Lattice parameters and orthorhombic distortion of CaMnO3

2010 ◽  
Vol 25 (1) ◽  
pp. 46-59 ◽  
Author(s):  
Wojciech Paszkowicz ◽  
Jarosław Piętosa ◽  
Scott M. Woodley ◽  
Piotr A. Dłużewski ◽  
Mirosław Kozłowski ◽  
...  
Keyword(s):  
Graphical Representation ◽  
Structure Refinement ◽  
Parent Compound ◽  
Mean Field ◽  
Study Data ◽  
Lattice Parameters ◽  
Cubic Phase ◽  
Orthorhombic Distortion ◽  
Unit Cell Size ◽  
Structural Distortions

CaMnO3 is a parent compound for numerous multicomponent manganese perovskite oxides. Its crystallographic data are of primary importance in the science and technology of functional CaMnO3-based materials. In the present study, data were collected for a CaMnO3 sample at 302 K. The crystal structure refinement yields accurate absolute values of lattice parameters, a=5.281 59(4) Å, b=7.457 30(4) Å, and c=5.267 48(4) Å, leading to orthorhombic distortion of (c/a, √2c/b)=(0.997 33,0.998 95). The orthorhombic distortion of the CaMnO3 structure is discussed on the basis of comparison of our unit-cell size with data already published. At a graphical representation of the distortion, it is observed that there is a considerable scatter of the distortion values among the literature data but, interestingly, a considerable fraction of experimental results (including the present one) for stoichiometric samples are grouped around the distortion (c/a, √2c/b)=(0.9973,0.9990), which lies close to a maximum in the extent of orthorhombicity. The influence of off-stoichiometry on the orthorhombic distortion is discussed on the basis of available experimental data. Simulations, employing a mean-field approach for low temperatures, predict an increase in cell volume and structural distortions with the concentration of oxygen vacancies when the additional electrons are localized on the manganese. A simple model of delocalization produced the opposite effect, which is expected to combine with lattice vibrations to recover the cubic phase at high temperatures.

Nature of Non-magnetic Strongly-Correlated State in Plutonium

2006 ◽  
Vol 986 ◽  
Author(s):  
Leniod Purovskii ◽  
Alexander Shick ◽  
Ladislav Havela ◽  
Mikhail Katsnelson ◽  
Alexander Lichtenstein
Keyword(s):  
Field Theory ◽  
Density Functional ◽  
Local Density ◽  
Mean Field Theory ◽  
Mean Field ◽  
Dynamical Mean Field Theory ◽  
Cubic Phase ◽  
Face Centered Cubic ◽  
Strongly Correlated ◽  
Starting Point

AbstractLocal density approximation for the electronic structure calculations has been highly successful for non-correlated systems. The LDA scheme quite often failed for strongly correlated materials containing transition metals and rare-earth elements with complicated charge, spin and orbital ordering. Dynamical mean field theory in combination with the first-principle scheme (LDA+DMFT) can be a starting point to go beyond static density functional approximation and include effects of charge, spin and orbital fluctuations. Ab-initio relativistic dynamical mean-field theory is applied to resolve the long-standing controversy between theory and experiment in the “simple” face-centered cubic phase of plutonium called δ-Pu. In agreement with experiment, neither static nor dynamical magnetic moments are predicted. In addition, the quasiparticle density of states reproduces not only the peak close to the Fermi level, which explains the large coefficient of electronic specific heat, but also main 5f features observed in photoelectron spectroscopy.

Approximants to the icosahedral and decagonal phases in the Al–Cu–Cr system

1991 ◽  
Vol 6 (8) ◽  
pp. 1641-1649 ◽  
Author(s):  
S. Ebalard ◽  
F. Spaepen
Keyword(s):  
Electron Diffraction ◽  
Icosahedral Phase ◽  
Lattice Parameters ◽  
Cubic Phase ◽  
Decagonal Phase ◽  
Bcc Lattice ◽  
Selected Area Electron Diffraction ◽  
Phase Ordering ◽  
Cr System

A 1/1-type approximant to the AlCuCr icosahedral phase and approximants to a decagonal phase have been found in an as-cast Al65Cu20Cr15 ingot. Selected area electron diffraction indicates that the 1/1-type approximant consists of Mackay icosahedra arranged on a bcc lattice, similar to the α-AlMnSi cubic phase. Ordering of the glue atoms produces a base-centered orthorhombic superstructure, making the overall structure monoclinic P2/m, with lattice parameters a = 12.6 Å, c = 17.92 Å, and α = 90°.

