Optical Properties of Ca3Ga2Ge4O14 Crystals

The optical absorption, induced-absorption, luminescence, and excitation spectra and temperature-dependent luminescence intensity of thermochemically colored Ca₃Ga₂Ge₄O₁₄ crystals were measured. The results indicate that the induced-absorption bands at 34000–28000 and 28000–20000 cm^–1 and the emission band at 14800 cm^–1 are related to F-centers.     

Synthesis, crystal structure and X-ray powder diffraction data of the phosphor matrix 4SrO·7Al2O3

The white phosphor matrix 4SrO·7Al₂O₃ has been synthesized by firing the appropriate mixture of SrCO₃, Al(OH)₃ and H₃BO₃ in the molar ratios 1:3.5:0.135 at 1300°C for 4–7 h. The crystal structure of 4SrO·7Al₂O₃ has been determined as a orthorhombic Pmma space group with a=24.7451(2)Å, b=8.4735(6)Å, c=4.8808(1)Å, V=1023.41(3)ų, Z=2, and D=3.66 g cm^–3 by the Rietveld analysis. The refinement figures of merit are R_p=8.26, R_wp=11.60, R_bragg=4.44 and s=2.61 for 844 reflections with 2<119.94°. And the corresponding X-ray powder diffraction data are presented for search/match analysis.     

X-ray Diffraction and Thermodynamic Studies of GdLiCr2O5

GdLiCr₂O₅ is synthesized from Gd₂O₃, Cr₂O₃, and Li₂CO₃ by solid-state reaction. This compound has an orthorhombically distorted perovskite structure with lattice parametersa= 10.78 Å, b= 10.63 Å, and c= 11.04 Å (V = 1263.9 ų, V _subcell = 158.0 ų, _x = 3.66 g/cm³, _meas = 3.57 ± 0.09 g/cm³). The heat capacity of GdLiCr₂O₅ is measured between 298.15 and 673 K by dynamic calorimetry. At 423 K, C _p ⁰ exhibits a lambda-type anomaly due to a second-order phase transition. The best fit equations for C _p ⁰(T) are derived, and the thermodynamic functions S ⁰(T), H ⁰() – H ⁰(298.15 K), and "(T) are calculated.     

Dielectric and Magnetic Properties of Pb(Fe1 /2Nb1 /2)O3–Pb(Fe2 /3W1 /3)O3Solid Solutions

Pb(Fe_1/2Nb_1/2)O₃–Pb(Fe_2/3W_1/3)O₃solid solutions were characterized by dielectric measurements at low frequencies and in the microwave range and magnetic measurements at high frequencies. The observed microwave dispersion was tentatively attributed to the domain mechanism of polarization. The obtained results suggest that the solid solutions studied are potential microwave-absorbing materials.     

Macroscopic volume changes of PVF2 undergoing uniaxial tension and creep

Uniaxial tension and creep tests were performed on apolar cristalline PVF₂ at room temperature and above the high glassy transition temperature (T_g=40°C and T_g=60°C), for different strain-rates (tension) or applied stresses (creep). Volume changes were simultaneously measured to study cavitation damage occuring in this polymer when strained. Damage mechanisms were explicated. Influence of experimental conditions such as strain-rate or temperature was studied: onset of cavitation is delayed and volume changes more pronounced when molecular motions in amorphous phase are hindered, for lower temperature or higher strain-rates. This work brings elements for a better comprehension of PVF₂ global mechanical behaviour as damage is very linked to yield or creep studies.     

Application of Raman in phase equilibrium studies: the structures of substitutional solid solutions of KNO3 by RbNO3

Raman spectroscopy was employed to investigate the KNO₃-RbNO₃ system. Raman studies indicated that Rb⁺ may substitute K⁺ up to 67 mol% in the solid solutions of the KNO₃ II structure (denoted as K_1–x Rb_xNO₃ (KII)) and up to 80 mol% in the solid solutions of the KNO₃ III structure (denoted as K_1+x Rb_xNO₃ (KIII)). The substitutional crystals retained the transitions of I to III to II of KNO₃ on cooling and the metastable property of KNO₃ III at room temperature. It was found that rubidium nitrate had a considerable tendency to have the structure of potassium nitrate. This accounts for the fact that larger rubidium ions can replace many more smaller potassium ions in the nitrate than vice versa. When the concentration of rubidium ions was more than 67 mol%, the substituted crystals underwent the mixed structural phase transition of the KNO₃ III structure to the RbNO₃ IV structure, and K_1–x Rb_xNO₃ (KIII) seemed to consist of disordered R3m microstructure.     

Liquid phase sintering of RE2O3: YSZ ceramics Part I Grain growth and expelling of the grain boundary glass phase

Experiments on silicate liquid phase sintering of YSZ ceramics with addition of 0.5 mol% of rare earth ions have been done in order to study the effect of these ions on the kinetics of grain growth and the expulsion of glass through the grain boundaries. Kinetics follow a third power law in the following order YPr>YPrEr>YY>YEr. The expelled glass does not spread over the ceramic grains and its mass is inversely related to grain size. Glass phase separation inside the grain boundaries is found to be a necessary condition for glass expulsion.     

