Estimation of The Critical Radius for The Nucleation of the C54 Phase in C49 TiSi2: Role of The Difference in Density

1999 ◽  
Vol 580 ◽  
Author(s):  
D.B. Migas ◽  
M. Iannuzzi ◽  
Leo Miglio ◽  
F. La Via ◽  
M.G. Grimaldi
Keyword(s):  
Ab Initio ◽  
Elastic Strain ◽  
Critical Radius ◽  
Lattice Parameters ◽  
X Ray Diffraction ◽  
X Ray ◽  
The Difference ◽  
Two Phases ◽  
The One

AbstractWe discuss the rather scattered measurements of the lattice parameters for C49 TiSi2, which are reported in literature, along with new and accurate X-ray diffraction measurements and ab-initio calculations. Both agree in indicating that the density of the metastable C49 structure cannot be much smaller than the one for the polymorphic C54 phase, as it is commonly reported. We conclude by demonstrating that only in the case of such a smaller difference in density between the two phases, the elastic strain contribution to the nucleation energy of the C54 structure in the C49 matrix can be neglected. The estimation of the critical radius strongly depends on this issue.

In-Situ X-ray Diffraction Study of Lithium Intercalation in Nanostructured Anatase Titanium dioxide

1998 ◽  
Vol 536 ◽  
Author(s):  
R. Van de Krol ◽  
E. A. Meulenkamp ◽  
A. Goossens ◽  
J. Schoonman
Keyword(s):  
Phase Transformation ◽  
Maximum Amount ◽  
Lithium Intercalation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Before And After ◽  
The Difference ◽  
Two Phases ◽  
Reversible Phase

AbstractElectrochemical lithium intercalation in nanostructured anatase TiO2 is investigated with in-situ X-ray diffraction. A complete and reversible phase transformation from tetragonal anatase TiO2 to orthorhombic anatase Li0.5TiO2 is observed. The difference of the XRD spectra before and after insertion can be fitted with the lattice parameters of the two phases as fit parameters. The maximum amount of lithium that can be dissolved in anatase TiO2 before the phase transformation occurs is found to be very small.

Addition of Ammonium Molybdate in Geopolymer Formulation

2014 ◽  
Vol 92 ◽  
pp. 8-13
Author(s):  
Laëticia Vidal ◽  
Emmanuel Joussein ◽  
Joseph Absi ◽  
Sylvie Rossignol
Keyword(s):  
High Temperature ◽  
Silicate Solution ◽  
Ammonium Molybdate ◽  
Inorganic Materials ◽  
Complexing Agent ◽  
Polycondensation Reaction ◽  
X Ray Diffraction ◽  
X Ray ◽  
Two Phases

Geopolymers are inorganic materials obtained by the alkaline activation of aluminosilicate sources. The ammonium molybdate could be used as a complexant for silica in order to complex the siliceous species in the alkaline solution. According to this, the aim of this work is to control the siliceous species and to understand the role of ammonium molybdate as a complexing agent acting on the formation of the different networks. To do this, additions of ammonium molybdate (up to 0.32% molar) in the silicate solution were realized along the formulation of geopolymer using two metakaolins. The results highlight that the addition of ammonium molybdate in geopolymer results in a decrease of the shrinkage at high temperature. Moreover, X-ray diffraction data and SEM after calcination show that geopolymers without ammonium molybdate form two phases (KAlSi2O6 and KAlSiO4) while with additions of molybdate, there were only the phase KAlSi2O6 associated with Al2O3 doped Mo and K2Mo2O7. Finally, SEM observations show that additions of ammonium molybdate seem to favor crystallization. The results allow to evidence the role of molybdate in the control of the polycondensation reaction in order to influence the formation of specific network

Comparative Study on Mn-Zn Ferrites by One-Step Synthesis and Conventional Two-Step Synthesis