Assessing the awareness of the agile manufacturing for organizational change in Indian small manufacturing firms

2016 ◽  
Vol 29 (5) ◽  
pp. 713-731 ◽  
Author(s):  
Varun Kumar ◽  
Ganesh Babu ◽  
Saravanan Muthusamy
Keyword(s):  
Graphical Representation ◽  
Final Analysis ◽  
Agile Manufacturing ◽  
Study Data ◽  
Global Market ◽  
Manufacturing Firms ◽  
Content Type ◽  
Agile Practices ◽  
Large Sector ◽  
Representation Method

Purpose Agile manufacturing (AM) has the new scenario in the business system and it is widely seen as a “New Revolution” in the manufacturing firms. AM, which continuously focusses on the adoption of new methodologies and quickly respond to the customer expectation. For this reason, many of the research studies are focussed on the AM environment and this system is mainly followed in large sector only and most of the small- and medium-sized enterprises (SMEs) are not aware of it. Especially in the developing countries which are still lagging behind in the implementation of AM. Considering the above reason, the purpose of this paper is to assess the awareness of AM in Indian SMEs. Design/methodology/approach By means of researching many literature reviews and empirical data collected by using a self-administrated instrument distributed to the selected Indian SMEs and the awareness about the AM was investigated. The authors have selected 100 SMEs in Indian service sectors and sent the data sheets through by e-mail and also by directly visiting the company and collected the information. A total of 68 useable survey data’s were identified from the final analysis. The study data sample consists of a group of selected Indian SMEs, from different industries including the pump and foundry industries. The collected data were analyzed using the graphical representation method and by the statistical analysis. Findings The analysis revealed the significance and usage of AM in the Indian SMEs. The results also suggested that the Indian SMEs are well aware of the AM system, through more efforts need to be focussed on implementing this system properly and effectively to improve these standards. By the use of agile models and frameworks in small and medium sized enterprises (SMEs), would result in cost-effectiveness in their quality and services and can be continuously improving the ongoing agile practices. Research limitations/implications Indian SMEs managers seem to be stronger familiar with the agile concepts and practices and they believe that agile environment would guaranteeing in their services and high-quality products. Therefore, SMEs should concentrate and invest in agile practices that would help them to improve their competitiveness in the global market. Further, Indian SMEs managers and practitioners would concentrate more about this maintenance of standards and with this dynamic approach it takes toward the agile environment to meet the future challenges. Practical implications The data collected and the results provided in this paper will help in understanding, the awareness about the AM environment in Indian SMEs. Also, suggest some additional improvements in the knowledge of agile to the managers and practitioners in the Indian SMEs, which could enhance the level of agile implementation. Originality/value The assessment of agile awareness in Indian SMEs, along with the concepts of understanding the AM environment, has been explained in the literature on AM in the Indian SMEs.

Crystallographic & Electrical Properties of Pr Substituted Gd-123 Nanometre Sized High Temperature Superconductors

2013 ◽  
Vol 678 ◽  
pp. 172-176
Author(s):  
Vishnu R. Huse ◽  
Vishwanath D. Mote ◽  
Yadav Purushotham ◽  
Sudesh K. Dhar ◽  
Suresh S. Shah ◽  
...  
Keyword(s):  
Oxygen Content ◽  
Hole Concentration ◽  
High Temperature Superconductors ◽  
Resistivity Measurement ◽  
Content Volume ◽  
Unit Cell ◽  
Lattice Parameters ◽  
Average Charge ◽  
Orthorhombic Distortion ◽  
Ceramic Route

