Neutron Rietveld Analysis of Anion and Cation Disorder in the Fast-Ion Conducting Pyrochlore System Y2(ZrxTi1−x)2O7

1989 ◽  
Vol 166 ◽  
Author(s):  
Sossina M. Haile ◽  
B. J. Wuensch ◽  
E. Prince
Keyword(s):  
Scattering Length ◽  
Rietveld Analysis ◽  
Atomic Displacements ◽  
Cation Disorder ◽  
Fluorite Type ◽  
Ion Conducting ◽  
Negative Scattering Length ◽  
Fast Ion ◽  
Cation Sites ◽  
Oxygen Site

ABSTRACTAll information on the site occupancies and atomic displacements which relate a pyrochlore superstructure to the parent fluorite-type subcell is contained in the normally-weak superstructure diffraction intensities. As Ti has a negative scattering length, the supercell maxima in the present phases are up to three times as intense as the fluorite-like reflections, and neutron diffraction provides an especially sensitive probe of the state of disorder. Y2Ti2O7 is found to have a fullyordered anion array and slight disorder, Y0.984Ti0.015, among the cations. In Y2(Zro.6TiO.4)2O7 the oxygen site normally vacant in pyrochlore is half filled and on the order of 15% exchange between cation sites has occurred.

Crystal Chemistry of Y2(ZrySn1-y)2O7 Pyrochlore Solid Solutions and its Relation to Fast-Ion Conduction

1998 ◽  
Vol 547 ◽  
Author(s):  
Esther M. Ku ◽  
Evangeline M.E. Yeo ◽  
Bernhardt J. Wuensch
Keyword(s):  
Solid Solutions ◽  
Rietveld Analysis ◽  
Fuel Cell Materials ◽  
Oxygen Ion ◽  
Ion Conducting ◽  
A Site ◽  
Fast Ion ◽  
Cation Sites ◽  
Electronic Conductors ◽  
Progressive Disorder

AbstractPyrochlore oxides, A2B2O7, are of interest as fuel cell materials and sensors because, with suitable doping, they may be fast-ion conducting or p- or n-type electronic conductors. An earlier analysis of Y2(ZryTi1-y)2O7 solid solutions showed that substitution of the larger Zr ion for Ti induced progressive disorder in both the cation and anion arrays causing a 103 increase in oxygen ion conductivity. In contrast, Y2(SnyTi1-y)2O7 solid solutions remained essentially fully ordered over their entire range of composition even though the range of average radii of the cation species in the B site overlapped to a considerable degree with those of the (ZryTi1-y) materials. The present work used Rietveld analysis of both neutron and x-ray powder profiles to examine Y2(ZrySn1-y)2O7 compositions along the third leg of the pseudo-ternary system: solid solutions between the stannate, with strong tendency to remain ordered, and the zirconate which has predilection toward complete disorder. Progressive disorder in the oxygen ion array was again observed with increasing y. Mixing between cation sites was found to progress at a rate independent of anion disordering. The behavior was very similar to Y2(ZryTi1-y)2O7, suggesting that the differing behavior of the three systems is due to the ability of Zr to readily enter the eight-coordinated A site.

scholarly journals Neutron Rietveld analysis of fast ion conducting Ca-doped (Y0.95Ca0.05)2Ti2O7pyrochlore

1996 ◽  
Vol 52 (a1) ◽  
pp. C414-C414
Author(s):  
K. Eberman ◽  
P. Önnerud ◽  
B. J. Wuensch ◽  
J. K. Stalick
Keyword(s):  
Rietveld Analysis ◽  
Ion Conducting ◽  
Fast Ion

Fast-Ion Conducting Y2(Zr Ti1-)2O7 Pyrochlores: Neutron Rietveld Analysis of Disorder Induced by Zr Substitution

