Sintering of strontium titanate in the presence of lithium salts in a reducing atmosphere

The possibility of preparing Type III ceramics for multilayer applications has been investigated in the strontium-titanium-oxygen system, using La₂O₃, Nd₂O₃and La_2/3TiO_3– as dopants and lithium salts as sintering agents. The introduction of bismuth was also explored. The sintering process is carried out by adding the lithium salts to mixtures of strontium titanate and dopants which are previously calcined in a reducing atmosphere. The dielectric properties and the microstructure of the ceramics have been studied. The best characteristics have been observed for the particular nominal composition SrTiO₃+0.75 mol% La_2/3Ti_3–+3 mol% Bi₂O₃+10 mol % LiNO₃leading to =20000, tan < 2%,R _i= 10¹¹ cm. These results are interpreted in terms of the formation of anionic vacancies and defects in the A sites of the perovskite ABO₃and of extended defects SrO and Bi₂O ₂ ²⁺ which are coherent with the perovskite matrix.     

Thermodynamic properties of superconducting niobium

The thermodynamic properties of superconducting Nb are calculated numerically from the solution of the Eliashberg equations on the imaginary axis for several possible electron-phonon spectral densities ²()F(). Comparison with experiment is made in order to see which spectrum gives the best agreement, and functional derivatives with respect to ²()F() are used to estimate how this agreement might be improved by small changes in ²()F(). Possible gap anisotropy effects are also considered with the help of a simple model anisotropy for the interaction.Research supported by Natural Science and Engineering Research Council of Canada.     

Synthesis of the mineral geikielite MgTiO3

The preparation of pure geikielite, MgTiO₃, is carried out by precipitation with NaOH solution at pH 12 from solutions Ti⁴⁺/Mg²⁺ in molar ratio 1/1 M and calcination of the precipitate at 600°C in a dynamic atmosphere: heating rate 300°Ch^–1.At room temperature and a 1 KHz of frequency the dielectric constant () and the electric resistivity () were measured. The values were = 1 5.0 and = 1.1×10¹⁰ cm^–1.     

Ageing characteristics of furnace cooled eutectoid Zn-Al based alloy

Phase transformations and microstructural changes of a furnace cooled eutectoid Zn-Al based alloy were studied during ageing at 100 and 170°C using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. Three phase transformations occurred in the furnace cooled eutectoid Zn-Al alloy. The metastable _FC phase decomposed during isothermal ageing. The four-phase transformation, + T + followed the discontinuous decomposition of the _FC phase. Typical morphologies of the decomposition of the _FC and phases were observed in scanning electron microscopy. Decomposition of Al-rich phase was observed during the prolonged ageing by transmission electron microscopy. The different types of decomposition of the different metastable phases dominated at different stages of ageing.     

Hydrolysis of Np(IV)

Hydrolysis of Np(IV) at p[H⁺] from 0 to 2.7 and ionic strength I = 0.1-1.0 was studied spectrophotometrically. In the p[H⁺] range from 0 to 2.2 and Np(IV) concentrations of 4.5 ×10^{- 5}-1.75 ×10^{- 4} M, polymerization and formation of colloids are negligible and do not noticeably affect the hydrolysis constant measurements. The hydrolysis is completely reversible. With increasing p[H⁺] to 2, only the NpOH^{3 +} complex is formed; the spectrum of this hydroxy complex was calculated. The typical narrow band of Np(IV) aqua ion occurs at 732.2 nm; in hydroxy complex, it is shifted to 729.5 nm and its intensity decreases by a factor of about 2.7. The average constant of Np(IV) hydrolysis equilibrium [Np^{4 +} + H₂O NpOH^{3 +} + H⁺] recalculated to the ionic strength I = 0 was determined as logK ₁ ⁰ = -1.23±0.06, which corresponds to the stability constant of the complex NpOH^{3 +} log₁ ⁰ = 12.77±0.06. The stability constant of the complex Np(OH)₂ ^{2 +} was calculated to be log₂ ⁰ = 24.3.     

