Showing papers on "Solid solution published in 1989"

Lattice Parameters, Ionic Conductivities, and Solubility Limits in Fluorite-Structure MO2 Oxide [M = Hf4+, Zr4+, Ce4+, Th4+, U4+] Solid Solutions

Abstract: Changes in the lattice parameters of fluorite type MO2 oxides (M = Hf4+, Zr4+, Ce4+, Th4+, U4+) due to the formation of solid solutions can be predicted by proposed empirical equations. The equations show the generalized relationship between dopant size and ionic conductivity in the binary systems of these oxides, illustrating that the smaller the difference between the dopant ionic radius and the critical dopant radius, the higher the conductivity. The solubility limit of the same periodic group elements in fluorite-structure MO2 oxides decreaes linearly with the square of Vegard's slope for each solute as determined from the proposed equations.

Olivine-modified spinel-spinel transitions in the system Mg2SiO4-Fe2SiO4: Calorimetric measurements, thermochemical calculation, and geophysical application

Abstract: The olivine(α)-modified spinel(β)-spinel (γ) transitions in the system Mg2SiO4-Fe2SiO4 were studied by high-temperature solution calorimetry. Enthalpies of the β-γ and a α-γ transitions in Mg2SiO4 at 975 K and of the α-γ transition in Fe2SiO4 at 298 K were measured. The γ solid solution showed a positive enthalpy of mixing. Phase relations at high pressures and high temperatures were calculated from these thermochemical data including correction for the effect of nonideality of α, β, and γ solid solutions. The calculated phase diagrams agree well with those determined experimentally by Katsura and Ito very recently. The α − (Mg0.89, Fe0.11)2SiO4 transforms to β through a region of α+β without passing through the α+γ phase field at around 400 km depth in the mantle with an interval of about 18(±5) km. Temperatures at 390 and 650 km depths are estimated to be about 1673 and 1873 K, respectively, assuming an adiabatic geotherm.

Thermodynamic theory of the lead zirconate-titanate solid solution system, part III: Curie constant and sixth-order polarization interaction dielectric stiffness coefficients

Abstract: Vaiues of the Curie constant (C) and sixth-order polarization interaction dielectric stiffness coefficients (α112 and α123) are needed for the development of a thermodynamic theory for the entire lead zirconate-titanate (PZT) solid solution system. Low-temperature dielectric data measured on pure homogeneous polycrystalline PZT samples were used to determine values of these coefficients at several compositions across the phase diagram. Equations were then fitted to these data to determine the compositional dependence of the coefficients. The Curie constant was found to form a peak in the middle of the phase diagram at the PZT 50/50 composition.

Phases and their relations in the Bi-Sr-Cu-O system

Abstract: Solid phases and their relations in the Bi-Sr-Cu-O system were investigated at 840°C in air. Bi 2+ x Sr 2− x Cu 1+ y O Z (0.1 x y x /2), Bi 17 Sr 16 Cu 7 O Z , Bi 2 Sr 3 Cu 2 O Z , Bi 4 Sr 8 Cu 5 O Z and BiSr 3 O Z have newly been found. Structural data obtained by means of powder XRD and TEM for these are presented. The superconductor with a T c ∼ 10 K corresponds to the Bi-poorest end of the solid solutions mentioned above. Carrier holes are created by the presence of excess oxygen but these tend to be trapped locally for x > 0.13. The one-dimensional modulation mode showed an interesting composition dependence, from which a modified mechanisms of the modulation has been deduced.