1995 ◽  
Vol 117 (1) ◽  
pp. 108-121 ◽  
Author(s):  
Catherine Heremans ◽  
Bernhardt J. Wuensch ◽  
Judith K. Stalick ◽  
Edward Prince
Keyword(s):  
Rietveld Analysis ◽  
Ion Conducting ◽  
Fast Ion

Decoding ionic conductivity and reordering in cation-disordered pyrochlores

2021 ◽  
Vol 379 (2211) ◽  
Author(s):  
Ajay Annamareddy ◽  
Jacob Eapen
Keyword(s):  
Ionic Conductivity ◽  
Solid Electrolytes ◽  
Atomistic Simulations ◽  
Oxygen Ions ◽  
Tetrahedral Sites ◽  
Cation Disorder ◽  
Fast Ion ◽  
Antisite Disorder ◽  
Oxygen Site ◽  
Cation Disordering

The ordered structure A 2 B 2 O 6 O’ in pyrochlores engenders twin rows of inequivalent anion sublattices each centred on alternating cations. While it is known that cation antisite disorder augments the ionic conductivity by several orders of magnitude, the local cation environment around the anions and the dynamic anion reordering during the cation disordering are not well-elucidated. Using atomistic simulations on Gd 2 Zr 2 O 7 , we first show that the anions engage in concerted hops to the neighbouring tetrahedral sites mostly along with the 〈1 0 0〉 direction while completely avoiding the octahedral sites. While the initially vacant 8 a sites start accommodating oxygen ions with increasing cation disorder, they show noticeable reluctance even at significant levels of disorder. We have also tracked both the distribution of available oxygen sites following random cation disorder, which is dependent only on cation disordering, and the probability of occupation of these sites. Interestingly, the available oxygen sites show a non-monotonic dependence on the number of B ions in the nearest neighbouring shell while the occupation probability of all the available oxygen sites increases monotonically. A tetrahedral oxygen site thus has a better probability of being occupied when it has a greater number of second neighbour B ions. This article is part of the Theo Murphy meeting issue 'Understanding fast-ion conduction in solid electrolytes'.

scholarly journals Type II Bi1 − x W x O1.5 + 1.5x : a (3 + 3)-dimensional commensurate modulation that stabilizes the fast-ion conducting delta phase of bismuth oxide

2015 ◽  
Vol 71 (6) ◽  
pp. 679-687 ◽  
Author(s):  
Julia Wind ◽  
Josie E. Auckett ◽  
Ray L. Withers ◽  
Ross O. Piltz ◽  
Andrey Maljuk ◽  
...  
Keyword(s):  
Full Range ◽  
Type Ii ◽  
Modulated Structure ◽  
3 Dimensional ◽  
Solid Solution Range ◽  
Fluorite Type ◽  
Pyrochlore Type ◽  
Ion Conducting ◽  
Fast Ion ◽  
Modulation Vector

The Type II phase in the Bi1 − x W x O1.5 + 1.5x system is shown to have a (3 + 3)-dimensional modulated δ-Bi2O3-related structure, in which the modulation vector ∊ `locks in' to a commensurate value of 1/3. The structure was refined in a 3 × 3 × 3 supercell against single-crystal Laue neutron diffraction data. Ab initio calculations were used to test and optimize the local structure of the oxygen sublattice around a single mixed Bi/W site. The underlying crystal chemistry was shown to be essentially the same as for the recently refined (3 + 3)-dimensional modulated structure of Type II Bi1 − x Nb x O1.5 + x (Ling et al., 2013), based on a transition from fluorite-type to pyrochlore-type via the appearance of W4O18 `tetrahedra of octahedra' and chains of corner-sharing WO6 octahedra along 〈110〉F directions. The full range of occupancies on this mixed Bi/W site give a hypothetical solid-solution range bounded by Bi23W4O46.5 (x = 0.148) and Bi22W5O48 (x = 0.185), consistent with previous reports and with our own synthetic and analytical results.

