Solid Solution Field Research Articles

Investigation of the surface of the liquidus of the Fe-Ni-S system at X s<0.51

Methods of thermal analysis, X-ray, optical, and electron microscopy were used to study the liquidus surface of the Fe-Ni-S system in the field of 35 to 51 at. pct sulfur. The FeS-NiS, FeS-Ni3S2, Fe0.55S0.45-Ni0.55S0.45, and Fe0.61S0.39-Ni0.61S0.39 sections and some additional samples were examined. A microscopic study of the samples slowly cooled and annealed enabled referring of all the samples to the fields of primary crystallization of the monosulfide solid solution (Fe x Ni1−x )S1+y (MSS), the Fe-Ni solid solution with the γ-Fe structure (TN), and the (Fe x Ni1−x )3±y S2 heazlewoodite solid solution (HZSS). The data, obtained by a method of derivative thermal analysis, have been used to describe analytically the MSS and HZSS surface of primary crystallization. Previous results were used together with our own data to construct the TN surface of primary crystallization. These parts of the liquidus surface have been approximated by polynomial equations, the coefficients of which were determined by the least-squares method. As a result of the absence of experimental data in the δ-Fe-based solid-solution primary crystallization field, this liquidus part is approximated on the basis of the Fe-S and Ni-Fe phase diagram data. The equations are used to construct the boundaries between various areas of phase primary crystallization, to define the coordinates of a triple point, and to construct isotherms.

Perovskite solid solutions in the BaO-CuO-Y 2O 3-Nb 2O 5 system

Freeze dried complex carboxylates are highly reactive precursors for complex perovskite solid solutions in the system BaO-CuO-Y 2O 3-Nb 2O 5 On thermal decomposition of the amorphous precursors the formation of complex crystalline phases begins at 600 °C. In most cases the themodynamically controlled phase composition is reached after a reaction time of two hours at about 900 °C. Beginning from the perovskite compound Ba 2YNbO 6 a partial substitution of Y by Cu or by a combination 2/3 Cu,1/3 Nb leads to extended fields of solid solutions with cubic perovskite structure. Substitution according to Y 0,5xBa 2(Y 1-0,5xCu xNb)O 6+x is limited to x ≤ 0,4. A compound LBa 2Cu 2NbO 8 (x=2), well characterized for L=La, does not exist for L=Y. The composition of solid solutions depends on the preparation conditions. There are some signs for an inhomogeneous distribution of B-cations in the cubic perovskites.

Mixed (Oxygen Ion and n‐Type) Conductivity and Structural Characterization of Titania‐Doped Stabilized Tetragonal Zirconia

By using X‐ray diffraction lattice parameter measurements and Raman spectroscopy studies, both the solid solubility limit of titania in yttria tetragonal zirconia polycrystalline solid solutions and the tetragonal solid solution field in the system have been established. Valence state, site symmetry, and changes in local structures of Ti ions in Y‐TZP with 5 and 10 mol % are studied for the first time using EXAFS (extended X‐ray absorption fine structure), XANES (X‐ray absorption near edge structure), and X‐ray photoelectron spectroscopy. The total electrical conductivity in air of the tetragonal solid solution decreases with increasing titania content. XANES results show that as the dissolves into the tetragonal zirconia Y‐TZP matrix, a displacement of ions from the center of symmetry seem to take place which leads to a nonrandom substitution of ions on lattice sites. Ti‐O bond distances derived from EXAFS results indicate that ion can be in a square‐pyramidal arrangement, i.e., fivefold oxygen‐coordinated. As a consequence, two kind of cation‐oxygen vacancy associations ( and ) with different diffusion dynamics are created. This results in a decrease of the global concentration of moving oxygen vacancies and therefore, a decrease of ionic conductivity. Electronic conductivity, n‐type, only appeared at oxygen partial pressure lower than atm and above 800°C in Y‐TZP containing 10 mol % titania. Such an n‐type electronic conduction was attributed to a hopping of electrons between and cations by a small polaron hopping mechanism. © 1999 The Electrochemical Society. All rights reserved.

