1,082 research outputs found
Carlhintzeite, Ca2AlF7âąH2O, from the Gigante granitic pegmatite, CĂłrdoba province, Argentina: Description and crystal structure
Carlhintzeite, Ca2AlF7âąH2O, has been found at the Gigante pegmatite, Punilla Department, CĂłrdoba Province, Argentina. It occurs as colourless prismatic crystals up to 0.8 mm long, ubiquitously twinned on {001}. Electron microprobe analyses provided the empirical formula Ca1.98Al1.02F6.24(OH) 0.76âąH1.62O. A crystal fragment used for the collection of structure data provided the triclinic, C1 cell: a = 9.4227(4), b = 6.9670(5), c = 9.2671(7) Ă
, α = 90.974(6), ÎČ = 104.802(5), Îł = 90.026(6)°, V = 558.08(7) Ă
3 and Z = 4. The crystal structure, solved by direct methods and refined to R 1 = 0.0322 for 723 Fo > 4ÏF reflections, is made up of linkages of AlF6 octahedra, CaF8 polyhedra and CaF 6(H2O)2 polyhedra. The AlF6 octahedra are isolated from one another, but share polyhedral elements with Ca polyhedra. Most notably, the Al1 octahedron shares trans faces with two CaF 8 polyhedra and the Al2 octahedron shares trans edges with two CaF6(H2O)2 polyhedra. The linkage of the Ca polyhedra alone can be described as a framework in which edge-sharing chains along b are cross-linked by edge-sharing. Edge-sharing chains of Ca polyhedra along b in the carlhintzeite structure are similar to those along c in the structures of gearksutite, CaAlF4(OH)âą(H2O), and prosopite, CaAl2F4(OH)4. © 2010 Mineralogical Society.Fil: Kampf, A. R.. Natural History Museum of Los Angeles County; Estados UnidosFil: Colombo, Fernando. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de CĂłrdoba. Facultad de Ciencias Exactas FĂsicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: GonzĂĄlez Del TĂĄnago, J.. Universidad Complutense de Madrid; Españ
Lead-tellurium oxysalts from Otto Mountain near Baker, California: IV. Markcooperite, Pb(UO_2)Te^(6+)O_6, the first natural uranyl tellurate
Markcooperite, Pb_2(UO_2)Te^(6+)O_6, is a new tellurate from Otto Mountain near Baker, California, named in honor of Mark A. Cooper of the University of Manitoba for his contributions to mineralogy. The new mineral occurs on fracture surfaces and in small vugs in brecciated quartz veins. Markcooperite is directly associated with bromian chlorargyrite, iodargyrite, khinite-4O, wulfenite, and four other new tellurates: housleyite, thorneite, ottoite, and timroseite. Various other secondary minerals occur in the veins, including two other new secondary tellurium minerals: paratimroseite and telluroperite. Markcooperite is monoclinic, space group P2_1/c, a = 5.722(2), b = 7.7478(2), c = 7.889(2) Ă
, ÎČ = 90.833(5)°, V = 349.7(2) Ă
^3, and Z = 2. It occurs as pseudotetragonal prisms to 0.2 mm with the forms {100} and {011} and as botryoidal intergrowths to 0.3 mm in diameter; no twinning was observed. Markcooperite is orange and transparent, with a light orange streak and adamantine luster, and is non-fluorescent. Mohs hardness is estimated at 3. The mineral is brittle, with an irregular fracture and perfect {100} cleavage. The calculated density is 8.496 g/cm3 based on the empirical formula. Markcooperite is biaxial (+), with indices of refraction α= 2.11, ÎČ = 2.12, Îł= 2.29 calculated using the Gladstone-Dale relationship, measured α-ÎČ birefringence of 0.01 and measured 2V of 30(5)°. The optical orientation is X = c, Y = b, Z = a. The mineral is slightly pleochroic in shades of orange, with absorption: X > Y = Z. No dispersion was observed. Electron microprobe analysis provided PbO 50.07, TeO_3 22.64, UO_3 25.01, Cl 0.03, OâĄCl â0.01, total 97.74 wt%; the empirical formula (based on O+Cl = 8) is Pb_(2.05)U_(0.80)Te^(6+)_(1.18)O_(7.99)Cl_(0.01). The strongest powder X-ray diffraction lines are [d_(obs) in Ă
(hkl) I]: 3.235 (120, 102, 1[overbar]02) 100, 2.873 (200) 40, 2.985 (1[overbar]21, 112, 121) 37, 2.774 (022) 30, 3.501 (021, 012) 29, 2.220 (221, 2[overbar]21, 212) 23, 1.990 (222, 2[overbar]22) 21, and 1.715 (320) 22. The crystal structure (R_1 = 0.052) is based on sheets of corner-sharing uranyl square bipyramids and tellurate octahedra, with Pb atoms between the sheets. Markcooperite is the first compound to show Te^(6+) substitution for U^(6+) within the same crystallographic site. Markcooperite is structurally related to synthetic Pb(UO_2)O_2