NMR studies of fluoride and fast ion conducting glasses

1983 ◽  
Vol 56 (1-3) ◽  
pp. 27-32 ◽  
Author(s):  
P.J Bray ◽  
D.E Hintenlang ◽  
R.V Mulkern ◽  
S.G Greenbaum ◽  
D.C Tran ◽  
...  
Keyword(s):  
Nmr Studies ◽  
Ion Conducting ◽  
Fast Ion

A systematic neutron reflectometry study on hydrogen absorption in thin Mg1-xAlx alloy films Special issue on Neutron Scattering in Canada.

2010 ◽  
Vol 88 (10) ◽  
pp. 723-728 ◽  
Author(s):  
H. Fritzsche ◽  
E. Poirier ◽  
J. Haagsma ◽  
C. Ophus ◽  
E. Luber ◽  
...  
Keyword(s):  
Hydrogen Absorption ◽  
Scattering Length ◽  
Catalyst Layer ◽  
Neutron Reflectometry ◽  
Hydrogen Distribution ◽  
Hydrogen Atoms ◽  
Alloy Films ◽  
Negative Scattering Length ◽  
Insight Into ◽  
Optimum Alloy

In this article, we show how neutron reflectometry (NR) can provide deep insight into the absorption and desorption properties of commercially promising hydrogen storage materials. NR benefits from the large negative scattering length of hydrogen atoms, which changes the reflectivity curve substantially, so that NR can determine not only the total amount of stored hydrogen but also the hydrogen distribution along the film normal, with nanometer resolution. To use NR, the samples must have smooth surfaces, and the film thickness should range between 10 and 200 nm. We performed a systematic study on thin Mg1–xAlx alloy films (x = 0.2, 0.3, 0.4, 0.67) capped with a Pd catalyst layer. Our NR experiments showed that Mg0.7Al0.3 is the optimum alloy composition with the highest amount of stored hydrogen and the lowest desorption temperature. All the thin films expand by about 20% because of hydrogen absorption, and the hydrogen is stored only in the MgAl layer with no hydrogen content in the Pd layer.

Leucite-pollucite structure-type variability and the structure of a synthetic end-member calcium wairakite (CaAl2Si4O12·2H2O)

1998 ◽  
Vol 62 (2) ◽  
pp. 165-178 ◽  
Author(s):  
C. M. B. Henderson ◽  
A. M. T. Bell ◽  
S. C. Kohn ◽  
C. S. Page
Keyword(s):  
Rietveld Analysis ◽  
Structure Type ◽  
Magic Angle Spinning ◽  
Resonance Spectroscopy ◽  
Magic Angle ◽  
Synthetic Sample ◽  
Cation Site ◽  
Wide Range ◽  
Angle Spinning ◽  
Cation Sites

AbstractThe structure of a synthetic end-member wairakite (CaAl2Si4O12·2H2O) has been determined using Rietveld analysis of high-resolution, synchrotron X-ray powder diffraction data, and 29Si and 27Al magic angle spinning nuclear magnetic resonance spectroscopy. The framework in the synthetic sample is more disordered than that in natural wairakite. Ca is distributed over the cavity cation sites M2, M12A, M12B in the approximate proportions 0.8:0.1:0.1, respectively, with M11 being vacant. 29Si MAS NMR data are consistent with about 80% of the Si occupying tetrahedral T11 and T12 sites linked to two Al atoms [Q4(2Al) silicons]. Tetrahedral and cavity cation site disorder are coupled so that Al mainly occupies T2 sites, with Ca in M12A and M12B being balanced by Al in T12A and T12B; T11A and T11B sites appear to only contain Si, in agreement with the M11 site being vacant. The crystal chemistries of the wide range of stoichiometries which crystallize with the leucite/pollucite structure-type are also reviewed, with particular attention being paid to the tetrahedral ordering configurations present in these phases, and the implications to crystallographic phase transitions.

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