ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

1

Electronic Resource

2p X-ray Absorption Spectroscopy in the Earth Sciences (1995)

Schofield, P. F. ; Henderson, C. M. B. ; Cressey, G. ; [et al.]

Chester : International Union of Crystallography (IUCr)

Journal of synchrotron radiation 2 (1995), S. 93-98

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ISSN: 1600-5775

Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001

Topics: Geosciences , Physics

Notes: A complete knowledge of 3d transition-metal valencies, site occupancies and site symmetries is essential for a full understanding of mineral/melt energetics and behaviour. Over the last few years, significant advances in both instrumentation and theory associated with synchrotron radiation sources and experiments have enabled the development of 2p X-ray absorption spectroscopy as a sensitive, element-specific site and valency probe. The potential of this technique in the Earth sciences is discussed in this paper with examples reflecting the variety of problems set by 3d transition metals in natural systems.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1107/S0909049595000598

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2

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Development of X-ray photoemission electron microscopy (X-PEEM) at the SRS (1998)

Smith, A. D. ; Cressey, G. ; Schofield, P. F. ; [et al.]

Chester : International Union of Crystallography (IUCr)

Journal of synchrotron radiation 5 (1998), S. 1108-1110

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ISSN: 1600-5775

Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001

Topics: Geosciences , Physics

Notes: The use of synchrotron radiation sources for X-ray spectroscopy is a well known and developed field. The majority of applications, however, have been limited to studies of materials containing only a single phase of the element of interest. Owing to limited availability of suitable instrumentation, the study of materials comprising intergrowths of different phases has presented difficulties in analysis. The majority of natural materials, including mineralogical samples, fall into this category. However, by applying the technique of photoemission electron microscopy (PEEM) to view the X-ray stimulated photoemission generated at an absorption edge, micro-area-selectable spectroscopy becomes possible. An instrument for X-ray PEEM (X-PEEM) is being developed at the Daresbury SRS and this paper shows how it can be used to obtain characteristic L-edge XANES spectra from finely intergrown iron oxide minerals.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1107/S0909049597015811

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3

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Distortion Characteristics Across the Structural Phase Transition in (Cu1−xZnx)WO4 (1997)

Schofield, P. F. ; Knight, K. S. ; Redfern, S. A. T. ; [et al.]

Copenhagen : International Union of Crystallography (IUCr)

Acta crystallographica 53 (1997), S. 102-112

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ISSN: 1600-5740

Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001

Topics: Chemistry and Pharmacology , Geosciences , Physics

Notes: 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 e22. 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.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1107/S0108768196010403

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4

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Temperature evolution between 50 K and 320 K of the thermal expansion tensor of gypsum derived from neutron powder diffraction data (1999)

Knight, K. S. ; Stretton, I. C. ; Schofield, P. F.

Springer

Physics and chemistry of minerals 26 (1999), S. 477-483

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ISSN: 1432-2021

Keywords: Key words gypsum ; thermal expansion tensor ; Rietveld analysis ; neutron powder diffraction

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Geosciences , Physics

Notes: Abstract The unit cell parameters, extracted from Rietveld analysis of neutron powder diffraction data collected between 4.2 K and 320 K, have been used to calculate the temperature evolution of the thermal expansion tensor for gypsum for 50 ≤ T ≤ 320 K. At 300 K the magnitudes of the principal axes are α 11 = 1.2(6) × 10−6 K−1, α 22 = 36.82(1) × 10−6 K−1 and α 33 = 25.1(5) × 10−6 K−1. The maximum axis, α 22 , is parallel to b, and using Institution of Radio Engineers (IRE) convention for the tensor orthonormal basis, the axes α 11 and α 33 have directions equal to (−0.979, 0, 0.201) and (0.201, 0, 0.979) respectively. The orientation and temperature dependent behaviour of the thermal expansion tensor is related to the crystal structure in the I2/a setting.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s002690050210

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5

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Cu 2p absorption spectroscopy as a probe for the site occupancy of (ZnxCu1−x)WO4 solid solution (1993)

Schofield, P. F. ; Henderson, C. M. B. ; Redfern, S. A. T. ; [et al.]

