Tony Bell
Solid state chemist and powder diffraction expert.
B.Sc Sheffield 1984
M.Sc Keele 1992
Ph.D Cambridge 1999
Supervisors: M.Sc supervisor Dr. Andrew Fitch, now at ESRF Grenoble France and Ph.D supervisor Prof. Paul Attfield FRS, now at University of Edinburgh, Scotland
Phone: +441142253401
Address: ACES/MERI
Sheffield Hallam University
Sheffield
S1 1WB
UK
B.Sc Sheffield 1984
M.Sc Keele 1992
Ph.D Cambridge 1999
Supervisors: M.Sc supervisor Dr. Andrew Fitch, now at ESRF Grenoble France and Ph.D supervisor Prof. Paul Attfield FRS, now at University of Edinburgh, Scotland
Phone: +441142253401
Address: ACES/MERI
Sheffield Hallam University
Sheffield
S1 1WB
UK
less
Related Authors
Stavroula Fili
University of Massachusetts Amherst
Vivian Stojanoff
Brookhaven National Laboratory
Gérard Férey
Université de Versailles Saint-Quentin-en-Yvelines
Elspeth Garman
University of Oxford
Uploads
1987 by Tony Bell
using 15N n.m.r. spectroscopy and X-ray crystallography, to be substituted 1,2,4-oxadiazolidinones and
not the previously reported 1,3,4-oxadiazolidinones.""
1990 by Tony Bell
singlecrystal data, for phases encountered in the preparation of yttrium barium
copper oxide ceramics. These patterns have been used to characterise samples
from a small programme of work at NRL-Springfields on novel production
techniques for superconductor materials.""
P2/n, a = 7.8346 (25), b = 6.4729 (26), c =
9.5817 (50) A, /3 = 93.768 (35) °, V = 484.86 A 3, Z =
2, Dx = 2.0776 g cm -3, Mo Kc~ (A = 0.71069/~),/z =
68.66 cm- 1, F(000) = 300, room temperature, final R
= 0.0449 for 940 unique observed reflexions. The
yttrium is coordinated, as expected, by two chlorines
and six water molecules in a square antiprismatic
arrangement.""
1992 by Tony Bell
station 2.3, some half the distance from a dipole radiation source with the same nominal
1.2T field. The purpose of this paper is to detail the changes and modifications to the
diffractometer operation."
1994 by Tony Bell
diffraction patterns of dry-synthesized MFemSi206
leucites (M = K, Rb, Cs) showed that the K- and Rbcontaining
leucites (iron potassium silicate, KFeSi206,
and iron rubidium silicate, RbFeSi206) each have a
tetragonal 141/a structure and the Cs-containing leucite
(caesium iron silicate, CsFeSi206) has a cubic la3d
structure. The structures of these materials have been refined
by the Rietveld method. In CsFeSi206 leucite, Fe tu
and Si are disordered on tetrahedral framework sites
as required by space-group constraints. In KFeSi206
leucite, Fe shows significant ordering and is concentrated
on the T3 tetrahedral site. RbFeSi206 leucite
shows less pronounced T-site ordering reflecting the fact
that it is closer to the tetragonal-cubic phase transition
at which the T sites become identical.""
diffraction pattern of a dry-synthesized rubidium zinc silicate,
leucite analogue Rb2ZnSi5Ol2, showed that this material
has a cubic la43d structure. The structure of this material
has been refined by the Rietveld method. Si and Zn atoms are disordered on tetrahedral framework sites and
Rb occupies large channel sites along the [ 111] direction.""
been determined for synthetic Cs2CdSi5O12. NMR
spectroscopy shows that there are five distinct tetrahedral
sites (T-sites) occupied by Si and one T-site
occupied by Cd in the framework structure, while
analysis of the synchrotron X-ray powder diffraction
pattern establishes that this material is orthorhombic,
Pbca [RI = 13.1%, R wp = 16.1%, Rex p =
13.1%; eight formula units per unit cell; unit-cell
parameters a= 13.6714(1), b= 13.8240 (1), c=
13.8939 (1) ,~, V = 2625.83 (6) ,~3]. Tetrahedral
cation ordering rates for Si and Cd are sufficiently
high for both hydrothermally and dry-synthesized
samples to be fully ordered. The symmetry relations
between leucites with P2/c and Pbca structures are
discussed and it is shown that such materials are
related by a displacive phase transition, in which the
number of T-sites is reduced from 12 in P2/c to 6 in
Pbca. The 295i MAS NMR data are, at present, less
useful than the X-ray results for providing absolute
T---O distances and T--O--T bond angles.""
the title compound have been determined using
integrated TEM, MAS NMR and Rietveld analysis
of synchrotron X-ray powder diffraction data. Both
samples have a 'leucite-like' framework topology.
