Crystallographic Studies of Cobalt Arsenate. III. Crystal Structure of Co6.95As3.62O16

1974 ◽  
Vol 52 (1) ◽  
pp. 46-50 ◽  
Author(s):  
Narasimhan Krishnamachari ◽  
Crispin Calvo
Keyword(s):  
Population Analysis ◽  
Inversion Symmetry ◽  
Unit Cell Parameters ◽  
Full Matrix ◽  
Cell Parameters ◽  
Bond Lengths ◽  
The Mean ◽  
R Value ◽  
Cation Sites ◽  
Site Population

Crystals of Co7.0As3.6O16 (1.8 × 3.84 CoO.As2O5) are orthorhombic with unit cell parameters a = 10.526(5), b = 5.985(2), and c = 4.871(2) Å. The space group is Pnma with Z = 1 and, except for fractionally occupied cation sites, the crystals have a structure closely related to that of the mineral olivine. The structure was refined by full-matrix least-squares with isotropic thermal parameters, using 1175 independent reflections measured with MoKα radiation, to a final R value of 0.075. The composition was determined by site population analysis. The structure is based upon a hexagonally close-packed arrangement of oxygen layers with As in tetrahedrally and Co in octahedrally coordinated interstices. The mean As—O bond length is 1.676 Å and the mean Co—O bond lengths are 2.139 Å for the site with m symmetry and 2.174 Å for the site showing inversion symmetry. These bond lengths are uncorrected for the effects of fractional occupancy of some of the cation sites.

Structure of Nickel Orthophosphate

1975 ◽  
Vol 53 (10) ◽  
pp. 1516-1520 ◽  
Author(s):  
Crispin Calvo ◽  
Romolo Faggiani
Keyword(s):  
Bond Length ◽  
Least Squares ◽  
Monoclinic System ◽  
Full Matrix ◽  
Space Group ◽  
Bond Lengths ◽  
The Mean ◽  
R Value ◽  
Cation Sites

Ni3P2O8 crystallizes in the monoclinic system with space group P21/c with a = 5.830(2), b = 4.700(2), c = 10.107(4) Å, β = 91.22(2)°, and Z = 2. The structure was refined by full-matrix least squares methods to a final R value of 0.035 using 986 symmetry independent reflections. The structure is isotypic with that of sarcopside, which in turn is related to that of olivine with vacant cation sites ordered. The Ni ions are octahedrally coordinated in two types of sites with average Ni—O bond lengths of 2.081 and 2.067 Å. The mean P—O bond length is 1.547 Å although the tetrahedron shows some unusually large distortions with bond lengths ranging from 1.521 to 1.595 Å.

Crystal Structure of Zn3V0.5P1.5O8

1975 ◽  
Vol 53 (23) ◽  
pp. 3665-3668 ◽  
Author(s):  
K. Loralee Idler ◽  
Crispin Calvo
Keyword(s):  
Crystal Structure ◽  
Bond Length ◽  
Least Squares ◽  
Population Analysis ◽  
Stable Phase ◽  
Zinc Ions ◽  
Unit Cell Parameters ◽  
Full Matrix ◽  
Cell Parameters ◽  
Site Population

The stable phase in the Zn3(PO4)2–Zn3(VO4)2 system near 25 mol% Zn3(VO4)2 is monoclinic with space group C2/c and unit cell parameters a = 15.941(6), b = 5.314(2), c = 8.265(2) Å, β = 106.96(3)° and Z = 4. The structure was refined by full-matrix least-squares methods using 910 reflections, R = 0.073. The composition, Zn3P1.50V0.50(4)O8, was determined by site population analysis with the V and P randomly distributed. One-third of the zinc ions lie on twofold axes and these show an average Zn—O bond length of 1.955 Å while the remaining ZnO4 group has a mean Zn—O bond length of 1.948 Å. The structure consists of sheets parallel to (100) formed of chains containing rings of corner shared Zn(1)O4 and (V,P)O4 tetrahedra. The Zn(2)O4 groups, in turn, form chains parallel to the b axis through corner sharing.

