Neutron Rietveld refinement of the incommensurate phase of the ordered perovskite Pb2CoWO6

The incommensurate structure of lead cobalt tungstate has been refined by the Rietveld method on neutron data collected at 250 K. The space group is planar monoclinic I2/m(\alpha0\gamma)0s [a = 7.9602 (4), b = 5.6779 (3), c = 5.6967 (3) Å, \beta = 90.047 (5)°, \bf q_{\rm inc} = 0.9000 (9)\bf a^* + 0.1735 (6)\bf c^*]. The use of powder diffraction techniques to investigate ferroelastic modulated phases is discussed and compared with a previous polydomain single-crystal structural analysis. The modulated displacements of light atoms have been determined, allowing an accurate description of the modulation of both the cations and the O-atom framework. The refinement suggests a displacive model for the phase transition, involving significant atomic shifts for Pb atoms and a quite complex mixing of tilt and deformation of the oxygen octahedra. The average character of this modulated structure is antiferroelectric.

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Compression of glycolide-h4 to 6 GPa

Acta Crystallographica Section B Structural Science Crystal Engineering and Materials ◽

10.1107/s2052520617015657 ◽

2017 ◽

Vol 73 (6) ◽

pp. 1151-1157 ◽

Cited By ~ 5

Author(s):

Ian B. Hutchison ◽

Craig L. Bull ◽

William G. Marshall ◽

Simon Parsons ◽

Andrew J. Urquhart ◽

...

Keyword(s):

Phase Transition ◽

Structural Analysis ◽

Powder Diffraction ◽

Structural Characterization ◽

Neutron Powder Diffraction ◽

Low Background ◽

Zirconia Toughened Alumina

This study details the structural characterization of glycolide-h4 as a function of pressure to 6 GPa using neutron powder diffraction on the PEARL instrument at ISIS Neutron and Muon source. Glycolide-h4, rather than its deuterated isotopologue, was used in this study due to the difficulty of deuteration. The low background afforded by zirconia-toughened alumina anvils nevertheless enabled the collection of data suitable for structural analysis to be obtained to a pressure of 5 GPa. Glycolide-h4 undergoes a reconstructive phase transition at 0.15 GPa to a previously identified form (II), which is stable to 6 GPa.

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Reinvestigation of the Incommensurate Structure of αPbO.

MRS Proceedings ◽

10.1557/proc-755-dd12.8 ◽

2002 ◽

Vol 755 ◽

Cited By ~ 3

Author(s):

Gianguido Baldinozzi ◽

Jean-Marc Raulot ◽

Vaclav Petricek

Keyword(s):

Powder Diffraction ◽

Structural Model ◽

Rietveld Method ◽

Microscopy Study ◽

Electron Microscopy Study ◽

Incommensurate Phase ◽

Lead Monoxide ◽

Incommensurate Structure ◽

Diffraction Patterns ◽

Integrated Intensities

ABSTRACTLead monoxide exists at room temperature in two forms, namely α-PbO, litharge (red, tetragonal) and β3-PbO massicot (yellow, orthorhombic). The weak bonds along the c axis and the ferroelastic nature of the incommensurate phase prevent the growth of single crystals suitable for high quality diffraction techniques (very small ferroelastic domains and frequent stacking faults in these layered structures). A structural determination of the incommensurate structure was proposed in the superspace group C2mb(0β;0) using the integrated intensities extracted from powder diffraction patterns. More recently an electron microscopy study suggested the existence of systematic extinctions affecting the satellite reflections and it supports the more symmetric space group Cmma(0β0)s. In this paper, high resolution powder diffraction patterns (synchrotron) were refined in the incommensurate phase using the Rietveld method. Various superspace groups and forms for the modulated displacements were tested. The consequences of this structural model on the electronic structure are analysed using also ab-initio calculations.

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X-ray Powder Diffraction Structural Phase-Transition Study of La(Cr1-xMnx)O3 (x = 0 to 0.25) Using the Rietveld Method of Analysis

Journal of the American Ceramic Society ◽

10.1111/j.1151-2916.1992.tb04247.x ◽

1992 ◽

Vol 75 (6) ◽

pp. 1685-1687 ◽

Cited By ~ 15

Author(s):

Scott A. Howard ◽

Jen-Kuan Yau ◽

Harlan U. Anderson

Keyword(s):

Phase Transition ◽

Structural Phase Transition ◽

Powder Diffraction ◽

Rietveld Method ◽

Structural Phase ◽

X Ray ◽

Transition Study

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Structural studies of α-Bi2O3by neutron powder diffraction

Powder Diffraction ◽

10.1154/1.1401200 ◽

2001 ◽

Vol 16 (4) ◽

pp. 227-230 ◽

Cited By ~ 32

Author(s):

S. A. Ivanov ◽

R. Tellgren ◽

H. Rundlo¨f ◽

V. G. Orlov

Keyword(s):

Experimental Data ◽

Phase Transition ◽

High Temperature ◽

Powder Diffraction ◽

Rietveld Method ◽

Structural Phase ◽

Magnetic Behavior ◽

Neutron Powder Diffraction ◽

Structural Studies ◽

Electron Subsystem

A detailed neutron powder diffraction study of the atomic structure of α-Bi2O3at high temperatures using the Rietveld method was performed to clarify the nature of the unusual magnetic behavior and the origin of the high temperature dielectric anomalies of α-Bi2O3in the temperature interval 300–700 K. Analysis of obtained experimental data shows that there are no evidence of a structural phase transition in α-Bi2O3between 295 and 660 K. The observed high temperature dielectric anomalies in α-Bi2O3are evidently governed by changes in the electron subsystem of the bismuth oxide.

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The incommensurately and commensurately modulated crystal structures of chromium(II) diphosphate

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768106010238 ◽

2006 ◽

Vol 62 (4) ◽

pp. 556-566 ◽

Cited By ~ 24

Author(s):

Lukáš Palatinus ◽

Michal Dušek ◽

Robert Glaum ◽

Brahim El Bali

Keyword(s):

Phase Transition ◽

High Temperature ◽

Low Temperature ◽

Structure Analysis ◽

Structure Model ◽

Ambient Conditions ◽

Coordination Polyhedra ◽

Modulated Structure ◽

Incommensurate Structure ◽

Distorted Octahedra

Chromium(II) diphosphate, Cr2P2O7, has an incommensurately modulated structure at ambient conditions with a = 7.05, b = 8.41, c = 4.63 Å, β = 108.71° and q = (−0.361, 0, 0.471). It undergoes a phase transition towards a commensurate structure with a commensurate q vector, q = (−{1\over 3}, 0, ½), at Tc = 285 K. The incommensurate structure has been solved by the charge-flipping method, which yielded both the basic positions of the atoms and the shapes of their modulation functions. The structure model for the commensurate structure was derived directly from the incommensurate structure. The structure analysis shows that the modulation leads to a change of the coordination of the Cr2+ ions from distorted octahedra in the average structure towards a sixfold coordination in the form of a more regular octahedron and a fivefold coordination in the form of a square pyramid. The fivefold and sixfold coordination polyhedra alternate along the lattice direction a with the pattern 5-6-5 5-6-5 in the commensurate structure. In the incommensurate structure this pattern is occasionally disturbed by a 5-6-5-5 motif. Both structures can be described in superspace using the same superspace group and a similar modulated structure model. The same superspace model can also be used for the low-temperature phases of other metal diphosphates with the thortveitite stucture type at high temperature. Their low-temperature structures can be obtained from the superspace model by varying the q vector and the origin in the internal dimension t 0.

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