The photoelectrochemistry of transition metal-ion-doped TiO2 nanocrystalline electrodes and higher solar cell conversion efficiency based on Zn2+-doped TiO2 electrode

Metal-ion-doped TiO₂ nanoparticles were prepared with hydrothermal method. The change of photocurrents at different electrode potentials and wavelengths of incident light showed two different characteristics for various transition metal-ion-doped TiO₂ electrodes. In Zn²⁺ and Cd²⁺-doped TiO₂ electrodes, a characteristic of n-type semiconductor was observed and the incident photon to conversion efficiency (IPCE) were larger than that of pure TiO₂ electrode at the thickness of electrode film of 0.5 m when the content of doped metal ion was less than 0.5%. The effect of the thickness of films on IPCE was also investigated. The IPCE of pure TiO₂ electrode was strongly dependent on the thickness of films. The change tendency of the IPCE for Zn²⁺-doped TiO₂ (0.5% Zn²⁺) electrodes with its thickness was different from that of pure TiO₂. In Fe³⁺, Co²⁺, Ni²⁺, Cr³⁺ and V⁵⁺-doped TiO₂ electrodes, a phenomenon of p-n conversion was observed. The difference of photoresponse and the value of photocurrents are dependent on the doping method and concentration of the doped metal ions. The maximum conversion efficiency of RuL₂(SCN)₂-sensitized Zn²⁺-doped TiO₂ solar cell (1.01%) was larger than that of RuL₂(SCN)₂-sensitized pure TiO₂ solar cell (0.82%) at the same conditions when 0.5 mol·l^–1 (CH₃)₄N·I+0.05 mol·l^–1 I₂ in propylene carbonate solution was used as electrolyte.     

The kinetics of clustering reactions in iron-doped MgO

Quenched samples of iron-doped MgO crystals have been studied during isothermal annealing treatments using high-temperature EPR spectroscopy. The concentration decay of supersaturated Fe _Mg ^. -v _Mg associates was found to follow second order kinetics. Several different characteristics of the process kinetics are in agreement with our hypothesis that the reaction being observed is the aggregation of two Fe _Mg ^. -v _Mg associates and an unassociated Fe _Mg ^. to form a 3-cluster. Analysis of the decay rate permitted determination of a diffusion coefficient for the associate.     

Magnetic field dependence of zero-sound attenuation close to the pair-breaking edge in3He-B due toJ=1−,J z =±1 collective modes

Our previous theory yielded for the Zeeman splitting of the imaginaryJ=1 collective mode in³He-B the result =2+0.25J _z ( is the effective Larmor frequency). In this paper we take into account the downward shift of the pair-breaking edge from 2 to 2₂– (₂ and ₁ are the longitudinal and transverse gap parameters). This leads to a complex Landé factor: the frequencies of theJ _z =±1 components become =2+0.39J _z , and the linewidths of these resonances become finite: =0.18. The coupling amplitudes of theJ _z =±1 components to density are found to be proportional to gap distortion, (₁–₂/(/)². Our results for the ultrasonic attenuation due to theJ _z =±1,J=1 modes are capable of explaining the field dependence of the attenuation close to the pair-breaking edge as observed by Dobbs, Saunders, et al. The observed peak is caused by theJ _z =–1 component: its height increases due to gap distortion as the field is increased, and the peak shifts downward in temperature and its width increases with the field due to the complex Landé factor. TheJ _z =+1 component gives rise to a corresponding dip relative to the continuum attenuation.     

Order parameter relaxation and excess conductivity of current-carrying superconductors

The dependence of the conductivity of long, one-dimensional samples of superconducting tin on a large bias current I has been measured using a small superposed rf current in the frequency range 30–1000 MHz. From our data we find that the order parameter relaxation time _R is given by _R = (0.23±0.03) µ1–(T/T_c)]^–1/2 nsec for temperature T/T _c> 0.9. We also find evidence for an anomalous excess conductivity in the presence of I. For frequencies below 1000 MHz, the excess conductivity can be described by _ex = (t_*/₀²)(q/q_m)², where is the experimentally determined superconducting penetration depth, q/q _mis the momentum of the supercurrent I/I _c, and I _cis the Ginzburg-Landau critical current. The value of t ^*is about 3 × 10^–11 sec for 0.9 T/T _c 0.97, and decreases to zero at T _c.This work was supported in part by National Science Foundation Grant DMR 76-11109.     

