XRD Based Methods of Investigation the Order - Disorder Transformation in the Spinel Structure - A Comparative Study

2013 ◽  
Vol 203-204 ◽  
pp. 129-132 ◽  
Author(s):  
Jacek Podwórny
Keyword(s):  
Spinel Structure ◽  
Cation Sublattice ◽  
Measured Temperature ◽  
Temperature Dependent ◽  
Ionic Radii ◽  
Cation Site ◽  
Cell Edge ◽  
Advantages And Disadvantages ◽  
Positional Parameter ◽  
Atomic Scattering

Three synthetic and stoichiometric 2:3 type spinels (Fd3m symmetry): MgAl2O4, MgFe2O4, NiAl2O4 with a different initial structural order in cation sublattice were investigated. Investigations by means of high temperature XRPD method at temperatures ranging from 25°C to 1100°C were carried out. Diffraction patterns at each temperature in isothermal conditions were measured. For each tested spinel changes in several temperature-dependent parameters were measured: oxygen positional parameter u(T), cell edge a0(T), cation site occupancies Occ(T) in tetrahedral and octahedral positions and a cation-anion distance in tetrahedral TO(T) and octahedral MO(T) positions. Temperatures of initial order-disorder transformation were determined on the basis of the course of these dependences. Basing on changes of the cell edge a0(T), the values of thermal expansion coefficient and for spinel before and after the beginning of order-disorder transformation, respectively, were calculated. The values of measured temperature-dependent parameters were used to calculate the degree of inversion x in the spinel structure defined as the number of 3+ cations in tetrahedral sites. In each case two methods of calculating the degree of inversion from experimental data were applied. The first method involved observing the changes in sites occupancy in the cation sublattice versus temperature, which resulted in a change of diffraction lines intensities. The second method was based on observing the changes in cation-anion distances in tetra- and octahedral coordination versus temperature. The results obtained by both methods were compared, discussed and advantages and disadvantages of each of them were presented. It was shown that when atomic scattering factors of cations 2+ and 3+ in the spinel structure differ significantly, the most precise method is the one based on changes in sites occupancies versus temperature. The method based on calculation of changes in cation-anion distances is recommended when atomic scattering factors of cations differ slightly but oxygen positional parameter and cation-anion distances changes significantly during order-disorder transformation like in normal spinel structure when effective ionic radii of 2+ and 3+ cations differ significantly.

Temperature dependence of the inversion degree in three-cation spinel solid solutions: experimental evaluation by XRD

2015 ◽  
Vol 30 (S1) ◽  
pp. S104-S110 ◽  
Author(s):  
Jacek Podwórny
Keyword(s):  
Phase Transformation ◽  
Solid Solutions ◽  
Spinel Structure ◽  
Diffraction Method ◽  
Measured Temperature ◽  
Temperature Dependent ◽  
Cation Site ◽  
Advantages And Disadvantages ◽  
Octahedral Sites ◽  
Spinel Solid Solutions

The method of degree of inversion calculation presented in the present paper was based on the determination of several temperature-dependent parameters such as: oxygen positional parameter, lattice parameter, cation site occupancies, and a cation–anion distance in tetrahedral and octahedral sites. The theoretical basis of the method as well as the required derivation of formulae and the conditions of its application has been described.The values of the measured temperature-dependent parameters were used to calculate the degree of inversion vs. temperature in the spinel structure. Initial temperatures of the order–disorder transformation were determined. The described method of investigating the order–disorder phase transformation based on three examples of spinel solid solutions: Mg(Al0.5Fe0.5)2O4, (Mg0.75Ni0.25)Al2O4, and (Mg0.75Co0.25)Al2O4 has been presented. Investigations by means of the high-temperature X-ray diffraction method at temperatures ranging from 25 to 1100 °C were carried out. It has been shown that using the present method, it is possible to determine the distribution of each cation in tetrahedral and octahedral sites at each temperature. In consequence, the unidirectional order–disorder phase transformation as well the bidirectional transformation in the spinel structure can be investigated. The advantages and disadvantages of the method have been discussed and its uncertainties presented.

Transport Properties and Conduction Band Offset of n-ZnO/n-6H-SiC Heterostructures

2006 ◽  
Vol 957 ◽  
Author(s):  
Yahya Alivov ◽  
Xiao Bo ◽  
Fan Qian ◽  
Daniel Johnstone ◽  
Cole Litton ◽  
...  
Keyword(s):  
Conduction Band ◽  
Deep Level Transient Spectroscopy ◽  
Deep Level ◽  
Band Offset ◽  
Measured Temperature ◽  
Temperature Dependent ◽  
Conduction Band Offset ◽  
Current Voltage ◽  
Current Voltage Characteristics ◽  
Transient Spectroscopy

ABSTRACTThe conduction band offset of n-ZnO/n-6H-SiC heterostructures fabricated by rf-sputtered ZnO on commercial n-type 6H-SiC substrates has been measured. Temperature dependent current-voltage characteristics, photocapacitance, and deep level transient spectroscopy measurements showed the conduction band offsets to be 1.25 eV, 1.1 eV, and 1.22 eV, respectively.