2010 ◽  
Vol 177 ◽  
pp. 260-263 ◽  
Author(s):  
Qing Kai Xing ◽  
Zhi Jian Peng ◽  
Xiu Li Fu ◽  
Zhi Qiang Fu ◽  
Cheng Biao Wang ◽  
...  
Keyword(s):  
Magnetic Hysteresis ◽  
Initial Permeability ◽  
Synthesis Methods ◽  
Vibrating Sample Magnetometer ◽  
X Ray Diffraction ◽  
X Ray ◽  
Magnetic Performance ◽  
One Step ◽  
The Difference ◽  
The One

Mn-Zn ferrites doped with Cr3+ were prepared by “one-step synthesis” and conventional two-step synthesis methods, respectively. Their phase compositions and microstructures were characterized by X-ray diffraction and scanning electron microscopy, respectively. And their magnetic magnetic performance, such as saturation magnetization (Ms), magnetic hysteresis, initial permeability μi and power loss were comparatively investigated by vibrating sample magnetometer. It was observed that the difference of magnetic performance of the samples prepared by both methods is little. The similar performance of both methods makes the “one-step synthesis” especially attractive for application when considering energy economization.

Combustion synthesis of MoSi2−TiC composites

1995 ◽  
Vol 10 (5) ◽  
pp. 1226-1234 ◽  
Author(s):  
J. Subrahmanyam ◽  
R. Mohan Rao ◽  
G. Sundarasarma
Keyword(s):  
Combustion Synthesis ◽  
Phase Formation ◽  
Adiabatic Temperature ◽  
Homogeneous Distribution ◽  
X Ray Diffraction ◽  
Temperature Synthesis ◽  
X Ray ◽  
High Temperature Synthesis ◽  
Two Phases ◽  
The One

Stability of the binary phases in the quaternary system Mo–Ti–Si–C was examined for the combustion synthesis or Self-propagating High-temperature Synthesis (SHS) of MoSi2−TiC composites. Thermochemical calculations were carried out to obtain the adiabatic temperatures and the amounts of molten phases at the adiabatic temperature for the SHS of these composites. MoSi2−20 wt. % TiC and MoSi2−40 wt. % TiC composites were prepared by thermal explosion and SHS modes of combustion from elemental powders. The phase formation was confirmed by x-ray diffraction, and the morphologies were observed under SEM. No general correlation was obtained between the phase formation or product morphology on the one hand, and the adiabatic temperature or the amount of molten phase formed at the adiabatic temperature, on the other. MoSi2−40 wt. % TiC composites obtained by SHS mode of combustion show a highly homogeneous distribution of the two phases with negligible amounts of ternary phases.

scholarly journals Role of the extra Fe in K2−xFe4+ySe5 superconductors

2019 ◽  
Vol 116 (4) ◽  
pp. 1104-1109 ◽  
Author(s):  
Chih-Han Wang ◽  
Chih-Chien Lee ◽  
Gwo-Tzong Huang ◽  
Jie-Yu Yang ◽  
Ming-Jye Wang ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Parent Compound ◽  
Superconducting Transition ◽  
X Ray Diffraction ◽  
X Ray ◽  
Heat Treated ◽  
Different Temperatures ◽  
Two Phases ◽  
Best Fit

The exact superconducting phase of K2−xFe4+ySe5 has so far not been conclusively decided since its discovery due to its intrinsic multiphase in early material. In an attempt to resolve this mystery, we have carried out systematic structural studies on a set of well-controlled samples with exact chemical stoichiometry K2−xFe4+xSe5 (x = 0–0.3) that are heat-treated at different temperatures. Using high-resolution synchrotron radiation X-ray diffraction, our investigations have determined the superconducting transition by focusing on the detailed temperature evolution of the crystalline phases. Our results show that superconductivity appears only in those samples that have been treated at high-enough temperature and then quenched to room temperature. The volume fraction of superconducting transition strongly depends on the annealing temperature used. The most striking result is the observation of a clear contrast in crystalline phase between the nonsuperconducting parent compound K2Fe4Se5 and the superconducting K2−xFe4+ySe5 samples. The X-ray diffraction patterned can be well indexed to the phase with I4/m symmetry in all temperatures investigated. However, we need two phases with similar I4/m symmetry but different parameters to best fit the data at a temperature below the Fe vacancy order temperature. The results strongly suggest that superconductivity in K2−xFe4+ySe5 critically depends on the occupation of Fe atoms on the originally empty 4d site.