Paramagnetic resonance in a “dirty” spin-glass

For a spin-glass with nonmagnetic defects (n _m ^1/3l 1, where n _m is the magnetic impurity concentration and l is the mean free path) an absorption function () is derived. Three ranges of temperature and external magnetic field are considered. In the vicinity of the transition the value of () d is estimated as a function of temperature and field.     

Spectral parameters of Nd<Superscript>3+</Superscript> ion in Sr<Subscript>6</Subscript>NdSc(BO<Subscript>3</Subscript>)<Subscript>6</Subscript> crystal

The spectroscopic study of Nd³⁺ in Sr₆NdSc(BO₃)₆ crystal had been performed. Based on the Judd-Ofelt theory to analyze the optical strengths measured in absorption spectra, the following spectral parameters were obtained: intensity parameters are ₂ = 1.108 × 10^–20 cm², ₄ = 2.884 × 10^–20 cm², ₆ = 3.085 × 10^–20 cm², the radiative lifetime is 385 s, the quantum efficiency is 12.5%. The fluorescence branch ratios were calculated: ₁ = 0.423, ₂ = 0.482, ₃ = 0.092, ₄ = 0.005.     

Preparation of Au-paste by liquid-phase reaction

Preparation of Au-paste by sol-gel-like reactions from the liquid phase was investigated. The Au-paste thus obtained was a well dispersed colloidal gold. The films sintered from the paste were good metallic conductors. These films showed good resistivity despite the presence of included metal oxides such as titania or zirconia in the matrix. The resistivity of the films thus obtained is about 3.0×10^–7m, which is not so different from that of pure gold (2.35 ×10^–8m).     

Rate of heating and sintering temperature effect on the electrical properties of Nd ferrite

The real part of the dielectric constant () and the dielectric loss angle (tan ) as well as the ac conductivity of ferrite Mg_1+x Ti _x Nd _y Fe_2–2x–y O₄ 0.1 x 0.9 at fixed Nd concentration of 0.025 were measured at different temperatures as a function of frequencies. The variation of activation energy as a function of the applied frequency was reported. The obtained data were discussed on the basis of the valence exchange between (Fe³⁺, Fe²⁺), (Fe²⁺, Nd³⁺) and (Fe²⁺, Ti⁴⁺). Also the effect of sintering temperature and heating rate of preparation were discussed.     

Dynamic scaling and ultrasonic attenuation in 4He near the superfluid transition point

Attenuation of first sound has been measured in ⁴He under saturated vapor pressure near the lambda temperature T at frequencies /2 ranging from 10.2 to 271 MHz. The frequency dependence of the critical part of the attenuation is determined and the dynamic scaling hypothesis is examined. Above the lambda point, it is found that the critical attenuation is described by a scaling function (, ) = ^1+y F(), where = ₀^–x and = T/T – 1, with the results x = 1.02±0.05 and y = 0.33±0.03. The characteristic frequency of the order-parameter fluctuation with the wave number k equal to the inverse correlation length is then proportional to ^x , which is in an excellent agreement with the prediction of dynamic scaling. Below the lambda point, a characteristic relaxation time or times shorter than previously expected at lower frequencies appears to exist in the present frequency range.Based on a Ph.D dissertation submitted by K. Tozaki to the University of Tokyo (1977).     

Volume and surface resistivity of low-density polyethylene filled with stainless steel fibres

D.c. electrical properties of low-density polyethylene filled with stainless steel fibres have been studied at various concentrations above the percolation threshold. The volume fractions used were 2, 5 and 10% of stainless steel fibre. The volume resistivity of polyethylene varied between 6.15×10⁷ cm at 2% loading level and 3.71×10⁵ cm at 10%. Corresponding values for surface resistivity varied between 2.77×10⁷ at 2% and 3.94×10⁴ at 10%. The value of the critical exponent for percolation was estimated to be around 2.4 for volume resistivity and 3 for surface resistivity.     

