The Defect Fluorite Phase in the ZrO2-PrO1.5 System and Its Relationship to the Structure of Pyrochlore

1992 ◽  
Vol 45 (9) ◽  
pp. 1375 ◽  
Author(s):  
RL Withers ◽  
JG Thompson ◽  
PJ Barlow ◽  
JC Barry
Keyword(s):  
Solid Solution ◽  
Point Defects ◽  
Phase Field ◽  
Fluorite Phase ◽  
X Ray ◽  
Average Structure ◽  
Transmission Electron ◽  
Solution Field ◽  
Close Relationship ◽  
Fluorite Type

A detailed transmission electron microscope and X-ray powder diffraction study has been made of the so-called 'defect fluorite' phase field in the ZrO2-PrO1.5 system and of its close relationship to the pyrochlore solid solution field in the same system. Even for the lowest possible PrO1.5 content within the 'defect fluorite' phase field, it is clear that the sharp Bragg reflections characteristic of the underlying fluorite average structure are accompanied by some of the 'satellite reflections' characteristic of the pyrochlore solid solution field. As the PrO1.5 content increases, these satellite reflections increase systematically in intensity as well as sharpening very considerably. It is shown that this 'defect fluorite' phase field cannot be adequately described either in terms of random point defects within an average fluorite-type matrix or in terms of a diphasic texture of pyrochlore domains embedded coherently into a fluorite matrix, but must be regarded as enuinely intermediate between these two end-member structures and of commensurately modulated fluorite type. A group theoretical approach is used to propose a model for the structural deviation from the underlying fluorite average structure.

scholarly journals The impact of point defects in n-type GaN layers on thermal decomposition of InGaN/GaN QWs

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Mikolaj Grabowski ◽  
Ewa Grzanka ◽  
Szymon Grzanka ◽  
Artur Lachowski ◽  
Julita Smalc-Koziorowska ◽  
...  
Keyword(s):  
Quantum Wells ◽  
High Temperatures ◽  
Point Defects ◽  
X Ray Diffraction ◽  
Helium Ions ◽  
X Ray ◽  
Sapphire Substrates ◽  
Transmission Electron ◽  
The Impact ◽  
Ingan Quantum Wells

AbstractThe aim of this paper is to give an experimental evidence that point defects (most probably gallium vacancies) induce decomposition of InGaN quantum wells (QWs) at high temperatures. In the experiment performed, we implanted GaN:Si/sapphire substrates with helium ions in order to introduce a high density of point defects. Then, we grew InGaN QWs on such substrates at temperature of 730 °C, what caused elimination of most (but not all) of the implantation-induced point defects expanding the crystal lattice. The InGaN QWs were almost identical to those grown on unimplanted GaN substrates. In the next step of the experiment, we annealed samples grown on unimplanted and implanted GaN at temperatures of 900 °C, 920 °C and 940 °C for half an hour. The samples were examined using Photoluminescence, X-ray Diffraction and Transmission Electron Microscopy. We found out that the decomposition of InGaN QWs started at lower temperatures for the samples grown on the implanted GaN substrates what provides a strong experimental support that point defects play important role in InGaN decomposition at high temperatures.

scholarly journals Synthesis of Ce1−xPdxO2−δ Solid Solution in Molten Nitrate

Catalysts ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 640
Author(s):  
Hideaki Sasaki ◽  
Keisuke Sakamoto ◽  
Masami Mori ◽  
Tatsuaki Sakamoto
Keyword(s):  
Electron Microscopy ◽  
Solid Solution ◽  
Solid Solutions ◽  
Photoelectron Spectroscopy ◽  
Synthesis Method ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Co Precipitation ◽  
Ionic States

CeO2-based solid solutions in which Pd partially substitutes for Ce attract considerable attention, owing to their high catalytic performances. In this study, the solid solution (Ce1−xPdxO2−δ) with a high Pd content (x ~ 0.2) was synthesized through co-precipitation under oxidative conditions using molten nitrate, and its structure and thermal decomposition were examined. The characteristics of the solid solution, such as the change in a lattice constant, inhibition of sintering, and ionic states, were examined using X-ray diffraction (XRD), scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM−EDS), transmission electron microscopy (TEM)−EDS, and X-ray photoelectron spectroscopy (XPS). The synthesis method proposed in this study appears suitable for the easy preparation of CeO2 solid solutions with a high Pd content.