Monopyroxenic Basalt‐Based Glass‐Ceramics

Uniform, ultrafine, microcrystalline, hard, pyroxenic glass‐ceramic materials have been obtained successfully from basalt rock; instead of adding nucleation catalysts, the FeO:Fe2O3, CaO:Na2O, and CaO:MgO ratios have been rectified. This process has been accomplished by deliberately adding the smallest permissible amounts of oxidizers, limestone, dolomite, and soda ash (as additives) that are necessary to fulfill the monominerality requirements; these requirements affect the melting, workability, crystallization, and microstructure of the glass‐ceramics. The melting temperature decreases as the ratios decrease (beyond certain limits); in addition, the workability, crystallization, and microstructure also improve as the ratios decrease. An almost‐stable solid solution of augite or aegirine‐augite composition is the only crystalline phase that is formed. The minimal FeO:Fe2O3 ratio and the likelihood of a greater affinity of the Na+ cation for the Fe3+ cation, rather than the Al3+ cation, may be responsible for increasing the stability and widening of the crystallization field of the complex aluminum‐bearing pyroxene solid solution.

Solidus surface of the equilibrium diagram of the HfO2—Y2O3—La2O3 system

The phase equilibria on the solidus surface of the phase diagram of the HfO2−Y2O3−La2O3 system have been investigated using DTA in helium up to 2500°C, TA with solar energy in air up to 3000°C, X-ray phase analysis, petrography, and electron microscopy. Five solid solution fields based on hexagonal (H) and cubic (C) crystal modifications of Y2O3, cubic modifications of HfO2 with fluorite structure (F), high-temperature cubic modifications of La2O3 (X), and crystallization field of the ordered phase La2Hf2O7 with the pyrochlorine (Py) type structure have been found on the solidus surface. The ternary system has three quaternary novariant equilibria of the eutectic (1) and peritectic (2) type.

High pressure phase equilibria in the system CaTiO 3 -CaSiO 3 : stability of perovskite solid solutions

Phase relations in the system CaTiO3-CaSiO3 were experimentally examined at 5.3–14.7 GPa and 1200–1600 °C with a 6–8 type multianvil apparatus. As pressure increases, stability field of perovskite solid solution extends from CaTiO3 to CaSiO3, and the perovskite becomes stable for the entire composition range above about 12.3 GPa. The stability field of Ca(Ti1−X, SiX)2O5 (0.78<x≦1) titanite solid solution +Ca2SiO4 larnite exists in the CaSiO3-rich composition range at 9.3–12.3 GPa and 1200 °C. Perovskite solid solutions containing CaSiO3 component of 0 to 66 mol% could be quenched to 1 atm. The composition-molar volume relationship of perovskite solid solution showed that molar volume of perovskite solid solution linearly reduces from the value of CaTiO3 to that of CaSiO3.

GEOLOGY AND GEOCHEMISTRY OF THE BOA VISTA NICKEL SULFIDE DEPOSIT, CRIXÁS GREENSTONE BELT, CENTRAL BRAZIL.

The Boa Vista nickel-sulfide deposit is located at the NW edge of the late Archean Crixas greenstone belt. The nickel-sulfide deposit is associated with a narrow 7 km-long EW-trending sequence of meta-ultramafic and metabasic rocks. The volcanic sequence was overprinted by regional ductile deformation and associated metamorphism but primary volcanic structures and textures are preserved within low-strain zones. Two types of ultramafic flows are recognized in these zones (spinifex-textured flows and unsettled flows). The ultramafic rocks exhibit some of the classical geochemical and textural features that become the main criterion for the recognition of komatiitic lavas. The MgO content (from 22.1 to 28.7 wt. %) on spinifex-textured and unsettled flows is typical for peridotitic komatiites. Geochemical variations of major elements indicate the importance of olivine fractional crystallization. Scattering of the data suggests that regional metamorphism has chemically modified the ultramafic rocks. The sulfide mineralization is always present at the lowest part of an ultramafic sequence overlying a mafic sequence. The thickness of the mineralized horizon is variable but it is usually less than few-meters thick. Four types of ore are recognized in the Boa Vista deposit. In order of decreasing abundance they are: stringer ore, disseminated ore, massive ore and matrix ore. The sulfide ore mineralogy is typical of magmatic sulfides associated with ultramafic komatiites. It consists mainly of pyrrhotite ( 70 vol. %) associated with pentlandite and chalcopyrite and minor magnetite and sphalerite. The Fe-Ni-S variation of the ore is consistent with a primary magmatic origin for the nickel mineralization. Analyses of sulfide ore recalculated to 100 % sulfides plot within the field of the monosulfide solid solution at high temperature. The Ni/Cu ratio of the ore is high (± 10) and comparable to most Archean KHNS deposits. The Boa Vista deposit provided the first opportunity to study nickel-sulfide mineralization processes in the Crixas greenstone belt. Considering that KHNS deposits occuring in greenstone belts worldwide tend to be restricted to specific ultramafic units, geological and petrological studies of the Boa Vista deposit provide important clues for future nickel-sulfide exploration work in the extensive greenstone belt terranes of central Brazil.

