An EXAFS study of cation site distortions through the P2/c-P1̄ phase transition in the synthetic cuproscheelite-sanmartinite solid solution

1994 ◽  
Vol 58 (391) ◽  
pp. 185-199 ◽  
Author(s):  
P. F. Schofield ◽  
J. M. Charnock ◽  
G. Cressey ◽  
C. M. B. Henderson
Keyword(s):  
Phase Transition ◽  
Solid Solution ◽  
Stability Field ◽  
Cation Site ◽  
Cu Content ◽  
Square Planar ◽  
Jahn Teller ◽  
Exafs Study ◽  
Four Square ◽  
The Stability

AbstractEXAFS spectroscopy has been used to monitor changes in divalent cation site geometries across the P2/c-P1̄ phase transition in the sanmartinite (ZnWO4)-cuproscheelite (CuWO4) solid solution at ambient and liquid nitrogen temperatures. In the ZnWO4 end member, Zn occupies axially-compressed ZnO6 octahedra with two axial Zn-O bonds at approximately 1.95 Å and four square planar Zn-O bonds at approximately 2.11 Å. The substitution of Zn by Cu generates a second Zn environment with four short square planar Zn-O bonds and two longer axial Zn-O bonds. The proportion of the latter site increases progressively as the Cu content increases. Cu EXAFS reveals that the CuO6 octahedra maintain their Jahn-Teller axially-elongate geometry throughout the majority of the solid solution and only occur as axially-compressed octahedra well within the stability field of the Zn-rich phase with monoclinic long-range order.

A further study of analcime solid solutions in the system NaAlSi3O8-NaAISiO4-H20, with particular note of an analcime phase transformation

1980 ◽  
Vol 43 (332) ◽  
pp. 1035-1045 ◽  
Author(s):  
Ki-Tae Kim ◽  
B. J. Burley
Keyword(s):  
Phase Transition ◽  
Solid Solution ◽  
Phase Transformation ◽  
Solid Solutions ◽  
Total Pressure ◽  
Room Temperature ◽  
Water Pressure ◽  
Stability Field ◽  
Cell Parameters ◽  
The Stability

SummaryThe stability field of analcime solid solutions in the system NaAlSi3O8-NaAlSiO4-H2O has been previously determined by Kim and Burley (1971a). These experiments are re-examined with a view to determining the variations of the room-temperature cell parameters of analcime as a function of temperature of synthesis and composition. It is shown from this evidence that most of the analcime solid solutions in these experiments are equilibrium compositions. The increase in the cell dimension of quenched analcime solid solution is found to be 5 × 10−5 Å/°C. It is suggested that birefringence in analcime is induced by low water-pressure relative to total pressure. A phase transition appears to be observed in quenched analcimes of this study and is thought to be the same as that in the Golden analcime reported by Yoder and Weir (1960).

Cu0.8Mg1.2Si2O6 : a copper-bearing silicate with the low-clinopyroxene structure

2016 ◽  
Vol 80 (2) ◽  
pp. 325-335 ◽  
Author(s):  
Lei Ding ◽  
Céline Darie ◽  
Claire V. Colin ◽  
Pierre Bordet
Keyword(s):  
X Ray Diffraction ◽  
Soft Chemistry ◽  
X Ray ◽  
Cu Content ◽  
Distorted Structure ◽  
Mechanisms Of Formation ◽  
Jahn Teller ◽  
The Stability ◽  
Insight Into

AbstractThe Cu0.8Mg1.2Si2O6 pyroxene has been synthesized using a soft chemistry method. Its crystal structure was determined from powder X-ray diffraction data. Cu0.8Mg1.2Si2O6 crystallizes with the lowclinopyroxene monoclinic structure (space group P21/c). The role of the Jahn-Teller-distorted Cu2+ cation on the stability of this strongly distorted structure is investigated. Cu2+ shows a strong preference for the M2 site, attributed to a better adaptation of its JT-distorted coordination polyhedron to this already distorted and more flexible site. Comparison with previously reported compounds indicates that increasing the Cu content enhances the M2 site distortion, eventually leading to symmetry lowering from orthorhombic Pbca to monoclinic P21/c. These observations bring new insight into the mechanisms of formation and chemical composition of pyroxene minerals in the presence of JT cations.