Influence of the α/β-SiC phase transformation on microstructural development and mechanical properties of liquid phase sintered silicon carbide

The transformation kinetics and microstructural development of liquid phase sintered silicon carbide ceramics (LPS-SiC) are investigated. Complete densification is achieved by pressureless and gas pressure sintering in argon and nitrogen atmospheres with Y2O3 and AlN as sintering additives. Studies of the phase transformation from to -SiC reveals a dependency on the initial -content and the sintering atmosphere. The transformation rate decreases with an increasing -content in the starting powder and in presence of nitrogen. The transformation is completely supressed for pure -SiC starting powders when the additive system consists of 10.34 wt% Y2O3 and 2.95 wt% AlN. Materials without phase transformation showed a homogeneous microstructure with equiaxed grains, whereas microstructures with elongated grains were developed from SiC powders with a high initial /-ratio (>1:9) when phase transformation occurs. Since liquid phase sintered silicon carbide reveals predominantly an intergranular fracture mode, the grain size and shape has a significant influence on the mechanical properties. The toughness of materials with platelet-like grains is about twice as high as for materials with equiaxed grains. Materials exhibiting elongated microstructures show also a higher bending strength after post-HIPing.     

Deposition of Pb1 – x Cu x S1 – δ Substitutional Solid Solutions from Aqueous Solutions

Thin films of Pb_{1 – x} Cu _x S_{1 –} metastable substitutional solid solutions containing up to 3.5 mol % Cu₂S were deposited from aqueous solutions and characterized by physicochemical methods.     

Structural Changes in the Surface Layers of PdHx Alloys Caused by the Hydride Phase Decomposition

By the method of optical microscopy, we perform the in-situ investigation of the plane polished surfaces of PdH _x alloys (with video recording of the processes of transformation) in the case of their rapid cooling at a rate of 11–20°C·sec^–1 from T _c = 292°C ( = 1.97MPa) with simultaneous lowering of the pressure of hydrogen within the temperature range 100–160°C. In the course of decomposition of the PdH_0.24 alloy according to a scheme ₀ + , the formation of nuclei of the - and -phases and their growth were not detected. However, we observe a simultaneous coherent transformation of the entire surface accompanied by the formation of a surface topography similar to the modulated structures formed as a result of the spinodal decomposition. We discuss the possibility of realization of spinodal decomposition under the described experimental conditions.     

Internally Consistent Thermodynamic Description of Three-Component Liquid-Metal Systems at High Temperatures in the Entire Region of Concentration Triangle

A method is suggested for the investigation of the thermodynamic properties of ternary liquid-metal alloys at high temperatures in the entire region of concentration triangle. The method is demonstrated for a Na–K–Cs ternary system. Data are obtained for the enthalpy and Gibbs energy of formation of alloy in the temperature range of 200 T 1200 K and concentration range of 0 x _{i (j, k)} 1. The results reveal a very fine effect associated with the temperature rise, namely, the inversion of excess partial Gibbs energy G¯ _i ^*= RTln _i ( _i is the activity coefficient of the liquid component) and the change of sign of deviation of partial pressure, as well as of total pressure, from the respective values in accordance with Raoult's law. The obtained results may be used to interpret the available literature data on independent measurements of the saturation pressure.     

Pressureless sintering of B4C whisker reinforced Al2O3 matrix composites

Al₂O₃-B₄C whisker composites have been successfully densified by pressureless sintering. Low oxygen partial pressures, below 10 atmospheres, were determined to be suitable for the composite densification, and the maximum densities were achieved at 1800°C for 60 minutes. The B₄C whiskers were screened classified into five size fractions and the effect of size and size distribution on the densification were studied. The small whiskers with a narrow size distribution (–325+400 mesh) yielded the highest density results. The maximum value of relative densities was 98%, 97%, 94% and 89% at 10, 20, 30 and 40 vol % B₄C whiskers, respectively. Addition of B₄C between 5 and 15 vol% proved to be a sintering aid to the alumina densification via mechanisms other than being a grain growth inhibitor. An increased fracture toughness up to 6.2 MPa·m was achieved in the composites containing 10–20 vol% B₄C whiskers.     

Temperature effects on the properties of Ge thin films

The effects of substrate temperature (T_s) on the properties of vacuum evaporated p-type Ge thin films have been investigated for 25s<400°C. Increase in the substrate temperature improves the crystallinity and increases the grain size resulting a gradual change from amorphous to polycrystalline structure which was attained above a substrate temperature of 225°C. Low resistive (1×10^–2 ohm-cm) and high mobility (280 cm²/V·s) films were obtained at T_s=400°C. It has been observed that the conduction mechanism in polycrystalline films was dominated successively by hopping, tunneling and thermionic emission as the sample temperature was increased from 40 to 400 K. In amorphous samples, conduction was described in terms of different hopping mechanisms.     

