Refinement In Space Group Research Articles

Rietveld refinement of chromian clinochlore from the chromitites of Golyamo Kamenyane serpentinite (Eastern Rhodopes)

The structure of a disordered IIb chromian clinochlore from the chromitites of Golyamo Kamenyane serpentinite (Eastern Rhodopes) was studied using Rietveld refinement techniques and powder X-ray diffraction (CuKα, 3–100° 2Θ in 0.013° 2Θ increments). The refinement in space group C–l yielded the following lattice parameters: a = 5.299(2) Å, b = 9.2625(5) Å, c = 14.4726(6) Å, α = 90.103(7)°, β = 97.191(13)°, γ = 90.320(11)°, and cell volume of 704.69(21) Å3. The structure of the studied mineral is characterized by a semi-random stacking of adjacent chlorite layers creating a situation in which not all atoms positions could be precisely located. Despite this limitation, the crystal chemical plausibility of the final structural model could be achieved due to the fact that most of the atomic positions (all octahedral cations and anions) repeat at intervals of ±b/3 and could be uniquely determined. The type of structural information that can be derived from the test compound and similar structurally related materials by applying the Rietveld method is discussed and ways to achieve this are considered.

The Crystal Chemistry of Rathite Based on New Electron-Microprobe Data and Single-Crystal Structure Refinements: The Role of Thallium

Crystal-structure refinements in space group P21/c were performed on five grains of rathite with different types and degrees of thallium, silver, and antimony substitutions, as well as quantitative electron-microprobe analyses of more than 800 different rathite samples. The results of these studies both enlarged and clarified the complex spectrum of cation substitutions and the crystal chemistry of rathite. The [Tl+ + As3+] ↔ 2Pb2+ scheme of substitution acts at the structural sites Pb1, Pb2, and Me6, the [Ag+ + As3+] ↔ 2Pb2+ substitution at Me5, and the Sb-for-As substitution at the Me3 site only. The homogeneity range of rathite was determined to be unusually large, ranging from very Tl-poor compositions (0.16 wt%; refined single-crystal unit-cell parameters: a = 8.471(2), b = 7.926(2), c = 25.186(5) Å, β = 100.58(3)°, V = 1662.4(6) Å3) to very Tl-rich compositions (11.78 wt%; a = 8.521(2), b = 8.005(2), c = 25.031(5) Å, β = 100.56(3)°, V = 1678.4(6) Å3). The Ag content is only slightly variable (3.1 wt%–4.1 wt%) with a mean value of 3.6 wt%. The Sb content is strongly variable (0.20 wt%–7.71 wt%) and not correlated with the Tl content. With increasing Tl content (0.16 wt%–11.78 wt%), a clear increase of the unit-cell parameters a, b, and V, and a slight decrease of c is observed, although this is somewhat masked by the randomly variable Sb content. The revised general formula of rathite may be written as AgxTlyPb16−2(x+y)As16+x+y−zSbzS40 (with 1.6 < x < 2, 0 < y < 3, 0 < z < 3.5). Based on Pb–S bond lengths, polyhedral characteristics and Pb-site bond-valence sums, we conclude that the Pb1 site is more affected by Tl substitution than the Pb2 site. When Tl substitution reaches values above 13 wt% (or 3 apfu), a new phase (“SR”), belonging to the rahite group, appears as lamellar exsolution intergrowths with Tl-rich rathite (11.78 wt%). Rathite is found only in the Lengenbach and Reckibach deposits, Binntal, Canton Wallis, Switzerland.