The dry-synthesized sample is cubic, la3d [a=
13.4190 (1) ,~, V= 2416.33 (5) A 3] with disordered
Mg and Si in tetrahedral framework sites. The
hydrothermally synthesized analogue is monoclinic,
P21/c [a = 13.168 (5), b = 13.652 (1), c =
13.072 (5)/~,/3 = 91.69 °, V = 2348 (2) A3], and has a
fully ordered framework with four K, ten Si and two
Mg sites per 24 O atoms (one quarter of the unit
cell). Two of these Si sites are linked to Si tetrahedra
only [Q4(4Si)], while the other eight Si sites have one
Mg and three Si tetrahedra as next-nearest neighbours
[Q4(3Si, IMg)]. Q4(4Si) and Mg tetrahedra share opposite corners of four rings. Si and Mg
ordering is accompanied by a volume contraction of
2.8%. The X-ray structural data for the ordered
sample allow the 29Si MAS NMR peaks to be
assigned to particular Si tetrahedra, and thus to
particular values of the mean T--O---T angle. The
nature of the polymorphism between the disordered
and ordered samples is discussed and related to the
different synthesis conditions. Water in the hydrothermal
synthesis accelerates Si-Mg ordering, allowing
the thermodynamically more stable phase to be
formed.""
1995 by Tony Bell
synchrotron X-ray powder pattern and a single crystal X-ray data set. The compound is monoclinic,
a = 7.538(l), b = 11.062(l), c = 7.105( 1) A, 0 = 105.42(l)“, space group P21/c, with Z = 4. The precision
of the structure arrived at with the synchrotron X-ray powder pattern is not as high as that obtained with the
single crystal X-ray data. The barium atoms are bonded to the. oxalate ions and to the water molecules
with nine barium oxygen- bonds in the range 2.71(l)-2.97(l)A. The structure has hydrogen bonds in
the range 2.72(2)-2,91(2)A, and the oxalate ion has only a minor deviation from planarity."
1996 by Tony Bell
1998 by Tony Bell
metal oxides: it leads to metal-insulator transitions in manganite
perovskites (which show `colossal' magnetoresistances), and the
Verwey transition in magnetite (in which the material becomes
insulating at low temperatures when the conduction electrons
freeze into a regular array). Charge-ordered `stripes' are found in
some manganites and copper oxide superconductors; in the
latter case, dynamic fluctuations of the stripes have been
proposed as a mechanism of high-temperature superconductivity.
But an important unresolved issue is whether the chargeordering
in oxides is driven by electrostatic repulsions between
the charges (Wigner crystallization), or by the strains arising
from electron-lattice interactions (such as Jahn-Teller distortions)
involving different localized electronic states. Here we
report measurements on iron oxoborate, Fe2OBO3, that support
the electrostatic repulsion charge-ordering mechanism: the
system adopts a charge-ordered state below 317 K, in which Fe2+
and Fe3+ ions are equally distributed over structurally distinct
Fe sites. In contrast, the isostructural manganese oxoborate,
Mn2OBO3, has been previously shown to undergo charge-ordering
through Jahn-Teller distortions. We therefore conclude that
both mechanisms occur within the same structural arrangement."
1999 by Tony Bell
andMIIMIIIOBO3 materials can be grown from borate fluxes. In the FeII–FeIII–B–O system, flux growth results in
Fe3O2BO3 crystals, but solid state reaction at higher temperatures has yielded Fe2OBO3 as a polycrystalline powder.
This has been characterised by synchrotron and neutron diffraction, electron microscopy, Mo¨ssbauer spectroscopy,
and conductivity and magnetic measurements. Two notable transitions occur, a broad semiconductor–
semiconductor change accompanied by a structural transition at 317 K, and L-type ferrimagnetic order below a
Curie temperature of 155 K. An average (Fe2+)0.5(Fe3+)0.5 valence is observed at the two crystallographically
distinct sites in Fe2OBO3, indicating that charge ordering occurs."
2000 by Tony Bell
collected at 60 K are fitted using a simple rhombohedral distortion of the cubic unit cell. This model accounts for all of the
peak splittings that occur upon cooling through the Verwey transition temperature (TV). Lower resolution data collected
between 2 and 280 K are fitted using the same model, which gives TV11095 K. These data show a change in the thermal
expansion due to the softening of phonons above TV and a change in crystallite extinction arising from twinning at the
transition."
k-MnO2 phase which can act as a lithium selective sorbent. The substitution of manganese by other metals, such as Co,
Cr, Ti and Ga allow the structural properties of the spinel lattice to be modi"ed and tailored. This work uses neutron
di!raction, inelastic neutron scattering, XAFS and atomistic calculations to show that in the non-substituted spinel,
inserted protons are present predominantly as hydroxyl groups directed into the vacant 8a site, with an orientation
in#uenced by the presence of manganese vacancies. The in#uence of cation substitution is explained within this
context."
