃ glasses is subpicosecond, which is predominantly due to the distortion of the electron cloud. The value of χ⁽³⁾ in 0.95GeS₂–0.05In₂S₃ glass is also as large as 2.7 × 10⁻¹³ esu, and it reduces with the addition of In₂S₃, which may be ascribed to the microstructure evolution of GeS₂–In₂S₃ glasses. It is deduced that the intrinsic [Ge(In)S₄] tetrahedral structure units that possess the high hyperpolarizability may do great contribution to the enhancement of third-order optical nonlinearity while [S₃Ge–GeS₃] ethane-like molecular units make no considerable contribution to that in femtosecond time scale. These GeS₂–In₂S₃ and GeS₂–In₂S₃-based chalcogenide glasses would be expected to be the promising materials for all-optical switching devices.     

Structural characterization of the sol–gel oxide powders from the ZnO–TiO2–SiO2 system

This work is a study that deals with the synthesis by the sol–gel method and the structural characterization of the oxide powders belonging to the ternary system ZnO–TiO₂–SiO₂ (ZTS). The sol–gel synthesis starts from inorganic precursors, which have been processed under the variation of different technological parameters. We have investigated the dependence of the gelling time on pH and on the temperature of synthesis as well as on water and ammonia amounts. In the case of ZTS samples, the shortest gelling duration appears for low pH values when ZnO content is increased and at small ammonia concentrations when the ZnO content is decreased, respectively. On the contrary, ZTS samples containing high amounts of TiO₂ provide evidence of a short gelling time for high pH and large ammonia amounts. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy provided structural information on these ternary oxide powders. These analyses revealed that relative high amounts of ZnO yields in a change from octahedral [ ZnO₆] units to tetrahedral [ ZnO₄] units in the powder structure. Optical phonons specific for SiO₂ and TiO₂ in both octahedral and tetrahedral groups are shown. High thermal and chemical stability was put in evidence by differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) in the 20–1000 C temperature range.     

Sintering of glasses in the system RO–Al2O3–BaO–SiO2 (R=Ca, Mg, Zn) studied by hot-stage microscopy

Glass–ceramics for sealing solid oxide fuel cells (SOFCs) were developed by sintering and crystallization of the powdered glass seal. The non-isothermal sintering kinetics and crystallization kinetics were studied for four glasses in the system 50SiO₂·(45−x)BaO·xRO·5Al₂O₃ (R=Ca, Mg, Zn and x=0, 15) (mol%). Hot-stage microscopy (HSM) and differential thermal analysis (DTA) measurements demonstrated that it is possible to first sinter and then crystallize these glasses obtaining glass–ceramic seals with thermal expansion coefficients in the range 9–12×10⁻⁶ K⁻¹.

The non-isothermal sintering kinetics was analyzed by computer simulations using a previously reported model of sintering for polydispersed glass powders which takes into account the particle size distribution, surface energy and viscosity. Good agreement was found between the measured kinetics with HSM and the calculated kinetics for all glasses.     

Surface and interface characteristics of TiO2–muscovite nanocomposites

The morphology and chemical characteristics of the surface and the interface of TiO₂–muscovite nanocomposites were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Our results clearly showed that TiO₂ grains formed on the TiO₂ thin film surface, whereas the presence of TiO₂ grains on the interface between TiO₂ thin films and the muscovite substrates was not obvious. While euhedral rutile grains were found in samples doped with Zn ions, none were found in samples doped with Sn ions. The XPS results showed that cations present in the muscovite substrates diffused into the TiO₂ thin films. Etching measurements revealed that diffusion abilities of cation impurities varied: Si and Al diffused more easily than K. The observed differences in chemical composition and oxidation of the elements, especially on the surface and the subsurface, may influence the different crystallization behaviors of elements in TiO₂ thin films and the different active degree of elements diffusing from muscovite substrates.     

Effect of BiFeO3 addition on Bi2O3–ZnO–Nb2O5 based ceramics

In this paper, low temperature sintering of the Bi₂(Zn_1/3Nb_2/3)₂O₇ (β-BZN) dielectric ceramics was studied with the use of BiFeO₃ as a sintering aid. The effects of BiFeO₃ contents and the sintering temperature on the phase structure, density and dielectric properties were investigated. The results showed that the sintering temperature could be decreased and the dielectric properties could be retained by the addition of BiFeO₃. The structure of BiFeO₃ doped β-BZN was still the monoclinic pyrochlore phase. The sintering temperature of BiFeO₃ doped β-BZN ceramics was reduced from 1000 °C to 920 °C. In the case of 0.15 wt.% BiFeO₃ addition, the β-BZN ceramics sintered at 920 °C exhibited good dielectric properties, which were listed as follows: ε_r = 79 and tan δ = 0.00086 at a frequency of 1 MHz. The obtained properties make this composition to be a good candidate for the LTCC application.     

Preparation and properties of composite ceramic coating containing Al2O3–ZrO2–Y2O3 on AZ91D magnesium alloy by plasma electrolytic oxidation

A composite ceramic coating containing Al₂O₃–ZrO₂–Y₂O₃ was successfully prepared on AZ91D magnesium alloy by plasma electrolytic oxidation (PEO) technique in an alkaline aluminate electrolyte. The morphology, elemental and phase composition, corrosion behavior and thermal stability of the uncoated and coated samples were studied by environmental scanning electron microscopy (ESEM), energy dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD), electrochemical corrosion test, high temperature oxidation test and thermal shock test. The results showed that the composite ceramic coating was composed of Al₂O₃, c-ZrO₂, t-ZrO₂, Y₂O₃ and some magnesium compounds, such as MgO, MgF₂ and MgAl₂O₄. After PEO treatment, the corrosion potential of AZ91D alloy was increased and the corrosion current density was significantly reduced. Besides, the coated magnesium alloys also showed excellent high temperature oxidation resistance and thermal shock resistance at 500 °C environment.     

Electrical conductivity of the molten EuBr2–MBr binary mixtures (M = Li, Na, K, Rb, or Cs)

The electrical conductivity of all EuBr₂–alkali metal bromide liquid mixtures was measured as function of temperature over the whole composition range. The activation energy, E_A, was evaluated for all liquid mixtures. It was revealed that the classical Arrhenius dependence did not stand for any individual mixture. The obtained results were discussed in terms of complex formation in the melts.