Ruderman-Kittel-Kasuya-Yosida Magnetic Interactions in Chemically Synthesized Zn-Fe-AlO Nanocrystallites

2013 ◽  
Vol 748 ◽  
pp. 65-69
Author(s):  
Asif Mahmood ◽  
Yousef Al-Zeghayer
Keyword(s):  
Magnetic Interactions ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
Ionic Radii ◽  
X Ray ◽  
Wurtzite Crystal Structure ◽  
Auto Combustion ◽  
Phase Pure ◽  
Combustion Technique ◽  
Lower Resistivity

Chemically derived auto-combustion technique is employed to synthesize the Zn0.95-xFe0.05AlxO (x=00.07 in 0.02 increment) nanocrystallites. X-ray diffraction studies of all compositions revealed the phase pure wurtzite crystal structure with space group P63mc. The lattice parameters and crystallite size is changed with doping of Al attributed to the diversity in size of ionic radii. Temperature dependent electrical resistivity shows a decreased trend with the rise of temperature, confirming the semiconductor nature of compositions. The lower resistivity and enhanced saturation magnetization values in Al doped compositions correspond to the increase in density of carriers. Carriers mediated RKKY interactions are found to observe for enhancement of magnetization.

scholarly journals Selective Nitration of Chlorobenzene by NO2 in the Alkali Zeolite NaZSM-5

2013 ◽  
Vol 2013 ◽  
pp. 1-5
Author(s):  
Scott J. Kirkby
Keyword(s):  
Gas Phase ◽  
Room Temperature ◽  
Temperature Dependent ◽  
Reaction Conditions ◽  
Cation Site ◽  
Zeolite Lattice ◽  
Reaction Proceeds ◽  
Ft Ir ◽  
Electron Donation

Chlorobenzene was reacted with NO2, in the initially acid-free zeolite NaZSM-5, to yield para-chloronitrobenzene exclusively. The precursors were loaded sequentially into self-supporting pellets of the zeolite, contained within a stainless steel cell, from the gas phase. The reaction proceeds spontaneously at room temperature. It is, however, very temperature dependent and effectively ceases at zero degrees Celsius. The reaction was monitored in situ using FT-IR. The active nitrating agent is formed from the partial electron donation by the NO2 to the Na+ cations present in the zeolite lattice. Under the reaction conditions, chlorobenzene is not readily mobile through the pore system; thus, only the molecules adsorbed near a cation site react to form para-chloronitrobenzene.

FEM-Based Simulation of Temperature in Speed Stroke Grinding with 3D Transient Moving Heat Sources

2011 ◽  
Vol 223 ◽  
pp. 733-742 ◽  
Author(s):  
Barbara Linke ◽  
Michael Duscha ◽  
Anh Tuan Vu ◽  
Fritz Klocke
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Material Removal ◽  
Structural Changes ◽  
Numerical Technique ◽  
Temperature Fields ◽  
Fe Model ◽  
Measured Temperature ◽  
Temperature Dependent ◽  
Removal Rates

The grinding process is one of the most important finishing processes to obtain high surface quality. Nowadays, grinding is also considered as a high performance process with high material removal rates. Nevertheless, to avoid thermally-induced structural changes poses a major challenge for this manufacturing technology. Until now, the Finite Element Method (FEM) has been widely applied as a proper numerical technique to predict workpiece properties in machining processes. However, actual models in grinding are limited to conventional grinding processes with simple workpiece profiles and low table speeds. In this paper, finite element simulations are expanded to 3-dimensional (3D) models with temperature-dependent material properties and heat source profiles derived from experimental results, i.e. tangential forces. Both temperature simulation and measurement were conducted for deep grinding, pendulum grinding and speed stroke grinding in the table speed range of vw= 12 m/min to 180 m/min and specific material removal rates of Q’w= 40 mm³/mms. Overall, the simulation results show a good agreement with the measured temperature and surface integrity after grinding. This research indicates that a 3D FE model with temperature dependent material properties can predict realistic temperature fields in speed stroke grinding. Therefore, the experiment and measurement costs and time can be reduced by FEM simulation.

