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.

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.

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.

scholarly journals Relationships between the Structural, Vibrational, and Optical Properties of Microporous Cancrinite

Crystals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 280
Author(s):  
Roman Shendrik ◽  
Ekaterina Kaneva ◽  
Tatiana Radomskaya ◽  
Igor Sharygin ◽  
Alexander Marfin
Keyword(s):  
Optical Properties ◽  
Structural Features ◽  
Resonance Spectroscopy ◽  
Ir Absorption ◽  
Blue Color ◽  
Fold Axis ◽  
Visible Absorption ◽  
X Ray ◽  
Cell Parameters ◽  
Cation Sites

The crystal-chemical, vibrational, and optical properties of microporous aluminosilicate cancrinite have been investigated by combining electron probe microanalysis, single-crystal X-ray diffraction, infrared (IR) absorption, Raman, UV-Visible absorption, and electron spin resonance spectroscopy. The behavior of the peaks in the IR spectra was also studied during the dehydration of the sample. The analyzed sample has the following unit cell parameters (P63): a = 12.63189(14) Å, c = 5.13601(7) Å. The empirical formula, based on 12(Si + Al), is Na6.47Ca1.23K0.01[Al5.97Si6.03O24] (CO3)1.45(SO4)0.03Cl0.01·2H2O. The Al-Si framework of AB-type is formed by columns of based-shared “cancrinite” (CAN) cages, containing Na and H2O positions located on the 3-fold axis, and channels with CO3 groups, lying in two mutually exclusive and partially occupied positions in the center of the channel, and split Na/Ca cation sites. The revealed characteristics are somewhat different in comparison with the cancrinite structural features previously described in the literature. Studied crystals change color from grayish-pink to blue after X-ray irradiation (104 Gy). The blue color of the irradiated cancrinite is caused by the formation (CO3)−● radicals in the crystals. Combining the results obtained using the selected methods will provide a better understanding of the relationships between the structural, chemical, and optical-physical properties of microporous aluminosilicates.

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 Cd2P2O7

1969 ◽  
Vol 47 (18) ◽  
pp. 3409-3416 ◽  
Author(s):  
C. Calvo ◽  
P. K. L. Au
Keyword(s):  
Bond Angle ◽  
Divalent Metal ◽  
Unit Cell ◽  
Small Radius ◽  
Large Radius ◽  
Divalent Metal Ions ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Bond Lengths ◽  
Atom Bond

Cadmium pyrophosphate forms crystals having triclinic symmetry with the unit cell parameters a = 6.672(8) Å, b = 6.623(8) Å, c = 6.858(7) Å, α = 95.80(10)°, β = 115.38(8)°, and γ = 82.38(8)°. The space group is [Formula: see text] and there are two molecules per unit cell. The structure was refined by least squares methods using 1326 reflections. The pyrophosphate anion, P2O74−, has a bent P—O—P bond with a bond angle of 132° and with average inner and outer PO bond lengths of 1.62 and 1.51 Å, respectively. The cations are coordinated to five and six oxygen atoms with average cadmium–oxygen atom bond lengths of 2.33 and 2.31 Å, respectively. This pyrophosphate structure differs from that adopted by other divalent metal ions of small radius in that the ends of the anion are in a nearly eclipsed orientation but shows some similarity to those A2B2O7 compounds, where A has a large radius and B a small one.

Thomas Aquinas on Sexual Difference: The Metaphysical Biology and Moral Significance of Human Sexuality

Pro Ecclesia ◽  
2021 ◽  
Vol 30 (2) ◽  
pp. 177-215
Author(s):  
Paul Gondreau
Keyword(s):  
Sexual Difference ◽  
Human Sexuality ◽  
Thomas Aquinas ◽  
Moral Significance ◽  
Male And Female ◽  
Biological Design ◽  
Moral Excellence ◽  
Structural Differences ◽  
The Mean ◽  
And Gender

