Fractal Surfaces of ZrO2 , WO3 , and CeO2 Powders

The surface fractal properties of ZrO₂, WO₃, and CeO₂ powders prepared by the thermal decomposition of ZrO(NO₃)₂, (NH₄)₄W₅O₁₇, and (NH₄)₂Ce(NO₃)₆, respectively, were studied by mercury porosimetry. The results demonstrate that these oxides may, in principle, have fractal surfaces owing to topochemical processes of the type A(s) B(s) + C(g). The surface fractal dimension of individual crystallites and their aggregates are determined.     

Phase separation during the melting of oxide borates LnCa4O(BO3)3 (Ln=Y, Gd)

GdCa₄O(BO₃)₃ (GdCOB) and YCa₄O(BO₃)₃ (YCOB) single crystals have been grown from the melt by the Czochralski method. Subsequent DTA analysis of the single crystals showed different behavior for both substances. During the first heating both crystals showed a single sharp melting peak at 1490°C (GdCOB) or at 1504°C (YCOB), respectively. In subsequent heating/cooling runs only GdCOB shows one single peak, whereas YCOB shows five peaks. Moreover, phase separation of the melt can be observed by optical observation and by EDX measurements. This behavior can be explained by a miscibility gap in the YCOB melt. The YCOB crystal is formed from the stoichiometric melt by a monotectic reaction.     

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.     

Development of new NLO borate crystals

Recently new borate crystals, CsLiB₆O₁₀ (CLBO), YCa₄O(BO₃)₃ (YCOB) and Gd _x Y_1−x Ca₄O(BO₃)₃ (Gd _x Y_1−x COB) have been developed by the present authors. Here, the growth and nonlinear optical properties of CLBO, YCOB and Gd _x Y_1−x COB crystals are reviewed and their properties are discussed in relation to those of other nonlinear optical crystals, such asβ-BaB₂O₄ (BBO), and LiB₃O₅ (LBO).     

Growth and Properties of CuAlS2x Se2(1 – x) Single Crystals

CuAlS₂, CuAlSe₂, and CuAlS_2x Se_{2(1 – x)} (0 < x < 1) single crystals were grown by chemical vapor transport in a close-spaced geometry and characterized by x-ray diffraction and differential thermal analysis. The results were used to map out the CuAlSe₂–CuAlS₂ phase diagram. The density of the crystals was found to vary linearly with x, while microhardness shows a maximum. The transmission and reflection data obtained near the intrinsic edge were used to determine the band gap E _g of CuAlS₂, CuAlSe₂, and the solid solutions. E _g was found to vary nonlinearly with composition.     

Densities of Sulfur Hexafluoride and Dinitrogen Monoxide over a Wide Temperature and Pressure Range in the Sub- and Supercritical States

Densities of sulfur hexafluoride (SF₆) and dinitrogen monoxide (N₂O) have been measured with a fully computer-controlled high-temperature high-pressure vibrating tube densimeter system in the sub- and supercritical states. The uncertainty in density measurement was estimated to be between ±0.2 and ±0.3kg·m^–3 depending on the temperature. With respect to accuracy, reliability, suitability, and time consumption, this system has significant advantages for measuring PT properties in the compressed liquid and supercritical states. The densities were measured for temperatures from 273 to 623K and at pressures up to 30MPa for SF₆ (442 data points) and from 273 to 473K and up to 40MPa for N₂O (251 data points), which encompassed density ranges between 142.9 and 1778.5kg·m^–3 for SF₆ and between 124.4 and 1051.1kg·m^–3 for N₂O. Furthermore, the liquid densities of SF₆ and N₂O were correlated with a new three-dimensional density correlation system (TRIDEN) and the complete set of PT data in the sub- and supercritical states were correlated with a virial-type equation of state. For checking the accuracy and suitability of the vibrating tube densimeter system, the experimental densities of SF₆ were compared with published data and with the results of a reference equation of state.     

Cross Sections of Excitation of 3F-Levels of Nickel Atom by Electron Impact

The excitation of ³ F-levels of the nickel atom during collisions with slow electrons is investigated by the method of extended crossing beams using optical spectroscopy. Forty excitation cross sections are measured at the electron energy of 50 eV and seven optical excitation functions. The obtained data are used to calculate the total excitation cross sections of the levels e ³ F, f³ F, g ³ F, h ³ F, and i ³ F. The levels of the state 3d ⁸4s(⁴ F)5sf³ Fare excited most effectively.     

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.     