2001 by Tony Bell
the Mn cations in the nonmetallic K2NiF4-like phase La0.8Sr1.2Mn0.6Rh0.4O4 become significant below 200
K. Negative magnetoresistance (F/F(0) 0.5 in 14 T at 108 K) is apparent below this temperature. Neutron
diffraction has shown that an applied magnetic field of 5 T is sufficient to induce saturated (3.38(7)íB per
Mn) long-range ferromagnetic ordering of the atomic moments at 2 K, and that the induced ordering persists
up to a temperature of 50 K in 5 T. Spin glass behavior is observed below 20 K in the absence of an applied
field. The induced magnetic ordering is attributed to the subtle changes in band structure brought about by the
external field, and to the controlling influence of Rh3+ over the relative strength of competing magnetic exchange
interactions."
2002 by Tony Bell
SrCaMnGaO5+d (d ¼ 0:035) has been refined from neutron
powder diffraction data; space group Ima2, a ¼ 15:7817ð6Þ;
b ¼ 5:4925ð2Þ, c ¼ 5:3196ð2ÞA( . Mn and Ga occupy 99.0(2)% of
the 6- and 4-coordinate sites, respectively. A combination of
magnetometry, neutron diffraction and lSR spectroscopy has
shown that the compound orders magnetically at 180 K, and that
the low-temperature phase has a G-type antiferromagnetic
structure, with an ordered magnetic moment of 3.30(2) lB per
Mn at 2K. Displaced hysteresis loops provide evidence that the
atomic moment has an additional, glassy component. Magnetometry
shows that significant short-range magnetic interactions
persist above 180 K, and lSR that the spin fluctuations are
thermally activated in this temperature region. The compound is
an electrical insulator which at 159K shows an unusually large
magnetoresistance of 85% in 6T, increasing to 90% in
13 T."
2005 by Tony Bell
on the effectiveness of stabilization and storage treatments of copper artefacts in aqueous solution. The electrochemical cell used here was
designed for in situ, time resolved SR-XRD studies of corrosion and inhibition studies on cultural heritage materials. Key objectives of
the new cell were to monitor corrosion layers on alloys with realistic metallographic structures and to obtain co-incident, time resolved,
electrochemical data such as reduction measurements, oxidation measurements and corrosion potential (Ecorr) measurements. Here we
present some early results from the cell. Firstly, a correlated SR-XRD and corrosion potential (Ecorr) study of the reduction of nantokite
during storage in sodium sesquicarbonate, which shows that the surface chemistry continues to change after Ecorr has stabilized. Secondly,
the use of X-ray data to identify specific changes occurring as a function of potential in the forced reduction of a more complex
system.
2007 by Tony Bell
(96% dense), grain size 6–7 lm, with dielectric properties (at
4 GHz) of er46, Qf 38 000 GHz, and sf113 ppm/1C,
were studied at 251–13001C using synchrotron X-ray powder
diffraction. At room temperature, CTLA exhibits a distorted
orthorhombic structure, with two tilt systems: a55.40383 (4)
A ˚
, b55.41106 (6) A ˚ , and c57.64114 (7) A ˚ with space group
Pbnm. At 105017251C, there is a transition from orthorhombic
(Pbnm) to tetragonal (I4/mcm), with a simpler tilt arrangement.
The lattice parameters at 11001C were: a55.44285 (4) A ˚ and
c57.68913 (8) A ˚ ."
(Fe3O4) by the reduction of amorphous Fe(III) oxyhydroxide coupled to the oxidation of
organic matter in the anoxic subsurface as an alternative to oxygen respiration. G. sulfurreducens
can transfer electrons to solid Fe(III)-bearing minerals through either direct contact
between the cell and the mineral surface or by using an electron shuttling compound. Highresolution
synchrotron X-ray powder diffraction has been used to study samples taken at
different stages of this reaction. This shows that an initial amorphous phase first transforms
to goethite (FeO(OH)), before undergoing a further transformation to magnetite. Magnetite is
formed faster in the presence of the electron shuttling compound disodium anthraquinone 2,6
disulphonate.
using 15N n.m.r. spectroscopy and X-ray crystallography, to be substituted 1,2,4-oxadiazolidinones and
not the previously reported 1,3,4-oxadiazolidinones.""
singlecrystal data, for phases encountered in the preparation of yttrium barium
copper oxide ceramics. These patterns have been used to characterise samples
from a small programme of work at NRL-Springfields on novel production
techniques for superconductor materials.""