Springer

Physics and chemistry of minerals 20 (1993), S. 375-381

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ISSN: 1432-2021

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Geosciences , Physics

Notes: Abstract The solid solution sanmartinite (ZnWO4)—cuproscheelite (CuWO4) has been studied using Cu 2p X-ray absorption spectroscopy. While a single L3 absorption peak is observed for CuWO4, two distinct L3 absorption peaks with a separation of ∼0.8 eV are observed for the intermediate samples in the solid solution. The two peaks represent distinct Cu sites: one with all CuO6 next nearest neighbours in the (Cu,Zn)O6 chains, another having at least one ZnO6 next nearest neighbour. Both sites show a linear increase in covalency as a function of increasing Cu-content. The relative intensities of the two absorption peaks is dependent upon the Cu-content and has been used to model the site occupancies. The results reveal that the local structural effects can be associated with a composition-dependent structural phase transition from P2/c (ZnWO4) to P $$\bar 1$$ (CuWO4). Deviations from a single-site model are explained in terms of the local environments, and evidence for site preferences and local clustering are explored.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00203106

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6

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Neutron powder diffraction study of the scintillator material ZnWO4 (1996)

Schofield, P. F. ; Knight, K. S. ; Cressey, G.

Springer

Journal of materials science 31 (1996), S. 2873-2877

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ISSN: 1573-4803

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract With a view to the technological applications of ZnWO4 crystals, we have performed Rietveld profile refinement of medium-resolution, time-of-flight, neutron powder diffraction data of synthetic ZnWO4 to improve the quality of the current crystal structure derived from single crystal X-ray techniques that produced a final solution with an R factorof only 10%. The new structural data for ZnWO4, monoclinic space group P2/c, lattice parameters of 0.469263(5), 0.572129(7), 0.492805(5) nm for a, b and c respectively, and a β angle of 90.6321(9) ° with two formula units per unit cell. The ZnO6 octahedra contain 3 pairs of Zn-O bonds of 0.2026(2), 0.2090(2) and 0.2227(3) nm and the WO6 octahedra contain 3 pairs of W-O bonds 0.1789(2), 0.1914(2) and 0.2133(3) nm. These new data confirm the basic structure of ZnWO4 and provide accurate off-centring magnitudes for the Zn and W cations.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00355995

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7

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Measurement of the Solubility of Xenon-133 in Blood and Human Brain (1965)

Isbister, W H ; Schofield, P F ; Torrance, H B

Institute of Physics

In: Physics in Medicine and Biology. 1965; 10(2): 243-250. 308. Published 1965 Apr 01. doi: 10.1088/0031-9155/10/2/308.

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Publication Date: 1965-04-01

Print ISSN: 0031-9155

Electronic ISSN: 1361-6560

Topics: Biology , Medicine , Physics

Published by Institute of Physics

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Substitution of Ti3+ and Ti4+ in hibonite (CaAl12O19) (2014)

Doyle, P. M., Schofield, P. F., Berry, A. J., Walker, A. M., Knight, K. S.

Mineralogical Society of America

In: American Mineralogist

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Publication Date: 2014-07-02

Description: The structures of eight synthetic samples of hibonite, with variable Ti oxidation state and Ti concentration (2.4–15.9 wt% TiO 2 ) that span the range reported for natural hibonite found in meteorites, were determined by Rietveld refinements of neutron powder diffraction data. Ti 3+ was found to exclusively occupy the octahedral face-sharing M4 site irrespective of the presence or absence of Ti 4+ . Ti 4+ partitions between the trigonal bipyramidal M2 site and the M4 site. The ratio (Ti 4+ on M2):(Ti 4+ on M4) appears to be constant for all the samples, with an average of 0.18(2) irrespective of the concentrations of Ti 3+ and Ti 4+ . These substitutional sites were shown to be the most stable configurations for Ti in hibonite from calculations using density functional theory, although the predicted preference of Ti 4+ for M4 over M2 is not as strong as is observed. This is attributed to the different Ti contents of the experimental and calculated structures and suggests that the Ti site occupancies might change between these concentrations. Furthermore, it is shown that Ti has a preference to occupy neighboring M4 sites such that Ti-Ti interactions occur with stabilization energies of 83 kJ/mol for Ti 3+ -Ti 3+ and at least 15 kJ/mol for Ti 4+ -Ti 4+ . Features in optical spectroscopy and electron spin resonance data from meteoritic and synthetic hibonites that have been used to infer Ti 3+ /Ti 4+ are shown to actually derive from these Ti-Ti interactions. The amount of Ti 4+ in hibonite can be determined from the unit-cell parameters if Ti is determined independently. Ti 3+ /Ti 4+ in hibonite may record the oxygen fugacity ( f O 2 ) of the early solar nebula, however, the existence of Ti 3+ -Ti 3+ and Ti 4+ -Ti 4+ interactions and the potential for Ti 4+ -Ti 3+ interactions need to be considered when interpreting spectroscopic data in terms of Ti valence state and f O 2 . Hibonite as a single-mineral oxybarometer must be used with caution due to the potential role of crystal chemistry (including Ti-Ti interactions) to stabilize Ti oxidation states independently of f O 2 .

Print ISSN: 0003-004X

Electronic ISSN: 1945-3027

Topics: Geosciences