Complete Range Of Solid Solutions Research Articles

Single crystal growth of solid solutions from the Ga-Pd-Sn system for basic research in heterogeneous catalysis

Abstract Intermetallic compounds in the binary Ga-Pd system have proved to be superior as catalysts in the semi-hydrogenation of acetylene. Partial substitution of Ga by Sn even increases the activity. In order to study elementary processes of catalytic reactions, well-oriented surfaces of single-crystalline slaps are needed, i.e. single crystal growth is a prerequisite. For the first time, solid/liquid equilibria including the solid solutions Ga1−xSnxPd and Ga1−xSnxPd2 were studied. Based on these findings single crystal growth of the two solid solution series succeeded using the Czochralski method from (Ga,Sn)-rich solutions. Inclusion-free single crystals of a few cm3 in size could be obtained. Due to different crystal structures of the end members, Sn substitution in Ga1−xSnxPd is restricted to x ≈ 0.15 in the cubic phase. Although a complete solid solution range for Ga1−xSnxPd2 has been reported by Armbruster et al. (2018), mixed crystals of the 1:2 phase can be grown from a native ternary melt only up to approx. x = 0.54 due to missing solid/liquid equilibria at a higher ratio of Sn substitution for Ga.

Thermodynamics of Fe3O4-Co3O4 and Fe3O4-Mn3O4 spinel solid solutions at the bulk and nanoscale.

High temperature oxide melt solution calorimetry has been performed to investigate the enthalpies of mixing (ΔmixH) of bulk and nanophase (1 -x)Fe3O4-xM3O4 (M = Co, Mn) spinel solid solutions. The entropies of mixing (ΔmixS) were calculated from the configurational entropies based on cation distributions, and the Gibbs free energies of mixing (ΔmixG) were obtained. The ΔmixH and ΔmixG for the (1 -x)Fe3O4-xCo3O4 system are negative over the complete solid solution range, for both macroscopic and nanoparticulate materials. In (1 -x)Fe3O4-xMn3O4, the formation enthalpies of cubic Fe3O4 (magnetite) and tetragonal Mn3O4 (hausmannite) are negative for Mn3O4 mole fractions less than 0.67 and slightly positive for higher manganese content. Relative to cubic Fe3O4 and cubic Mn3O4 (stable at high temperature), the enthalpies and Gibbs energies of mixing are negative over the entire composition range. A combination of measured mixing enthalpies and reported Gibbs energies in the literature provides experimental entropies of mixing. The experimental entropies of mixing are consistent with those calculated from cation distributions for x > 0.3 but are smaller than those predicted for x < 0.3. This discrepancy may be related to the calculations, having treated Fe(2+) and Fe(3+) as distinguishable species. The measured surface energies of the (1 -x)Fe3O4-xM3O4 solid solutions are in the range of 0.6-0.9 J m(-2), similar to those of many other spinels. Because the surface energies are relatively constant, the thermodynamics of mixing at a given particle size throughout the solid solution can be considered independent of the particular particle size, thus confirming and extending the conclusions of a recent study on iron spinels.

Thermochemistry of La 0.7Sr 0.3Mn 1− xFe xO 3 solid solutions (0< x

The structure, the energetics and the internal redox reactions of La 0.7Sr 0.3Fe x Mn 1− x O 3 have been studied in the complete solid solution range 0.0< x<1.0. High temperature oxide melt drop solution calorimetry was performed to determine the enthalpies of formation from binary oxides and the enthalpy of mixing. There is a noticeable change in the energetics of the solid solution near x=0.7, which is due to the growing concentration of Fe 4+ at higher Fe/(Fe+Mn) ratio. The balance between different valences of the transition metals, Mn and Fe, is the main factor in determining the energetics of the La 0.70Sr 0.30Fe x Mn 1− x O 3 solid solution.

Anomaly in dielectric and piezoelectric properties of (1− x)Pb[Mg 1/3Nb 2/3]O 3– xPbZrO 3 ceramic

(1− x)Pb(Mg 1/3Nb 2/3)O 3– xPbZrO 3 ceramic has been investigated for dielectric and piezoelectric behavior for the complete solid solution range. The dielectric constant ( ε ′ ), coupling coefficient ( k 31 ) and piezoelectric strain coefficient ( d 33 ) show anomaly in the composition range of 0.40 < x < 0.50 . The optimal properties ( ε m ′ = 19 , 500 , k 31 = 0.16 and d 33 = 100 pC / N ) were observed at x = 0.44 . This is similar to the behavior observed in well-known relaxor based solid solutions at their morphotropic phase boundary composition. However, the absolute values are substantially lower than these analogous solid solutions. The low value is attributed to the absence of low symmetry intermediate phase in the crossover region.