Jianshuiite in oceanic manganese nodules at the Paleocene-Eocene boundary

Synchrotron powder X-ray diffraction and scanning electron microscopy examinations of manganese oxide concretions/nodules (~0.3–1.0 mm diameter) from ODP Site 1262 on Walvis Ridge in the Southeastern Atlantic Ocean revealed that they consist primarily of the layered Mn oxide phase jianshuiite [(Mg,Mn,Ca)Mn34+O7·3H2O]. The nodules are from an interval with severe carbonate dissolution that represents the Paleocene/Eocene (P/E) thermal maximum (~55.8 Ma). Most nodules from the middle of the carbonate dissolution interval contain internal open space, and consist almost entirely of euhedral plate-like jianshuiite crystals, 2–4 μm in diameter and ~0.1–0.5 μm thick. Backscattered electron images and energy-dispersive X-ray analyses revealed stacks of interleaved Al-rich and Al-poor jianshuiite crystals in some nodules. The crystals in other nodules contain predominantly Mg (with trace K and Al) in addition to Mn and O, making them near “end-member” jianshuiite. Rietveld refinements in space group R 3 confirmed the isostructural relationship between jianshuiite and chalcophanite, with Mg occupying the interlayer position above and below the vacant sites in the Mn/O octahedral sheet, and coordinated to 3 octahedral layer O atoms (1.94 A) and 3 interlayer water O atoms (2.13 A). Final refined occupancy factors suggest that small quantities of Ni and possibly Mn2+ are located on the Mg site. The transient appearance of the Mg-rich birnessite-like phase jianshuiite, probably abiotically produced, must indicate an exceptional transient change in the chemistry of the pore fluids within deep ocean sediments directly following the P/E boundary, possibly as a result of decreasing oxygen levels and pH, followed by a return to pre-event conditions.

Sr21Bi8Cu2(CO3)2O41, a Bi5+ Oxycarbonate with an Original 10L Structure

The layered structure of Sr21Bi8Cu2(CO3)2O41 (Z = 2) was determined by transmission electron microscopy, infrared spectroscopy, and powder X-ray diffraction refinement in space group P63/mcm (No. 194), with a = 10.0966(3)Å and c = 26.3762(5)Å. This original 10L-type structure is built from two structural blocks, namely, [Sr15Bi6Cu2(CO3)O29] and [Sr6Bi2(CO3)O12]. The Bi5+ cations form [Bi2O10] dimers, whereas the Cu2+ and C atoms occupy infinite tunnels running along c⃗. The nature of the different blocks and layers is discussed with regard to the existing hexagonal layered compounds. Sr21Bi8Cu2(CO3)2O41 is insulating and paramagnetic.

Structure and modeling of disorder in miserite from the Murun (Russia) and Dara-i-Pioz (Tajikistan) massifs

The structure, structural disorder and chemistry of miserite from the charoite-bearing rocks of the Murun massif (Russia) and from alkaline-syenite pegmatitic rocks of the Dara-i-Pioz massif (Tajikistan) were investigated employing a combination of electron microprobe, single crystal diffraction and micro-Fourier transform infrared spectroscopy analysis. Chemical analysis of the sample investigated by X-ray diffraction evidenced that Dara-i-Pioz miserite has a greater REE concentration than Murun miserite (~0.22 vs. 0.05 apfu, respectively) and also contains Y (0.14 apfu), which is absent in Murun miserite. The occurrence of a band at about 1,600 cm−1 testified to the presence of H2O in miserite at hand. Structural analyses yielded average cell parameters of a = 10.092, b = 16.016, c = 7.356 A, α = 96.60°, β = 111.27° and γ = 76.34°. Anisotropic structural refinement in space group P $$\bar{1}$$ converged at similar values for the analyzed samples (R ~3.4, R w ~3.8 %). An interesting feature shown by both the miserite specimen is the presence, revealed by difference Fourier analysis, of a disordered part of the structure. This turned out to be due to the flipping of the tetrahedra belonging to the isolated [Si2O7]6− diorthogroups, one of the two radicals (the other is [Si12O30]12−) characterizing the miserite structure. The sixfold and seven-vertex Ca polyhedra linked to the inverted diorthogroups show variation in coordination number with respect to those of the ordered structure.

K and Ca exchange behavior of zeolite A

Powdered samples of zeolite-A ([Na 11.8Al 11.8Si 12.2O 48 · 26H 2O] 8, LTA, Na-A) were completely Ca and K exchanged. Several compositions between the end members Na-, Ca-, and K-zeolite A were produced. Combined results from X-ray powder diffraction including lattice parameter refinements in space group F m 3 ¯ c, energy dispersive X-ray spectroscopy, and thermal gravimetric analyses are presented. Rietveld refinements are performed for the three Na-rich samples in the Ca exchange series. The linear dependence of the lattice parameter a on the Ca and K contents is described as well as the relationship between water, Ca and K content. The lattice parameter a decreases with increasing Ca and K content, ranging from 24.62 to 24.46 Å for the Ca-exchanged forms and from 24.63 to 24.58 Å for the K-exchanged forms. Higher Ca content results in a higher amount of water incorporated in the zeolite, ranging from 25 (Na-A) to 28 (Ca-A) molecules per formula unit (m.p.f.u.) whereas the water content in the K-exchanged forms varies about 23.5 ± 1.0 m.p.f.u. not directly correlated with the K contents but significantly lower than the 26 m.p.f.u. of the Na-A starting material. The Ca and K contents can be estimated from lattice parameter a by linear regression.