Determination of the Fe−Ni phase diagram below 400°C

Abstract: The phase diagram for the Fe−Ni system below 400°C has been determined experimentally in the composition range from 0 to 52 wt pct Ni using analytical electron microscopy techniques. High spatial resolution X-ray microanalysis and electron diffraction were conducted on the Fe−Ni regions of meteorites. Both stable and metastable phase boundaries were defined. Our phase diagram is consistent with the available theoretical diagram in that firm experimental evidence was found for a miscibility gap and an associated, asymmetrical spinodal decomposition region. The spinodal decomposition resulted in a two-phase, isotropic microstructure, as expected. The miscibility gap is a metastable construction arising from the presence of a tricritical point due to magnetic interactions. Our experimental diagram differs from the theoretical diagram in three ways. First, observations of meteorite structures show that Fe−Ni solid solution containing 4.0 wt pct Ni is in local equilibrium with ordered FeNi containing 51.4 wt pct Ni and not Ni3Fe as in the theoretical diagram. Second, our miscibility gap below 400°C, located between 11.7 and 51.9 wt pct Ni at 200°C, is wider than the calculated miscribility gap, especially at the high Ni end. Third, we also find evidence for an ordered structure around ∼25 wt pct Ni. This structure may be either Fe3Ni or a two-phase structure incorporating ordered FeNi.

Electrical properties of novel mixed-conducting oxides

Abstract: Zirconia-titania-yttria oxide solutions are novel mixed-electrical conductors in which both oxygen-ions and electrons are mobile. A determination of their electrical properties is necessary for an evaluation of their potential applications. Single-phase oxide solutions have been prepared and characterized. Phase studies indicates extensive solid solution of titania into zirconia stabilized with 12 mol % yttria. The observed decrease in lattice parameter with increasing titania concentration in these oxide solutions indicates that titanium cations substitute for the zirconium cations in the fluorite lattice. The lattice and grain-boundary electrical conductivities have been determined using impedance spectroscopy at temperatures between 400 and 950 °C.

Hydrogen solubility and diffusion in the shape-memory alloy NiTi

Abstract: The solubility and the diffusion coefficient of hydrogen were determined in the austenitic (cubic) high-temperature phase of the shape-memory alloy NiTi The measurements were made between 500 and 950 degrees C, with hydrogen gas pressures of up to 13 bar, and with hydrogen-to-NiTi ratios of up to 0027 The hydrogen was in interstitial solid solution The absorption process is exothermic The enthalpy of solution per hydrogen atom is -183+or-40 meV The diffusion coefficient can be described by an Arrhenius relation with an activation energy E=480+or-50 meV and a pre-exponential factor D0=(47-25+39)*10-3 cm2s-1 NiTi hydride was synthesised in experiments with a higher hydrogen gas pressure (p=150 bar, T=500 K) Because of its brittleness, the hydride is readily pulverised by mechanical methods This yields, after extraction of the hydrogen, NiTi powder which is difficult to prepare by other experimental techniques

X-ray study of CuGaxIn1−xSe2 solid solutions

Abstract: The semiconducting compound CuGaxIn1 − xSe2 crystallizes in the chalcopyrite structure (space group I{\bar 4}2d, Z = 4). The X-ray powder data for x = 1, 0.75, 0.6, 0.5, 0.4, 0.25 and 0.0 have been collected and it is found that the lattice parameters a and c and their ratio c/a vary linearly with x. Thus the composition of any chalcopyrite in the pseudo-binary system CuGaSe2 and CuInSe2 can be obtained from the accurate lattice parameters. The crystallite size determined from the (112) plane is minimum for x = 0.50 (~ 1000 A) and away from x = 0.50 it increases. A value of u = 0.240 (5) has been established for fixing the Se-atom positions in the CuGa0.5In0.5Se2 solid solution. The JCPDS Diffraction File No. for CuInSe2 is 40-1487 and for CuGa0.5In0.5Se2 is 40-1488.

X-ray Study of CuGaxlnl_xSe2 Solid Solutions

Abstract: The semiconducting compound CuGax I n~_xSe2 crystallizes in the chalcopyrite structure (space group I42d, Z -- 4). The X-ray powder data for x = 1, 0.75, 0.6, 0.5, 0.4, 0.25 and 0.0 have been collected and it is found that the lattice parameters a and c and their ratio c/a vary linearly with x. Thus the composition of any chalcopyrite in the pseudo-binary system CuGaSe2 and CuInSe2 can be obtained from the accurate lattice parameters. The crystallite size determined from the (112) plane is minimum for x--0.50 (--~1000,A) and away from x=0.50 it increases. A value of u = 0.240 (5) has been established for fixing the Se-atom positions in the CuGao.5Ino.sSe2 solid solution. The JCPDS Diffraction File No. for CuInSe2 is 40-1487 and for CuGao.sIno.sSe: is 40-1488•

