Crystallization and Melting in Multilayered Structures

1987 ◽  
Vol 103 ◽  
Author(s):  
W. Sevenhans ◽  
H. Vanderstraeten ◽  
J. P. Locquet ◽  
Y. Bruynseraede ◽  
H. Homma ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Melting Temperature ◽  
Layered Structure ◽  
Broad Temperature Range ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
Multilayered Structures ◽  
X Ray ◽  
Temperature Range ◽  
The Stability

ABSTRACTThe stability of Pb/Ge and Pb/C multilayers has been studied over a broad temperature range by x-ray diffraction experiments. In the Pb/Ge system an amorphous to microcrystalline phase transformation of the Ge-layers was already observed at ≃ 100 °C. This transition destroys the modulation structure and improves the Pb(111) texture. In the Pb/C multilayers, the layered structure was still present at temperatures higher than the melting temperature of Pb. Contrary to recent publications, no depression of the melting temperature of the two-dimensional Pb layers could be observed.

scholarly journals Zirconium tetrachloride revisited

2018 ◽  
Vol 74 (3) ◽  
pp. 307-311
Author(s):  
Rosendo Borjas Nevarez ◽  
Samundeeswari Mariappan Balasekaran ◽  
Eunja Kim ◽  
Philippe Weck ◽  
Frederic Poineau
Keyword(s):  
Phase Transformation ◽  
Single Crystal ◽  
Structural Parameters ◽  
X Ray Diffraction ◽  
Zirconium Tetrachloride ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
X Ray ◽  
Temperature Range ◽  
Crystallographic Study

Zirconium tetrachloride, ZrCl4, is a strategic material with wide-ranging applications. Until now, only one crystallographic study on ZrCl4has been reported [Krebs (1970).Z. Anorg. Allg. Chem.378, 263–272] and that was more than 40 years ago. The compound used for the previous determination was prepared from ZrO2and Cl2–CCl4, and single-crystal X-ray diffraction (SCXRD) studies on ZrCl4obtained from Zr metal have not yet been reported. In this context, we prepared ZrCl4from the reaction of Zr metal and Cl2gas in a sealed tube and investigated its structure at 100, 150, 200, 250, and 300 K. At 300 K, the SCXRD analysis indicates that ZrCl4crystallizes in the orthorhombic space groupPca21[a= 6.262 (9),b= 7.402 (11),c= 12.039 (17) Å, andV= 558.0 (14) Å3] and consists of infinite zigzag chains of edge-sharing ZrCl6octahedra. This chain motif is similar to that observed previously in ZrCl4, but the structural parameters and space group differ. In the temperature range 100–300 K, no phase transformation was identified, while elongation of intra-chain Zr...Zr [3.950 (1) Å at 100 K and 3.968 (5) Å at 300 K] and inter-chain Cl...Cl [3.630 (3) Å at 100 K and 3.687 (9) Å at 300 K] distances occurred.

The Structure of Two-Dimensional Layered Cu (ΙΙ) Complex Material

2011 ◽  
Vol 366 ◽  
pp. 392-395
Author(s):  
Xi Shi Tai
Keyword(s):  
Hydrogen Bonds ◽  
Layered Structure ◽  
Sulfonic Acid ◽  
Copper Nitrate ◽  
Monoclinic Space Group ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
One Pot ◽  
X Ray ◽  
Π Stacking Interaction

A Cu (II) complex has been obtained by one-pot reaction of copper nitrate with 4-aminobenzene sulfonic acid, 2-acetylpyridine and sodium hydroxide. Unfortunately, the complex does not contain 2-acetylpyridine molecules, and 4-aminobenzene sulfonic acid coordinate to Cu (II) ion. The structure of Cu (II) complex was characterized by single-crystal X-ray diffraction. The results show that the complex crystallizes in monoclinic, space group P2(1)/n with a = 0.7437(3) nm, b = 1.7408(6) nm, c = 0.7644(3) nm, V = 0.8846(5) nm3, Z = 2, F (000) = 494, Rint = 0.0697, and the complex formed two dimensional layered structure through intramolecule and intermolecule hydrogen bonds and π-π stacking interaction.

scholarly journals Structural and optical characterization of the crystalline phase transformation of electrospinning TiO2 nanofibres by high-temperatures annealing

2019 ◽  
Vol 65 (5 Sept-Oct) ◽  
pp. 459
Author(s):  
O. Secundino-Sánchez ◽  
J. Diaz-Reyes ◽  
J. F. Sánchez-Ramírez ◽  
And J.L. Jiménez-Pérez
Keyword(s):  
Phase Transformation ◽  
Raman Scattering ◽  
High Temperatures ◽  
Crystalline Phase ◽  
Annealing Temperature ◽  
Crystal Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Temperature Range ◽  
Wide Range