The Solid‐State Structures of Dimethylzinc and Diethylzinc

The synthesis of dimethylzinc (Me2Zn) and diethylzinc (Et2Zn) by Frankland in the mid-nineteenth century marks a cornerstone in the history of chemistry.1 Not only were they among the first organometallic compounds, but studies on their chemical reactions and vapor densities led to the first clear exposition of valency theory.2 Since then both compounds have found widespread applications: They are important reagents in organic synthesis,3 for example in the enantioselective alkylation of carbonyls4 and imines5 and in cyclopropanation reactions.6 Their high vapor pressures have led to extensive uses in metalorganic chemical vapor deposition (MOCVD) for the preparation of wide band gap II–VI semiconducting films (e.g. ZnS, ZnSe, ZnTe),7 ZnO nanostructures, and as p-dopant precursors for III–V semiconductors (e.g. GaAs, InP, AlxGa1−xAs), which have numerous electronic and photonic applications.8

Substitution mechanisms and implications for the estimate of water fugacity for Ti-rich phlogopite from Mt. Vulture, Potenza, Italy

The crystal chemistry of Ti-rich phlogopite from deposits of the oldest activity (~740 ka) of Mt. Vulture, Potenza, Italy, was investigated to identify the substitution mechanisms in Ti-rich phlogopite and to determine its potential as a geohygrometer. Substitution mechanisms were determined by electron probe microanalysis (EPMA), single-crystal X‑ray diffraction (SCXRD), Mössbauer spectroscopy, and micro-Fourier transform infrared (FTIR) spectroscopy. Magnetite and sanidine from the mica-rich host rocks were also analyzed. Use of the biotite-magnetite-sanidine geohygrometer in these volcanics (essentially trachytic-phonolitic ignimbrites) is exploited. All investigated phlogopite samples consist of the 1M polytype, with 5.3275(2) ≤ a ≤ 5.3635(4) Å, 9.2211(4) ≤ b ≤ 9.2958(8) Å, 10.1211(5) ≤ c ≤ 10.281(1) Å, and 99.980(3) ≤ β ≤ 100.097(2)°. Structure refinements in space group C2/m converged to 2.42 ≤ R 1 ≤ 4.00% and 2.04 ≤ wR 2 ≤ 4.50%. VI Fe 3+ /Fe tot from Mössbauer analyses ranged from 34(1)-89(1)%. The main bands in the OH-stretching region are 3709, 3682, and 3658 cm -1 , and were assigned to 3Mg-OH - -K-OH - , 3Mg-OH - -K-O 2- , and 2MgFe 3+ - OH - -K-O 2- local configurations, respectively. The overall crystal chemical features are compatible with the M3 + -Tschermak substitutions ( VI M 2+ + IV Si 4+ ↔ VI M 3+ + IV Al, with M 3+ = Al,Fe 3+ ), M 3+ -oxy [ VI M 2+ + (OH)- ↔ M 3+ + (O) 2- + ½H 2 ↑] and Ti-oxy substitutions [ VI M 2+ + 2(OH) - → VI Ti 4+ + 2(O) 2- + H 2 ↑]. The magnetite composition varies between Mt 82 Uv 18 and Mt 93 Uv 07 , whereas the proportion of orthoclase with respect to albite plus anorthite is 0.77 ≤ X Or ≤ 0.82. A partly ionic model was used to estimate annite activity, starting from experimentally determined substitutions in phlogopite. The resulting water fugacity was an order of magnitude lower than that calculated using stoichiometry to determine the phlogopite formula. The results are consistent with the occurrence of a well-developed hydrothermal system that altered the magmatic oxygen fugacity conditions at Mt. Vulture.