3.3μm Pyrometry In Single Sided Rta From 400–700°C Using In-Situ Measurement Of Reflection And Transmission

1997 ◽  
Vol 470 ◽  
Author(s):  
D. L. Marcy ◽  
S. Chial ◽  
M. Beneš ◽  
J. C. Sturm
Keyword(s):  
Temperature Measurement ◽  
A Priori ◽  
Measured Temperature ◽  
Temperature Dependent ◽  
Reflection And Transmission ◽  
Accurate Temperature ◽  
Heavily Doped ◽  
Accurate Temperature Measurement ◽  
Initial Results

ABSTRACTPyrometry of silicon wafers under 700°C at wavelengths over 1μm is difficult because lightly doped wafers become partially transparent. In this work, a modified commercial RTCVD reactor with 8” wafer capability was used to study the temperature measurement of Si wafers over the range of 400–700°C using top and bottom pyrometric detectors. We present initial results on measurements of both reflection and transmission in-silu to determine emissivity at 3.3μm. For heavily doped wafers emissivity was independent of temperature and the measured temperature by pyrometry agreed well with that measured by thermocouple for 400–700°C. For lightly doped wafers, emissivity was temperature dependent due to the increased transparency of the wafer at low temperatures. Using fixed emissivity, the measured temperature severely underestimates the actual temperature below 550°C. By calculating emissivity from the measured reflection and transmission, accurate temperature measurement was achieved from 400–700°C without any a priori knowledge of the wafer.

Comparisons of atomic thermal motions for graphite at 300 K based on X-ray, neutron, and phonon-spectrum data

1978 ◽  
Vol 34 (6) ◽  
pp. 979-982 ◽  
Author(s):  
R. Chen ◽  
P. Trucano
Keyword(s):  
Phonon Spectrum ◽  
Mean Square ◽  
Temperature Dependent ◽  
X Ray ◽  
The Core ◽  
Out Of Plane ◽  
Density Analysis ◽  
Atomic Scattering ◽  
The Mean ◽  
Spectrum Model

The mean-square amplitudes of vibration in graphite based on an X-ray charge-density analysis are 0.0032 (2) and 0.0140 (3) Å2 parallel to and perpendicular to the basal plane, respectively. Values for the parallel vibrations of 0.0031 (6) and 0.0032 Å2 were derived from temperature-dependent neutron measurements and a calculated phonon spectrum. The neutron measurements and the phonon spectrum both predict lower values [0.0090 (20) and 0.0098 Å2] for the out-of-plane vibrations. This small discrepancy may be caused by small changes in the core atomic scattering factors from the free-atom values or by a deficiency in the phonon-spectrum model.

scholarly journals Effect of Premelting on Conductivity of DNA-Lipid Films

2009 ◽  
Vol 2009 ◽  
pp. 1-5 ◽  
Author(s):  
A. Yu. Kasumov ◽  
S. Nakamae ◽  
M. Cazayous ◽  
T. Kawasaki ◽  
Y. Okahata
Keyword(s):  
Molecular Structure ◽  
Electrical Conductivity ◽  
Raman Spectroscopy ◽  
Measured Temperature ◽  
Dna Denaturation ◽  
Temperature Dependent ◽  
Cast Film ◽  
Lipid Films

We have measured temperature-dependent (between 20 and80∘C) electrical conductivity and molecular structure (Raman spectroscopy) of DNA-lipid cast film. Our findings show that the conductivity is strongly influenced by premelting effects in the molecular structure starting near physiological temperatures (∼40∘C), prior to the global DNA denaturation.

scholarly journals Prediction of the unit cell edge length of cubic A22+BB′O6 perovskites by multiple linear regression and artificial neural networks

2005 ◽  
Vol 3 (1) ◽  
pp. 198-215 ◽  
Author(s):  
Sandra Dimitrovska ◽  
Slobotka Aleksovska ◽  
Igor Kuzmanovski
Keyword(s):  
Linear Regression ◽  
Multiple Linear Regression ◽  
Cell Parameter ◽  
Edge Length ◽  
Unit Cell ◽  
Ionic Radii ◽  
New Members ◽  
Cell Edge ◽  
Lattice Cell Parameter ◽  
Artificial Neural

AbstractThe unit cell edge length, a, of a set of complex cubic perovskites having the general formula A22+BB′O6 is predicted using two methodologies: multiple linear regression and artificial neural neworks. The unit cell edge length is expressed as a function of six independent variables: the effective ionic radii of the constituents (A, B and B′), the electronegativities of B and B′, and the oxidation state of B. In this analysis, 147 perovskites of the A22+BB′O6 type, having the cubic structure and belonging to the Fm3m space group, are included. They are divided in two sets; 98 compounds are used in the calibration set and 49 are used in the test set. Both models give consistent results and could be successfully use to predict the lattice cell parameter of new members of this series.

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