Subsolidus Phase Relations in the Systems M2 +O–M2+O–V2O5(M+ = Li, Na, K, Rb, Cs; M2+ = Mg, Ca)

Subsolidus phase relations in the M₂O(M₂CO₃)–MgO–V₂O₅ and M₂O(M₂CO₃)–CaO–V₂O₅ (M = Li, Na, K, Rb, Cs) systems are studied. Twenty mixed vanadates are obtained, of which Rb₂CaV₂O₇, Cs₂CaV₂O₇, LiMg₄(VO₄)₃, RbCaVO₄, and CsCaVO₄ are identified for the first time. Structural data are summarized for all of the mixed vanadates: the space group and lattice parameters are indicated for 14 compounds (for 6 compounds, such data are obtained for the first time), and I and d data are presented for 8 compounds. Partial series of Ca₃(VO₄)₂-based solid solutions with the general formula Ca_{3 – x} M_2x (VO₄)₂ (M = Na, K, Rb, Cs) are identified in the range 0 < x 0.14. Six phase diagrams (M⁺ = Li, Rb, Cs; M²⁺ = Mg, Ca) are investigated and are compared with the phase diagrams of the other ternary systems in question. The key features of the ternary phase diagrams and, hence, the reactivity of the constituent oxides are shown to vary systematically in going from Li₂O to Cs₂O and from MgO to SrO, which is interpreted in terms of the variation in the ionic radius of the alkali and alkaline-earth metals.     

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.     

Effect of TaC Microadditions on the Microstructure and Properties of (Bi,Pb)2Sr2Ca2Cu3O10 + x Superconducting Ceramics

Information-theoretical approaches are used to assess the effect of nanocrystalline TaC microadditions on the thermodynamic conditions of microstructure evolution in (Bi,Pb)₂Sr₂Ca₂Cu₃O_{10 + x} superconducting ceramics. Optimization analysis of property–structure–composition relationships indicates that the introduction of TaC makes it possible to raise the midpoint transition temperature T _c of the ceramics by 4 K and their 77-K critical current density j _c by 1000 A/cm². It is shown using information interpretation of multifractal formalism that the optimal TaC content is about 0.14 wt %. At this doping level, the expected increase in T _c is 8 K, and that in j _c is 1300 A/cm². The crystallite and pore substructures in Bi-2223 ceramics are shown to be correlated.     

Metastability of the K2NiF4 type structure of the solid solution LaCa(Cr x Al1−x )O4(0⩽x⩽0.10)

Metastability of the K₂NiF₄ type aluminate LaCaAlO₄ and its chromium diluted solid solution LaCaCr _x Al_1–x O₄ (x0.10) was evidenced at 1400C in air, in terms of demixing into the parent structures of the 11 intergrowth, i.e. the perovskite and rocksalt type LaAlO₃ (LaCr _x Al_1–x O₃) and CaO, respectively. This behaviour is discussed comparatively with YCaAlCO₄ and LaSrAlO₄ whose structures are stable under the same thermodynamic conditions. The results of a structure analysis are used to emphasize the role of the nine-fold co-ordination of the (A ³⁺=Y³⁺, La³⁺; A²⁺=Ca²⁺, Sr²⁺) cations as mixing the twelve-fold co-ordination of A ³⁺ in A ³⁺AlO₃ perovskite and the six-fold one of A ²⁺ in A ²⁺O rocksalt. Calcium-oxygen underbonding in the (La, Ca)-O-Al bridge is assumed to trigger the metastability of the intergrowth structure at high temperature.     

Steady-State Photocurrent Characteristics in Sillenite Crystals

The steady-state photocurrent through Bi₁₂TiO₂₀, Bi₁₂GeO₂₀, and Bi₁₂SiO₂₀ crystals was measured as a function of temperature (77–300 K) and illumination. The four-level energy-band diagram inferred from the experimental data adequately describes the carrier generation, recombination, and photocurrent quenching processes in wide-gap sillenite semiconductors.     

High-Pressure Phase Transitions of M2O5(M = V, Nb, Ta) and Thermal Stability of New Polymorphs

The stability regions of various M₂O₅(M = V, Nb, Ta) polymorphs were studied by quenching samples from 600–1300°C at pressures in the range 5.0–8.0 GPa. Above 7.0 GPa, Nb₂O₅and Ta₂O₅were found to have a new polymorph (Zphase) in which the metal atoms are in sevenfold coordination. In addition, the samples contained the high-pressure polymorph B-M₂O₅ with the rutile-related structure. Differential thermal analysis at atmospheric pressure showed a weak, broad exotherm, indicating that the transformation of Z-M₂O₅into other phases begins at 100–150°C and reaches completion at 400°C in Nb₂O₅and 550°C in Ta₂O₅. At p 8.0 GPa and t> 750°C, a new high-pressure phase B-V₂O₅, isostructural with B-Nb₂O₅, was identified (a= 11.9640(6) Å, b= 4.6986(3) Å, c= 5.3249(3) Å, = 104.338(4)°, V= 290.01 ų, Z= 4, sp. gr. C2/c). At atmospheric pressure, B-V₂O₅transforms into -V₂O₅, with two strong exothermic peaks at 230 and 270°C. Experiments in the pressure range 5.0–8.0 GPa confirmed that the high-pressure phase -V₂O₅has a broad stability region.     