Hydrogen Behavior in NdRh3-Based Hydrides

2016 ◽  
Vol 369 ◽  
pp. 163-167
Author(s):  
Stepan Alexandrovich Lushnikov ◽  
Tatyana Victorovna Filippova
Keyword(s):  
Diffraction Method ◽  
Hydrogen Desorption ◽  
X Ray Diffraction ◽  
Hydrogen Atoms ◽  
X Ray ◽  
Cubic Lattice ◽  
Cubic Lattices ◽  
Rate Of Heating ◽  
The Difference ◽  
Two Phases

Samples of desorbed NdRh3-based hydrides have been investigated by the X-ray diffraction method. X-ray data analysis showed that the samples contain two phases with hexagonal and cubic lattices. It was revealed that proportion of these phases in the samples depends on the rate of heating before the hydrogen desorption. At high rates of the heating in the desorbed samples amount of the phase with cubic lattice increased. This behaviour of the hydrogen in hydrides can be explained by the difference in the diffusion of disordered and ordered hydrogen atoms.

scholarly journals Exceptional phonon point versus free phonon coupling in Zn1−xBexTe under pressure: an experimental and ab initio Raman study

2022 ◽  
Vol 12 (1) ◽  
Author(s):  
M. B. Shoker ◽  
T. Alhaddad ◽  
O. Pagès ◽  
V. J. B. Torres ◽  
A. V. Postnikov ◽  
...  
Keyword(s):  
Ab Initio ◽  
Mixed Crystals ◽  
Exceptional Point ◽  
Phonon Coupling ◽  
X Ray Diffraction ◽  
X Ray ◽  
Point Versus ◽  
Raman Study ◽  
Effective Transfer

AbstractRaman scattering and ab initio Raman/phonon calculations, supported by X-ray diffraction, are combined to study the vibrational properties of Zn1−xBexTe under pressure. The dependence of the Be–Te (distinct) and Zn–Te (compact) Raman doublets that distinguish between Be- and Zn-like environments is examined within the percolation model with special attention to x ~ (0,1). The Be-like environment hardens faster than the Zn-like one under pressure, resulting in the two sub-modes per doublet getting closer and mechanically coupled. When a bond is so dominant that it forms a matrix-like continuum, its two submodes freely couple on crossing at the resonance, with an effective transfer of oscillator strength. Post resonance the two submodes stabilize into an inverted doublet shifted in block under pressure. When a bond achieves lower content and merely self-connects via (finite/infinite) treelike chains, the coupling is undermined by overdamping of the in-chain stretching until a «phonon exceptional point» is reached at the resonance. Only the out-of-chain vibrations «survive» the resonance, the in-chain ones are «killed». This picture is not bond-related, and hence presumably generic to mixed crystals of the closing-type under pressure (dominant over the opening-type), indicating a key role of the mesostructure in the pressure dependence of phonons in mixed crystals.

scholarly journals Exceptional Phonon Point Versus Free Phonon Coupling in Zn1-xBexTe Under Pressure: An Experimental and ab Initio Raman Study

2021 ◽  
Author(s):  
M. B. Shoker ◽  
T. Alhaddad ◽  
O. Pagès ◽  
V. J. B. Torres ◽  
A. V. Postnikov ◽  
...  
Keyword(s):  
Ab Initio ◽  
Mixed Crystals ◽  
Exceptional Point ◽  
Phonon Coupling ◽  
X Ray Diffraction ◽  
X Ray ◽  
Point Versus ◽  
Raman Study ◽  
Effective Transfer