The crystal structure determination of the crystalline layered silicic acid H-RUB-18

Abstract The layer silicate H-RUB-18 (chemical compo-sition: Si4O7(OH)2) was prepared by ion exchange from the parent material Na-RUB-18. The high degree of structural disorder typical for this material precluded a classical structure analysis based on diffraction data only. Nevertheless, a detailed picture of the structure was obtained by a step by step process using a combination of complementary methods: Crystal chemical considerations and solid state NMR spectroscopy allowed to establish a rough model of the structure which was optimized by forcefield molecular dynamics (MD) simulations. A subsequent Rietveld refinement in space group I41/amd confirmed the model consisting of a sequence of pseudo tetragonal silicate layers with an intra-layer repeat unit a = 7.38 Å and inter-layer distances of c = 7.44 Å. The main type and degree of disorder was analyzed by the simulation of various stacking sequences of rigid silicate layers which served as the building blocks. The random displacement of consecutive layers is accompanied by a slight distortion of the layers as indicated by an additional density functional theory (DFT) energy minimization calculation in triclinic symmetry. The given displacement and distortion allow for the formation of hydrogen bonds between the terminal OH groups necessary for the stabilization of the structure. The concept of a structure analysis presented in this paper may be suitable as a guide line to be applied to many other disordered materials.

Single-crystal in situ high-temperature structural investigation on strontium feldspar

A single crystal of ordered strontium feldspar (SrAl 2 Si 2 O 8 ) was used for in situ X-ray intensity data collection at T = 20, 160, 330, 510, and 670 °C. The crystal was synthesized from the melt and thermally treated at T = 1450 °C for 146 h (a = 8.379, b = 12.963, c = 14.245 Å, β = 115.46 °, V = 1397.0 Å 3 ; Q od = 0.82). At room temperature 1517 reflections of a-type and 988 reflections of b-type with F o ≥ 2σ (F o ) were observed with R = 4.0% for refinement in space group I2/c. The dimensions of the tetrahedra do not change significantly with increasing temperature implying that the Al-Si configuration remains unchanged throughout the experimentally investigated temperature range. The Sr-coordination polyhedron expands regularly with temperature. The linear coefficient of volume expansion (α v = 1.69 × 10 -5 /°C) is close to that observed for the other feldspars. The thermal expansion ellipsoid shows a remarkable anisotropy and the main expansion occurs close to a*, as observed in the other monoclinic K-, Ba-, and Pb-feldspars. The variation along a* is related to the flexing of the double-crankshaft chains in response to the expansion of the Sr-polyhedron. As in Pb-feldspar, a progressive displacement of the non-tetrahedral cation towards the c-glide plane with increasing temperature is observed. However, in Sr-feldspar, the temperature increase does not cause the atoms of the M polyhedron to approach C2/m symmetry. These results suggest that the atoms of the Srpolyhedron retain I2/c symmetry at elevated temperatures and the Sr-polyhedron does not assume a configuration that may significantly favor Al-Si disorder.

High-pressureCmcaand hcp phases of germanium

Structural phase transitions of germanium at pressures up to 190 GPa have been investigated by means of angle-dispersive x-ray powder diffraction using synchrotron radiation. Near 100 GPa the primitive hexagonal modification of Ge transforms to an orthorhombic phase with 16 atoms per unit cell. The results of full-profile Rietveld refinements in space group $\mathrm{Cmca}$ indicate that the orthorhombic modification of Ge is isotypic to the phase Si-VI. Near 160--180 GPa Ge undergoes a transition to a structure assigned as hexagonal close packed (hcp). Ab initio calculations of pressure-dependent enthalpies and optimized structural parameters are presented for different structures of Ge. The calculated results clearly support the observed occurrence of the $\mathrm{Cmca}$ structure in Ge.

Neutron powder diffraction refinement of the crystal structure of La4Ti3O12

Results from full profile analysis of powder neutron diffraction patterns (λ=1.05 A ̊ and λ=2.475 A ̊ ) taken at room temperature are presented. The refinements in space group R 3 ̄ yielded considerably better reliability factors than those obtained in group R 3 ̄ m as suggested in previous X-ray diffraction works.