Arrangement of C atoms in the SiC–C solid solution

1999 ◽  
Vol 55 (3) ◽  
pp. 297-305 ◽  
Author(s):  
O. O. Mykhaylyk ◽  
M. P. Gadzira
Keyword(s):  
Solid Solution ◽  
Point Defects ◽  
Strain Field ◽  
Field Model ◽  
Fine Powder ◽  
Lattice Parameter ◽  
Acta Cryst ◽  
Planar Defects ◽  
X Ray ◽  
Higher Temperature

The microstructure of a silicon carbide–carbon solid-solution powder (SiC–C), obtained from a fine powder of silicon and thermal expansive graphite, is investigated by X-ray powder diffraction methods. The microstructure is characterized by Williamson–Hall analysis and the strain-field model suggested by van Berkum et al. [Acta Cryst. (1996), A52, 730–747]. SiC–C adopts a layered structure like the solid solutions formed by compounds possessing a diamond-like structure, e.g. SiC–AlN. Superstoichiometric C atoms are located as planar defects. The SiC–C solid solution is destroyed on heating in a vacuum in the temperature range of graphitization of diamond but is maintained after sintering at high pressure (4–8 GPa) and high temperature (1673 and 2073 K). However, at the higher temperature (2073 K), it is observed that planar defects formed by C atoms decompose to non-correlated point defects accompanied simultaneously by a decrease in the lattice parameter from 4.3540 (2) to 4.35234 (5) Å.

Effect of temperature on formation of murataite and murataite-pyrochlore ceramics

2002 ◽  
Vol 757 ◽  
Author(s):  
O. I. Kirjanova ◽  
S. V. Stefanovsky ◽  
S. V. Yudintsev
Keyword(s):  
Effect Of Temperature ◽  
Cold Crucible ◽  
Iron Group ◽  
X Ray Diffraction ◽  
X Ray ◽  
Oxide Solid Solution ◽  
Transmission Electron ◽  
Heat Treated ◽  
Unit Cells ◽  
Fluorite Type

ABSTRACTProcesses of phases formation in the ceramic mixtures with basic compositions (wt.%) 10 CaO, 10 MnO, 5 Al2O3, 5 Fe2O3, 55 TiO2, 5 ZrO2, 10 UO2 (M1) and 8 CaO, 8 MnO, 4 Al2O3, 4 Fe2O3, 20 Gd2O3, 44 TiO2, 4 ZrO2, 8 UO2 (M4) were studied using X-ray diffraction, scanning and transmission electron microscopy. The batches were milled, compacted in pellets at 200 MPa, and heat-treated in a resistive furnace at 1100 °C, 1300 °C, 1400 °C, and 1500 °C as well as melted in a cold crucible at ∼1600 °C. Reactions in the mixtures heat-treated at 1100 °C were not completed and samples contained significant amount of unreacted and intermediate (altered rutile, cubic oxide solid solution, perovskite) phases. Within the temperature range 1100–1300 °C reactions are mainly completed and ceramics sintered at 1300 °C are composed of major murataite and minor rutile (M1) or major murataite and pyrochlore and minor zirconolite and perovskite (M4). However full homogenization at 1300 °C has not been reached yet and to obtain the ceramics with uniform compositions of the phases sintering at 1400 °C or melting at 1500–1600 °C were required.In the ceramic sample M1 two murataite varieties with five- (murataite-5C) and eight-fold (mu-rataite-8C) fluorite-type unit cells were found. The sample M4 is composed of pyrochlore, murataite-8C and zirconolite-3O. In the sample M1 murataite-5C is enriched with U and Ca and depleted with iron group elements as compared to murataite-8C. Fraction of murataite-5C concentrates about 80% of total U and about 70% of Mn+Fe (corrosion products). Waste elements partitioning among the phases in the M4 sample depends significantly on temperature of heat-treatment.

Nanoporous Ni and Ni-Cu Fabricated by Dealloying

2009 ◽  
Vol 1228 ◽  
Author(s):  
Masataka Hakamada ◽  
Yasumasa Chino ◽  
Mamoru Mabuchi
Keyword(s):  
Electron Microscopy ◽  
Solid Solution ◽  
Noble Metals ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
The Difference ◽  
20 Nm ◽  
Good Workability ◽  
Scanning Electron

AbstractMetallic nanoporous architecture can be spontaneously attained by dealloying of a binary alloy. The nanoporous architecture can be often fabricated in noble metals such as Au and Pt. In this study, nanoporous Ni, Ni-Cu are fabricated by dealloying rolled Ni-Mn and Cu-Ni-Mn alloys, respectively. Unlike conventional Raney nickel composed of brittle Ni-Al or Cu-Al intermetallic compounds, the initial alloys had good workability probably because of their fcc crystal structures. After the electrolysis of the alloys in (NH4)2SO4 aqueous solution, nanoporous architectures of Ni and Ni-Cu with pore and ligament sizes of 10–20 nm were confirmed by scanning electron microscopy and transmission electron microscopy. X-ray diffraction analyses suggested that Ni and Cu atoms form a homogeneous solid solution in the Ni-Cu nanoporous architecture. The ligament sizes of nanoporous Ni and Ni-Cu were smaller than that of nanoporous Cu, reflecting the difference between diffusivities of Ni and Cu at solid/electrolyte interface. Ni can reduce the pore and ligament sizes of resulting nanoporous architecture when added to initial Cu-Mn alloys.