The Crystal Structure of KAlP2O7

1973 ◽  
Vol 51 (16) ◽  
pp. 2613-2620 ◽  
Author(s):  
Hok Nam Ng ◽  
Crispin Calvo
Keyword(s):  
Crystal Structure ◽  
Spherical Shell ◽  
Bond Length ◽  
Least Squares ◽  
Least Squares Method ◽  
Full Matrix ◽  
Bond Lengths ◽  
The Mean ◽  
R Value ◽  
Oxygen Atoms

KAlP2O7 crystallizes as monoclinic crystals with a = 7.308(8), b = 9.662(6), c = 8.025(4) Å, β = 106.69(7)°, z = 4 and space group P21/c. The structure was refined from 1394 observed reflections by full-matrix least-squares method to a final R value of 0.032. The P2O74− anion consists of a pair of corner-sharing PO4 groups in a nearly staggered configuration. The mean bridging and terminal P—O bond lengths are 1.607 and 1.509 Å, respectively, and the P—O—P angle is 123.2°. The anions lie in planes parallel to (001). The Al ions are bonded to six oxygen atoms contributed by anions in three layers of P2O7 groups. The average Al—O bond length is 1.889 Å. The potassium ion is coordinated to ten oxygen atoms lying within a spherical shell with inner and outer radii of 2.739 and 3.185 Å.

Crystal Structure of Ca3(AsO4)2

1971 ◽  
Vol 49 (7) ◽  
pp. 1036-1046 ◽  
Author(s):  
R. Gopal ◽  
C. Calvo
Keyword(s):  
Fold Axis ◽  
Hydrogen Atoms ◽  
Half Cell ◽  
Cell Parameters ◽  
Bond Lengths ◽  
Structural Differences ◽  
The Mean ◽  
Trial Structure ◽  
Cation Sites ◽  
Atom Bond

Ca3(AsO4)2 crystallizes in the rhombohedral space group R3c with unit cell parameters a = 14.05(1) Å, α = 45.05(2)°, and ZR = 7. The equivalent hexagonal axes are a = 10.77(1) and c = 37.81(3) Å with ZH = 21. The structure was refined, using 769 symmetry independent reflections and a full matrix least squares program from a trial structure obtained from Patterson functions, to a final R value of 0.063. The structure consists of interconnected chains of CaOn polyhedra and AsO4 tetrahedra paralleling the c axis. The six chains surrounding the three-fold axes are each much like those in Ba3(PO4)2 with 3Ca followed by two AsO4 groups per half cell. The chain on the three-fold axis has only one AsO4 per half cell with one and half cations between adjacent arsenic atoms. The mean As—O bond lengths are 1.69, 1.65, and 1.69 Å for the three independent tetrahedra. The cation sites show coordination to 6, 7, or 8 oxygen atoms in contrast to the 10 or 6 + 6 found in Ba3(PO4)2. These structural differences arise primarily from the shorter cation – oxygen atom bond lengths in this compound. This structure is the same as that of Ca3(VO4)2 and although closely related to that of Whitlockite differs from it because of the need to accommodate hydrogen atoms in the latter compound.

Crystal Structure of the Glaserite Form of BaNaPO4

1975 ◽  
Vol 53 (12) ◽  
pp. 1849-1853 ◽  
Author(s):  
Crispin Calvo ◽  
Romolo Faggiani
Keyword(s):  
Crystal Structure ◽  
Bond Length ◽  
Least Squares ◽  
Coordination Number ◽  
Cation Site ◽  
Full Matrix ◽  
Space Group ◽  
Bond Lengths ◽  
R Value ◽  
Cation Sites

Crystals of BaNaPO4 were grown from a Ba3P2O8–Na2B4O7 melt. The crystals are trigonal, space group [Formula: see text]with a = 5.622(4) and c = 7.259(5) Å. The structure, isotypic with that of glaserite, was refined by full-matrix least-squares methods to a final R value of 0.042 using 218 unique reflections. There are three different cation sites. Na and Ba lie at sites of [Formula: see text] symmetry and are coordinated to 6 and 12 oxygen atoms respectively. The Na—O bond lengths are 2.344(7) Å and the two unique Ba—O bond lengths are 2.788(7) and 3.247(9) Å. The remaining cation site has 3m symmetry, a coordination number of 10, and contains equal amounts of Na+ and Ba2+. The bond lengths range from 2.548(12) to 3.017(7) Å. The phosphate group also has 3m symmetry with mean P—O bond lengths of 1.538 Å. The underbonded apical P—O bond length is 1.520 Å.