Structural variations induced by thermal treatment in lead feldspar (PbAl2Si2O8)

Other| February 01, 1998 Structural variations induced by thermal treatment in lead feldspar (PbAl 2 Si 2 O 8 ) Mario Tribaudino; Mario Tribaudino Dipartimento di Scienze Mineralogiche e Petrologiche, Turin, Italy Search for other works by this author on: GSW Google Scholar Piera Benna; Piera Benna Search for other works by this author on: GSW Google Scholar Emiliano Bruno Emiliano Bruno Search for other works by this author on: GSW Google Scholar American Mineralogist (1998) 83 (1-2): 159–166. https://doi.org/10.2138/am-1998-1-216 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Mario Tribaudino, Piera Benna, Emiliano Bruno; Structural variations induced by thermal treatment in lead feldspar (PbAl 2 Si 2 O 8 ). American Mineralogist 1998;; 83 (1-2): 159–166. doi: https://doi.org/10.2138/am-1998-1-216 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Lead feldspar single crystals were annealed at T = 1050 and 1000 degrees C, starting from a disordered metastable configuration (PbF H , Q od = 0) and from an ordered configuration (PbF L , Q od = 0.89). Single-crystal data collection and refinement in space group I2/c show that the degree of Al-Si order increases to Q od = 0.42 after annealing the disordered PbF H at 1050 degrees C and decreases to Q od = 0.70 after annealing the ordered PbF L sample at 1000 degrees C. This suggests that the equilibrium Q od is between 0.70 and 0.42 for temperatures between 1000 and 1050 degrees C, where anorthite or strontium feldspar are almost completely ordered. A residual in the difference-Fourier map because of positional disorder was observed near the Pb site in all the refined crystals. The average y/b Pb coordinate changes with increasing Al-Si disorder, as Pb approaches the glide plane. A significant decrease in the intensity of b-type reflections was consequently observed. A spontaneous strain, with the main axis almost parallel to the a axis, is associated with Al-Si ordering. Pb polyhedral deformation related with Q od accounts for the observed strain. A calibrating equation, Q od = [(8.427(2)-a) / 0.048(3)] (super 1/2) , has been calculated and applied to the unit-cell parameters obtained from subsequent thermal treatments and from Bruno and Facchinelli (1972) to define the evolution of the Q od vs. the treatment temperature. The thermal behavior of the Q od could then be bracketed, suggesting T c between 1150 and 1200 degrees C for the I2/c-C2/m phase transition induced by the Al-Si order-disorder process. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Crystal Structure and Magnetic Properties of the One-Dimensional Oxide, Sr3ZnIrO6: Zinc in Trigonal Prismatic Coordination

The structure of Sr3ZnIrO6was determined by powder X-ray Rietveld refinement in space group R 3c(No. 167),a= 9.6392(1) andc= 11.2145(2) Å. Neutron diffraction refinements confirm the structure analysis. The structure contains zinc in a highly unusual trigonal prismatic coordination environment. The structure consists of infinite one-dimensional chains of alternating face-shared IrO6octahedra and ZnO6trigonal prisms. Magnetic measurements show that Sr3ZnIrO6correlates antiferromagnetically near 20 K. No magnetic ordering, however, was found by the neutron diffraction experiments performed at room temperature and at 10K. The magnetic data were fit using an Ising model, which gave a coupling valueJ/kB∼ 18.5.

Synthesis, structure und thermochemical reactivity of bismuth methoxide, BiOOCH 3

Microcrystalline bismuth methoxide, BiOOCH 3, was synthesized by reacting bismuth nitrate pentahydrate in a sodium hydroxide/methanol mixture. The structure was determined with a Rietveld refinement in space group P4/nmm (a = 3.740 A ̊ , c = 10.513 A ̊ ) from X-ray powder data. The thermochemical reactivity is discussed with respect to its dependence of the gas atmosphere and the morphology as well as with respect to the formation of bismuth oxide exhibiting tailor-made textures and morphologies. The significance of the title compound as potential precursor compound for the generation of ternary or polynary oxides is discussed.

Structure and charge localization in Pb 2Sr 2Tb 1−xCa xCu 3O 8 for x= 0.0 and 0.5

The crystal structure refinements of Pb 2Sr 2Tb 1−xCa xCu 3O 8 for x=0.0and0.5 was performed as a constrained refinement in space group Pī and bond valency sums for the cations were calculated from the interatomic distances. Ca-doping causes an oxidation of Pb in the PbO layers but no oxidation of Cu in the CuO 2 layers was observed. Magnetic susceptibility measurements showed that Pb 2Sr 2Tb .5Ca .5Cu 3O 8 was none superconducting down to 15 Kelvin which is in contrast to superconducting Pr 2Sr 2Y .5Ca .5Cu 3O 8.