The samples of Gd1-xPrxBa2Cu3O7-δ with compositions x = 0.0, 0.1 & 0.3 were prepared by ceramic route. The XRD study of all samples is carried out. The XRD studies of the samples prepared by ceramic route show GdPr-123 system have an orthorhombic pervoskite structure. The lattice parameters, oxygen content, volume of unit cell, orthorhombic distortion, hole concentration in CuO2 plane and charge on Cu-O plane were evaluated using XRD data. It is found that the lattice parameters, volume of unit cell increase while oxygen content orthorhombic distortion, hole concentration (Psh) and average charge (p) decrease as doping percentage of Pr increases. The resistivity measurement shows the transition temperature decreases while transition width increases with increasing Pr concentration. The suppression of superconductivity may be due to reduction in hole concentration or magnetic pair breaking. We report such qualitative results of Pr substituted Gd-123 in this paper quantitatively.

scholarly journals Ultrafast structural dynamics of the orthorhombic distortion in the Fe-pnictide parent compound BaFe2As2

2016 ◽  
Vol 3 (2) ◽  
pp. 023611 ◽  
Author(s):  
L. Rettig ◽  
S. O. Mariager ◽  
A. Ferrer ◽  
S. Grübel ◽  
J. A. Johnson ◽  
...  
Keyword(s):  
Structural Dynamics ◽  
Parent Compound ◽  
Orthorhombic Distortion

Structures des phases paraélectrique et ferroélectrique de Pb2KNb5O15

1999 ◽  
Vol 55 (4) ◽  
pp. 459-466 ◽  
Author(s):  
Philippe Sciau ◽  
Gilbert Calvarin ◽  
Jean Ravez
Keyword(s):  
Lattice Distortion ◽  
Paraelectric Phase ◽  
Rietveld Method ◽  
Lattice Parameters ◽  
Powder Diffraction Data ◽  
Orthorhombic Distortion ◽  
Special Position ◽  
Space Group ◽  
X Ray ◽  
Local Polarization

The paraelectric and the ferroelectric/ferroelastic structures of Pb2KNb5O15 have been refined by the Rietveld method from neutron and X-ray powder diffraction data. The paraelectric phase is tetragonal (space group P4/mbm) with lattice parameters a t = 12.646 (1) and c t = 3.9551 (2) Å at 790 K. The Pb- and K-atom distribution has been determined. It was established that the Pb atoms situated on the 15-coordinate sites are not on the special position (2mm) but are distributed over two disordered positions as in the tetragonal phase of Pb2KTa5O15. The ferroelectric/ferroelastic phase is orthorhombic. The space group of the average structure is Cm2m and the lattice parameters are a o = 17.779 (2), b o = 18.015 (2), c o = 3.9209 (4) Å at 294 K and a o = 17.756 (1), b o = 18.019 (1), c o = 3.9141 (2) Å at 81 K. It is isostructural with the average ferroelectric/ferroelastic structure of PbNb2O6. The orthorhombic distortion is of the same order but the Curie temperature is lowered by the substitution 2K+–Pb2+. The structures of PbNb2O6, PbTa2O6, Pb2KNb5O15 and Pb2KTa5O15 are compared. The ferroelectric polarization of the niobates is due to both the Pb off-site position and the Nb displacements, which induce a distortion of the oxygen lattice. In PbTa2O6, the oxygen-lattice distortion is very weak. The polarization seems to be due only to the Pb atom. In the tantalates the substitution 2K+–Pb2+ should weaken the correlations between the Pb atoms and consequently suppress the ferroelectric transition. Only a local polarization should take place; this might be the origin of the dielectric relaxation observed in this compound.

Phase transformation kinetic study and microstructure characterization of ball-milledm-ZrO2–10 mol%a-TiO2by Rietveld method

2003 ◽  
Vol 36 (2) ◽  
pp. 260-268 ◽  
Author(s):  
H. Dutta ◽  
S. K. Manik ◽  
S. K. Pradhan
Keyword(s):  
Particle Size ◽  
Rietveld Method ◽  
Structure Refinement ◽  
Molar Fraction ◽  
Rietveld Analysis ◽  
High Energy ◽  
Transformation Kinetic ◽  
Cubic Phase ◽  
Milled Sample ◽  
Energy Ball

