Neutron-diffraction studies and interatomic distances in CaPr doped NdBa2Cu3O7−δ

1996 ◽  
Vol 269 (3-4) ◽  
pp. 231-241 ◽  
Author(s):  
P Lundqvist ◽  
C Tengroth ◽  
Ö Rapp ◽  
R Tellgren ◽  
Z Hegedüs
Keyword(s):  
Neutron Diffraction ◽  
Interatomic Distances

SUPPRESSION OF SPIN FLUCTUATIONS IN YMn2 BY HYDROSTATIC PRESSURE

1993 ◽  
Vol 07 (01n03) ◽  
pp. 826-829 ◽  
Author(s):  
E. BAUER ◽  
I.S. DUBENKO ◽  
E. GRATZ ◽  
R. HAUSER ◽  
A. MARKOSYAN ◽  
...  
Keyword(s):  
Hydrostatic Pressure ◽  
Neutron Diffraction ◽  
Pressure Dependence ◽  
Ambient Pressure ◽  
Paramagnetic State ◽  
Spin Fluctuations ◽  
Interatomic Distances ◽  
Effective Moment ◽  
Large Pressure ◽  
Phase Compound

The cubic Laves phase compound YMn2 exhibits a huge spontaneous volume magnetostriction at the Néel temperature (TN=100 K). The magnetic moment per Mn atom is 2.7 μB at 2 K. From polarized neutron diffraction in the paramagnetic state it has been shown that the effective moment persisting above TN is reduced (1.6 μB at 120 K). The anomalously large pressure dependence of TN (dTN/dp=–35 K/kbar) is an evidence for the sensitive role played by the Mn—Mn interatomic distances. In the paramagnetic state, the influence of spin fluctuations dominates the physical properties. We have studied the effect of pressure on the resistivity up to 16 kbar. From dρ/dT we have estimated the spinfluctuation temperature as a function of pressure. The value at ambient pressure is 15 K which is in agreement with that determined in the paramagnetic Y0.9Lu0.1Mn2 compound.

Verfeinerung der Struktur des Nitrids MgSiN2 - eine Neutronenbeugungsuntersuchung / A Refinement of the Structure of the Nitride MgSiN2 - a Study by Neutron Diffraction

1980 ◽  
Vol 35 (5) ◽  
pp. 604-606 ◽  
Author(s):  
M. Wintenberger ◽  
F. Tcheou ◽  
J. David ◽  
J. Lang
Keyword(s):  
Neutron Diffraction ◽  
Type Structure ◽  
Complete Agreement ◽  
Interatomic Distances

Abstract The tetrahedral wurtzite type structure of MgSiN2 has been refined with the help of neutron diffraction. The interatomic distances for Mg-N and Si-N are in complete agreement with the previously known values and the SiN4 tetrahedra in the structure are slightly deformed.

Interlayer interactions in M(OH)2: a neutron diffraction study of Mg(OH)2

1996 ◽  
Vol 52 (1) ◽  
pp. 82-86 ◽  
Author(s):  
L. Desgranges ◽  
G. Calvarin ◽  
G. Chevrier
Keyword(s):  
Neutron Diffraction ◽  
Temperature Dependence ◽  
Diffraction Study ◽  
Magnesium Hydroxide ◽  
Room Temperature ◽  
Interlayer Spacing ◽  
Neutron Diffraction Study ◽  
Thermal Motion ◽  
Interatomic Distances ◽  
Atom Model

Magnesium hydroxide, Mg(OH)2: Mr = 58.3, trigonal, P{\bar 3}m1, a = 3.148 (1), c = 4.779 (2) Å, V = 41.015 Å3, Dx = 2.36 g cm−3 at room temperature; a = 3.145 (1), c = 4.740 (2) Å, V = 40.602 Å3, Dx = 2.39 g cm−3 at 70 K; Z = 1, λ = 0.8330 (5) Å, μ = 1.78 cm−1, F(000) = 9.503 fm; final R = 2.42, wR = 2.40, S = 3.22 for 82 unique reflections at room temperature; R = 1.84, wR = 1.82, S = 2.54 for 81 unique reflections at 70 K. Refinements have been carried out using anisotropic thermal coefficients for all atoms. To interpret the very large thermal motion of the H atom, subsequent refinements have been carried out with an anharmonic model and with a three-site split-atom model, and results are compared with those previously reported for Ca(OH)2. By comparing the interatomic distances O...O, H...H and H...O in the interlayer spacing of Mg(OH)2 and Ca(OH)2, as well as their temperature dependence, the nature and the strength of interlayer interactions in both compounds are discussed.