Thermal decomposition of mechanically alloyed nanocrystalline fcc Fe60Cu40

1996 ◽  
Vol 11 (11) ◽  
pp. 2717-2724 ◽  
Author(s):  
J. Y. Huang ◽  
Y. D. Yu ◽  
Y. K. Wu ◽  
H. Q. Ye ◽  
Z. F. Dong
Keyword(s):  
Solid Solution ◽  
Grain Size ◽  
Magnetic Measurement ◽  
Orientation Relationships ◽  
Maximum Solubility ◽  
Mechanically Alloyed ◽  
X Ray ◽  
Cu Content ◽  
Cu Alloys ◽  
Transmission Electron

A ferromagnetic and supersaturated fcc Fe60Cu40 solid solution was prepared by mechanical alloying (MA). The phase transformations of the as-milled Fe60Cu40 powder upon heating to 1400 °C and subsequently cooling to room temperature were characterized by differential thermal analysis (DTA) and thermal magnetic measurement. The fcc Fe60Cu40 solid solution decomposes into α–Fe(Cu) + γ–Fe(Cu) + Cu(Fe) upon heating from 300 to 460 °C, and on further heating, α–Fe(Cu) transforms to γ–Fe(Cu) at 640 → 760 °C; during cooling, the reverse transformation occurs from 800 → 640 °C (obtained from thermomagnetic measurement) or from 700 → 622 °C (obtained from DTA). The γ ⇆ α transformation in mechanically alloyed Fe60Cu40 nanocrystalline occurs in a wide temperature range; the transformation temperature is higher than that of the martensite transformation in as-cast Fe–Cu alloys, but is much lower than that of the allotropic transformation of pure Fe. These differences may be caused by the different fabrication process, the nonequilibrium microstructure of MA, as well as the inhomogeneous grain size in α–Fe(Cu). High resolution transmission electron microscope (HRTEM) observations carried out in the specimen after the DTA run show that N-W or K-S orientation relationships exist between α–Fe(Cu) and Cu(Fe), which also represent the orientation relationship between α–Fe(Cu) and γ–Fe(Cu) due to excellent coherency between γ–Fe(Cu) and Cu(Fe). The grain size of the α–Fe(Cu) is inhomogeneous and varies from 50–600 mm. Energy dispersive x-ray spectroscopy (EDXS) result shows that the Cu content in these α–Fe(Cu) grains reaches as high as 9.5 at. % even after DTA heating to 1400 °C, which is even higher than the maximum solubility of Cu in γ–Fe above 1094 °C. This may be caused by the small grain size of α–Fe(Cu).

Clay minerals in the Namacotche Pegmatite Group from Zambezia Province, Mozambique: main constituents of late-stage secondary paragenesis

Clay Minerals ◽  
2008 ◽  
Vol 43 (4) ◽  
pp. 597-613 ◽  
Author(s):  
M. A. Sequeira Braga ◽  
C. Leal Gomes ◽  
J. Duplay ◽  
H. Paquet
Keyword(s):  
Electron Microscopy ◽  
Clay Minerals ◽  
Late Stage ◽  
Polarized Light ◽  
Chemical Analyses ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Close Relationship ◽  
Xrd Patterns

AbstractNamacotche gem-bearing pegmatites of Alto Ligonha pegmatite district are heterogeneous, strongly fractionated, and have large Li and Ta and extremely large Cs contents. Clay samples were collected in fracture infillings and dilation cavities with gemstones and were studied using X-ray diffraction (XRD), polarized light microscope, scanning electron microscopy-energy dispersive spectroscopy, high-resolution transmission electron microscopy and chemical analyses. The <2 μm fraction contains cookeite, illite, illite-smectite and suggested irregular mixed-layer cookeite-smectite, beidellite, montmorillonite, kaolinite and goethite.The XRD patterns of chlorite and their d values suggest the presence of ‘di-trioctahedral chlorite’ similar to cookeite-Ia polytype. Cookeite chemical analyses show that Li contents range from 0.82 to 1.08 atoms per half unit cell.A close relationship has been established between occurrences of gemstones and clay minerals. Some important textures and crystal chemistry are discussed.The main gemstones related to the Namacotche Pegmatite are: morganite (pink cesian beryl), kunzite (spodumene) and elbaite tourmaline. As the mechanisms responsible for the gemstone formation take place at low temperature, the clay minerals paragenesis cookeite ± cookeite-smectite interstratification ± beidellite + montmorillonite ± illite-smectite interstratification, represents a late-stage secondary paragenesis, generated by hydrothermal alteration.