The structures of marialite (Me6) and meionite (Me93) in space groups P42/n and I4/m, and the absence of phase transitions in the scapolite series

2011 ◽  
Vol 26 (2) ◽  
pp. 119-125 ◽  
Author(s):  
Sytle M. Antao ◽  
Ishmael Hassan
Keyword(s):  
Phase Transitions ◽  
High Resolution ◽  
Crystal Structures ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
X Ray ◽  
Space Groups ◽  
Cell Parameters ◽  
The Mean

The crystal structures of marialite (Me6) from Badakhshan, Afghanistan and meionite (Me93) from Mt. Vesuvius, Italy were obtained using synchrotron high-resolution powder X-ray diffraction (HRPXRD) data and Rietveld structure refinements. Their structures were refined in space groups I4/m and P42/n, and similar results were obtained. The Me6 sample has a formula Ca0.24Na3.37K0.24[Al3.16Si8.84O24]Cl0.84(CO3)0.15, and its unit-cell parameters are a=12.047555(7), c=7.563210(6) Å, and V=1097.751(1) Å3. The average ⟨T1-O⟩ distances are 1.599(1) Å in I4/m and 1.600(2) Å in P42/n, indicating that the T1 site contains only Si atoms. In P42/n, the average distances of ⟨T2-O⟩=1.655(2) and ⟨T3-O⟩=1.664(2) Å are distinct and are not equal to each other. However, the mean ⟨T2,3-O⟩=1.659(2) Å in P42/n and is identical to the ⟨T2′-O⟩=1.659(1) Å in I4/m. The ⟨M-O⟩ [7]=2.754(1) Å (M site is coordinated to seven framework O atoms) and M-A=2.914(1) Å; these distances are identical in both space groups. The Me93 sample has a formula of Na0.29Ca3.76[Al5.54Si6.46O24]Cl0.05(SO4)0.02(CO3)0.93, and its unit-cell parameters are a=12.19882(1), c=7.576954(8) Å, and V=1127.535(2) Å3. A similar examination of the Me93 sample also shows that both space groups give similar results; however, the C–O distance is more reasonable in P42/n than in I4/m. Refining the scapolite structure near Me0 or Me100 in I4/m forces the T2 and T3 sites (both with multiplicity 8 in P42/n) to be equivalent and form the T2′ site (with multiplicity 16 in I4/m), but ⟨T2-O⟩ is not equal to ⟨T3-O⟩ in P42/n. Using different space groups for different regions across the series implies phase transitions, which do not occur in the scapolite series.

scholarly journals Bi3+ and Eu3+ Activated Luminescent Behaviors in Non-Stoichiometric LaO0.65F1.7 Structure

Materials ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2326
Author(s):  
Sungjun Yang ◽  
Sangmoon Park
Keyword(s):  
Optical Materials ◽  
Emission Spectra ◽  
Lattice Energy ◽  
Host Lattice ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
X Ray ◽  
Cell Parameters ◽  
Diffraction Patterns ◽  
Cation Sites

Optical materials composed of La1-p-qBipEuqO0.65F1.7 (p = 0.001–0.05, q = 0–0.1) were prepared via a solid-state reaction using La(Bi,Eu)2O3 and NH4F precursors at 1050 °C for two hours. X-ray diffraction patterns of the phosphors were obtained permitting the calculation of unit-cell parameters. The two La3+ cation sites were clearly distinguished by exploiting the photoluminescence excitation and emission spectra through Bi3+ and Eu3+ transitions in the non-stoichiometric host lattice. Energy transfer from Bi3+ to Eu3+ upon excitation with 286 nm radiation and its mechanism in the Bi3+- and Eu3+-doped host structures is discussed. The desired Commission Internationale de l’Eclairage values, including emissions in blue-green, white, and red wavelength regions, were obtained from the Bi3+- and Eu3+-doped LaO0.65F1.7 phosphors.