Atomic orientation effects in proton stopping at low velocity

1983 ◽  
Vol 41 ◽  
pp. 708-709
Author(s):  
Kin Lam
Keyword(s):  
Polycrystalline Material ◽  
Charged Particles ◽  
Target Material ◽  
Stopping Power ◽  
Low Velocity ◽  
Electronic Density ◽  
Interatomic Distances ◽  
Frame Work ◽  
Image Position ◽  
Atomic Orientation

The energy of moving ions in solid is dependent on the electronic density as well as the atomic structural properties of the target material. These factors contribute to the observable effects in polycrystalline material using the scanning ion microscope. Here we outline a method to investigate the dependence of low velocity proton stopping on interatomic distances and orientations.The interaction of charged particles with atoms in the frame work of the Fermi gas model was proposed by Lindhard. For a system of atoms, the electronic Lindhard stopping power can be generalized to the formwhere the stopping power function is defined as

Texture measurements in Al2O3 using BEKP

1994 ◽  
Vol 52 ◽  
pp. 608-609
Author(s):  
M. D. Vaudin ◽  
J. P. Cline
Keyword(s):  
Neutron Diffraction ◽  
Rapid Method ◽  
Crystallographic Orientation ◽  
Specimen Surface ◽  
X Ray Diffraction ◽  
Anisotropic Crystal ◽  
X Ray ◽  
Verification Method ◽  
Crystal Properties ◽  
Backscattered Electron

The study of preferred crystallographic orientation (texture) in ceramics is assuming greater importance as their anisotropic crystal properties are being used to advantage in an increasing number of applications. The quantification of texture by a reliable and rapid method is required. Analysis of backscattered electron Kikuchi patterns (BEKPs) can be used to provide the crystallographic orientation of as many grains as time and resources allow. The technique is relatively slow, particularly for noncubic materials, but the data are more accurate than any comparable technique when a sufficient number of grains are analyzed. Thus, BEKP is well-suited as a verification method for data obtained in faster ways, such as x-ray or neutron diffraction. We have compared texture data obtained using BEKP, x-ray diffraction and neutron diffraction. Alumina specimens displaying differing levels of axisymmetric (0001) texture normal to the specimen surface were investigated.BEKP patterns were obtained from about a hundred grains selected at random in each specimen.

A study of oxygen and vacancy ordering in YBa2Cu3O7−x

1989 ◽  
Vol 47 ◽  
pp. 164-165
Author(s):  
Y. P. Lin ◽  
A. H. O’Reilly ◽  
J. E. Greedan ◽  
M. Post
Keyword(s):  
Electron Microscopy ◽  
Neutron Diffraction ◽  
Oxygen Content ◽  
Carbon Film ◽  
Nitrogen Atmosphere ◽  
Vacancy Ordering ◽  
Powder Samples ◽  
Vacancy Chains ◽  
Chain Ordering

In the basal planes of the orthorhombic YBa2Cu3O7-X compound with x=0.07, which has a Tc of around 90K, chains of copper-oxygen are formed along the [010] direction. Previous investigations on the variation of Tc with oxygen content have shown the existence of a plateau at Tc = 60K for x=0.3 to 0.4, suggesting the presence of a separate phase. This phase has also been identified to be orthorhombic, but with a 2x superlattice along [100] of the parent structure, and the superlattice has been attributed to the formation of alternating copper-oxygen and copper-vacancy chains. In our work, we have studied the chain ordering phenomenon by electron microscopy and neutron diffraction on samples with different oxygen contents. We report here some of our electron microscopy findings for samples with x=0.4.Powder samples of YBa2Cu3O7-X were prepared by controlled re-oxidation of previously reduced material. For electron microscopy, the sample was dry ground using a mortar and pestle in a dry nitrogen atmosphere without the use of any solvent and transferred dry onto holey carbon film for examination in a Philips CM12 microscope.

Some Aspects of Exelfs Analysis in the Electron Microscope

1980 ◽  
Vol 38 ◽  
pp. 118-119
Author(s):  
D. E. Johnson ◽  
S. Csillag
Keyword(s):  
Fine Structure ◽  
Electron Microscope ◽  
Energy Loss ◽  
Analytical Electron Microscopy ◽  
Interference Effects ◽  
Interatomic Distances ◽  
X Ray ◽  
Structure Information ◽  
Microanalytical Technique ◽  
Analytical Electron

Recently, the applications area of analytical electron microscopy has been extended to include the study of Extended Energy Loss Fine Structure (EXELFS). Modulations past an ionization edge in the energy loss spectrum (EXELFS), contain atomic fine structure information similar to Extended X-ray Absorbtion Fine Structure (EXAFS). At low momentum transfer the main contribution to these modulations comes from interference effects between the outgoing excited inner shell electron waves and electron waves backscattered from the surrounding atoms. The ability to obtain atomic fine structure information (such as interatomic distances) combined with the spatial resolution of an electron microscope is unique and makes EXELFS an important microanalytical technique.

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