P2/n, a = 7.8346 (25), b = 6.4729 (26), c =
9.5817 (50) A, /3 = 93.768 (35) °, V = 484.86 A 3, Z =
2, Dx = 2.0776 g cm -3, Mo Kc~ (A = 0.71069/~),/z =
68.66 cm- 1, F(000) = 300, room temperature, final R
= 0.0449 for 940 unique observed reflexions. The
yttrium is coordinated, as expected, by two chlorines
and six water molecules in a square antiprismatic
arrangement.""
station 2.3, some half the distance from a dipole radiation source with the same nominal
1.2T field. The purpose of this paper is to detail the changes and modifications to the
diffractometer operation."
diffraction patterns of dry-synthesized MFemSi206
leucites (M = K, Rb, Cs) showed that the K- and Rbcontaining
leucites (iron potassium silicate, KFeSi206,
and iron rubidium silicate, RbFeSi206) each have a
tetragonal 141/a structure and the Cs-containing leucite
(caesium iron silicate, CsFeSi206) has a cubic la3d
structure. The structures of these materials have been refined
by the Rietveld method. In CsFeSi206 leucite, Fe tu
and Si are disordered on tetrahedral framework sites
as required by space-group constraints. In KFeSi206
leucite, Fe shows significant ordering and is concentrated
on the T3 tetrahedral site. RbFeSi206 leucite
shows less pronounced T-site ordering reflecting the fact
that it is closer to the tetragonal-cubic phase transition
at which the T sites become identical.""
diffraction pattern of a dry-synthesized rubidium zinc silicate,
leucite analogue Rb2ZnSi5Ol2, showed that this material
has a cubic la43d structure. The structure of this material
has been refined by the Rietveld method. Si and Zn atoms are disordered on tetrahedral framework sites and
Rb occupies large channel sites along the [ 111] direction.""
been determined for synthetic Cs2CdSi5O12. NMR
spectroscopy shows that there are five distinct tetrahedral
sites (T-sites) occupied by Si and one T-site
occupied by Cd in the framework structure, while
analysis of the synchrotron X-ray powder diffraction
pattern establishes that this material is orthorhombic,
Pbca [RI = 13.1%, R wp = 16.1%, Rex p =
13.1%; eight formula units per unit cell; unit-cell
parameters a= 13.6714(1), b= 13.8240 (1), c=
13.8939 (1) ,~, V = 2625.83 (6) ,~3]. Tetrahedral
cation ordering rates for Si and Cd are sufficiently
high for both hydrothermally and dry-synthesized
samples to be fully ordered. The symmetry relations
between leucites with P2/c and Pbca structures are
discussed and it is shown that such materials are
related by a displacive phase transition, in which the
number of T-sites is reduced from 12 in P2/c to 6 in
Pbca. The 295i MAS NMR data are, at present, less
useful than the X-ray results for providing absolute
T---O distances and T--O--T bond angles.""
the title compound have been determined using
integrated TEM, MAS NMR and Rietveld analysis
of synchrotron X-ray powder diffraction data. Both
samples have a 'leucite-like' framework topology.
The dry-synthesized sample is cubic, la3d [a=
13.4190 (1) ,~, V= 2416.33 (5) A 3] with disordered
Mg and Si in tetrahedral framework sites. The
hydrothermally synthesized analogue is monoclinic,
P21/c [a = 13.168 (5), b = 13.652 (1), c =
13.072 (5)/~,/3 = 91.69 °, V = 2348 (2) A3], and has a
fully ordered framework with four K, ten Si and two
Mg sites per 24 O atoms (one quarter of the unit
cell). Two of these Si sites are linked to Si tetrahedra
only [Q4(4Si)], while the other eight Si sites have one
Mg and three Si tetrahedra as next-nearest neighbours
[Q4(3Si, IMg)]. Q4(4Si) and Mg tetrahedra share opposite corners of four rings. Si and Mg
ordering is accompanied by a volume contraction of
2.8%. The X-ray structural data for the ordered
sample allow the 29Si MAS NMR peaks to be
assigned to particular Si tetrahedra, and thus to
particular values of the mean T--O---T angle. The
nature of the polymorphism between the disordered
and ordered samples is discussed and related to the
different synthesis conditions. Water in the hydrothermal
synthesis accelerates Si-Mg ordering, allowing
the thermodynamically more stable phase to be
formed.""
synchrotron X-ray powder pattern and a single crystal X-ray data set. The compound is monoclinic,
a = 7.538(l), b = 11.062(l), c = 7.105( 1) A, 0 = 105.42(l)“, space group P21/c, with Z = 4. The precision
of the structure arrived at with the synchrotron X-ray powder pattern is not as high as that obtained with the
single crystal X-ray data. The barium atoms are bonded to the. oxalate ions and to the water molecules
with nine barium oxygen- bonds in the range 2.71(l)-2.97(l)A. The structure has hydrogen bonds in
the range 2.72(2)-2,91(2)A, and the oxalate ion has only a minor deviation from planarity."
metal oxides: it leads to metal-insulator transitions in manganite
perovskites (which show `colossal' magnetoresistances), and the
Verwey transition in magnetite (in which the material becomes
insulating at low temperatures when the conduction electrons
freeze into a regular array). Charge-ordered `stripes' are found in
some manganites and copper oxide superconductors; in the
latter case, dynamic fluctuations of the stripes have been
proposed as a mechanism of high-temperature superconductivity.