Bismuth and bismuth–antimony sulphosalts from Neogene vein mineralisation, Baia Borşa area, Maramureş, Romania

AbstractSeveral complex Cu-Pb-Bi, Cu-Pb-Bi-Sb and Ag-Pb-Bi sulphosalt minerals have been identified in samples from hydrothermal vein mineralisation associated with the Toroiaga sub-volcanic body in the Baia Borşa area of Maramureş County, northwest Romania. This is the first chemically-documented report of Bi-sulphosalts in the Neogene metallogenic province around Baia Mare. The investigated samples contain abundant amounts of matildite solid solution within galena, the Cu-Pb/Bi sulphosalts aikinite, friedrichite, krupkaite, hammarite, lindströmite and gladite as well as nuffieldite and berryite. Within the Ag-Pb/Bi group, the majority of analysed grains can be regarded as members of the lillianite homologous series. Three distinct lillianite homologues were identified, which correspond to (i) phases along the lillianite-gustavite solid solution join (Pb3Bi2S6-AgPbBi3S6), (ii) phases within solid solution field of heyrovskyite, and (iii) compositions which best correspond to ‘schirmerite’,sensuMakovicky and Karup-Møller (1977b), but may represent disordered gustavite, vikingite or eskimoite. Some of the analysed lillianite homologues contain excess Cu, which may occupy interstitial sites. Furthermore, a large proportion of the lillianite homologues display significant substitution of Sb for Bi within the limits predicted by experimental investigations. Cosalite, also showing a range of compositions including Sb-rich varieties is recognised. Izoklakeite, Cu2Pb22(Sb,Bi)22S57, is an abundant phase throughout the analysed samples, its composition is in good agreement with previously published analyses, except for excess Cu and Fe beyond the limits previously reported. The description of several minerals from this new occurrence and compositional data on them, including the Sb-bearing varieties, provides valuable additional information on compositional limits in natural samples.

Electron Diffraction Study of Interstitial Transition Metal Ordering inT2+xSn2(T= Co, Ni)B8-Type Solid Solutions

Interstitial transition metal ordering in the “disordered,” wide-range nonstoichiometric Ni2+xSn2, 0.70 <x< 1.19, and Co2+xSn2, 0.76 <x< 1.26, solid solution fields has been investigated via electron and X-ray powder diffraction. The sublattice is of the NiAs type with additional interstitial transition metal ions occupying trigonal bipyramidal sites in the Sn sub-lattice. That the distribution of interstitial sites is far from random in these “disordered” phases is clear from the presence of a spectacular and highly structured diffuse intensity distribution which appears to take the form of undulating, approximately cylindrical channels of diffuse intensity running along the c* direction of reciprocal space. The strongest satellite reflections of a low-temperature superstructure phase in each system are shown to fall more or less directly onto the diffuse distribution of the “disordered” phase. The characteristic extinction conditions of the superstructure phase are mirrored in the characteristic shape of the diffuse distribution of the “disordered” phase. The composition dependence of the diffuse distribution is investigated.

Ferroelectric perovskite solid solutions in high magnetic fields; diagrams of the phase growth

Diagrams of the phase growth of ferroelectric perovskite solid solutions in strong magnetic fields are obtained by calculation. It is shown that high magnetic fields accelerate the growth of either paraelectric or ferroelectric phases. The width and velocity of the interphase boundary are calculated as functions of magnetic field and chemical composition of the perovskite solid solution.

Regularities of the Mg sides of the Mg-RE (magnesium-rare earth metal) phase diagrams: Comments on evaluations

Mg sides of the binary Mg phase diagrams with individual rare-earth metals are considered. The assessed versions of Mg-La, Mg-Ce, Mg-Pr, and Mg-Nd ones presented earlier are criticized because they show no regular change of solid solubility in Mg as the atomic number of the rare-earth metal increases. Other experimental data on the solid solubility of the rare-earth metals in Mg are presented, which show the regular extension of Mg solid solution field as the rare-earth metal atomic number becomes successively higher. The latter results are assumed to be more reliable because of using the more exact method of the solid solubility determination.