Carbon monoxide oxidation on (Mg6−x Al x )MnO8 (0⩽x⩽0.6)

Murdochite-type (Mg_6–x Al _x )MnO_m8 (0x0.6) was synthesized at low temperature (700 °C) with the sol-gel process. The specific surface area, crystallite size, catalytic activity for the CO oxidation, and adsorption isotherms of oxygen on (Mg_6–x Al _x )MnO₈ were measured. The increase of the specific surface area with increasing Al³⁺ ion content was explained by the decrease of the particle size. The catalytic activity increased with increasing Al³⁺ ion content, and this increase was caused by the valence deviation from the Mn⁴⁺ ion to the Mn^3.5+ ion.     

Electro-conducting glass-ceramics produced by ion-exchange and reduction treatments

The crystallization characteristics of some bismuth-containing soda-lime-silica glasses have been studied. The addition of bismuth reduces the glass transition temperature as well as the crystallization temperatures of these glasses. Electrically conducting layers have been induced in such glass-ceramics by subjecting them to a Na⁺ Ag⁺ ionexchange reaction followed by a reduction treatment in hydrogen. Resistances of the surfaces vary from 0.08 /square to 14.76 /square depending on the glass composition as well as the reduction parameters. Induced surface conductance tends to rise with the increase of volume of the crystalline phase in the parent glass. The TCR values range between 400 and 2300 p.p.m. K^–1. The thicknesses of these layers are about 130 m. The high surface conductivity arises from the percolation of the silver metallic phase in the glass-crystal boundary region. The glass-crystal interface is believed to act as heterogeneous nucleation sites.     

The specific heat and critical magnetic field of superconducting PdH(D)

From the solution of the Eliashberg equations on the imaginary axis, the thermodynamic properties, specific heat, and critical magnetic field of PdH(D) have been calculated. The Eliashberg kernels ²()F() were constructed using a published value of ²(), and F() was obtained from inelastic neutron scattering data. The results for the specific heat are in good agreement with published experimental data. The critical magnetic field shows a nearly parabolic behavior as a function of temperature, in disagreement with the linear experimental behavior. The deviation function D(t) and the ratios C(T _c)/T _c and [T _c/H _c(0)]² indicate that the PdH(D) system is BCS-like. The functional derivative of T _c with respect to changes in the kernel is also calculated.On sabbatical leave from the Instituto de Investigaciones en Materiales, UNAM, Mexico.     

Superconducting state in M3C60: Strong vs. weak coupling

The superconducting state in the doped fullerenes is due to strong coupling (e.g.,2.1 for Rb₃C₆₀) to low-frequency intramolecular modes _L 250 cm^–1 (^21/2). The analysis is based on an equation describingT _c for any strength of the coupling and on recent isotope effect and NMR data.     

The optical properties and a.c. conductivity of magnesium phosphate glasses

Magnesium phosphate [X MgO-(100–X) P₂O₅] glasses in the composition range [X=20, 25, 30, 40, 45, 50 mol %] have been made. The optical properties and a.c. conductivities were measured and their amorphous nature confirmed by X-ray diffraction technique. The variation of relative density with x was anomalous. In the ultraviolet/visible regions it was found that the fundamental absorption edge is a function of glass compositions and lower absorption coefficients, () follow the so-called Urbach edge. At lower absorption levels (1<<10⁴cm^–1), the width of the tail of localized states in the band gap, E _g, did not vary significantly with glass composition and lay in the range (0.26–0.343) eV. In the high absorption region (()>10⁴ cm^–1), the behaviour of () suggests that there are two different transition energies for electrons in k-space, namely direct allowed transitions and non-direct transitions. In the infrared region at wavelengths =2.5–30 m, the transmission spectrum has four absorption bands. Using the Kramers-Kronig theory, the optical constants (refractive index n and extinction coefficient k) have been determined from the transmission spectrum. The a.c. conductivity, (), real and imaginary dielectric constants, ₁, ₂, and loss factor, tan , have been determined at room temperature in the frequency region, = 2×10⁴–10⁶ Hz. It has previously been established theoretically that () ^s and s was found to be in the range 0.64–0.73, depending on glass composition.