But an important unresolved issue is whether the chargeordering
in oxides is driven by electrostatic repulsions between
the charges (Wigner crystallization), or by the strains arising
from electron-lattice interactions (such as Jahn-Teller distortions)
involving different localized electronic states. Here we
report measurements on iron oxoborate, Fe2OBO3, that support
the electrostatic repulsion charge-ordering mechanism: the
system adopts a charge-ordered state below 317 K, in which Fe2+
and Fe3+ ions are equally distributed over structurally distinct
Fe sites. In contrast, the isostructural manganese oxoborate,
Mn2OBO3, has been previously shown to undergo charge-ordering
through Jahn-Teller distortions. We therefore conclude that
both mechanisms occur within the same structural arrangement."
andMIIMIIIOBO3 materials can be grown from borate fluxes. In the FeII–FeIII–B–O system, flux growth results in
Fe3O2BO3 crystals, but solid state reaction at higher temperatures has yielded Fe2OBO3 as a polycrystalline powder.
This has been characterised by synchrotron and neutron diffraction, electron microscopy, Mo¨ssbauer spectroscopy,
and conductivity and magnetic measurements. Two notable transitions occur, a broad semiconductor–
semiconductor change accompanied by a structural transition at 317 K, and L-type ferrimagnetic order below a
Curie temperature of 155 K. An average (Fe2+)0.5(Fe3+)0.5 valence is observed at the two crystallographically
distinct sites in Fe2OBO3, indicating that charge ordering occurs."
collected at 60 K are fitted using a simple rhombohedral distortion of the cubic unit cell. This model accounts for all of the
peak splittings that occur upon cooling through the Verwey transition temperature (TV). Lower resolution data collected
between 2 and 280 K are fitted using the same model, which gives TV11095 K. These data show a change in the thermal
expansion due to the softening of phonons above TV and a change in crystallite extinction arising from twinning at the
transition."
k-MnO2 phase which can act as a lithium selective sorbent. The substitution of manganese by other metals, such as Co,
Cr, Ti and Ga allow the structural properties of the spinel lattice to be modi"ed and tailored. This work uses neutron
di!raction, inelastic neutron scattering, XAFS and atomistic calculations to show that in the non-substituted spinel,
inserted protons are present predominantly as hydroxyl groups directed into the vacant 8a site, with an orientation
in#uenced by the presence of manganese vacancies. The in#uence of cation substitution is explained within this
context."
the Mn cations in the nonmetallic K2NiF4-like phase La0.8Sr1.2Mn0.6Rh0.4O4 become significant below 200
K. Negative magnetoresistance (F/F(0) 0.5 in 14 T at 108 K) is apparent below this temperature. Neutron
diffraction has shown that an applied magnetic field of 5 T is sufficient to induce saturated (3.38(7)íB per
Mn) long-range ferromagnetic ordering of the atomic moments at 2 K, and that the induced ordering persists
up to a temperature of 50 K in 5 T. Spin glass behavior is observed below 20 K in the absence of an applied
field. The induced magnetic ordering is attributed to the subtle changes in band structure brought about by the
external field, and to the controlling influence of Rh3+ over the relative strength of competing magnetic exchange
interactions."
SrCaMnGaO5+d (d ¼ 0:035) has been refined from neutron
powder diffraction data; space group Ima2, a ¼ 15:7817ð6Þ;
b ¼ 5:4925ð2Þ, c ¼ 5:3196ð2ÞA( . Mn and Ga occupy 99.0(2)% of
the 6- and 4-coordinate sites, respectively. A combination of
magnetometry, neutron diffraction and lSR spectroscopy has
shown that the compound orders magnetically at 180 K, and that
the low-temperature phase has a G-type antiferromagnetic
structure, with an ordered magnetic moment of 3.30(2) lB per
Mn at 2K. Displaced hysteresis loops provide evidence that the
atomic moment has an additional, glassy component. Magnetometry
shows that significant short-range magnetic interactions
persist above 180 K, and lSR that the spin fluctuations are
thermally activated in this temperature region. The compound is
an electrical insulator which at 159K shows an unusually large
magnetoresistance of 85% in 6T, increasing to 90% in
13 T."
on the effectiveness of stabilization and storage treatments of copper artefacts in aqueous solution. The electrochemical cell used here was
designed for in situ, time resolved SR-XRD studies of corrosion and inhibition studies on cultural heritage materials. Key objectives of
the new cell were to monitor corrosion layers on alloys with realistic metallographic structures and to obtain co-incident, time resolved,
electrochemical data such as reduction measurements, oxidation measurements and corrosion potential (Ecorr) measurements. Here we
present some early results from the cell. Firstly, a correlated SR-XRD and corrosion potential (Ecorr) study of the reduction of nantokite
during storage in sodium sesquicarbonate, which shows that the surface chemistry continues to change after Ecorr has stabilized. Secondly,
the use of X-ray data to identify specific changes occurring as a function of potential in the forced reduction of a more complex
system.