Olivenite-Adamite Solid Solution From Oxidation Zone in Rędziny (West Sudetes, Poland)

Mineralogia ◽  
2006 ◽  
Vol 37 (2) ◽  
pp. 101-110 ◽  
Author(s):  
Boźena Gołębiowska ◽  
Adam Pieczka ◽  
Wojciech Franus
Keyword(s):  
Solid Solution ◽  
Carbonate Rocks ◽  
Oxidation Zone ◽  
Stability Field ◽  
Mineral Phases ◽  
West Sudetes ◽  
Polymetallic Mineralization ◽  
The Stability ◽  
Weathering Zone ◽  
Ubiquitous Presence

Olivenite-Adamite Solid Solution From Oxidation Zone in Rędziny (West Sudetes, Poland)An extensive hydrothermal polymetallic mineralization with a well developed oxidation zone rich in secondary minerals occurs in dolostones several hundred meters from the Karkonosze granite at Rędziny. Using XRD and FTIR methods, mineral phases representing transitional members of the olivenite-adamite solid solution have been identified. Electron microprobe analyses reveal the most common varieties to be zincian olivenite and cuprous adamite with compositions ranging from (Cu1.17Zn0.83)(AsO4)(OH) to (Zn1.38Cu0.62)(AsO4)(OH). The two minerals are subordinate in the weathering zone which can be characterized as having been a zone of low Cu2+and Zn2+activity and with mineralizing solutions of increased pH. A high Ca2+concentration due to the ubiquitous presence of carbonate rocks resulted in the expansion of the stability field of another arsenate, conichalcite (or Zn-bearing conichalcite), which is a common mineral there.

Phase Equilibria in the System NaAlSi3O8–NaAlSiO4–H2O with Special Emphasis on the Stability of Analcite

1971 ◽  
Vol 8 (3) ◽  
pp. 311-337 ◽  
Author(s):  
Ki-Tae Kim ◽  
B. J. Burley
Keyword(s):  
Solid Solution ◽  
Phase Equilibria ◽  
Phase Diagrams ◽  
Solid Solutions ◽  
Singular Points ◽  
Phase Relations ◽  
The Other ◽  
Stability Field ◽  
Narrow Zone ◽  
The Stability

Phase equilibria were determined in the P–T range of 0.5–10 Kb and 150–900 °C in the system NaAlSi3O8 – NaAlSiO4 – H2O. Two isobaric (2 Kb and 5.15 Kb) T–X phase diagrams (projected to a dry base) were completely determined and show that the stability field of analcite solid solutions has a large distorted pentagonal shape. The phase relations for the transition: nepheline hydrate I [Formula: see text] nepheline + H2O on the composition join NaAlSiO4 – H2O are not binary. It was found that there exists a narrow zone for the transition. The true P–T curve was found and determined in terms of a ternary univariant reaction: nepheline hydrate I + analcite [Formula: see text] nepheline + H2O. In the system NaAlSi3O8 – SiO2 – H2O, albite contains about 5 wt % silica in solid solution at 5.15 Kb and 670 °C.The equilibrium compositions of various univariant phases were determined essentially on the basis of the T–X phase diagrams. Another univariant reaction (zeolite species P = analcite + nepheline – hydrate I + H2O) was found at 2 Kb/215 °C and 5.15 Kb/235 °C and determined on a P–T projection. Three singular points were determined; two of them are located at 0.8 Kb/390 °C and 9.4 Kb/475 °C respectively on a univariant P–T curve for the reaction nepheline hydrate I + analcite = nepheline + H2O; the other one is located at 6 Kb/655 °C on a univariant P–T curve along which nepheline, analcite, liquid, and vapor coexist. The petrogenetic implication of analcite is discussed fully.

Crystal structure of CdZn2(PO4)2 and Cd2Zn(PO4)2

1968 ◽  
Vol 46 (6) ◽  
pp. 903-915 ◽  
Author(s):  
C. Calvo ◽  
J. S. Stephens
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Solid Solution ◽  
Oxygen Atom ◽  
Crystal Structures ◽  
Interatomic Distance ◽  
The Other ◽  
Miscibility Gap ◽  
Cation Site ◽  
Two Phases