Abstract Raman scattering and ab initio Raman/phonon calculations, supported by X-ray diffraction, are combined to study the vibrational properties of Zn1-xBexTe under pressure. The dependence of the Be-Te (distinct) and Zn-Te (compact) Raman doublets that distinguish between Be- and Zn-like environments is examined within the percolation model with special attention to x~(0,1). The Be-like environment hardens faster than the Zn-like one under pressure, resulting in the two sub-modes per doublet getting closer and mechanically coupled. When a bond is so dominant that it forms a matrix-like continuum, its two submodes freely couple on crossing at the resonance, with an effective transfer of oscillator strength. Post resonance the two submodes stabilize into an inverted doublet shifted in block under pressure. When a bond achieves lower content and merely self-connects via (finite/infinite) treelike chains, the coupling is undermined by overdamping of the in-chain stretching until a phonon exceptional point is reached at the resonance. Only the out-of-chain vibrations "survive" the resonance, the in-chain ones are "killed". This picture is not bond-related, and hence presumably generic to mixed crystals of the closing-type under pressure (dominant over the opening-type), indicating a key role of the mesostructure in the pressure dependence of phonons in mixed crystals.

Antiphase Boundaries in Ordered Ni3FE Crystals

1969 ◽  
Vol 27 ◽  
pp. 62-63
Author(s):  
Y. H. Liu
Keyword(s):  
Domain Size ◽  
Antiphase Domain ◽  
X Ray Diffraction ◽  
X Ray ◽  
Hardening Mechanism ◽  
Superlattice Structure ◽  
Disordered Phase ◽  
Domain Boundaries ◽  
Atomic Scattering ◽  
The Difference

Ordered Ni3Fe crystals possess a LI2 type superlattice similar to the Cu3Au structure. The difference in slip behavior of the superlattice as compared with that of a disordered phase has been well established. Cottrell first postulated that the increase in resistance for slip in the superlattice structure is attributed to the presence of antiphase domain boundaries. Following Cottrell's domain hardening mechanism, numerous workers have proposed other refined models also involving the presence of domain boundaries. Using the anomalous X-ray diffraction technique, Davies and Stoloff have shown that the hardness of the Ni3Fe superlattice varies with the domain size. So far, no direct observation of antiphase domain boundaries in Ni3Fe has been reported. Because the atomic scattering factors of the elements in NijFe are so close, the superlattice reflections are not easily detected. Furthermore, the domain configurations in NioFe are thought to be independent of the crystallographic orientations.

Defect structures of Nb1+αS2 sulfidation scales

1992 ◽  
Vol 50 (1) ◽  
pp. 38-39
Author(s):  
Chuxin Zhou ◽  
L. W. Hobbs
Keyword(s):  
Stacking Faults ◽  
Rhombohedral Structure ◽  
Stacking Sequence ◽  
Defect Structures ◽  
X Ray Diffraction ◽  
X Ray ◽  
Plane Normal ◽  
Lower Case ◽  
Sulfur Layer ◽  
Two Phases

One of the major purposes in the present work is to study the high temperature sulfidation properties of Nb in severe sulfidizing environments. Kinetically, the sulfidation rate of Nb is satisfactorily slow, but the microstructures and non-stoichiometry of Nb1+αS2 challenge conventional oxidation/sulfidation theory and defect models of non-stoichiometric compounds. This challenge reflects our limited knowledge of the dependence of kinetics and atomic migration processes in solid state materials on their defect structures.Figure 1 shows a high resolution image of a platelet from the middle portion of the Nb1+αS2 scale. A thin lamellar heterogeneity (about 5nm) is observed. From X-ray diffraction results, we have shown that Nb1+αS2 scale is principally rhombohedral structure, but 2H-NbS2 can result locally due to stacking faults, because the only difference between these 2H and 3R phases is variation in the stacking sequence along the c axis. Following an ABC notation, we use capital letters A, B and C to represent the sulfur layer, and lower case letters a, b and c to refer to Nb layers. For example, the stacking sequence of 2H phase is AbACbCA, which is a ∼12Å period along the c axis; the stacking sequence of 3R phase is AbABcBCaCA to form an ∼18Å period along the c axis. Intergrowth of these two phases can take place at stacking faults or by a shear in the basal plane normal to the c axis.

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