(96% dense), grain size 6–7 lm, with dielectric properties (at
4 GHz) of er46, Qf 38 000 GHz, and sf113 ppm/1C,
were studied at 251–13001C using synchrotron X-ray powder
diffraction. At room temperature, CTLA exhibits a distorted
orthorhombic structure, with two tilt systems: a55.40383 (4)
A ˚
, b55.41106 (6) A ˚ , and c57.64114 (7) A ˚ with space group
Pbnm. At 105017251C, there is a transition from orthorhombic
(Pbnm) to tetragonal (I4/mcm), with a simpler tilt arrangement.
The lattice parameters at 11001C were: a55.44285 (4) A ˚ and
c57.68913 (8) A ˚ ."
(Fe3O4) by the reduction of amorphous Fe(III) oxyhydroxide coupled to the oxidation of
organic matter in the anoxic subsurface as an alternative to oxygen respiration. G. sulfurreducens
can transfer electrons to solid Fe(III)-bearing minerals through either direct contact
between the cell and the mineral surface or by using an electron shuttling compound. Highresolution
synchrotron X-ray powder diffraction has been used to study samples taken at
different stages of this reaction. This shows that an initial amorphous phase first transforms
to goethite (FeO(OH)), before undergoing a further transformation to magnetite. Magnetite is
formed faster in the presence of the electron shuttling compound disodium anthraquinone 2,6
disulphonate.
LIII edge EXAFS spectroscopy at 296, 348 and 423 K. Data were collected using the ID26 High Brilliance X-ray Spectroscopy
beamline at the ESRF. Analysis of these EXAFS spectra shows Hg coordinated by two S atoms at 2.30 Å; multiple scattering
analyses reveal a linear [–S–Hg–S–] arrangement in the solution complex. These results are in agreement with earlier results on
more concentrated solutions of these complexes. There is also evidence in the data for polynuclear sulfide complexes at 296 K and
348 K for samples with the lowest sulfide concentrations although this is complicated by multiple scattering effects.
of two natural illitic clays were investigated through
XRD measurements, ex situ at room temperature with conventional
set up and in situ with synchrotron radiation, in order to
understand the origin of the corundum phase, which is one of
the main characteristics of the red glaze (slip) of Terra Sigillata
from south Gaul. These clays were chosen on the basis of their
chemical composition and for the quality of vitrification in the
firing temperature range of sigillata (1030–1080 ◦C). Results
show that corundum can be formed above 1000 ◦C if the amount
of Mg is not too high. The corundum formation does not result
directly from the total decomposition of illite (< 900 ◦C)
but from the formation and disruption of an intermediate potassium
aluminum silicate phase. On the other hand, if chlorite is
present in the raw clay so that the amount of Mg > 3–4 wt. %,
this intermediate phase is not observed and only a spinel phase
is formed.
X-ray scintillation detector is presented. The detectors are intended for use on
the new I11 powder diffraction beamline at the third-generation Diamond
synchrotron facility where X-ray beams of high photon brightness are generated
by insertion devices. The performance characteristics of these detection units
were measured first using a radioactive source (efficiency of detection and
background count rate) and then synchrotron X-rays (peak stability, light yield
linearity and response consistency). Here, the results obtained from these tests
are reported, and the suitability of the design for the Diamond powder beamline
is demonstrated by presenting diffraction data obtained from a silicon powder
standard using a prototype multicrystal analyser stage."
Proto-magnetite is identified by long tetrahedral (2.113 Å) and short octahedral (1.943 Å) Fe-O bonds compared to stoichiometric magnetite, possibly indicative of a coordination crossover caused by charge density [Fe(II)] migration to tetrahedral sites. Fe(II) in solution or sorbed to the mineral surface is considered to be the catalyst causing the mineral transformations. The Fe(II) is thought to form predominantly from the reductive dissolution of 2-line ferrihydrite by G. sulfurreducens.
metastable phases III0 and III of cyclohexanol, C6H11OH,
have been determined using high-resolution neutron powder,
synchrotron X-ray powder and single-crystal X-ray diffraction
techniques. Cyclohexanol-II is formed by a transition from the
plastic phase I cubic structure at 265 K and crystallizes in a
tetragonal structure, space group P4421c (Z0 = 1), in which the
molecules are arranged in a hydrogen-bonded tetrameric ring
motif. The structures of phases III0 and III are monoclinic,
space groups P21/c (Z0 = 3) and Pc (Z0 = 2), respectively, and
are characterized by the formation of hydrogen-bonded
molecular chains with a threefold-helical and wave-like
nature, respectively. Phase III crystallizes at 195 K from a
sample of phase I that is supercooled to ca 100 K.