Phase Equilibria and Crystal Chemistry in the Quaternary System Ba‐Sr‐Y‐Cu‐O in Air

Abstract: Studies in the Sr-Y-Cu-O and Ba-Sr-Y-Cu-O systems have revealed that Sr will substitute for Ba in (Ba,Sr)2YCu3O6+x up to about 60%. There are no ternary compounds in the Sr-Y-Cu-O system equivalent to the three ternary phases in the Ba system. A new binary phase, “Sr14Cu24O41”(CuO ∼ 63.158 mol%), was found which forms a solid solution with Y2O3 to a Sr:Y ratio of approximately 2:1. This phase can also incorporate considerable amounts of Ba and Ca and many other large ions.

High‐Temperature Behavior of the Aluminum Oxycarbide Al2OC in the System Al2O3–Al4C3 and with Additions of Aluminum Nitride

Abstract: A large number of high-temperature experiments involving binary mixtures of alumina and aluminum carbide (Al4C3) were performed to clarify the behavior of the aluminum oxycarbide Al2OC. It is first shown from heat treatments on the molar composition 55Al2O3·45 Al4 C3 that, in conditions of stable equilibrium, Al2OC decomposes to Al4O4 C and Al4 C3 at 1715°C according to the reaction 4Al2 OC → Al4 O4 C+Al4 C3. However, Al2 OC can be obtained at room temperature from compositions of lower carbide contents (<20 mol%) and by rapid cooling. In that case Al2 OC is solidified in a metastable state, and, when subsequently annealed to temperatures above 1200°C, its lattice reorganizes and progressively transforms into the lattice of Al4 O4 C according to the reaction Al2 O3+xAl2 OC → (1—x)Al2 O3+xAl4 O4 C. This transformation is described in terms of TTT curves and is accompanied by a decrease in hardness and wear resistance. Additions of AlN to Al2 O3 and Al4 C3 have been found to create a solid-solution Al2 OC—AlN in an unexpected region of the ternary system Al2 O3—Al4 C3—AlN. As a result the quasi-binary section Al2 OC—AIN of the ternary diagram Al2 O3—Al4 C3—AlN was extensively investigated. We report the solubility limit of AlN in Al2OC, the improved high-temperature stability of the Al2OC—AlN solid solution compared with pure Al2OC, and eventually the existence of a possible intermediate ternary compound of formula Al10O3C3N4.

Long-range order in InAsSb

Abstract: For the first time, {111} ordering (CuPt type) has been observed in InAs1−xSbx alloys in a wide compositional range from x=0.22 to 0.88. The order‐induced spots show the highest intensity for x≊0.5 samples and the lowest intensity toward each binary end compound. Only two of the four variants are formed during growth. In some areas the degree of order for these two variants is equal, and in other areas one variant dominates.

Effect of Nb on the high-temperature sulfidation behavior of cobalt

Abstract: The sulfidation behavior of Co-Nb alloys containing up to 30wt.% Nb was studied in sulfur vapor at a pressure of 0.01 atm in the temperature range of 600–700°C. Increasing niobium content decreased the sulfidation rate, following the parabolic rate law. An activation energy of 25.6 kcal/mole was obtained for Co-10Nb, Co-20Nb, and Co-25Nb, while a value of 20.5 kcal/mole was found for Co-30Nb. All were two-phase alloys, consisting of solid solution α-Co and the intermetallic compound, NbCo3. The two-phase alloys formed a rather thick outer layer of cobalt sulfides and a heterophasic inner layer that was complex. The inner layer always contained the mixed sulfide CoNb2S4 which, depending on the alloy composition, coexisted with cobalt sulfide, NbS2, and / or NbCo3 particles. Short-time sulfidations showed that the solid solution initially sulfidized rapidly to form nodules of cobalt sulfide, whereas the NbCo3 phase formed a thin protective layer of NbS2. The nodules grew laterally until they coalesced into the continuous, outer thick layer, while the NbS2 completely or partially reacted with the cobalt sulfide to form CoNb2S4. Platinum markers were always found at the interface between the inner and outer scales, the location of the original metal surface.