High-energy ball milling of a monoclinic ZrO2–10 mol% anatase TiO2mixture results in the formation of a nanocrystalline cubic ZrO2polymorphic phase with equimolar fraction of the starting materials. The cubic phase is presumed to have formed from them-ZrO2solid solution based on the (001) plane of them-ZrO2phase. In the course of milling, the most dense (111) plane of the cubic lattice became parallel to the most dense (\bar{1}11) plane of the monoclinic lattice due to an orientation effect. Annealing of a 12 h milled sample at 773, 873 and 973 K for 1 h results in almost complete transformation of them-ZrO2to thec-ZrO2phase. At 1273 K annealing temperature (1 h), the nanocrystalline sample decomposed into individual starting phases. This suggests that the cubic phase is a metastable one and its stability depends on particle size as well as the working temperature. Formation of the cubic phase at such a low temperature using anatase TiO2as a phase stabilizer has not been reported previously. The microstructures of the unmilled, all the ball-milled and the annealed samples have been characterized by employing Rietveld's X-ray powder structure refinement methodology. The particle size, root mean square (r.m.s.) lattice strain, lattice parameters, molar fraction,etc., of individual phases have been estimated from Rietveld analysis and are utilized to interpret the results.

scholarly journals Magnetic Susceptibility of Quasi-two-dimensional Cuprate Antiferromagnets

2013 ◽  
Vol 37 (1) ◽  
pp. 19-32
Author(s):  
Milica S. Rutonjski ◽  
Milan R. Pantić ◽  
Slobodan M. Radošević ◽  
Milica V. Pavkov-Hrvojević
Keyword(s):  
Magnetic Susceptibility ◽  
Low Temperatures ◽  
Parent Compound ◽  
Random Phase ◽  
Mean Field ◽  
Three Dimensional ◽  
Quantum Spin ◽  
Spin Fluctuations ◽  
High Tc ◽  
Lsw Theory

Abstract Parallel magnetic susceptibility temperature dependence of the high-TC superconducting parent compound La2CuO4 is calculated in both antiferromagnetic (AFM) and paramagnetic phase. By making use of the quantum Heisenberg three-dimensional AFM model including the in-plane spin anisotropy, the calculation is performed within the framework of three different theories: Green’s function theory in random-phase approximation (RPA), linear spinwave (LSW) theory and mean-field (MF) theory. The results suggest that at low temperatures quantum spin fluctuations play an important role, while at the temperatures above the critical one short-range correlations have a great impact on the behavior of the system. This leads to the discrepancy between RPA and MF results, since the later neglects the above phenomena. Further, LSW theory expectedly agrees with RPA results only at low temperatures where the magnon interactions are negligible. Comparison to the theoretical and experimental results quoted in literature confirms that RPA method presents the most appropriate method among the applied ones, suggesting that this approach is satisfactory in the case of the parallel magnetic susceptibility, while in order to reproduce the transversal one, spin-orbit coupling must be included.

scholarly journals Understanding nanoscale structural distortions in Pb(Zr0.2Ti0.8)O3 by utilizing X-ray nanodiffraction and clustering algorithm analysis

2021 ◽  
Vol 28 (1) ◽  
pp. 207-213
Author(s):  
Joyce Christiansen-Salameh ◽  
Morris Yang ◽  
Geoffrey Rippy ◽  
Jianheng Li ◽  
Zhonghou Cai ◽  
...  
Keyword(s):  
Phase Separation ◽  
Clustering Algorithm ◽  
Three Dimensional ◽  
Local Strain ◽  
Lattice Parameters ◽  
Algorithm Analysis ◽  
Nondestructive Technique ◽  
Heterogeneous Distribution ◽  
X Ray ◽  
Structural Distortions

Hard X-ray nanodiffraction provides a unique nondestructive technique to quantify local strain and structural inhomogeneities at nanometer length scales. However, sample mosaicity and phase separation can result in a complex diffraction pattern that can make it challenging to quantify nanoscale structural distortions. In this work, a k-means clustering algorithm was utilized to identify local maxima of intensity by partitioning diffraction data in a three-dimensional feature space of detector coordinates and intensity. This technique has been applied to X-ray nanodiffraction measurements of a patterned ferroelectric PbZr0.2Ti0.8O3 sample. The analysis reveals the presence of two phases in the sample with different lattice parameters. A highly heterogeneous distribution of lattice parameters with a variation of 0.02 Å was also observed within one ferroelectric domain. This approach provides a nanoscale survey of subtle structural distortions as well as phase separation in ferroelectric domains in a patterned sample.

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