Substitution of oxygen by fluorine in the GdSr_2AlO_5:Ce^3+ phosphors: Gd_1−xSr_2+xAlO_5−xF_x solid solutions for solid state white lighting

Solid solutions between two isotypic host compounds: GdSr(2)AlO(5) and Sr(3)AlO(4)F; Gd(1-x)Sr(2+x)AlO(5-x)F(x):Ce(3+) (GSAF:Ce(3+)), have been prepared across the complete solid solution range x. Depending on x, the series display considerable optical tunability of emission wavelengths in the range 574 nm to 474 nm, which is attributed to the decreased crystal field splitting arising from increased host ionicity with fluorine addition. Applying the GSAF:Ce(3+) phosphors on InGaN LEDs (lambda (max) = 405 nm and 450 nm) permits white lighting sources to be prepared. The characteristics of these are reported.

Thermodynamic Properties and Phase Diagram for the System MoO2–TiO2

The activity of molybdenum dioxide (MoO2) in the MoO2–TiO2 solid solutions was measured at 1600 K using a solid‐state cell incorporating yttria‐doped thoria as the electrolyte. For two compositions, the emf was also measured as a function of temperature. The cell was designed such that the emf is directly related to the activity of MoO2 in the solid solution. The results show monotonic variation of activity with composition, suggesting a complete range of solid solutions between the end members and the occurrence of MoO2 with a tetragonal structure at 1600 K. A large positive deviation from Raoult's law was found. Excess Gibbs energy of mixing is an asymmetric function of composition and can be represented by the subregular solution model of Hardy as follows image The temperature dependence of the emf for two compositions is reasonably consistent with ideal entropy of mixing. A miscibility gap is indicated at a lower temperature with the critical point characterized by Tc (K)=1560 and . Recent studies indicate that MoO2 undergoes a transition from a monoclinic to tetragonal structure at 1533 K with a transition entropy of 9.91 J·(mol·K)−1. The solid solubility of TiO2 with rutile structure in MoO2 with a monoclinic structure is negligible. These features give rise to a eutectoid reaction at 1412 K. The topology of the computed phase diagram differs significantly from that suggested by Pejryd.

Thermochemistry of La1-xSrxFeO3-δ Solid Solutions (0.0 ≤ x ≤ 1.0, 0.0 ≤ δ ≤ 0.5)

A series of compounds with the general formula La1-xSrxFeO3-δ have been synthesized in the complete solid solution range 0.0 ≤ x ≤ 1.0 and 0.0 ≤ δ ≤ 0.5 with a variety of heat treatments. High-temperature drop solution calorimetry in molten 2PbO·B2O3 at 702 °C was performed to determine their enthalpies of formation from oxides at room temperature. The enthalpy of oxidation involved in the reaction 2F + + 0.5O2(g) = 2F + is independent of oxygen nonstoichiometry in each La1-xSrxFeO3-δ series with a given x, and further is approximately constant at −200 ± 50 kJ/mol O2 for 0 < x ≤ 0.5 and −140 ± 30 kJ/mol O2 for 0.5 < x < 1.0. The enthalpies of formation from oxides in the LaFeO3−SrFeO2.5 solid solution can be fitted either by a quadratic equation or by two straight line segments intersecting at x = 0.5. The quadratic fit gives a positive interaction parameter, 36.1 ± 4.9 kJ/mol, suggesting a tendency toward phase separation. The two linear segment models two regions of oxygen vacancy presence: dilute (random distribution) for x ≤ 0.5 and concentrated (short-range ordering) for x > 0.5. Extrapolation to the end-member (x = 1) gives the enthalpy of formation of perovskite-type SrFeO2.5 and the enthalpy of the hypothetical brownmillerite−perovskite phase transition at room temperature is estimated as 5.5 ± 4.0 kJ/mol. This small value implies extensive short-range order in the perovskite phases with high x. The enthalpies of formation from oxides in the LaFeO3−SrFeO3 solid solution are virtually independent of Sr composition when x ≤ 0.67 and are a few kJ/mol more exothermic when x ≥ 0.7. This is interpreted by phase evolutions from low symmetries to cubic.