Characterization and superconducting properties of phases in the Bi–Sr–Cu–O system

Abstract: Phase formation in the system Bi–Sr–Cu–O has been examined as a function of composition, temperature, ambient atmosphere, cooling history, and annealing time. Ceramic processing and melt crystallization techniques were used. For the ceramic materials (using Bi2O3, SrCO3, and CuO) processed at 700 °C in air the Bi2Sr2CuO6 composition (221) crystallizes to a mixture of CuO, SrCO3, and the rhombohedral Bi2O3 · xSrO solid solution. At 800–830 °C in air for short durations (5 min to 2 h) the reacted products consist principally of the ideal 221 phase with minor amounts of CuO. For longer reaction times (2–400 h) the reacted products consist of the ideal 221-type structure with c = 24.64 A and a = 3.804 A, a “collapsed” 221 structure with c = 23.6 A, and CuO. With increasing reaction time the “collapsed” 221 phase grows gradually at the expense of the ideal 221 phase. The “collapsed” 221 phase is not an oxycarbonate and appears to be a distinct ternary compound near the 221 composition, with a layered structure having a 1 A smaller stacking repeat. The ideal 221 phase is a solid solution with variable Sr content. With decreasing Sr in the starting mixture [2 to 1.25 atoms per formula unit (afu)] we observe the following: (1) the formation of the “collapsed” 221 structure is inhibited; (2) for the ideal 221 phase the c-cell dimension decreases significantly (0.2 A) and the a-cell dimension increases slightly (0.02 A); (3) the low temperature resistivity behavior changes from superconducting with Tc onset of 6 K for Sr>1.5 afu to semiconducting for Sr > 1.5 afu; (4) the positions of the superlattice peaks around the (001) reflections become more incommensurate with respect to the parent structure. Rapid quenching (<5 s) from temperatures near the melting point (900 °C) can raise the superconducting Tc onset to 9 K. Independent of the cell variation with Sr content, quenching causes the c-cell dimension to expand by 0.03 A on average while the a-cell dimension remains invariant. A small number of oxygen vacancies are quenched in from high temperature, and presumably originate in the Bi2O2 layer. As grown from the melt, crystals of the ideal 221 phase exhibit semiconducting behavior at low temperature; but with an additional high-temperature anneal in oxygen, metallic resistivity is restored with a superconducting onset near 5 K. Ca doping does not increase Tc in the ideal 221 phase. La and Y substitution occurs for Sr in the ideal 221 phase and ruins superconductivity.

Process for producing sub-micron ceramic powders of perovskite compounds with controlled stoichiometry and particle size

Abstract: A single crystal, solid solution, chemically homogenous powder that comprises a perovskite compound having useful electrical properties and the general formula: ABO₃, wherein the perovskite compound is selected from the group consisting of lead zirconate titanate, lead lanthanum zirconate titanate, lead titanate, lead zirconate, barium titanate, lead magnesium niobate, or lead zinc niobate, and having 0-50 percent total dopant or solid solution substitutions; and a process for making it.

Melting relationships in the system Fe-Feo at high pressures: Implications for the composition and formation of the earth's core

