In-Situ High Temperature Optical Microscopic Observations of Crystallization Mechanism in NdBa2Cu3Ox

ABSTRACTThe pseudo-binary NdBa2Cu3O-Ba3Cu10O13phase diagrams and the crystallization of NdBa2Cu3Ox have been in-situ observed using high-temperature optical microscopy in air and under three different reduced oxygen atmospheres namely, 1%, 0.1% and 0.0097% oxygen in argon. The liquidus line was found to become narrower both in composition and temperature with reducing oxygen content in the atmosphere. These results suggested that while in air NdBa2Cu3Ox can be crystallized from both high-temperature solution and peritectic melt; under reduced oxygen atmospheres the crystallization of NdBa2Cu3Ox is only possible from a peritectic melt. The in-situ observations of crystallization of NdBa2Cu3Ox from high-temperature solutions revealed that the growth mechanism changes from 3D via 2D layer-by-layer to continuos dendritic growth with increasing cooling rate. On the other hand, the NdBa2Cu3Ox crystallization from a peritectic melt involved two distinct steps (i) conversion of Nd4Ba2Cu2Ox into NdBa2Cu3Ox and (ii) nucleation and growth of NdBa2Cu3Ox The growth morphology in this case was independent of the cooling rate. This result and the direct observation of the dissolution of Nd4Ba2Cu2Ox into the liquid suggested that the solute diffusion is the rate-limiting factor.

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In-Situ Observations of the Effect of Electron Irradiation on the Defect Microstructure of Alumina

Microscopy and Microanalysis ◽

10.1017/s1431927600009892 ◽

1997 ◽

Vol 3 (S2) ◽

pp. 601-602

Author(s):

S.-J. Chen ◽

U. Dahmen ◽

D.G. Howitt

Keyword(s):

High Temperature ◽

Electron Irradiation ◽

Shear Bands ◽

Valuable Insight ◽

High Velocity Impact ◽

Dislocation Densities ◽

In Situ Observations ◽

Very High ◽

Insight Into

The interaction of radiation produced point defects with a dislocation microstructure at high temperature is of considerable interest and careful high voltage microscopy experiments can provide valuable insight into the mechanisms. Veyssière and Westmacott carried out in-situ experiments monitoring the partial dislocation climbs in Ni3Al induced by thermal vacancies as well as by Frenkel pairs produced during irradiation.1 We report here the results of some preliminary experiments we performed on alumina (A12O3) single crystals with high dislocation densities to study the modification of the microstructure by electron irradiation at high temperature.The dislocation microstructures were produced by shock wave deformation using a high-velocity impact technique. The technique is capable of producing a very high density of defects consisting primarily of basal twins, and slips on the basal, pyramidal and rhombohedral planes in alumina. The dislocations are all of glide type, mostly forming shear bands. A typical microstructure prior to irradiation is shown in figure la.

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Coherency Strain Energy in any Crystal System: Applications to in Situ Observations of Cigm in Calcite

MRS Proceedings ◽

10.1557/proc-205-245 ◽

1990 ◽

Vol 205 ◽

Author(s):

R.S. May ◽

B. Evans

Keyword(s):

Driving Force ◽

Migration Rate ◽

Strain Energy ◽

Solute Concentration ◽

Coherency Strain ◽

Solute Diffusion ◽

Boundary Orientation ◽

In Situ Observations ◽

And Migration

AbstractIn situ observations of CIGM in CaCO3 bicrystals with a SrCO3 solute source were made. The change in boundary orientation and migration rate were compared with solute concentration. The liquid film model for coherency strain Induced migration was generalized to any non-cubic system and applied to CaCO3-SrCO3. The coherent layer was modeled as a thin film on an infinite half-space. The strain energy was found from solution of the Hooke's law expressions transformed to the appropriate coordinate system. For triclinic or monoclinic films the strain tensor was found by an eigenvector decomposition of the transformation matrix that defined the lattice parameter change with composition. High anisotropy of Vegard's law constants for CaCO3-SrCO3 caused (111) to have the lowest coherency strain per unit solute. Surfaces perpendicular to (111) in coherent equilibria were predicted to have half the solute concentration and three times the migration driving force of those perpendicular to (111). However, no correlation between solute concentration and boundary orientation was observed. Ambiguous and contradictory evidence for a relationship between solute concentration, boundary orientation, and migration rate was found. The self-stress state of a grain boundary in a solute diffusion field may be better modelled as hydrostatic rather than plane stress. Hydrostatic compression may interact with the boundary excess volume and cause a PV driving force for migration. Predictions based on coherent equilibrium at a surface have not been tested for that geometry in calcite; they should be tested before they are applied to grain boundaries.