Superlattice structures in solid solution of high-T c YBa 2Cu 3O 7− δ and (Pb,Cu)Sr 2(Ca,Y)Cu 2O 7− δ superconductors

A complete solid solution range exists between the systems YBa 2Cu 3O 7− δ and (Pb,Cu)Sr 2(Ca,Y)Cu 2O 7− δ has been found with general stoichiometry (Pb 0.75 x Cu 1−0.75 x )(Sr 2 x Ba 2−2 x )(Ca 0.5 x Y 1−0.5 x )Cu 2O 7− δ . Energy dispersive spectrometry and X-ray diffraction identified that a true solid solution exists. Superlattice structures observed by electron diffraction across the solid solution range have a modulation range have a modulation periods along a* which can be varied by altering both the compositional parameter x and the overall oxygen content. The existence of these superlattices infers that the solid solution is non-random and therefore thermodynamically non-ideal. The superconducting transition temperatures, T c, across the solid solution range are also strongly dependent on the composition, x, but no direct relationship with the modulation period has been established. From these studies it may be concluded that the solid solution between known superconductors is possible, although involving some partial ordering of the lattice, but ordering of cations in the rock-salt to charge reservoir layer is not a significant factor in determining the superconducting properities, which depend more closely on the overall composition and hence on the ability of the charge reservoir layer to transfer charge to the superconducting layers.

Characterization of green garnets from an Archean calc-silicate rock, Bandihalli, Karnataka, India: evidence for a continuous solid solution between uvarovite and grandite

Green garnets in a low-pressure metamorphic Archean calc-silicate rock from Bandihalli, Karnataka were characterized by optical microscopic, electron microprobe analysis, powder x-ray diffraction, ICP-mass spectroscopic and Fourier Transform Infrared (FT-IR) spectroscopic techniques. Earlier studies on these garnets indicated that these garnets are chrome grossularite (with the variation of uvarovite content from 2.6 to 44 mol%). Present studies on these garnets show that they have a wide range of uvarovite content from 27 to 72 mol%, bearing testimony to a complete range of solid solutions between uvarovite and grandite. As no IR data appear to be available for naturally occurring uvarovite, we also present here, the first FTIR spectroscopic studies on the uvarovite-rich garnet, along with the IR data on the grossularite from the same calc-silicate rock. The analysis on a single grain of uvarovite garnet (72 mol% Uv) shows an increase in the grossular content towards the rim pointing to the influence of calcareous composition of metasedimentary host rock on the garnet composition. The pyrope content in the studied samples is very low varying from 0.12 to 0.66 mol%. The composition of all the garnets when plotted in a MgO–FeO–CaO diagram (after Dawson and Stephens, 1975) suggests that these garnets are unlike kimberlitic garnets in their composition, thus ruling out the possibility of their being detrital garnets derived from a mantle rock like kimberlite as surmised by Radhakrishna (1994).

Phase equilibria and crystal chemistry in the system Sr-Ca-Cu-O under high oxygen pressure

Phase equilibria in the system SrO-CaO-CuO have been studied under high oxygen pressures. The recently discovered non-superconducting binary phase, Sr 0.74(3)CuO 2, which is stable only under high oxygen pressure, forms a complete range of solid solutions with the structurally related phase, Ca 0.81(1)CuO 2. These materials have complicated superstructures and may form a family of Vernier phases, such as was found in Sr 0.74(3)CuO 2. Stabilities and oxygen stoichiometries of tetragonal Sr 2−2 x Ca 2 x CuO 3+δ (0.0 ≤ x ≤ 0.1) and Sr 14−14 x Ca 14 x Cu 24O 38+δ (0.0 ≤ x ≤ 0.5) solid solutions under high oxygen pressures are also discussed.

