scholarly journals Magnetic and nuclear structure of goethite (α-FeOOH): a neutron diffraction study

2014 ◽  
Vol 47 (6) ◽  
pp. 1983-1991 ◽  
Author(s):  
Eloisa Zepeda-Alarcon ◽  
Heinz Nakotte ◽  
Alessandro F. Gualtieri ◽  
Graham King ◽  
Katharine Page ◽  
...  
Keyword(s):  
Phase Transition ◽  
Neutron Diffraction ◽  
Nuclear Structure ◽  
Pair Distribution Function ◽  
Color Space ◽  
Neutron Diffraction Study ◽  
Paramagnetic State ◽  
Magnetic Clusters ◽  
Space Group ◽  
Nanocrystalline Sample

The magnetic structure of two natural samples of goethite (α-FeOOH) with varying crystallinity was analyzed at 15 and 300 K by neutron diffraction. The well crystallized sample has thePb′nmcolor space group and remained antiferromagnetic up to 300 K, with spins aligned parallel to thecaxis. The purely magnetic 100 peak, identifying this color space group, was clearly resolved. The nanocrystalline sample shows a phase transition to the paramagnetic state at a temperature below 300 K. This lowering of the Néel temperature may be explained by the interaction of magnetic clusters within particles. The nuclear structure, refined with the Rietveld and pair distribution function methods, is consistent with reports in the literature.

Neutron diffraction study of [Pt(en)2][Pt(en)2I2](ClO4)4 at 20 K: structure and evidence of a new phase transition

1996 ◽  
Vol 52 (5) ◽  
pp. 854-864 ◽  
Author(s):  
J.-F. Bardeau ◽  
A. Bulou ◽  
W. T. Klooster ◽  
T. F. Koetzle ◽  
S. Johnson ◽  
...  
Keyword(s):  
Phase Transition ◽  
Neutron Diffraction ◽  
Room Temperature ◽  
Neutron Diffraction Study ◽  
The Other ◽  
Space Group ◽  
Cell Parameters ◽  
Diffraction Peaks ◽  
Expected Values ◽  
New Phase

The structure at 20 K of fully deuterated [Pt(en)2][Pt(en)2I2](ClO4)4, where en = ethylenediamine, has been determined by neutron diffraction on a single-crystal. It is shown that the symmetry is monoclinic with cell parameters a = 16.650 (7), b = 5.760 (2), c = 14.751 (2) Å and β = 99.19 (1)°, that is, with respect to the previously reported room-temperature structures, a doubling of the c parameter is observed. The space group is C2/c and the refinements lead to an R value of 0.0374. All the bond lengths (C—C, C—N, C—D, N—D and Cl—O) and angles are consistent with the expected values and the main difference with respect to the previously reported room-temperature structures results in an ordering of the stacking of the ethylenediamines. The iodines are distributed over two sites, which gives two Pt—I distances, 2.712 (3) Å, attributed to the PtIV—I bond, and 3.048 (3) Å, attributed to PtII—I. Actually, very weak diffraction peaks that provide evidence for an additional doubling of the a and b parameters are also observed and a space group C2 is therefore proposed. This could result from a very slight ordering of the chains with respect to one another, but, due to the weakness of such signals and the large number of atoms to be considered, no reliable refinement has been obtained in C2. On the other hand, on heating the crystal the diffraction peaks with I odd greatly decrease in intensity between 150 and 160 K, which unambiguously argues for the existence of a phase transition presumably connected to an order—disorder of the ethylenediamines.

scholarly journals Über die Strukturen der CuZrF6-Modifikationen - Neutronenbeugungsuntersuchungen an den Kristallpulvern / A Neutron Diffraction Study on the Modifications of CuZrF6

1978 ◽  
Vol 33 (3) ◽  
pp. 268-274 ◽  
Author(s):  
V. Propach ◽  
F. Steffens
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Neutron Diffraction ◽  
Experimental Evidence ◽  
Neutron Diffraction Study ◽  
Three Dimensions ◽  
Space Group ◽  
Powder Samples ◽  
Jahn Teller ◽  
Jahn Teller Effect

Abstract The structures of two modifications of CuZrF6 by means of neutron diffraction on powder samples in the temperature range from 298-560 K are reported. All modifications consist of octahedra, which share corners in three dimensions and which are centered alternately by Cu2+ or Zr4+. The high temperature α-modification crystallizes in space group Fm3 (No. 202) with α = 7.939 Å. There is experimental evidence, that the CuFe-octahedra are distorted by a static Jahn-Teller-effect. The space group P1̄ (No. 2) with Z = 2 is proposed for the low-temperature γ-modification.

NEUTRON DIFFRACTION STUDY ON (Bi−Pb)2Sr2Ca2Cu3O10

1990 ◽  
Vol 04 (12) ◽  
pp. 791-794 ◽  
Author(s):  
YANG JI-LIAN ◽  
YE CHUN-TANG ◽  
ZHANG BAI-SHENG ◽  
LI JI-ZHOU ◽  
KANG JIAN ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Neutron Diffraction ◽  
Diffraction Study ◽  
Single Phase ◽  
Polycrystalline Sample ◽  
Neutron Diffraction Study ◽  
Structure Study ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray

The polycrystalline sample of (Bi–Pb)2Sr2Ca2Cu3O10 with Tc=107 K was prepared. The X-ray diffraction proved that the sample is single phase. The crystal structure study on the sample has been carried out by neutron diffraction. The result shows that its structure is tetragonal body-centre structure with space group of I4/mmm, containing a few oxygen atoms at 4e site in Bi–Pb layers.

Structural Study on Ammonia Borane for Hydrogen Storage

2009 ◽  
Vol 610-613 ◽  
pp. 425-430 ◽  
Author(s):  
W.J. James ◽  
L. Jagat ◽  
Q. Cai ◽  
W.B. Yelon ◽  
J.B. Yang
Keyword(s):  
Phase Transition ◽  
Neutron Diffraction ◽  
Hydrogen Storage ◽  
Scattering Length ◽  
Ammonia Borane ◽  
Scanning Calorimetry ◽  
Space Group ◽  
Disorder Phase Transition ◽  
Group I ◽  
Significant Difference

Ammonia borane(BH3NH3) is a promising hydrogen storage material because of its high gravimetric (19.6 wt% H2) and volumetric hydrogen density with an accompanying moderate decomposition temperature. Previously reported structures determined by using x-ray and neutron diffraction on hydrides show differences in bond lengths and atomic coordination. Here, the crystal structures of fully and half deuterated ammonia borane were investigated as a function of temperature using powder neutron diffraction. The neutron diffraction patterns show a significant difference due to large difference in the scattering length of D and H. It is evident that an order-disorder phase transition occurs around 225 K for all compounds. At low temperature, the compound crystallizes in the orthorhombic structure with space group Pnm21 and gradually transforms to a high temperature disordered tetragonal structure with space group I/4mm at about 225K. The differential scanning calorimetry studies confirm this phase transformation and also indicate that all compounds melt and decompose at above 370 K. The c cell parameter remains unchanged in the orthorhombic phase from 16 K to 200K and increases liaa nearly above 225K. As the temperature is increased, the BH3-NH3 groups start to reorient along the c axis, and the D/H atoms become disordered, leading to the tetragonal phase transition around 225K.

Sign in / Sign up

Export Citation Format

Share Document