Thomas Aquinas offers for his time a novel take on human sexual difference, in that he grounds human sexuality in what we might term a metaphysical biology and accords it a privileged role in the moral life. Though his biology is drawn from Aristotle, which leads Aquinas to make problematic statements on sexual difference, he nonetheless offers a perspective that remains deeply relevant and significant for today. His method or approach of tethering sexual difference first and foremost to our animal-like biological design remains perennial, particularly at a time when many seek to dismiss biology as irrelevant to sexual identity and gender difference. The latest findings of the emerging field of neurobiology, which have uncovered structural differences between the male and female brains, offer key support to Aquinas’s approach. Even more important, he holds, in an unprecedented move, that sexual design and inclination provide a veritable source of moral excellence. He goes so far as to locate the mean of virtue in our sexual design and appetites.

scholarly journals Synthesis, Structure and Magnetic Properties of NiFe3O5

2022 ◽  
Author(s):  
Ka Hong ◽  
Elena Solana ◽  
Mauro Coduri ◽  
Clemens Ritter ◽  
Paul Attfield
Keyword(s):  
Exchange Interactions ◽  
Neutron Diffraction Data ◽  
Cation Site ◽  
Cell Parameters ◽  
Site Distribution ◽  
Rich Variety ◽  
Ordered Phases ◽  
The Rich ◽  
Cation Size ◽  
Cation Sites

Abstract A new CaFe3O5-type phase NiFe3O5 (orthorhombic Cmcm symmetry, cell parameters a = 2.89126(7), b = 9.71988(21) and c = 12.52694(27) Å) has been synthesised under pressures of 12-13 GPa at 1200 °C. NiFe3O5 has an inverse cation site distribution and reveals an interesting evolution from M2+(Fe3+ )2Fe2+O5 to Fe2+(M2+ 0.5Fe3+ 0.5)2Fe3+O5 distributions over three distinct cation sites as M2+ cation size decreases from Ca to Ni. Magnetic susceptibility measurements show successive transitions at 275, ~150, and ~20 K and neutron diffraction data reveal a series of at least three spin-ordered phases with evolving propagation vectors k = [0 0 0] [0 ky 0]  [½ ½ 0] on cooling. The rich variety of magnetically ordered phases in NiFe3O5 likely results from frustration of Goodenough-Kanamori exchange interactions between the three spin sublattices, and further interesting magnetic materials are expected to be accessible within the CaFe3O5-type family.

scholarly journals Electrochemical hydrogenation, lithiation and sodiation of the GdFe2–xMx and GdMn2–xMx intermetallics

2021 ◽  
pp. 139-149
Keyword(s):  
Electrode Materials ◽  
Electrochemical Impedance ◽  
Diffraction Method ◽  
Electrochemical Characteristics ◽  
Electrochemical Hydrogenation ◽  
Hydrogen Atoms ◽  
X Ray ◽  
Cell Parameters ◽  
The Difference ◽  
Better Than

Electrochemical hydrogenation, lithiation and sodiation of the phases GdFe2–xMx and GdMn2–xMx (M=Mn, Co, Ni, Zn, and Mg) and the influence of doping components on electrochemical characteristics of electrode materials on their basis were studied using X-ray powder diffraction method, scanning electron microscopy, energy dispersive X-ray analysis, X-ray fluorescent spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Phase analysis showed a simple correspondence between unit cell parameters of the phases and atomic radii of doping elements. Electrode materials based on GdFe2 and GdMn2 doped with 2 at.% of Co, Ni and Mg demonstrated better hydrogen sorption properties than those doped with Mn and Zn. Corrosion resistance of the doped electrodes was also better than of the binary analogues (e.g. corrosion potential of the GdFe2-based electrode was –0.162 V whereas that of GdFe1.96Ni0.04 was –0.695 V). The capacity parameters were increased in the following ranges: Zn<Mn<Mg<Co<Ni and Zn<Fe<Mg<Co<Ni for GdFe2–xMx and GdMn2–xMx, respectively. After fifty cycles of charge/discharge, we observed the changes in surface morphology and composition of the electrode samples. In the structure of studied Laves type phases with MgCu2-type structure, the most suitable sites for hydrogen atoms are tetrahedral voids 8a. During lithiation and sodiation of the phases, the atoms of the M-component of the structure are replaced by the atoms of lithium, and the atoms of gadolinium are replaced by the atoms of sodium. This difference in interaction is due to the difference in atomic sizes of the atoms. No insertion of lithium or sodium into the structural voids of the phases was observed.

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.

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