Abstract: A reconnaissance investigation has been carried out on melting relationships in the system Fe-FeO at pressures up to 25 GPa and temperatures up to 2200° C using an MA-8 apparatus. Limited studies were also made of the Co-CoO and Ni-NiO systems. In the system FeFeO, the rapid exsolution of FeO from liquids during quenching causes some difficulties in interpretation of textures and phase relationships. The Co-CoO and Ni-NiO systems are more tractable experimentally and provide useful analogues to the Fe-FeO system. It was found that the broad field of liquid immiscibility present at ambient pressure in the Co-CoO system had disappeared at 18 GPa, 2200° C and that the system displayed complete miscibility between molten Co and CoO, analogous to the behaviour of the Ni-NiO system at ambient pressure. The phase diagram of the system Fe-FeO at 16 GPa and from 1600–2200° C was constructed from interpretations based on the textures of quenched run products. The solubility of FeO in molten iron is considerably enhanced by high pressures. At 16 GPa, the Fe-FeO eutectic contains about 10–15 mol percent FeO and the eutectic temperature in this iron-rich region of the system occurs at 1700±25° C, some 350° C below the melting point of pure iron at the same pressure. The solubility of FeO in molten Fe increases rapidly as temperature increases from 1700 to 2200° C. A relatively small liquid immiscibility field is present above 1900° C but is believed to be eliminated above 2200° C. This inference is supported by thermodynamic calculations on the positions of key phase boundaries. A single run carried out on an Fe50 FeO50 composition at 25 GPa and 2200° C demonstrated extensive and probably complete miscibility between Fe and FeO liquids under these conditions. The melting point of iron is decreased considerably by solution of FeO at high pressures; moreover, the melting point gradient (dP/dT) of the Fe-FeO eutectic is much smaller than that of pure iron and is also smaller than that of mantle pyrolite under the P, T conditions studied. These characteristics make it possible for melting of metal phase and segregation of the core to proceed within the Earth under conditions where most of the mantle remains below solidus temperatures. Under these conditions, the core would inevitably contain a large proportion of dissolved FeO. It is concluded therefore, that oxygen is likely to be the principal light element in the core. The inner core may not be composed of pure iron, as often proposed. Instead, it may consist of a crystalline oxide solid solution (Ni, Fe)2O.

Effect of Additional Cu Element on Structure and Crystallization Behavior of Amorphous Fe-Nb-Si-B Alloys

Abstract: The addition of Cu to an amorphous Fe74.5Nb3Si13.5B9 alloy was found to significantly change the crystallization process, resulting in the formation of a bcc solid solution containing a large amount of the solute elements with fine grains. It was further observed that the inhomogeneity of the amorphous structure increases upon the addition of Cu. The inhomogeneous amorphous structure was presumed to enhance the instability of the amorphous phase and the formation tendency of the bcc solid solution with soft magnetic properties.

Structure refinements of lead-substituted calcium hydroxyapatite by X-ray powder fitting

Abstract: Structure d'hydroxyapatites obtenus a 1173 K par reaction a l'etat solide pour differentes concentrations en Pb substituant Ca (20, 45, 80% d'atomes Pb). Les atomes Pb preferent les sites (2) de la structure apatite

Ferroelectric microregion in KTa1−x Nb x O3 and SrTiO3

Abstract: Ferroelectric microregion (FMR) in SrTiO3 has been studied by means of Raman scattering. With lowered temperature, FMR, shape of which is ellipsoidal, increases the size concurrently with the correlation length. The ferroelectric transition of solid solution system such as Sr1−x Ca x TiO3 sets in when the FMR occupy the whole crystal volume. These characteristics are common to FMR in KTa1−x Nb x O3.

Correlations between clusterization and electrical properties within fluorite-type anions excess solid solutions: Setting of a model

Abstract: We proposed a model to correlate, in a continuous manner, the composition dependence of electrical properties and the progressive extension of clusterization when the substitution rate increases in a fluoride anion excess CaF2-type solid solution of M1−xM x ′2+α F2+αx(α=1,2,3) A new classification of clusters is given based on the presence or absence of coexistence between two types of interstitial fluoride ions The second part of the paper is devoted to the representation of the sum of interstitial fluoride ionsn F int and the sum of vacancies in normal sitesn □ according to the general equationy=(mx 3+λqx)/(x 2+q) This model allows us to correlate the structural and electrical properties of a large number of solid solutions with fluorite-type structure

Phase Diagram and Crystal Growth of Superconductive (NdCe)2CuO4

Abstract: Single crystals of (NdCe)2CuO4 have been grown by the travelling-solvent floating-zone (TSFZ) method. The single crystal grown in a deoxidized atmosphere exhibits superconductivity. Part of the crystallographic phase diagram of the Nd2O3-CuO system has been derived by conventional means to determine the concentration and temperature range of the liquidus line.