Corrosion of Iron in a Carbonate-Bicarbonate Solution. Part 1. Crystallographic Analysis of Passive Films

Visible passive films are formed on the surface of 1010 steel at 325K in a solution of 1N NaHCO₃ + 1N Na₂CO₃ at anodic potentials up to –320mV_NHE inclusively. For potentials below –400mV, they are dull and contain FeCO₃. For –(390–320)mV, the films are thin blackish bright. Most probably, the diffraction peaks are caused by Fe₃O₄–Fe₂O₃. For –(430–400)mV, the films are dull blackish. Probably, this color is caused by a composite of magnetite and siderite.     

Viscosity of the Grain-Boundary Phase and Sintering of TiB2-Modified Alumina

A model is proposed for the sintering of powders via the sliding of particles facilitated by a grain-boundary phase. Data on the initial-stage sintering kinetics of TiB₂-modified alumina are used to assess the temperature-dependent viscosity of the grain-boundary phase, formed by Al₂O₃, oxidation products of TiB₂, and impurities present on the surface of alumina particles. In the range 1570–1620 K, the temperature variation of viscosity is fitted well by the expression 25.9exp(143308/RT).     

Synthesis of SrCu1 /3Nb2 /3O3 from Strontium Cuprates and Niobates

The formation of the perovskite phase SrCu_1/3Nb_2/3O₃ in solid-state reactions between different strontium cuprates and niobates is studied. The effect of the starting reagents on the rate of SrCu_1/3Nb_2/3O₃ formation is analyzed. The reactions with the participation of SrCuO₂ are shown to proceed at a faster rate than those involving Sr₂CuO₃. The presence of excess SrO leads to the formation of by-products. Large strontium excesses inhibit the reaction.     

The AC electrical characterization of the solid-state reaction derived CaSnO3

The potential of CaSnO₃ (calcium metastannate) for its application as a capacitor component possessing small temperature coefficient of capacitance (TCC) in electrical systems, is examined via the ac small-signal measurements. The ac electrical data were acquired on these samples sintered at various combinations of temperature-time frames (1200°CT1350°C; 24 ht60 h) in the frequency range from 5 Hz to 13 MHz. The measurements were carried out over the temperature range 25–300°C. The electrical response was found to exhibit relaxation processes in more than one complex plane formalism in a simultaneous fashion. The resistance of the sintered samples was dominated by the grain boundaries. The capacitance showed almost linear behavior in this measurement temperature range. The resulting electrical behavior has been discussed with the evolved microstructure in the sintered bodies.     

Coherent Brillouin Spectroscopy in Solid Parahydrogen

We applied coherent Brillouin spectroscopy to solid parahydrogen, and measured the Brillouin spectra of longitudinal acoustic modes at 5.6K. It was found that the linewidth of these spectra is 1.5MHz. From the observed Brillouin shift and the crystal orientation, the elastic stiffness was determined as C ₁₁=0.355±0.016GPa and C ₃₃=0.432±0.022GPa.     

Barium–Strontium and Nickel–Cobalt Solid-State Interdiffusion between Hexagonal W-Ferrites BaM2Fe16O27and SrM2Fe16O27 (M = Ni2+, Co2+)

The Ni, Co, Ba, and Sr profiles in the diffusion zones produced between hexagonal W-ferrites (BaCo₂Fe₁₆O₂₇/BaNi₂Fe₁₆O₂₇, SrCo₂Fe₁₆O₂₇/SrNi₂Fe₁₆O₂₇, SrCo₂Fe₁₆O₂₇/BaCo₂Fe₁₆O₂₇, and SrCo₂Fe₁₆O₂₇/BaNi₂Fe₁₆O₂₇) by annealing at 1520 K were used to evaluate the interdiffusion coefficients of the cations involved by the Boltzmann–Matano method over the whole composition range.     

Characterization of hydroxyapatite powders prepared by ultrasonic spray-pyrolysis technique

The hydroxyapatite (HAp) powder was prepared by the ultrasonic spray-pyrolysis technique; the characterization of the resulting powders was performed. Five kinds of the starting solutions with the Ca/P ratio of 1.67 were prepared by mixing Ca(NO₃)₂, (NH₄)₂HPO₄ and HNO₃; the concentrations of Ca²⁺ and PO₄ ^3– were in the ranges of 0.10 to 0.90 mol·dm^–3 and 0.06 to 0.54 mol·dm^–3, respectively. These solutions were sprayed into the heating zone to prepare the HAp powders. The heating zone was composed of two electric furnaces; the lower furnace was used for the evaporation of the solvent from the droplets (300–500°C) and the upper furnace for the pyrolysis of the precipitated metal salts (750–900°C). The easily sinterable HAp powder was prepared by spray-pyrolysing the solution with Ca²⁺ (0.50 mol·dm^–3) and PO₄ ^3– (0.30 mol·dm^–3) at the temperatures of 800°C (the upper furnaces) and 400°C (the lower furnaces). The resulting powder was composed of the spherical particles with diameters of 1 m or below. Even without the calcination and grinding operations, the relative densities of the compacts fired at 1150 and 1200°C for 5 h attained maxima 95%. The microstructure of the sintered compacts appeared to be uniform; the average grain size was 3 m. The activation energies for the grain growth of the sintered HAp compacts were 120 to 147 kJ · mol^–1 · K^–1.