scholarly journals Polar nematic state in an iron-based superconductor LaFeAsO1-xHx

2020 ◽  
Author(s):  
Sachiko Maki ◽  
Jun-ichi Yamaura ◽  
Soshi Iimura ◽  
Hitoshi Abe ◽  
Hajime Sagayama ◽  
...  
Keyword(s):  
Structural Transition ◽  
Parent Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Local Structures ◽  
Nematic State ◽  
Mechanism Of Superconductivity ◽  
Iron Based ◽  
Carrier Doping ◽  
X Ray Absorption

Abstract High critical temperature (Tc) superconductivity is generally considered to result from a fluctuation-mediated Cooper-pairing derived from a parent phase. The question of what type of fluctuation forms in materials thus plays a key role in understanding the mechanism of superconductivity. The iron-based superconductor LaFeAsO1-xHx possesses bipartite magnetic parent phases with centrosymmetric (x ~ 0) and non-centrosymmetric (x ~ 0.5) structures. The latter is an intriguing polar-metal phase induced by temperature and carrier doping. Here, we investigate average and local structures of LaFeAsO1-xHx using X-ray diffraction and extended X-ray absorption fine-structure measurements. We found lattice C4 symmetry breaking far above the structural transition temperature, and the signature of a tiny split in As–Fe bond distances with broken spatial inversion symmetry in a wide temperature/doping range. The former reveals a nematic state, and the latter highlights a fluctuated state of polar structure which can be appropriately called polar nematic state.

scholarly journals Defect Persuade Paramagnetic Properties of Nickel Doped ZnS Nanocrystals and Identification of Structural, Optical, Local Atomic Structure

2021 ◽  
Author(s):  
Soumendra Ghorai ◽  
Dibyendu Bhattacharyya ◽  
Nirmalendu Patra ◽  
Shambhu Nath Jha ◽  
Anup K Ghosh
Keyword(s):  
Electron Microscopy ◽  
Atomic Structure ◽  
Defect Formation ◽  
Local Atomic Structure ◽  
X Ray Diffraction ◽  
Edge Structure ◽  
X Ray ◽  
Local Structures ◽  
Transmission Electron ◽  
X Ray Absorption

Abstract We have methodically investigated the structural, spectroscopic, local atomic structure and magnetic properties of aquatic Zn1-xNixS (0≤x≤0.04) nanocrystals. The structural study of synthesized samples are observed by X-ray diffraction datas with Rietveld refinement. Proficient decrease of lattice parameters and inter-planar spacing are determined on Zn1-xNixS nanocrystals. The nanocrystalline microstructure is identified by high resolution transmission electron microscopy. The sphalerite morphology of doped samples are observed by scanning electron microscopy. Shrinkage of energy band gap is observed for doped nanocrystals. Defect formation due to doping of Ni ion is observed by photoluminescence spectroscopy with cyan color emission. X-ray absorption spectroscopy is employed for identification of local structures surrounding of Zn and Ni sites of Zn1-xNixS nanocrystals. Extended X-ray absorption fine structure investigation evidenced the existence of nanocluster within the lattice of Zn1-xNixS nanocrystals. X-ray absorption near edge structure studies confirmed incorporation of Ni2+ in ZnS lattice of Zn1-xNixS nanocrystals. The single pre-edge feature at Ni K-edge is not relying on concentration of Ni dopant in Zn1-xNixS nanocrystals. The presence of interstitial Ni is identified by significant fraction of Ni-Ni scattering paths on doped samples. Zn1-xNixS nanocrystals exhibit defect persuaded paramagnetism at room temperature.