The electrospinning technique has been used to synthesize TiO2 nanofibres, which by annealing at high temperatures in a wide range achieves the crystal phase transformation of anatase to rutile passing through the anatase+rutile mixed. The investigated temperature range was 0-1000°C. The TiO2 nanofibres chemical stoichiometry and surface morphology were obtained by Scanning Electron Microscopy and Energy Dispersive Spectrometry. The nanofibres diameter was ranged from 137.0 to 115.3 nm in the annealing temperature interval of 0-1000°C. The influence of the annealing temperature on the structure and crystal phase quality of the TiO2crystal has been investigated by X-ray diffraction and Raman scattering. Clear evidence of nanofibres structural transformation from pure anatase to pure rutile structures, including the quasi-amorphous and anatase+rutile mixed phases has been confirmed by Raman scattering. By X-ray diffraction was found that the nanofibres crystalline phases present as preferential growth direction (101) for anatase and (110) for rutile. The Raman spectroscopy exhibits the anomalous behaviour for band broadening and shifting of Raman bands with increasing crystallite size that form the nanofibres. The room-temperature photoluminescence presents radiative bands whose main band redshifts, from 2.56 to 1.32 eV, as the crystalline phase transforms in the investigated annealing temperature range.

Study on Novel Structure of Gadolinium Complex: Gd (C3 H6O9)

2012 ◽  
Vol 557-559 ◽  
pp. 401-404
Author(s):  
Hai Xing Liu ◽  
Li Mei Wan ◽  
Qing Zhi Pan ◽  
Hui Juan Yue ◽  
Guang Zeng ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Layered Structure ◽  
Hydrothermal Reaction ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
X Ray ◽  
Gadolinium Complex ◽  
Hydrogen Bonding Interactions ◽  
Novel Structure

A novel Gadolinium complex Gd (C3O9H6) has been synthesized from a hydrothermal reaction and the crystal structure has been determined by means of single-crystal X-ray diffraction. The Gd atom is coordinated by sixteen O atoms. The two-dimensional layered structure is formed and exhibits extensive O-H…O hydrogen-bonding interactions.

Crystallization and Phase Transformation of ZrO2-SiO2 Gels

1990 ◽  
Vol 180 ◽  
Author(s):  
Xiaoming Li ◽  
P.F. Johnson
Keyword(s):  
Phase Transformation ◽  
Gravimetric Analysis ◽  
Acetate Solution ◽  
X Ray Diffraction ◽  
Transformation Behavior ◽  
X Ray ◽  
Zirconium Acetate ◽  
The Stability ◽  
T Phase ◽  
Initial Crystallization Temperature

ABSTRACTPure SiO2, ZrO2 and SiO2−ZrO2 gels have been prepared by hydrolysis and gelation of tetraethylorthosilicate (TEOS) and zirconium acetate solution. The crystallization and phase transformation of SiO2 and ZrO2 in these gels have been followed up to 1450°C using differential thermal analysis (DTA), thermal gravimetric analysis (TGA) and X-ray diffraction analysis (XRD). The crystallization and phase transformation behavior of SiO2 or ZrO2 is quite different in different gel systems. It was found that in pure SiO2 gel, the cristobalite phase was precipitated out at about 1000°C. In the pure ZrO2 system, tetragonal (t−) phase zirconia was crystallized at about 430°C, t-ZrO2 crystals grew three dimensionally and the activation energy for growth was calculated as about 365 kJmol−1. But in the SiO2-ZrO2 system, the presence of ZrO2 suppressed the crystallization of SiO2 , and SiO2 increased the initial crystallization temperature and the stability of t-ZrO2.

Thin Film Synthesis of Copper-Based Perovskites Having Two-Dimensional Cation Order: (La0.8Ba0.2CuO2.6±x) (AECuO2)n Superlattices

1998 ◽  
Vol 547 ◽  
Author(s):  
P.A. Salvador ◽  
T-D. Doan ◽  
B. Mercey ◽  
B. Raveau
Keyword(s):  
Structural Characteristics ◽  
Deposition Process ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
Structural Units ◽  
X Ray ◽  
Cation Order ◽  
Superlattice Structures ◽  
Film Synthesis ◽  
The Stability

AbstractUsing a multi-target pulsed laser deposition (PLD) process we synthesized superlattices in the (La0.8Ba0.2CuO2.6±x)m(AECuO2)n system, where AE = Ca or Sr, and m and n were varied. Owing to the sequential deposition process, two-dimensional order is obtained on the perovskite A-sites in the superlattice structures, as evidenced by X-ray diffraction for the materials where AE = Sr. However, when AE = Ca, the films were unstable. Structural units of CaCuO2 could be incorporated into the superlattices by containing them between layers of SrCuO2: (SrCuO2)l(CaCuO2)m(SrCuO2)l(La0.8Ba0.2CuO2.6±x)n. The stability and structural characteristics of particular stacking sequences are discussed with respect to their chemical preferences and are compared to bulk materials of similar stoichiometries, i.e., the (La,AE)CuO3-x system. The latter materials do not exhibit two-dimensional cation-order. Resistance measurements of as-synthesized and post-annealed materials are also discussed.