The CaO-SrO-CuO-O2 system: Phase equilibria and thermodynamic properties at 1123 K

Phase relationships in the CaO-SrO-CuO system in pure oxygen at 1.01 x 10(5) Pa pressure were determined by equilibrating different compositions at 1123 K for similar to 120 h and analyzing the phases present in the quenched samples using X-ray diffraction (XRD), optical and scanning electron microscopy, and energy dispersive analysis of X-rays (EDAX). Four solid solution series were observed in the system, The CawSr1-wO monoxide solid solution with rock-salt structure was found to exhibit an asymmetric miscibility gap, The mixing properties of the monoxide system were deduced using a subregular solution model, For the (CaxSr1-x)(2)CuO3 series, a complete solid solution range with orthorhombic space group Immm was obtained. Calcium substituted for strontium up to 68 at. % in SrCuO2+delta and 51.5 at. % in Sr14Cu24O41-delta. The tie lines between the solid solutions were determined accurately, The activity-composition relations in (CaxSr1-x)(2)CuO3, CaySr1-yCuO2+delta, and (Ca2Sr1-z)(14)Cu24O41-delta solid solutions were determined from experimental tie lines. Activities in the (CaxSr1-x)(2)CuO3 and CaySr1-yCuO2+delta series were close to the predictions of the Temkin model, The behavior of the (CazSr1-(z))(14)Cu24O41-delta solid solution was more complex, with the activity of SrCu(24/14)O-(41-delta/14) exhibiting both positive and negative deviations from ideality. Gibbs energy of formation of the CaCuO2+delta metastable phase at 1123 K was deduced from an analysis of the phase diagram.

Long-wavelength optical phonons in semiconducting mixed layer crystals of the series SnSxSe2-x(0⩽x⩽2)

Large single crystals of semiconducting layer compounds with composition SnSxSe2-x, where 0<or=x<or=2, have been successfully grown by a vertical Bridgman technique. The series forms a complete range of solid solutions and follows Vegard's law. Long-wavelength optical phonons have been studied experimentally for SnSe2, SnS2 and seven different solid solutions SnSxSe2-x by laser Raman scattering and far-IR absorption and reflection measurements in the region up to 500 cm-1. The frequencies of the vibrational modes for SnSe2(SnS2) do not tend towards the corresponding values for SnS2(SnSe2) with increasing (decreasing) x and the intensity decreases. This rules out any possibility of one-mode behaviour in the series. A two-mode behaviour is indicated; however, no local or gap modes are observed.

Optical properties of Bi12Si1−xTixO20 single crystals

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A Study of LaNi1−xCoxO3 System

AbstractA series of solid solutions of LaNi1−xCoxO3 systems has been prepared and characterized by x‐ray diffraction, electrical conductivity and Seebeck coefficient measurement and i.r. absorption spectroscopy. Complete range of solid solutions between LaNiO3 and LaCoO3 exists with rhombohedral perovskite structure. The variation of lattice parameters in the system suggests that the proportion of high‐spin‐ and low‐spin‐trivalent cobalt varies with x. While the electrical conductivity and Seebeck coefficient data show definite metallic behaviour in the system up to x = 0.3, i.r. absorption spectra reveal that the collective electron character persists up to x ∼ 0.7.

Substitution of aluminium by gallium in β-alumina

In the two-block structure of β-alumina the effects of the replacement of aluminium by gallium have been investigated. As alkali ions sodium and potassium have been chosen. The alkali to trivalent metal ratio varied between 1:6 and 1:7. In this composition range for the sodium derivative substitution could be accomplished up to an aluminium to gallium ratio of about 1:9 without the presence of a second phase. For potassium the two-block β-alumina phase does exist for the aluminate and for the gallate systems. A complete range of solid solutions appears to exist for these two compounds. From sintered, polycrystalline pellets (with a density between 85 and 90 per cent of the theoretical density), X-ray powder diffraction diagrams have been recorded. The unit cell parameters increase linearly with the gallium content in accordance with the larger radius of the trivalent gallium ion. The expansion of the lattice parameters did not change the electrical conductivity of the sodium β-alumina samples. However, for the analogous potassium specimens a decrease of the electrical conductivity has been observed with increasing gallium content.

The Chlorination Kinetics of Tungsten, Molybdenum, and their Alloys

The chlorination kinetics of tungsten, molybdenum, and three of their binary alloys have been studied as part of a Bureau of Mines effort to provide information of value when considering chlorine metallurgy processes. Tungsten and molybdenum were used for this initial investigation of alloys because they are chemically similar, form a complete range of solid solutions, and have been shown to chlorinate at temperatures sufficiently different so as to facilitate the determination of temperature dependency of reactivity by experiments based on the measurement of weight loss as the volatile chlorides are formed. Both the pure metals and alloys containing 22, 48, and 72 atomic per cent (a/o) molybdenum were found to chlorinate between 400° and 775°C at rates of 10−7 to 10−5 mole per square centimeter per minute, with the reaction rate dependent upon the 0.6 power of chlorine pressure. Molybdenum exhibited the highest reactivity, tungsten was the least reactive, and the alloys showed intermediate reactivity with respect to temperature. Single crystals of the pure metals showed marked anisotropy upon chlorination. When chlorinated, the polycrystalline alloy specimens of 22 and 72% molybdenum tended to show the crystalline anisotropy exhibited by the major component, while the 48% molybdenum specimen developed no pattern similarity to the pure metals.