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A new hydrothermal moissanite cell apparatus for optical in-situ observations at high pressure and high temperature, with applications to bubble nucleation in silicate melts

American Mineralogist ◽

10.2138/am-2017-6093 ◽

2017 ◽

Vol 102 (10) ◽

pp. 2022-2031 ◽

Cited By ~ 4

Author(s):

Matteo Masotta ◽

Hans Keppler

Keyword(s):

High Pressure ◽

High Temperature ◽

Bubble Nucleation ◽

Silicate Melts ◽

In Situ Observations

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In Situ Observations of Phase Transition Using High-Temperature Neutron and Synchrotron X-ray Powder Diffractometry

Journal of the American Ceramic Society ◽

10.1111/j.1151-2916.2002.tb00557.x ◽

2004 ◽

Vol 85 (12) ◽

pp. 2925-2930 ◽

Cited By ~ 47

Author(s):

Masatomo Yashima

Keyword(s):

Phase Transition ◽

High Temperature ◽

X Ray ◽

In Situ Observations

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CRACK-HEALING BEHAVIOR AND BENDING STRENGTH OF Al2O3/SiC COMPOSITE CERAMICS ACCORDING TO THE AMOUNT OF ADDITIVE Y2O3

International Journal of Modern Physics B ◽

10.1142/s0217979210065842 ◽

2010 ◽

Vol 24 (15n16) ◽

pp. 2910-2915 ◽

Cited By ~ 1

Author(s):

KI WOO NAM

Keyword(s):

High Temperature ◽

Vickers Hardness ◽

Bending Strength ◽

Composite Ceramic ◽

Crack Healing ◽

Composite Ceramics ◽

Strength Recovery ◽

In Situ Observations ◽

Healing Temperature

Three Al 2 O 3/ SiC composite ceramics were prepared, which included 1, 3 or 5 wt. % Y 2 O 3, and their high-temperature bending strengths and in-situ crack-healing behaviors examined. A surface elliptical-crack of about 100 µm in diameter was introduces on the specimens using a Vickers hardness indenter. From in-situ observations, the Al 2 O 3/ SiC composite ceramic with 3 wt.% Y 2 O 3 showed superior crack-healing ability than the 1 and 5 wt.% Y 2 O 3 ceramics. The as-cracked specimen with 3 wt.% Y 2 O 3 showed strength recovery on healing for 1 hr at 1473 K in air, which may have been due to the lower crack-healing temperature on the addition of 3 wt.% Y 2 O 3. The heat-resistance limit temperatures of the crack-healed Al 2 O 3/ SiC composite ceramics were 1073, 1373 and 873 K for 1, 3 and 5 wt.% Y 2 O 3, respectively.

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Rheed Intensity Observation of AlAs and GaAs by in situ Etching Using Arsenic Tribromide

MRS Proceedings ◽

10.1557/proc-405-67 ◽

1995 ◽

Vol 405 ◽

Cited By ~ 2

Author(s):

T. Kaneko ◽

T. Säger ◽

K. Eberl

Keyword(s):

Low Temperatures ◽

Reaction Rate ◽

Etching Rate ◽

Layer By Layer ◽

Supply Rate ◽

Limited Region ◽

Continuous Increase ◽

Higher Temperature ◽

Rate Limiting

AbstractThe first in situ layer-by-layer etching of AlAs(100) surfaces has been observed by using RHEED intensity oscillations technique and is contrasted with the results obtained for the etching of GaAs(100). The experiments were conducted by introducing the etchant, arsenic tribromide, directly into a conventional MBE chamber without the use of any carrier gas. RHEED intensity oscillations during the etching of AlAs are observed between 350 and 760°C indicating a continuous increase in the etching rate with temperatures, with no supply rate limiting conditions being reached. Conversely, oscillations from GaAs reveal a reaction rate limited region at low temperatures (≤500°C) and a supply rate limited region at higher temperature(>500°C). The maximum selectivity in the etching rates between GaAs and AlAs is obtained at 450°C (40:1). The selectivity, and the ability to monitor the layer-by-layer process by RHEED intensity oscillations is foreseen to be of great importance for more controlled fabrications of AlAs and GaAs heterointerfaces.

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