A TEM Study of Rhombohedral β Type Solid Solutions in the Bi 2O 3-SrO and Bi 2O 3-CaO Systems

Specimens within the (1 - x)BiO 1.5 · x M O ( M = Sr, Ca) rhombohedral β type solid solution fields have been synthesized and studied via TEM and powder XRD. Two distinct, fully three-dimensionally ordered, triclinic superstructure phases have been found for both the M = Sr and M = Ca systems. The first, S1, occurs for low x specimens whereas the second, S2, occurs for somewhat higher x specimens. In the case of the M = Sr system, a further incommensurately modulated (although somewhat disordered) superstructure phase was also found for x = 0.25.

The phase diagram of the water-hydrogen system in the crystallization field of solid solutions based on ices Ih and II at high pressures

The decomposition curves of the solid solutions based on ices Ih (α-solutions) and II (β-solutions) in the water-hydrogen system were studied by the DTA technique at pressures up to 7 kbar. The α-solution is destabilized by pressure but to a lesser degree than ice Ih and is stable up to 2.3 kbar. Theβ-solution is stabilized by pressure and at 7 kbar decomposes at about 20°C. TheP, T-phase diagram of the water-hydrogen system in the crystallization range is constructed on the basis of reference [1] and our data. All possible types of stoichiometric interrelationships in the guest —host system are demonstrated by the example of the water-hydrogen system.

Interactions in the Al2O3-ZrO2-Y2O3 system

The phase diagram of the Al2O3-ZrO2 system was replotted over a broad range of concentrations (0–100 mole %) and temperatures (1150–2800°C). The polymorphic transformation of zirconium F ⇄ T occurs via the metatectic reaction F ⇄ T + L at 2260°C. Phase triangulation was employed to plot the diagrams of the partially quasibinary sections in the Al2O3-ZrO2-Y2O3 system. Since there is a wide solubility range based on ZrO2 in the binary ZrO2-Y2O3 system, the triangulation conodes are displaced in the F-solid solution corners. The two-phase regions Y3A5-F are quite broad. The reactions in all three are of the eutectic type. The ternary solid solution fields in the Al2O3-ZrO2-Y2O3 system had no observable width.

Synthesis and Structure of a Compositely Modulated Solid Solution in the Zirconium Nitride Oxide Fluoride System

The phase Zr(N, O, F)x has been studied by X-ray powder diffraction and transmission electron microscopy. It had previously been described as an oxygen free nitride fluoride and the structure of one composition from the solid solution field solved as a so-called Vernier superstructure approximation. More correctly the phase should be described as an incommensurate, compositely modulated structure, with a continuously variable, composition-dependent, primary modulation wave-vector. The total anion to cation ratio can be uniquely determined from careful measurement of diffraction patterns and is shown to be continuously variable and to range between 2.12 and 2.25. The cell parameters of the component substructures are determined and show a linear dependence upon the union to cation ratio. Apparent valence calculations are used to investigate anion ordering.

A composite modulated structure approach to the lanthanide oxide fluoride, uranium nitride fluoride and zirconium nitride fluoride solid-solution fields

It is shown that the only generally applicable crystallographic approach to the anion excess, fluorite-related solid-solution fields reported in the zirconium nitride fluoride, uranium nitride fluoride and lanthanide oxide fluoride systems is a composite modulated structure approach. A TEM and powder XRD study has been made of the ZrN x F 4-3x (0.906 < x < 0.936) system