Growth of Intermetallics at Coated Silver Wire Bond Interfaces

2018 ◽  
Vol 2018 (1) ◽  
pp. 000578-000582 ◽  
Author(s):  
Sarangapani Murali ◽  
Wong Chin Yeung Jason
Keyword(s):  
Solid Solution ◽  
Thin Layer ◽  
Precise Measurement ◽  
Ion Beam ◽  
Thermal Ageing ◽  
X Ray ◽  
Transmission Electron ◽  
Free Air ◽  
Bond Interface ◽  
Focus Ion Beam

Abstract The newly developed gold (Au) coated silver (Ag) wire exhibits axi-symmetrical free air ball (FAB) formation under atmosphere similar to Au wire. FAB of coated Ag showed better corrosion resistance than FAB of alloyed Ag, as Au dissolved along the periphery of Ag FAB forming into a solid-solution, Ag-Au alloy. Composition of the solid-solution Ag-Au alloy along the periphery ranges between 10 and 28wt% of Au. The diffusion depth of Au is 4μm from surface towards the center of FAB. For precise measurement of the diffusion length of Au into Ag, a solid thin layer is been parted using focus-ion beam (FIB). The solid thin layer is further thinned down to observe in Transmission Electron Microscope (TEM) and analyzed using line scan energy dispersive X-ray analysis (EDX) attached to it. Near the neck of FAB and wire, Au diffusion is high up to 58wt%. On thermal ageing at 150/175°C for 500/1000h, the coated Ag wire bonded to Al-0.5wt%Cu pad revealed no degradation on ball pull/shear. Bond interface revealed significant growth of silver aluminide (AgAl) to a thickness of 3μm for 1000h of ageing and the growth rate fits to square-root power law.

Dislocations around scratches and indents on ±(111) surface of gallium arsenide

1989 ◽  
Vol 22 (6) ◽  
pp. 606-612 ◽  
Author(s):  
M. R. Surowiec ◽  
H. S. Leipner ◽  
J. Schreiber
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Point Defects ◽  
Nucleation Mechanism ◽  
Dislocation Loops ◽  
X Ray ◽  
Transmission Electron ◽  
Double Kink ◽  
Slip Planes ◽  
Scanning Electron

The dislocation configurations around microscratches and indents on ±(111) surfaces of GaAs single crystals were studied by X-ray transmission topography, scanning electron microscopy in cathodoluminescence mode and high-voltage transmission electron microscopy. Most of the dislocations generated are loops of screw – B(g) or screw –B(g) – screw character gliding on {111} slip planes parallel or inclined to the surface. The irregular shape of the extended loops gliding parallel to the B surface is due to interaction with other loops and apparent motion involving a double kink nucleation mechanism. The exhibited configuration of dislocation loops suggests a cross-slip orientation of the dissociated screw segments. The direction of propagation of dislocations does not depend on the sense of scratching. Grown-in dislocations are surrounded by a cloud of point defects and they are immobile in contrast to dislocations introduced by indentation.

Structural analysis of Gd2Ce2O7

2015 ◽  
Vol 1743 ◽  
Author(s):  
Maulik K. Patel ◽  
Gianguido Baldinozzi ◽  
Jeffery A. Aguiar ◽  
James A. Valdez ◽  
Sven C. Vogel ◽  
...  
Keyword(s):  
Room Temperature ◽  
Single Phase ◽  
Fluorite Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Peak Broadening ◽  
Transmission Electron ◽  
Refinement Method ◽  
History Of ◽  
Miscibility Gaps

ABSTRACTA complex cerium bearing oxide, Gd2Ce2O7 was synthesized in order to simulate Pu in a fluorite derivative oxide. X-ray diffraction (XRD) data was collected using a lab diffractometer at room temperature and analyzed by Rietveld refinement method using the xnd program. The diffraction pattern obtained from the material could be indexed as a C-type cubic bixbyite crystal structure however several peaks showed peak broadening and could not be accounted for within the single-phase bixbyite model. A full pattern refinement, assuming a possible existence of short order disordered bixbyite regions within an average disordered fluorite phase gave a good fit with the experimental data, providing an estimate for correlation length of those bixbyite regions. Transmission electron microscopy confirms the existence of these correlated domains of disordered bixbyite type phase inside a defect fluorite lattice. Understanding the extent of these domains as a function of composition and the thermal history of the samples may have a profound effect on our understanding of miscibility gaps in Re2O3-CeO2 phase diagrams. These effects could be eventually exploited to design materials with increased radiation resistance, a desired feature for oxide matrices where actinides can be safely disposed.

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