Application of Rietveld Refinement Techniques to a Disordered IIb Mg-Chamosite

AbstractThe structure of a disordered IIb Mg-chamosite was studied using Rietveld refinement techniques and powder X-ray diffraction (CuKα, 18–120° 2θ in 0.02° 2θ increments). The refinement in space group CĪ yielded high precision lattice parameters (a = 5.36982(5)Å, b = 9.3031(9)Å, c = 14.2610(6)Å, α = 90.315(5)°, β = 97.234(7)°, γ = 90.022(9)°) and atomic coordinates very similar to previous studies. However, the presence of semi-random stacking in this specimen created a situation in which not all atoms could be precisely located: the positions of the octahedral cations and anions which repeat at intervals of ±b/3 could be uniquely determined in three dimensions whereas only the z parameter of the other atoms could be refined. The reasonable appearance of the final model, despite the fact that many of the atom positions could be located in only one dimension, may have resulted because all of the atoms in this structure except O(5) repeat at intervals which are very nearly ±b/3.

Zur Struktur der Kupfer-Weberite Na2CuCrF7 und Na2CuFeF7 / Concerning the Structures of the Copper Weberites Na2CuCrF7 and Na2CuFeF7

Abstract The crystal structure of the compound Na-CuCrF7 (orthorhombic, a = 710.0, b = 1033.8, c = 751.8 pm, Z = 4) was refined in space group Pmnb to Rg= 0.028 (1545 independent reflections). The Jahn-Teller distortion of the CuF6 -octahedra (Cu-F = 191.1/193.8/212.4 pm. mean 199.1 pm) reduces the symmetry compared to the body-centered orthorhombic weberite type, to which it is otherwise closely related. The CrF6 -octahedra. interconnecting parallel chains of CuF6 -octahedra, are nearly undistorted (mean Cr-F = 190.6 pm). Na2CuFeF7 exhibits a supercell with a different structure (monoclinic, a = 2468.7, b = 734.7, c = 1245.2 pm, β = 99.29°, Z = 16). It may be interpreted as a new intermediate type between orthorhombic and trigonal weberites. Preliminary results obtained from refinement in space group A2/n (Rg = 0.076) are given and discussed (mean values Cu-F = 199 pm, Fe - F = 192 pm).

On the structure and twinning of monoclinic β-V2H

The structure of the monoclinic [a = 4.4566 (5), b = 3.0022 (2), c=4.4760(5) A,, /3=95.609 (8) °, Z=2] form of/3-V2H, formerly described in space group Cm [Noda, Masumoto, Koike, Suzuki & Sato (1986). Acta Cryst. B42, 529-533] is properly described in C2/m. The crystal used for the original intensity measurements was surely twinned, across the ab plane, so that all reflections of the type 5n, k, l were composite; the twin component was about 55% as large as the main crystal. When the intensities were corrected for this twinning, refinement in space group C2/m led to an R of 0.023 for 668 reflections, compared to 0.080 for the earlier investigation. Despite the improvement in refinement, the H atom could not be located from the X-ray data.

Crystal chemistry of kosmochlor-diopside solid solutions.

Crystal structure parameters have been determined for Ko75 (NaCrSi2O6; 75 mol%) Di25 (CaMgSi2O6; 25mol%), Ko50 Di50 and Ko25 D75 synthesized at 1200°C and 20 kb. Refinements in space group C2/c using anisotropic temperature factors and over 600 unrejected reflections for each set of data resulted in weighted R-factors ranging from 0.020 to 0.025. The nearest M1-M1 distances of Ko-Di solid solutions are significantly shorter than those expected from the averaged ionic radii of cations occupying the M1 sites. The longest M1-M1 distances werer found for the crystals having the compositions corresponded to the both sides of the misibility gap at high pressure. It is expected that Cr+3 within Ko solid solutions form Cr-O-Cr coupling and Cr+3 within Di solid solutions are completely disordered. Ko75 Di25 and Ko50 Di50 being stable only at high pressure have smaller cell volumes than those expected from the values of Ko, Ko25 Di75 and Di. They have shorter M1-O distances than those expected from the averaged ionic radii of cations occupying the M1 sites. Their mean 8 (M2-O) and (M2-0) distances are longer than those expected from the values of Ko, Ko25 Di75 and Di. The characteristic structures of Ko75 Di25 and Ko50 Di50 may suggest at least party those at high pressure.