The crystal structures of two solid solution phases found to occur in the Zn3(PO4)2–Cd3(PO4)2 system, one with composition near to CdZn2(PO4)2 and the other near to Cd2Zn(PO4)2, have been determined. Although these compounds are closely related structurally, there is a miscibility gap between the two phases and an apparent phase transition in only one of these. The compounds, named Bss and Css respectively, have lattice parameters a = 9.032(4) Å, b = 11.417(5) Å, c = 5.952(6) Å, β = 98.8(2), and Z = 4 for the former compound, and a = 9.056(8) Å, b = 11.86(1) Å, c = 6.190(9) Å, β = 100.1(2) and Z = 4 for the latter. Both compounds are monoclinic and crystallize with the space group P21/c with closely related, but not identical, structures to that of the mineral graftonite. The anions are slightly irregular PO43− tetrahedra with average P—O bond distances of 1.538 Å and 1.545 Å for those in Bss and 1.55 Å and 1.56 Å for those in Css. The cations are found to be coordinated to 7, 4, and 5 oxygen atoms for the 3 independent sites per unit cell. In Css the second cation site has a fifth oxygen atom at 2.57 Å in comparison with a length of over 2.9 Å for this same interatomic distance in Bss. The cations appear to be ordered with Cd++ preferentially in site 1 in Bss and Zn++ preferentially in site 2 in Css.

Phase transition at high pressure in Cu2CO3(OH)2 related to the reduction of the Jahn–Teller effect

2012 ◽  
Vol 68 (3) ◽  
pp. 266-274 ◽  
Author(s):  
Marco Merlini ◽  
Natale Perchiazzi ◽  
Michael Hanfland ◽  
Alexei Bossak
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Intermediate Phase ◽  
Structure Type ◽  
Teller Effect ◽  
Coordination Polyhedra ◽  
Bivalent Cations ◽  
Jahn Teller ◽  
Jahn Teller Effect ◽  
The Stability

Hydroxycarbonates with the general formula Me2(CO3)(OH)2 are widely used materials in industrial processes and are widespread in nature. The Cu term, malachite, Cu2CO3(OH)2, is monoclinic, P21/a. Substitution of Cu2+ with other bivalent cations such as Mg, Zn, Fe, Cu or Ni is possible and leads to a different structure type, rosasite, P21/a or P21/b11 in the same cell setting as malachite. Rosasite structure is topologically similar to malachite, but the symmetry elements are oriented differently with respect to structural units. The stability of the malachite-like structure (MS) compared with the rosasite-like structure (RS) has been suggested to be related to the Jahn–Teller effect in CuO6 coordination polyhedra. For this reason the hypothesis of the phase transition of malachite, Cu2CO3(OH)2, to a rosasite structure at high pressure, as a result of the reduced Jahn–Teller effect, has been tested and confirmed by powder and single-crystal diffraction structural studies: above 6 GPa the malachite structure is no longer stable and transforms to a RS structure. RS Cu2CO3(OH)2 is 3% more dense than malachite and the bulk modulus is remarkably higher, 80 (2) GPa compared with 48 (4) GPa. The longer apical Cu—O bonds in the distorted Me1 octahedral site are progressively shortened with increasing pressure, revealing a decrease in the Jahn–Teller effect at high pressure. The transition has a first-order character, is reversible with a significant hysteresis, and there is no evidence of any intermediate phase between the two structures. We then have further evidence that in the Me2(CO3)(OH)2 compounds, the two main structural types, MS and RS, are closely related. The former structure is stabilized only when Cu is the prevalent cation in the octahedral sites, and it can transform directly to the RS as a function of thermodynamic changes.

Stability of (Ni1_xLix)(Li1–yNiy)02Ordered Solid Solution

1995 ◽  
Vol 50 (2-3) ◽  
pp. 155-168 ◽  
Author(s):  
V. Massarotti ◽  
D. Capsoni ◽  
M. Bini
Keyword(s):  
Solid Solution ◽  
Rietveld Method ◽  
Structural Parameters ◽  
Diffusion Mechanism ◽  
Exchange Process ◽  
Reactive System ◽  
Lithium Content ◽  
Cation Site ◽  
Wide Range ◽  
The Stability

Abstract The stability of ordered solid solutions (OSS) with LiNiO2 structure has been studied in a wide range of the lithium cationic fraction (0.22< xt < 0.42). The OSS is obtained from the reactive system Ni0/Li2CO3 at 800 °C starting with high nominal lithium content (xt = 0.5). By analysis of the decrease of x, observed after annealing, during which evaporation and a contact reaction occurs, structure-composition relationships can be obtained.The transformation of the ordered phase, due to a cation exchange process, is observed for xt < 0.31 by accurate X-Ray powder pattern analysis (Rietveld method). By increasing the annealing time (decreasing lithium content), the data can be explained on the basis of progressive formation of the simple solid solution (SSS) with only one cation site and halved c axis value. The variations of structural parameters during the transformation are compared with those reported in the literature. The coherence domains of the OSS become smaller and the phase percentage decreases, while the SSS percentage increases. The rate of such a process can be well described on the basis of a two dimensional diffusion mechanism.