A Study of Rhombohedral Phase in Y2 O3 -Partially Stabilized Zirconia

1986 ◽  
Vol 78 ◽  
Author(s):  
Jukishige Kitano ◽  
Y. Mori ◽  
A. Ishitani ◽  
T. Masaki
Keyword(s):  
Heat Treatment ◽  
Phase Transformation ◽  
Hot Isostatic Pressing ◽  
Tetragonal Zirconia ◽  
Rhombohedral Phase ◽  
X Ray Diffraction ◽  
Stabilized Zirconia ◽  
Partially Stabilized Zirconia ◽  
X Ray ◽  
The Stability

ABSTRACTTetragonal to rhombohedral phase transformation was studied by X-ray diffraction technique on the ground surfaces of tetragonal zirconia polycrystals (Y-TZP) and partially stabilized zirconia (Y-PSZ) with 2.0 to 5.0 mol% Y2 O3 contents prepared by hot isostatic pressing. The rhombohedral phase increased with increase of Y2 O3 content from 2.0 to 5.0 mol%, and also with the increase of HIPing temperature from 1400 to 1600°C. The stability of the phase was also studied with regard to the surface finish and annealing. The subsequent heat treatment of the samples was found to promote the reverse rhombohedral to tetragonal transformation.

Subsolidus data for the join Ca2SiO4—CaMgSiO4 and the stability of merwinite

1956 ◽  
Vol 31 (233) ◽  
pp. 187-194 ◽  
Author(s):  
Della M. Roy
Keyword(s):  
Solid Solution ◽  
Room Temperature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Temperature Range ◽  
Infra Red ◽  
Pure Phases ◽  
The Stability ◽  
End Members ◽  
Unique Compound

SummaryA study of phase equilibria among the orthosilicates on the Ca2SiO4—CaMgSiO4 join was undertaken with the use of hydrothermal techniques in the temperature range 600–900°C. at water pressures from 1000 to 15000 psi. Monticellite, merwinite, and Ca2SiO4 crystallize as pure phases throughout this temperature range, and intermediate compositions contain mixtures of the end members. Powder X-ray diffraction data obtained on the mixtures indicate no change in lattice dimensions from the end members. Hence, very little or no solid solution is indicated at these temperatures. Ca2SiO4 was crystallized as the γ-form below 675°C. (at 2000 psi) and the β-form above this temperature (presumably having inverted from the α′-form on cooling to room temperature). Infra-red absorption spectra obtained on the compounds γ-Ca2SiO4, β-Ca2SiO4, merwinite, and monticellite show characteristic differences in the pattern within the 9–13 micron region. All the data thus appear to confirm merwinite as a unique compound stable in the temperature range studied.

Stability of Superalloys Doped with Rare Earth Elements

2013 ◽  
Vol 586 ◽  
pp. 141-145
Author(s):  
Walenty Jasinski ◽  
Paweł Zawada
Keyword(s):  
Phase Transformation ◽  
Rare Earth ◽  
Rare Earth Elements ◽  
Thermal Processing ◽  
Microstructure Analysis ◽  
Hardness Distribution ◽  
X Ray Diffraction ◽  
X Ray ◽  
Average Hardness ◽  
The Stability

The stability of the microstructure and properties of the iron superalloys of the secondgeneration IN 519 (24% Cr, 24% Ni, 1.5% Nb) modified with 0.1 and 0.2 [wt.%] rare earthelements was investigated. The alloys underwent annealing at 825 oC for 10, 100 and 1000 h. Thefollowing techniques were used to evaluate the phase transformation: X-ray diffraction on crosssectionand isolates extracted from the as-cast and annealed alloys, microstructure analysis byoptical microscopy, hardness measurements by Brinell and nanoindentation with a Berkovich tipmethod. The analysis of changes in hardness distribution due to thermal processing of superalloyswas conducted with respect to the average hardness of matrix and phase precipitates.

Thermal Expansion Behaviour of Inconel-690 by In Situ High Temperature X-Ray Diffraction

2015 ◽  
Vol 830-831 ◽  
pp. 367-370 ◽  
Author(s):  
D. Ramachandran ◽  
A.M. Kamalan Kirubaharan ◽  
Arul Maximus Rabel ◽  
P. Kuppusami
Keyword(s):  
Thermal Expansion ◽  
High Temperature ◽  
Thermal Exposure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Good Thermal Stability ◽  
Temperature Range ◽  
High Temperature Xrd ◽  
Inconel 690 ◽  
The Stability

Ni-Cr-Fe based alloy Inconel 690 is widely used in power plant, marine, chemical and nuclear applications due to its excellent mechanical properties, resistance to thermal creep deformation, good thermal stability and resistance to corrosive and oxidizing environments. In order to study the microstructure of the alloy and the precipitates formation during thermal exposure, the alloy was subjected to in-situ high temperature X-ray diffraction technique (HT-XRD) in the temperature range 298-1273K. Results of high temperature XRD patterns show (111), (200), (220) and (311) reflections confirming the stability of fcc structure in the temperature of investigation. With increase in the temperature, a shift in peak positions towards lower 2θ values due to lattice expansion was noticed. The average thermal expansion coefficient (TEC) of the alloy increased from 1.33 x 10-5 K-1 to 1.53 x 10-5 K-1 in the temperature range 298-1273 K. Scanning electron microscopy indicates austenitic grains of sizes in the range 100-150μm and chromium carbide precipitate at grain boundaries after the HT-XRD heat treatment.

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