Local atomic structure in tetragonal pure ZrO2nanopowders

2010 ◽  
Vol 43 (2) ◽  
pp. 227-236 ◽  
Author(s):  
Leandro M. Acuña ◽  
Diego G. Lamas ◽  
Rodolfo O. Fuentes ◽  
Ismael O. Fábregas ◽  
Márcia C. A. Fantini ◽  
...  
Keyword(s):  
Tetragonal Phase ◽  
Local Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Atomic Structures ◽  
Crystallite Sizes ◽  
Exafs Study ◽  
The Difference ◽  
X Ray Absorption ◽  
Good Agreement

The local atomic structures around the Zr atom of pure (undoped) ZrO2nanopowders with different average crystallite sizes, ranging from 7 to 40 nm, have been investigated. The nanopowders were synthesized by different wet-chemical routes, but all exhibit the high-temperature tetragonal phase stabilized at room temperature, as established by synchrotron radiation X-ray diffraction. The extended X-ray absorption fine structure (EXAFS) technique was applied to analyze the local structure around the Zr atoms. Several authors have studied this system using the EXAFS technique without obtaining a good agreement between crystallographic and EXAFS data. In this work, it is shown that the local structure of ZrO2nanopowders can be described by a model consisting of two oxygen subshells (4 + 4 atoms) with different Zr—O distances, in agreement with those independently determined by X-ray diffraction. However, the EXAFS study shows that the second oxygen subshell exhibits a Debye–Waller (DW) parameter much higher than that of the first oxygen subshell, a result that cannot be explained by the crystallographic model accepted for the tetragonal phase of zirconia-based materials. However, as proposed by other authors, the difference in the DW parameters between the two oxygen subshells around the Zr atoms can be explained by the existence of oxygen displacements perpendicular to thezdirection; these mainly affect the second oxygen subshell because of the directional character of the EXAFS DW parameter, in contradiction to the crystallographic value. It is also established that this model is similar to another model having three oxygen subshells, with a 4 + 2 + 2 distribution of atoms, with only one DW parameter for all oxygen subshells. Both models are in good agreement with the crystal structure determined by X-ray diffraction experiments.

Structural transition in epitaxic Co/Cr multilayers as studied by X-ray-absorption spectroscopy

1999 ◽  
Vol 6 (3) ◽  
pp. 746-748 ◽  
Author(s):  
W. F. Pong ◽  
Y. C. Liou ◽  
K. H. Chang ◽  
M.-H. Tsai ◽  
H. H. Hsieh ◽  
...  
Keyword(s):  
Absorption Spectroscopy ◽  
Structural Transition ◽  
X Ray ◽  
X Ray Absorption

The Relative Merits of Oxides of Hafnium, Cerium and Thorium as Surrogates for Plutonium Oxide in Calcium Phosphate Ceramics

2009 ◽  
Vol 1193 ◽  
Author(s):  
B. L. Metcalfe ◽  
S. K. Fong ◽  
L. A. Gerrard ◽  
I. W. Donald ◽  
E. S. Welch ◽  
...  
Keyword(s):  
Calcium Phosphate ◽  
Calcination Temperature ◽  
Cerium Oxide ◽  
Absorption Spectroscopy ◽  
Hafnium Oxide ◽  
Intermediate Level ◽  
X Ray Diffraction ◽  
X Ray ◽  
X Ray Absorption ◽  
Additional Phase

AbstractThe choice of surrogate for plutonium oxide for use during the initial stages of research into the immobilization of intermediate level pyrochemical wastes containing plutonium andamericium oxides in a calcium phosphate host has been investigated by powder X-ray diffraction and X-ray absorption spectroscopy. Two non-radioactive surrogates, hafnium oxide and cerium oxide, together with radioactive thorium oxide were compared. Similarities in behaviour were observed for all three surrogates when calcined at the lowest temperature, 750°C but differences became more pronounced as the calcination temperature was increased to 950°C. Although some reaction occurred between all the surrogates and the host to form a substituted whitlockite phase, increasing the temperature led to a significant increase in the cerium reaction and the formation of an additional phase, monazite. Additionally it was observed that the cerium became increasingly trivalent at higher temperatures.

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