Lead-tellurium oxysalts from Otto Mountain near Baker, California: V. Timroseite, Pb_2Cu_5^(2+)(Te^(6+)O_6)_2(OH)_2, and paratimroseite, Pb_2Cu_4^(2+)(Te^(6+)O_6)_2(H_2O)_2, two new tellurates with Te-Cu polyhedral sheets
Timroseite, Pb_2Cu_5^(2+)(Te^(6+)O_6)_2(OH)_2, and paratimroseite, Pb_2Cu_4^(2+)(Te^(6+)O_6)_2(H_2O)_2, are two new tellurates from Otto Mountain near Baker, California. Timroseite is named in honor of Timothy (Tim) P. Rose and paratimroseite is named for its relationship to timroseite. Both new minerals occur on fracture surfaces and in small vugs in brecciated quartz veins. Timroseite is directly associated with acanthite, cerussite, bromine-rich chlorargyrite, chrysocolla, gold, housleyite, iodargyrite, khinite-4O, markcooperite, ottoite, paratimroseite, thorneite, vauquelinite, and wulfenite. Paratimroseite is directly associated with calcite, cerussite, housleyite, khinite-4O, markcooperite, and timroseite. Timroseite is orthorhombic, space group P2_1nm, a = 5.2000(2), b = 9.6225(4), c = 11.5340(5) Ă
, V = 577.13(4) Ă
^3, and Z = 2. Paratimroseite is orthorhombic, space group P2_12_12_1, a = 5.1943(4), b = 9.6198(10), c = 11.6746(11) Ă
, V = 583.35(9) Ă
^3, and Z = 2. Timroseite commonly occurs as olive to lime green, irregular, rounded masses and rarely in crystals as dark olive green, equant rhombs, and diamond-shaped plates in subparallel sheaf-like aggregates. It has a very pale yellowish green streak, dull to adamantine luster, a hardness of about 2 1/2 (Mohs), brittle tenacity, irregular fracture, no cleavage, and a calculated density of 6.981 g/cm^3. Paratimroseite occurs as vibrant "neon" green blades typically intergrown in irregular clusters and as lime green botryoids. It has a very pale green streak, dull to adamantine luster, a hardness of about 3 (Mohs), brittle tenacity, irregular fracture, good {001} cleavage, and a calculated density of 6.556 g/cm^3. Timroseite is biaxial (+) with a large 2V, indices of refraction > 2, orientation X = b, Y = a, Z = c and pleochroism: X = greenish yellow, Y = yellowish green, Z = dark green (Z > Y > X). Paratimroseite is biaxial (â) with a large 2V, indices of refraction > 2, orientation X = c, Y = b, Z = a and pleochroism: X = light green, Y = green, Z = green (Y = Z >> X). Electron microprobe analysis of timroseite provided PbO 35.85, CuO 29.57, TeO_3 27.75, Cl 0.04, H_2O 1.38 (structure), OâĄCl â0.01, total 94.58 wt%; the empirical formula (based on O+Cl = 14) is Pb_(2.07) Cu^(2+)_(4.80)Te^(6+)_(2.04)O_(12)(OH)_(1.98)Cl_(0.02). Electron microprobe analysis of paratimroseite provided PbO 36.11, CuO 26.27, TeO_3 29.80, Cl 0.04, H_2O 3.01 (structure), OâĄCl â0.01, total 95.22 wt%; the empirical formula (based on O+Cl = 14) is Pb_(1.94)Cu^(2+)_(3.96)Te^(6+)_(2.03)O_(12)(H_2O)_(1.99)Cl_(0.01). The strongest powder X-ray diffraction lines for timroseite are [d_(obs) in Ă
(hkl) I]: 3.693 (022) 43, 3.578 (112) 44, 3.008 (023) 84, 2.950 (113) 88, 2.732 (130) 100, 1.785 (multiple) 33, 1.475 (332) 36; and for paratimroseite 4.771 (101) 76, 4.463 (021) 32, 3.544 (120) 44, 3.029 (023,122) 100, 2.973 (113) 48, 2.665 (131) 41, 2.469 (114) 40, 2.246 (221) 34. The crystal structures of timroseite (R_1 = 0.029) and paratimroseite (R_1 = 0.039) are very closely related. The structures are based upon edge- and corner-sharing sheets of Te and Cu polyhedra parallel to (001) and the sheets in both structures are identical in topology and virtually identical in geometry. In timroseite, the sheets are joined to one another along c by sharing the apical O atoms of Cu octahedra, as well as by sharing edges and corners with an additional CuO_5 square pyramid located between the sheets. The sheets in paratimroseite are joined only via Pb-O and H bonds
Lead-tellurium oxysalts from Otto Mountain near Baker, California: VI. Telluroperite, Pb_3Te^(4+)O_4Cl_2, the Te analog of perite and nadorite
