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.

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.

Spinel solid solutions in the systems MgAl2O4–ZnAl2O4 and MgAl2O4–Mg2TiO4

1997 ◽  
Vol 12 (10) ◽  
pp. 2584-2588 ◽  
Author(s):  
M. A. Petrova ◽  
G. A. Mikirticheva ◽  
A. S. Novikova ◽  
V. F. Popova
Keyword(s):  
Solid Solution ◽  
Phase Diagrams ◽  
Melting Temperature ◽  
Solid Solutions ◽  
Spinel Structure ◽  
Room Temperature ◽  
Binary Systems ◽  
Continuous Series ◽  
X Ray ◽  
Spinel Solid Solutions

Phase relations in two binary systems MgAl2O4–ZnAl2O4 and MgAl2O4–Mg2TiO4 have been studied and phase diagrams for them have been constructed. Based on the data of x-ray phase and crystal-optical analyses, the formation of a continuous series of solid solutions with spinel structure between the terminal members of the systems studied has been established. In the MgAl2O4–ZnAl2O4 system the solid solution is stable in the range from room temperature to melting temperature. In the MgAl2O4–Mg2TiO4 system the solid solution decomposes below 1380 °C, yielding the formation of limited regions of homogeneity on the basis of MgAlM2O4 and Mg2+2δ Ti1–δO4. Decomposition of the solid solution is accompanied by crystallization of MgTiO3.

Develop spinel structure and quantify phase transformation for nickel stabilization in electroplating sludge

2021 ◽  
Vol 131 ◽  
pp. 286-293
Author(s):  
Yunxue Xia ◽  
Fanling Meng ◽  
Zhong Lv ◽  
Jianshuai Zhang ◽  
Yuanyuan Tang ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Spinel Structure ◽  
Electroplating Sludge

Aging of iron manganite negative temperature coefficient thermistors

1998 ◽  
Vol 13 (5) ◽  
pp. 1238-1242 ◽  
Author(s):  
T. Battault ◽  
R. Legros ◽  
A. Rousset
Keyword(s):  
Temperature Coefficient ◽  
Spinel Structure ◽  
Negative Temperature Coefficient ◽  
Negative Temperature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Octahedral Sites ◽  
Before And After ◽  
Structural Equilibrium ◽  
Electrical Data

“Aging,” defined as the drift of resistance with temperature after 1000 h, was investigated for iron manganite temperature coefficient thermistors. For these devices, aging is relatively large, about 10%. The cationic distributions before and after aging were determined by Mössbauer spectroscopy. These distributions explain all the x-ray diffraction and correlated electrical data. The origin of the aging observed on iron manganites thermistors has been identified. It is due to the migration of Fe3+ ions from tetrahedral to octahedral sites of the spinel structure in order to reach a structural equilibrium.

scholarly journals Some Aspects of Spinodal Decomposition in Spinel Solid Solutions

1995 ◽  
Vol 50 (6) ◽  
pp. 525-532
Author(s):  
N. Burkert ◽  
R. Grüne ◽  
H. Schmalzried ◽  
S. Rahman
Keyword(s):  
Spinodal Decomposition ◽  
Solid Solutions ◽  
Common Property ◽  
Transport Theory ◽  
Decomposition Reaction ◽  
Sufficient Evidence ◽  
Spinel Crystal ◽  
Linear Transport Theory ◽  
Spinel Solid Solutions ◽  
Quasi Binary System

Abstract Decomposition morphologies of supersaturated spinel solid solutions in the quasi-binary system Co2TiO4-CoAl2O4 at 973 K show all pertinent features of spinodal decomposition. Since the decomposition morphology may not be considered as sufficient evidence for a spinodal process, the thermodynamics of the spinel solid solutions and the linear transport theory of spinodal decomposition were combined to corroborate the experimental results of the early decomposition reaction.Simultaneous ordering, a common property of ternary and higher nonequilibrium solid solutions, was also observed. These ordering processes occur locally in distinct regions of the spinel crystal. Moreover, the spinodal wavelength λ increases in time according to λ ∞ t, which is unusual and will be discussed in the light of cation diffusion in semiconducting oxides with two cation sublattices.

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