Synthesis and stability relations of Li2Mg2[Si4O11

The recently discovered phase Li 2 Mg 2 [Si 4 O 11 ] represents a new silicate structure type. It is a «loop-branched dreier single-chain silicate», in the classification of Liebau, and plays an important role in the phase relations of the system Li 2 O-MgO-SiO 2 -(H 2 O). New synthesis studies show that the composition is narrowly defined, with no evidence of a solid solution field in the stated system. A maximum substitution of 15 mol% of Mg by Fe 2+ has been achieved in the present study. The stability relations of Li 2 Mg 2 [Si 4 O 11 ] have been investigated at P(H 2 O) = P(total). The phase possesses a cusp-shaped stability field bounded to lower temperatures by reaction to amphibole + Li 2 Si 2 O 5 + Li 2 SiO 3 (reaction boundary passes through approximately 750°C/0.5 kbar and 795°C/l kbar). A curve of incongruent melting passing through the coordinates 920°C/l bar, 875°C/0.5 kbar and 855°C/l kbar limits the stability field to higher temperatures. Detailed phase relations near the projected intersection of the two terminal reactions at approximately 1.8 kbar are still undetermined. At pressures higher than 1 bar, melts can not be quenched to glass at the cooling rates attainable in the routine high-pressure apparatus employed. The metastable assemblage quartz + Li 2 SiO 3 + orthoenstatite always results. The present study indicates that the phase Li 2 Mg 2 [Si 4 O 11 ] must possess a liquidus field at 1 bar and that a redetermination of the classical Li 2 O-MgO-SiO 2 liquidus phase diagram will be necessary. Two brackets at 700 and 900°C indicate that the phase Li 2 Si 2 O 5 breaks down to the higher-pressure/higher-temperature assemblage Li 2 SiO 3 + quartz at 8.75 ± 0.25 kbar and 3.25 ± 0.25 kbar, respectively

Solid-state reaction, microstructure and phase relations in the ZrO2-rich region of the ZrO2-Yb2O3 system

Phase relations below 1700°C in the ZrO2-rich region of the zirconia-ytterbia system have been established using thermal expansion, room-temperature X-ray diffraction, precision lattice parameter measurements and microscopic observations. The solubility limits of ytterbia in both monoclinic and tetragonal zirconia were determined. A eutectoid reaction, tetragonal zirconia solid solution→ monoclinic + cubic zirconia solid solutions at 400 ± 20°C and 2.4 mol % ytterbia was found. The left-hand boundary of the cubic zirconia solid-solution field was redetermined between room temperature and about 1700°C. Long-range ordering was present at 40 mol % ytterbia and the formation of an ordered phase, Zr3Yb4O12, isostructural with M7O12-type compounds was found. Its thermal stability was established between room temperature and 1630 ± 10°C, in which it decomposes into cubic zirconia solid solution by an order-disorder reaction.

The incommensurately modulated(1 − x)Ta 2O 5· xWO 3, 0 ≤ x ≤ 0.267 solid solution

The phase(1 − x)Ta 2O 5 · WO 3, 0 ≤ x ≤ 0.267 has been studied by X-ray powder diffraction and transmission electron microscopy. It was previously described as an infinite series of anion-deficient, α-UO 3-type “line phases,” with compositions resulting from intergrowths of different blocks made up by small numbers of α-UO 3-type cells. More correctly(1 − x)Ta 2O 5· xWO 3, 0 ≤ x ≤ 0.267 is described as an incommensurately modulated structure with a linearly composition-dependent primary modulation wave-vector q prim. = q b*. The underlying orthorhombically distorted α-UO 3-type parent structure has space group symmetry Cmmm ( a ≈ 6.20−6.14, b ≈ 3.66, c ≈ 3.89−3.85Å). Characteristic extinction conditions imply a superspace group symmetry of P : Cmmmm : s, −1,1. The four previously reported crystal structures in the solid solution field are examined by means of apparent valence calculations. Crystal chemical reasons are proposed for the width of the composition range,0 ≤ x ≤ 0.267, observed for the title phase.

The Defect Fluorite Phase in the ZrO2-PrO1.5 System and Its Relationship to the Structure of Pyrochlore

A detailed transmission electron microscope and X-ray powder diffraction study has been made of the so-called 'defect fluorite' phase field in the ZrO2-PrO1.5 system and of its close relationship to the pyrochlore solid solution field in the same system. Even for the lowest possible PrO1.5 content within the 'defect fluorite' phase field, it is clear that the sharp Bragg reflections characteristic of the underlying fluorite average structure are accompanied by some of the 'satellite reflections' characteristic of the pyrochlore solid solution field. As the PrO1.5 content increases, these satellite reflections increase systematically in intensity as well as sharpening very considerably. It is shown that this 'defect fluorite' phase field cannot be adequately described either in terms of random point defects within an average fluorite-type matrix or in terms of a diphasic texture of pyrochlore domains embedded coherently into a fluorite matrix, but must be regarded as enuinely intermediate between these two end-member structures and of commensurately modulated fluorite type. A group theoretical approach is used to propose a model for the structural deviation from the underlying fluorite average structure.