Telluroperite, Pb_3Te^(4+)O_4Cl_2, is a new tellurite from Otto Mountain near Baker, California. The new mineral occurs on fracture surfaces and in small vugs in brecciated quartz veins in direct association with acanthite, bromine-rich chlorargyrite, caledonite, cerussite, galena, goethite, and linarite. Various other secondary minerals occur in the veins, including six new tellurates, housleyite, markcooperite, paratimroseite, ottoite, thorneite, and timroseite. Telluroperite is orthorhombic, space group Bmmb, a = 5.5649(6), b = 5.5565(6), c = 12.4750(14) Ă
, V = 386.37(7) Ă
^3, and Z = 2. The new mineral occurs as rounded square tablets and flakes up to 0.25 mm on edge and 0.02 mm thick. The form {001} is prominent and is probably bounded by {100}, {010}, and {110}. It is bluish-green and transparent, with a pale bluish-green streak and adamantine luster. The mineral is non-fluorescent. Mohs hardness is estimated to be between 2 and 3. The mineral is brittle, with a curved fracture and perfect {001} cleavage. The calculated density based on the empirical formula is 7.323 g/cm^3. Telluroperite is biaxial (â), with very small 2V (~10°). The average index of refraction is 2.219 calculated by the Gladstone-Dale relationship. The optical orientation is X = c and the mineral exhibits moderate bluish-green pleochrosim; absorption: X < Y = Z. Electron microprobe analysis provided PbO 72.70, TeO_2 19.26, Cl 9.44, OâĄCl â2.31, total 99.27 wt%. The empirical formula (based on O+Cl = 6) is Pb_(2.79)Te_(1.03)^(4+)O_(3.72)Cl_(2.28). The six strongest powder X-ray diffraction lines are [d_(obs) in Ă
(hkl) I]: 3.750 (111) 58, 2.857 (113) 100, 2.781 (020, 200) 43, 2.075 (024, 204) 31, 1.966 (220) 30, and 1.620 (117, 313, 133) 52. The crystal structure (R_1 = 0.056) is based on the Sillén X_1 structure-type and consists of a three-dimensional structural topology with lead-oxide halide polyhedra linked to tellurium/lead oxide groups. The mineral is named for the relationship to perite and the dominance of Te (with Pb) in the Bi site of perite
Chiral expansions of the pi0 lifetime
The corrections induced by light quark masses to the current algebra result
for the lifetime are reexamined. We consider NNLO corrections and we
compute all the one-loop and the two-loop diagrams which contribute to the
decay amplitude at NNLO in the two-flavour chiral expansion. We show that the
result is renormalizable, as Weinberg consistency conditions are satisfied. We
find that chiral logarithms are present at this order unlike the case at NLO.
The result could be used in conjunction with lattice QCD simulations, the
feasibility of which was recently demonstrated. We discuss the matching between
the two-flavour and the three-flavour chiral expansions in the anomalous sector
at order one-loop and derive the relations between the coupling constants. A
modified chiral counting is proposed, in which counts as . We have
updated the various inputs needed and used this to make a phenomenological
prediction.Comment: 20 pages, 1 figure; v2: comments and references added, accepted for
publication in PR
The crystal structure of munakataite, Pb_2Cu_2(Se^(4+)O_3)(SO_4)(OH)_4, from Otto Mountain, San Bernardino County, California, USA
Munakataite, Pb_2Cu_2(Se^(4+)O_3)(SO_4)(OH)_4, has been found in association with a variety of rare secondary Te minerals at Otto Mountain, San Bernardino County, California, USA. It is very rare and occurs as subparallel bundles of blue needles up to 1 mm long. Electron microprobe analyses provided the empirical formula Pb_(1.96)Cu_(1.60)[(Se^(4+)_(0.89)S_(0.11)_(â1)O_3](SO_4)[(OH)_(3.34)(H_2O)_(0.66)]_(â4). Munakataite is monoclinic, space group P2_1/m, with cell parameters a = 9.8023(26), b = 5.6751(14), c = 9.2811(25) Ă
, ÎČ = 102.443(6), V = 504.2(2) Ă
^3 and Z = 2. The crystal structure, solved by direct methods and refined to R_1 = 0.0308 for 544 F_o > 4ÏF reflections, consists of Jahn-Teller-distorted Cu^(2+)O_6 square bipyramids, which form chains along b by sharing trans edges across their square planes. The chains are decorated
by SO_4 tetrahedra and Se^4+O_3 pyramids, which bond to apical corners of adjacent bipyramids. The chains are linked to one another via bonds to two different PbO_9 polyhedra, only one of which exhibits one-sided coordination typical of Pb^(2+) with a stereochemically active 6s^2 lone-electron-pair. Munakataite is isostructural with schmiederite and the structure is closely related to that of linarite