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.     

Synthesis and Physicochemical Properties of Crystalline and Glassy La14 – x – y Gd x Eu y (BO3 )6(GeO4)2O8 Solid Solutions

Using solid-state reactions, La_{14 – x – y} Gd _x Eu _y (BO₃)₆(GeO₄)₂O₈ solid solutions isostructural with Ln₁₄(BO₃)₆(GeO₄)₂O₈ (Ln = Pr, Nd, Sm, Eu, Gd) were prepared for the first time, and their melting points and melting behavior were established. Liquid quenching of the solid solutions was found to yield thermally stable glasses containing as much as 60 mol % rare-earth oxides. The composition limits of the glass-forming region were determined, and the luminescence spectra of both crystalline and glassy solid solutions were studied.     

Effect of Gamma Irradiation on the Dielectric Properties of (CH3)2NH2Ga(SO4)2 · 6H2O Crystals in the Vicinity of the Ferroelectric Transition

The effect of gamma irradiation on the dielectric permittivity and loss tangent of (CH₃)₂NH₂Ga(SO₄)₂ · 6H₂O crystals was studied near the ferroelectric transition at different frequencies. Irradiation was found to sharply reduce and tan at gamma doses below 5 × 10⁷ R. At higher doses, and tan level off. With increasing gamma dose, the ferroelectric transition shifts to lower temperatures, irrespective of frequency.     

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.     

Mixed-Cation Cyclohexaphosphates: Synthesis and Crystal Structure of CsCuInP6O18-II

The cyclohexaphosphates CsM²⁺AlP₆O₁₈ (M²⁺ = Ni, Cu, Co, Mn, Cd), CsM²⁺GaP₆O₁₈ (M²⁺ = Ni, Cu, Mn, Cd), CsM²⁺VP₆O₁₈ (M²⁺ = Ni, Co), CsM²⁺FeP₆O₁₈ (M²⁺ = Ni, Cu, Co, Mn), CsM²⁺MnP₆O₁₈ (M²⁺ = Mg, Co), CsM²⁺InP₆O₁₈ (M²⁺ = Ni, Co) (type I), CsCuInP₆O₁₈, CsCuVP₆O₁₈, CsNiMnP₆O₁₈ (type II), Cs₃Cd₃Fe(P₆O₁₈)₂, Cs₃Cu₃Mn(P₆O₁₈)₂, Cs₃Mn₃In(P₆O₁₈)₂, and Cs₃Cd₃In(P₆O₁₈)₂ were prepared by crystallization from molten polyphosphoric acids. The crystal structure of CsCuInP₆O₁₈-II was determined: triclinic cell, sp. gr. P , Z = 1, a= 5.1360 Å, b= 8.917 Å,c = 9.237 Å, = 86.98°, = 75.04°, = 73.53°.     

Preparation of Bi2Sr2CaCu2O8 + x-Matrix Composites Containing Fine Strontium Calcium Indate Inclusions via Glass Crystallization

The crystallization of glass with a composition of Bi₂Sr₂CaCu₂O_{8 + x} + 0.25Sr_0.6Ca_0.4In₂O₄was studied in air between 400 and 800°C. Below 700°C, crystalline phases were formed in the following sequence: (Sr,Ca)_0.9Bi_1.1O_2.55, Cu₂O, Bi-2201, (Sr,Ca)In₂O₄, (Sr,Ca)₃Bi₂O₆, and Bi-2212. Above 700°C, the predominant phases were Bi-2212 and (Sr,Ca)In₂O₄. The introduction of In into Bi–Sr–Ca–Cu–O was shown to reduce the glass-forming capability of this system, without suppressing Bi-2212 formation. The Bi₂Sr₂CaCu₂O_{8 + x} + 0.25Sr_0.6Ca_0.4In₂O₄composites prepared by annealing the precursor glass contained 0.2- to 0.4-m inclusions and possessed enhanced superconducting properties.