Alternatively, phase III may be grown via phase III0, the
latter transforming from supercooled phase I at ca 200 K.
Phase III0 is particularly unstable and is metastable with
respect to both I and II. Its growth is realised only under very
restricted conditions, thus making its characterization especially
challenging. The cyclohexanol molecules adopt a chair
conformation in all three phases with the hydroxyl groups in
an equatorial orientation. No evidence was found indicating
hydroxyl groups adopting an axial orientation, contrary to the
majority of spectroscopic literature on solid-state cyclohexanol;
however, the H atom of the equatorial OH groups is
found to adopt both in-plane and out-of-plane orientations."""
analogue Cs2CuSi5O12 has been determined and refined using
the Rietveld method from high-resolution synchrotron X-ray
and neutron powder diffraction data. This structure is based
on the topology and cation-ordering scheme of the Pbca
leucite structure of Cs2CdSi5O12, and exhibits five ordered Si
sites and one ordered Cu tetrahedrally coordinated (T) site.
This structure for Cs2CuSi5O12 is topologically identical to
other known leucite structures and is different from that
originally proposed by Heinrich & Baerlocher [(1991), Acta
Cryst. C47, 237–241] in the tetragonal space group P41212. The
crystal structure of a dry-synthesized leucite analogue
Cs2CuSi5O12 has also been refined; this has the Ia33d cubic
pollucite structure with disordered T sites"
K2PtBr6 offer a way forward to solve, de novo, unknown
protein structures by powder diffraction involving dispersive
(measured at two X-ray wavelengths) and isomorphous
intensity differences as a complement to micro-crystallography
or by using both approaches in combination.
Towards this end, using the ESRF high resolution synchrotron
X-ray powder diffraction beamline ID31, we
have recorded high quality protein powder diffractograms
at the platinum LIII and bromine K absorption edges, as
well as reference wavelengths, for K2PtBr6 bound to lysozyme.
These experiments were conducted at 80K to protect
the sample against X-radiation damage as much as
possible and also to fix the K2PtBr6 bound state, which
seemed to show instability at room temperature. With multiple
powder pattern analysis we extracted intensities and
showed the PtBr6 bound in lysozyme using ‘omit electron
density maps’. In addition the wavelength dispersive Fourier
around the Br K edge shows up the bromine signal at
PtBr6 binding site 1 in one of the six samples tested. To
better understand the chemical properties of this heavy
atom compound we have elucidated the detailed binding
behaviour using single crystal analyses with time-resolved
freeze quenching after soak times of 10, 90 and 170 minutes.
Whilst the quick soaking of 10 to 30 minutes, used
at ESRF ID31 shows clear binding, there is increasing
binding strength with increasing soak time. Thus, these
time-resolved analytical chemistry results show that further
heavy atom signal optimizations are possible. Prospects
for extending our approach to the yet larger isomorphous
and wavelength dispersive signal case of Ta6Br12 bound to
lysozyme are also described."
plastic deformation. For thin films below a critical film thickness, plastic deformation is energetically unfavourable: thus, the system
stays coherent and stress remains. For PdHc films less than 22 nm thick, a new situation emerges: while the interfaces between matrix
and hydride precipitates remain coherent throughout the complete phase transition, misfit dislocations form between the hydride
phase and the substrate."
temperature. Two characteristic temperatures, T1 = 90 K and T2 = 25 K for Sr3CoIrO6, and T1 = 85 K and
T2 = 15 K for Sr3NiIrO6, were observed. Below T1 a significant increase of magnetization and below T2 a weak
temperature dependence of magnetization in the field-cooled and practically zero magnetization values in the
zero-field-cooled mode were detected for both compounds. The existence of Ir4+ in Sr3CoIrO6 was confirmed
by an Ir-LIII x-ray absorption measurement. Magnetoelastic effects have been observed in the temperature
dependence of the lattice parameters of Sr3CoIrO6 and Sr3NiIrO6. The magnetic structure of Sr3CoIrO6 in zero
fields can be described as a commensurate modulated antiferromagnet with a propagation vector k = (0,0,1).
Neutron powder diffraction with polarized neutrons gave evidence of short-range magnetic order, above and
below the magnetic ordering temperature."
using electron microscopy, calorimetric, synchrotron and magnetic measurements. The substitution of
Ga for Ge leads to decreasing on the martensitic transition temperature from 650 K to 315 K. CoMnGe0.95Ga0.05
has hexagonal structure (space group P63/mmc) above the martensitic transition temperature
and orthorhombic structure (space group Pnma) below this temperature. The magnetic field
dependence of magnetization measurements are performed in the heating and cooling processes around
the martensitic transition temperature to determine magnetocaloric effect. It is observed that the magnetic
entropy change associated with the martensitic transition temperature can be as high as
5.2 J kg1 K1 in field of 1 T.""
been studied at temperatures between 400 and 1000 C at the DORIS-III synchrotron source of Hasylab.