From local to nonlocal Fermi liquid in doped antiferromagnets
The variation of single-particle spectral functions with doping is studied
numerically within the t-J model. It is shown that corresponding self energies
change from local ones at the intermediate doping to strongly nonlocal ones for
a weakly doped antiferromagnet. The nonlocality shows up most clearly in the
pseudogap emerging in the density of states, due to the onset of short-range
antiferromagnetic correlations.Comment: 4 pages, 3 Postscript figures, revtex, submitted to Phys.Rev.Let
Anorpiment, As_(2)S_(3), the triclinic dimorph of orpiment
The new mineral anorpiment, As_(2)S_(3), the triclinic dimorph of orpiment, has space group P1 and cell parameters a = 5.7577(2), b = 8.7169(3), c = 10.2682(7) Ă
, α = 78.152(7), ÎČ = 75.817(7), Îł = 89.861(6)Âș, V = 488.38(4) Ă
^3 and Z = 4. It occurs at the Palomo mine, Castrovirreyna Province, Huancavelica Department, Peru. It is a low-temperature hydrothermal mineral associated with dufrĂ©noysite, muscovite, orpiment, pyrite and realgar. It occurs in drusy crusts of wedge-shaped, transparent, greenish yellow crystals. The streak is yellow. The lustre is resinous on crystal faces, but pearly on cleavage surfaces. The Mohs hardness is about 1Âœ. The mineral is sectile with an irregular fracture and one perfect and easy cleavage on {001}. The measured and calculated densities are 3.33 and 3.321 g cm^(-3), respectively. All indices of refraction are greater than 2. The mineral is optically biaxial (â) with 2V = 35-40Âș and no observed dispersion. The acute bisectrix (X) is approximately perpendicular to the {001} cleavage. Electron microprobe analyses yielded the averages and ranges in wt.%: As 58.21 (57.74-59.03), S 38.72 (38.33-39.00), total 96.94 (96.07-97.75), providing the empirical formula (based on 5 atoms) As_(1.96)S_(3.04). The strongest powder X-ray diffraction lines are [d (hkl) I] 4.867(002) 97, 4.519 (110,111) 77, 3.702 (111) 46, 3.609 (022,112) 82, 2.880 (201,022,121,023) 75, 2.552 (113,131,132) 100, 2.469 (114,130,131) 96. The structure of anorpiment [R_1 = 0.021 for 1484 reflections with F_o > 4Ï(F)] consists of layers of covalently bonded As and S atoms. Each S atom bonds to two As atoms at As-S-As angles between 100.45 and 104.15Âș. Each As atom is strongly bonded to three S atoms at S-As-S angles between 91.28 and 103.59Âș, forming an AsS_3 pyramid with As at its apex. The As-S linkages within the layers form rings of six AsS_3 pyramids. Interlayer bonding forces are interpreted as van der Waals. The structure of anorpiment is similar to that of orpiment in that it is composed of layers of As2S_3 macromolecules, but arranged in a different stacking sequence
Stripe orientation in an anisotropic t-J model
The tilt pattern of the CuO_6 octahedra in the LTT phase of the cuprate
superconductors leads to planar anisotropies for the exchange coupling and
hopping integrals. Here, we show that these anisotropies provide a possible
structural mechanism for the orientation of stripes. A t_x-t_y-J_x-J_y model
thus serves as an effective Hamiltonian to describe stripe formation and
orientation in LTT-phase cuprates.Comment: 3 pages, 3 figure
Doping Evolution of Oxygen K-edge X-ray Absorption Spectra in Cuprate Superconductors
We study oxygen K-edge x-ray absorption spectroscopy (XAS) and investigate
the validity of the Zhang-Rice singlet (ZRS) picture in overdoped cuprate
superconductors. Using large-scale exact diagonalization of the three-orbital
Hubbard model, we observe the effect of strong correlations manifesting in a
dynamical spectral weight transfer from the upper Hubbard band to the ZRS band.
The quantitative agreement between theory and experiment highlights an
additional spectral weight reshuffling due to core-hole interaction. Our
results confirm the important correlated nature of the cuprates and elucidate
the changing orbital character of the low-energy quasi-particles, but also
demonstrate the continued relevance of the ZRS even in the overdoped region.Comment: Original: 5 pages, 4 figures. Replaced: 6 pages and 4 figures, with
updated title and conten
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