The Structure of (NO)2[Ho(NO3)5], A 10-Coordinate Species

1975 ◽  
Vol 53 (6) ◽  
pp. 831-835 ◽  
Author(s):  
Gerald E. Toogood ◽  
Chung Chieh
Keyword(s):  
Ethyl Acetate ◽  
Heavy Atom ◽  
Full Matrix ◽  
Trigonal Bipyramidal ◽  
Anhydrous Ethyl Acetate ◽  
Dinitrogen Tetroxide ◽  
Stretching Vibration ◽  
The Mean ◽  
R Value ◽  
Heavy Atom Method

Nitrosonium pentanitratoholmate(III), (NO)2Ho(NO3)5, was prepared from holmium metal and dinitrogen tetroxide in anhydrous ethyl acetate. Its crystals are monoclinic with a = 8.094, b = 11.979, c = 14.170 Å and β = 104.7°,Z = 4, space group P21/c. The structure was solved by the heavy-atom method and refined by full matrix least-squares methods to an R value of 0.085 for 1514 observed reflections measured on the G.E. XRD-6 diffractometer. The structure consists of one Ho(NO3)52− and two NO+ ions. The holmium is 10-coordinated by five essentially symmetric bidentate nitrate groups which arrange themselves in a trigonal bipyramidal fashion around the metal with a mean Ho—O distance of 2.45 Å. The two NO+ ions per metal occupy slightly different environments and give rise to two i.r. bands at 2250 and 2285 cm−1, attributable to the (N, O+) stretching vibration. The mean N—O distance within these ions is 1.00 Å.

Crystal Structure of α-VPO5

1973 ◽  
Vol 51 (16) ◽  
pp. 2621-2625 ◽  
Author(s):  
Byron Jordan ◽  
Crispin Calvo
Keyword(s):  
Crystal Structure ◽  
Oxygen Atom ◽  
Least Squares ◽  
Least Squares Method ◽  
Fold Axis ◽  
Full Matrix ◽  
Bond Lengths ◽  
R Value ◽  
A Site ◽  
Vanadium Ion

α-VPO5 crystallizes in the tetragonal space group P4/n with a = 6.014(7) and c = 4.434(2) Å. The structure, isotypic with that of α-VSO5, was refined by full-matrix least-squares method to an R value of 0.089 using 239 independent reflections. The vanadium ion lies on a crystallographic four-fold axis, as does one of the oxygen atoms, and the P on a site of [Formula: see text] symmetry. A second oxygen atom, as a result of disorder, occurs in two positions which are mirror reflected with respect to the ac plane. The structure consists of highly distorted VO6 groups with bond lengths along the c axis of 1.580(11) and 2.853(11) Å while the remaining four V—O bond lengths are all 1.858(8) Å. The P—O bond lengths in the PO4. tetrahedron are 1.541(8) Å with the PO4 groups bridging across four chains of VO6 groups.

The structure of ice

1958 ◽  
Vol 247 (1251) ◽  
pp. 424-434 ◽  
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Atoms ◽  
Cell Parameters ◽  
Bond Lengths ◽  
Hexagonal Ice ◽  
A Value ◽  
Air Temperatures ◽  
The Mean ◽  
Thermal Vibrations ◽  
Low Pressures

A consistent set of unit cell parameters at various temperatures is not yet available for ordinary ice, but the mean of the most precise measurements leads to a density of 0·9164 g/cm 3 at 0°C (atmospheric pressure) with a cubical expansion coefficient of 11 x 10 -5 , increasing to 0·9414 and 21 x 10 -5 at liquid air temperatures. Corresponding figures for heavy ice are 1·0172 g/cm 3 and 12 x 10 -5 at 0°C, 1·0449 and 18 x 10 -5 at -180°C. The hydrogen-bond lengths are not significantly different for ordinary and heavy ice, but in both cases the mirror-symmetric bond (along the principal axis) is about 0·01 Å shorter than the centro-symmetric bond at 0°C. At low temperatures the bond lengths tend to equalize at a value some 1% lower than at 0°C. The hexagonal (tridymite-type) and cubic (cristobalite-type) forms of ice have approxi­mately the same density and hydrogen-bond lengths at —130°C, and both appear to have a statistical randomness of the water-molecule orientation, consistent with there being one hydrogen only (nearly or exactly) along each bond. The thermal vibrations of the hydrogen atoms in hexagonal ice are anisotropic, those of the oxygen atoms nearly spherical. The ranges of stability of hexagonal, cubic and amorphous ice are not exactly known, but cubic ice is only formed at low rates of deposition, low pressures and at temperatures of about -80 to -140°C.

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