Solids with high ionic conductivity in group 1 halide systems

Phase diagrams have been determined for the systems MI+AgI (M = Na, K, Rb, Cs, Tl or NH4), MBr+AgBr (M = K, Rb or Cs) and MI+CuI (M = K or Rb). A group of isomorphous compounds MAg4I5(M = K, Rb, NH4) with exceptionally high ionic conductivity has been identified. At 20°C the conductivity of polycrystalline RbAg4I5 is 0.124 ± 0.006 ohm–1 cm–1, i.e., higher than the ionic conductivity of any other known solid. At this temperature RbAg4I5 is stable, but KAg4I5 and NH4Ag4I5 slowly disproportionate to AgI and K2AgI3 or (NH4)2AgI3. The ternary system KI+RbI+AgI contains a complete range of solid solutions (K,Rb) Ag4I5. Analogous bromides have not been found, but a compound KCu4I5 is stable between 257 and 332°.

Miscibility of III-V Semiconductors Studied by Flash Evaporation

A study has been made of the mutual solid solubility of the phosphides, arsenides, and antimonides of gallium and indium, all of which crystallize in the zinc-blende structure. The films were prepared by flash evaporation of mixed powders. X-ray diffraction analysis of the films showed that all of the phosphides and arsenides form a complete range of solid solutions, while the phosphides and antimonides are largely immiscible. In the arsenide-antimonide systems, only those containing a common group III element are completely miscible (e.g., InAs–InSb, GaAs–GaSb). All quasibinary systems with a common group V element form a complete range of solid solutions. The results have been extrapolated to give a schematic representation of the limits of solubility in the multicomponent system In–Ga–P–As–Sb. The solubility has been correlated with the size of the component atoms involved in each system. Where solid solution occurred, the lattice constants were found to obey Vegard's law within the limits of accuracy. Epitaxy was achieved by depositing the films onto single-crystal germanium. Optical absorption has been measured on films covering a wide range of compositions.

Preparation, semiconduction and low-temperature magnetization of the system Ni 1− xMn 12+ xO 4

The preparation of a complete range of solid solutions between the cubic spinel nickel manganite, NiMn 2O 4, and the tetragonal spinel, Mn 3O 4, is described. Studies of the crystal symmetry, the semiconductor behavior and low-temperature magnetization are reported each as a function of composition. Analysis of the crystal-chemical and thermoelectric properties leads to a tentative chemical formula for the system which provides an explanation for the electrical conductivity and magnetization. The conductivity involves the “hopping” of electrons from octahedral-site Mn 3+ ions to octahedral-site Mn 4+ ions. The unpredictable magnetic moments are also accounted for by the properties of octahedral-site Mn 3+ and Mn 4+ ions.

Permanent Magnetic Properties of Iron-Cobalt-Phosphides

An investigation of the phase relations of the section Fe2P–Co2P in the system Fe–Co–P showed that at high temperature all (Fe, Co)2P alloys, including the final components Fe2P and Co2P, probably form a continuous range of solid solutions having the hexagonal Fe2P structure. At low temperatures Fe2P and Co2P form an almost complete range of solid solutions with the orthorhombic Co2P lattice. The Curie temperature of the hexagonal phase increases from about room temperature for Fe2P to a value of nearly 190°C for (Fe, Co)2P with an Fe:Co ratio of 70:30. The anisotropy field HA appeared to be a function of the Fe:Co ratio and possesses a maximum value of about 19 000 oe near an Fe:Co ratio of 90:10. Particles obtained by lixiviating an Fe–Co–Cu–P melt can possess a coercivity IHC up to 2000 oe. This value can be substantially increased by annealing. The temperature coefficient of IHC appears to be relatively large and seems to be linked to the change of K with temperature. The coercivity decreases appreciably after mechanical loading, e.g. pressing, but can be restored by annealing; the anisotropy field HA as well as the saturation magnetization σ∞ changes in the same sense. Anisotropic permanent magnets have been made with a BHmax value of about 2×106 gauss oe.