The measurements indicate the anatase phase appearance at temperatures above 500 C. No formation of
rutile phase was observed. The transformation kinetics for each fixed temperature is rapid and completes
within 5 min. The crystalline mass progressively increases with temperature and the full transformation
into anatase polymorph is achieved above 800 C. The results suggest higher surface energy of the anatase
phase compared to amorphous one, which delays the crystallization process.
P4bm tetragonal crystal structure of fresnoite (Ba2TiSi2O8) was used as a starting model for Sr-fresnoite. Small amounts of SrTiO3
and SrSiO3 were also found as impurities in this sample; therefore four-phase Rietveld refinements were done. The P4bm
fresnoite structure is retained over the temperature range 87-1223K.
oxidotitanium disilicate, has been prepared by high-temperature
solid-state synthesis. The results of a Rietveld refinement
study, based on high-resolution synchrotron X-ray powder
diffraction data, show that the title compound crystallizes in
the space group P4bm and adopts the structure of other
fresnoite-type mineral samples with general formula
A2TiO(Si2O7) (A = alkaline earth metal cation). The structure
consists of titanosilicate layers composed of corner-sharing
SiO4 tetrahedra (forming Si2O7 disilicate units) and TiO5
square-based pyramids. These layers extend parallel to the ab
plane and are stacked along the c axis. Layers of distorted
SrO6 octahedra lie between the titanosilicate layers. The Sr2+
ion, the SiO4 tetrahedron and the bridging O atom of the
disilicate unit are located on mirror planes whereas the TiO5
square-based pyramid is located on a fourfold rotation axis.""
10–300K temperature range using synchrotron X-ray powder diffraction. No phase transition was
observed down to10K.The lattice parameter of rock-salt ZnO was found to increase from 4.266Å in the
10–80 K range up to 4.2752(3)Å at 298K, while the volume thermal expansion coefficient increases from
slight negative values below 40K up to 4.7710-5 K-1 at 298K.
above room temperature. We have performed powder and single crystal neutron diffraction as well as
complementary polarization dependent soft X-ray absorption spectroscopy measurements on floating-zone
grown SmFeO3 single crystals in order to determine its magnetic structure. We found a k ¼ 0 G-type
collinear antiferromagnetic structure that is not compatible with inverse Dzyaloshinskii-Moriya interaction
driven ferroelectricity. While the structural data reveal a clear sign for magneto-elastic coupling at the
Néel-temperature of ∼675 K, the dielectric measurements remain silent as far as ferroelectricity is
concerned.
with M = Al, Ga, In, Sc, Cr, V, Fe, and CsCrTi0.5(MoO4)3 was synthesized by
solid state reactions and characterized by synchrotron powder diffraction,
differential scanning calorimetry, thermal conductivity measurements, and
magnetization measurements for compounds with a magnetic 3d transition
metal cation. The NASICON-type structure of these compounds represents a
three-dimensional framework of corner-sharing trigonal MoO4-pyramids and
MO6-octahedra, in which M and Zr (Ti) ions are randomly distributed. The Cs
ions occupy large channels along the c-axis. A combination of phenomena like
a drastic increase of thermal conductivity, endothermic signals in the DSC
curve and anomalies in the thermal expansion coefficients, observed for the
compounds with M = Cr, V, Fe, and CsCrTi0.5(MoO4)3 above 700 K, allows
one to propose a structural phase transition. The crystal structure of the hightemperature
phase is very close to the low-temperature one. A significant hysteresis in high-temperature electronic and thermal
conductivity was observed. A possible transition from the piezoelectric to the paraelectric state is discussed.
[dirubidium nickel(II) pentasilicate] and Mn [dirubidium manganese(II)
pentasilicate]} have been prepared by high-temperature solid-state synthesis.
The results of Rietveld refinements, using X-ray powder diffraction data
collected using Cu K X-rays, show that the title compounds crystallize in the
space group Pbca and adopt the cation-ordered structure of Cs2CdSi5O12 and
other leucites. The structures consist of tetrahedral SiO4 and XO4 units sharing
corners to form a partially substituted silicate framework. Extraframework Rb+
cations sit in channels in the framework. All atoms occupy the 8c general
position for this space group. In these refined structures, silicon and X atoms are
ordered onto separate tetrahedrally coordinated sites (T-sites). However, the Ni
displacement parameter and the Ni—O bond lengths suggest that for the X = Ni
sample, there may actually be some T-site cation disorder.