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High-resolution Neutron Powder Diffraction (high-resolution + neutron_powder_diffraction)

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Chemistry100%

Selected Abstracts

Order,disorder transition in monoclinic sulfur: a precise structural study by high-resolution neutron powder diffraction

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2006
W. I. F. David
High-resolution neutron powder diffraction has been used in order to characterize the order,disorder transition in monoclinic cyclo-octasulphur. Rapid data collection and the novel use of geometrically constrained refinements has enabled a direct and precise determination of the order parameter, based on molecular site occupancies, to be made. The transition is critical and continuous; with a transition temperature, Tc = 198.4,(3),K, and a critical exponent, , = 0.28,(3), which is indicative of three-dimensional ordering. Difficulties encountered as a consequence of the low thermal conductivity of the sample are discussed. [source]

Thermal expansion and atomic displacement parameters of cubic KMgF3 perovskite determined by high-resolution neutron powder diffraction

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2002
I. G. Wood
The structure of KMgF3 has been determined by high-resolution neutron powder diffraction at 4.2,K, room temperature and at 10,K intervals from 373,K to 1223,K. The material remains cubic at all temperatures. The average volumetric coefficient of thermal expansion in the range 373,1223,K was found to be 7.11,(3) × 10,5,K,1. For temperatures between 4.2 and 1223,K, a second-order Grüneisen approximation to the zero-pressure equation of state, with the internal energy calculated via a Debye model, was found to fit well, with the following parameters: ,D = 536,(9),K, Vo = 62.876,(6),Ĺ3, = 6.5,(1) and (VoKo/,,) = 3.40,(2) × 10,18,J, where ,D is the Debye temperature, Vo is the volume at T = 0, is the first derivative with respect to pressure of the incompressibility (Ko) and ,, is a Grüneisen parameter. The atomic displacement parameters were found to increase smoothly with T and could be fitted using Debye models with ,D in the range 305,581,K. At 1223,K, the displacement of the F ions was found to be much less anisotropic than that in NaMgF3 at this temperature. [source]

Order,disorder transition in monoclinic sulfur: a precise structural study by high-resolution neutron powder diffraction.

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2007
Corrigendum
Revised lattice parameters for Table 1 of the paper by David et al. (2006), Acta Cryst. B62, 953959, are given. [source]

Order,disorder transition in monoclinic sulfur: a precise structural study by high-resolution neutron powder diffraction

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2006
W. I. F. David
High-resolution neutron powder diffraction has been used in order to characterize the order,disorder transition in monoclinic cyclo-octasulphur. Rapid data collection and the novel use of geometrically constrained refinements has enabled a direct and precise determination of the order parameter, based on molecular site occupancies, to be made. The transition is critical and continuous; with a transition temperature, Tc = 198.4,(3),K, and a critical exponent, , = 0.28,(3), which is indicative of three-dimensional ordering. Difficulties encountered as a consequence of the low thermal conductivity of the sample are discussed. [source]

Structure of Ce2RhIn8: an example of complementary use of high-resolution neutron powder diffraction and reciprocal-space mapping to study complex materials

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2006
J. L. Sarrao
The room-temperature crystal structure of the heavy fermion antiferromagnet Ce2RhIn8, dicerium rhodium octaindide, has been studied by a combination of high-resolution synchrotron X-ray reciprocal-space mapping of single crystals and high-resolution time-of-flight neutron powder diffraction. The structure is disordered, exhibiting a complex interplay of non-periodic, partially correlated planar defects, coexistence and segregation of polytypic phases (induced by periodic planar `defects'), mosaicity (i.e. domain misalignment) and non-uniform strain. These effects evolve as a function of temperature in a complicated way, but they remain down to low temperatures. The room-temperature diffraction data are best represented by a complex mixture of two polytypic phases, which are affected by non-periodic, partially correlated planar defects, differ slightly in their tetragonal structures, and exhibit different mosaicities and strain values. Therefore, Ce2RhIn8 approaches the paracrystalline state, rather than the classic crystalline state and thus several of the concepts of conventional single-crystal crystallography are inapplicable. The structural results are discussed in the context of the role of disorder in the heavy-fermion state and in the interplay between superconductivity and magnetism. [source]