scholarly journals Tourmalinisation in peraluminous granitic context : from experiment to thermodynamic modelling

2021 ◽  
Author(s):  
Julien Fort ◽  
Stanislas Sizaret ◽  
Michel Pichavant ◽  
Arnault Lassin ◽  
Johann Tuduri ◽  
...  
Keyword(s):  
Solid Solution ◽  
Thermodynamic Properties ◽  
Stability Field ◽  
Peraluminous Granite ◽  
Physico Chemical ◽  
Fe Content ◽  
Chemical Conditions ◽  
Using Data ◽  
The Stability

&lt;p&gt;Tourmaline records the physico chemical conditions during its cristallisation, as its primary chemical zonations are generally unbalanced, its occurrence as alteration product could be used to decipher the physicochemical properties of mineralizing fluids. However, the role of the tourmalinisation in hydrothermal processes remains little studied, if not poorly understood. &amp;#160;The complexity of its thermodynamic properties is related to the presence of four cationic sites allowing the accommodation of a wide variety of elements (Henry and Dutrow, 2018). Moreover the phenomena of deprotonation, Si-&lt;sup&gt;IV&lt;/sup&gt;B and valence state, make the approach of solid solution properties complex (Hughes et al., 2001; Henry et al., 2011; Ba&amp;#269;&amp;#237;k, 2015; Morgan, 2016). Thus, thermodynamic properties are most often estimated&amp;#160; (Garofalo et al., 2000; Hinsberg and Schumacher, 2007) and only a few measurements could be carried out on a reduced number of near-endmembers crystals (Kuyunko et al., 1984; Ogorodova et al., 2012).&lt;/p&gt;&lt;p&gt;This study aims to investigate experimentally the stability field of schorl (Na-Fe) &amp;#8211; dravite (Na-Mg) solid solution at 2 kbar total pressure between 400&amp;#176; and 600&amp;#176;C as a function of the boron content of the fluid and fO2 condition, using an internally heated gas apparatus. Those metasomatic experiments have been conducted on a mixture of naturals crystals of cordierite + albite, representing a peraluminous granite composition in a Na-Mg-Fe-Al-Si-B-O-H system, characterized by a high-Mg, low-Fe content. These experiments were performed in order to simulate a classic aluminous host of these tourmaline alterations in granitic context. The results will be studied, in terms of stability of the tourmaline species, chemistry variation and texture. They will be compared with thermodynamic models build using data from the literature (Korges et al., 2018; Pan et al., 2019 among others) . Ultimately, the objective is to characterize in a P, T, W/R space, the chemical evolution of fluids, the alteration sequence of rocks and the variations in volumes related to the successive reactions.&lt;/p&gt;

Distortion Characteristics Across the Structural Phase Transition in (Cu1−x Zn x )WO4

1997 ◽  
Vol 53 (1) ◽  
pp. 102-112 ◽  
Author(s):  
P. F. Schofield ◽  
K. S. Knight ◽  
S. A. T. Redfern ◽  
G. Cressey
Keyword(s):  
Phase Transition ◽  
Solid Solution ◽  
Structural Phase Transition ◽  
Order Parameter ◽  
Structural Phase ◽  
Rietveld Analysis ◽  
Neutron Powder Diffraction Data ◽  
Jahn Teller ◽  
Jahn Teller Effect ◽  
Homogeneous Strain

Rietveld analysis of neutron powder diffraction data on the sanmartinite (ZnWO4)-cuproscheelite (CuWO4) solid solution has enabled the comparison of microscopic and macroscopic order parameters associated with the P2/c–P\overline 1 structural phase transition. The macroscopic spontaneous strain, calculated from the lattice parameters, conforms well with a second-order Landau model. Furthermore, this is also true of the symmetry-related atomistic M—O order parameter and the quadratic elongation of the MO6 octahedra. It is clear that the Jahn–Teller effect, associated with the divalent Cu cation, is the driving force for the phase transition and the excess elongation evident in the M—O(2) bond giving rise to the non-symmetry predicted strain element e 22. The existence of a large region of order parameter saturation at the copper-rich end of the solid solution is also associated with the MO6 elongation and the breakdown of the homogeneous strain field of the zinc solute atoms.

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