Crystallization behavior of Li1–5x Ta1+xO3 glasses synthesized from liquid precursors

1996 ◽  
Vol 11 (9) ◽  
pp. 2376-2387 ◽  
Author(s):  
J.A. Allemann ◽  
Y. Xia ◽  
R. E. Morriss ◽  
A. P. Wilkinson ◽  
H. Eckert ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Neutron Diffraction ◽  
Homogeneity Range ◽  
Crystallization Behavior ◽  
Second Phase ◽  
Amorphous Oxides ◽  
X Ray ◽  
Pyrolytic Decomposition ◽  
Liquid Precursors ◽  
Metastable Extension

The crystallization of amorphous oxides synthesized by pyrolytic decomposition of mixed Li and Ta 2-ethylhexanoates and alkoxides has been investigated. The study was motivated by thermodynamic considerations that, in the light of experience in other systems, suggest the potential for metastable extension of the LiTaO3 homogeneity range. Materials investigated are described by the general stoichiometry Li1–5xTa1+xO3 and include Li2O contents from 0 to 70 mol% (20.18 ≤ x ≤ 0.2). The samples were prepyrolyzed at 400 °C and subsequently crystallized by heat treatments in air at 550–700 °C for 0.1–100 h. The first product of crystallization for compositions from 30 to 65% Li2O is always the LiTaO3 phase. Extensive characterization by x-ray and neutron diffraction, as well as 7Li-NMR spectroscopy, revealed that this phase evolves with a structure and stoichiometry close to equilibrium. For Li+-deficient compositions, excess Ta5+ is rejected to the amorphous constituent during crystallization and eventually gives rise to the evolution of Ta2O5, with the LiTa3O8 phase suppressed in all cases. Similar observations were made for the Li+-rich compositions, but the evolving second phase is the equilibrium Li3TaO4. The absence of solubility extension in LiTaO3, which appears feasible from a thermodynamic viewpoint, is ascribed to the large differences in mobilities of the Li and Ta species in the parent amorphous oxide resulting from pyrolysis.

Analytical Electron Microscopy Study of Second-Phase Particles in 7075 and 7475 Aluminum Alloys

1985 ◽  
Vol 43 ◽  
pp. 348-349
Author(s):  
M. Raghavan ◽  
J. Y. Koo ◽  
J. W. Steeds ◽  
B. K. Park
Keyword(s):  
Aluminum Alloys ◽  
Silicon Oxide ◽  
Analytical Electron Microscopy ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Partial Substitution ◽  
Second Phase ◽  
X Ray ◽  
Second Phase Particles ◽  
Almost All

X-ray microanalysis and Convergent Beam Electron Diffraction (CBD) studies were conducted to characterize the second phase particles in two commercial aluminum alloys -- 7075 and 7475. The second phase particles studied were large (approximately 2-5μm) constituent phases and relatively fine ( ∼ 0.05-1μn) dispersoid particles, Figures 1A and B. Based on the crystal structure and chemical composition analyses, the constituent phases found in these alloys were identified to be Al7Cu2Fe, (Al,Cu)6(Fe,Cu), α-Al12Fe3Si, Mg2Si, amorphous silicon oxide and the modified 6Fe compounds, in decreasing order of abundance. The results of quantitative X-ray microanalysis of all the constituent phases are listed in Table I. The data show that, in almost all the phases, partial substitution of alloying elements occurred resulting in small deviations from the published stoichiometric compositions of the binary and ternary compounds.

Texture measurements in Al2O3 using BEKP

1994 ◽  
Vol 52 ◽  
pp. 608-609
Author(s):  
M. D. Vaudin ◽  
J. P. Cline
Keyword(s):  
Neutron Diffraction ◽  
Rapid Method ◽  
Crystallographic Orientation ◽  
Specimen Surface ◽  
X Ray Diffraction ◽  
Anisotropic Crystal ◽  
X Ray ◽  
Verification Method ◽  
Crystal Properties ◽  
Backscattered Electron

The study of preferred crystallographic orientation (texture) in ceramics is assuming greater importance as their anisotropic crystal properties are being used to advantage in an increasing number of applications. The quantification of texture by a reliable and rapid method is required. Analysis of backscattered electron Kikuchi patterns (BEKPs) can be used to provide the crystallographic orientation of as many grains as time and resources allow. The technique is relatively slow, particularly for noncubic materials, but the data are more accurate than any comparable technique when a sufficient number of grains are analyzed. Thus, BEKP is well-suited as a verification method for data obtained in faster ways, such as x-ray or neutron diffraction. We have compared texture data obtained using BEKP, x-ray diffraction and neutron diffraction. Alumina specimens displaying differing levels of axisymmetric (0001) texture normal to the specimen surface were investigated.BEKP patterns were obtained from about a hundred grains selected at random in each specimen.

An unusual reaction of a bridged triterpenoid α-diketone with acetic anhydride

1991 ◽  
Vol 56 (12) ◽  
pp. 2917-2935 ◽  
Author(s):  
Eva Klinotová ◽  
Václav Křeček ◽  
Jiří Klinot ◽  
Miloš Buděšínský ◽  
Jaroslav Podlaha ◽  
...  
Keyword(s):  
Acetic Acid ◽  
Nmr Spectroscopy ◽  
Acetic Anhydride ◽  
Spectral Methods ◽  
X Ray Diffraction ◽  
X Ray ◽  
Mild Conditions ◽  
Condensation Products ◽  
Unsaturated Lactones ◽  
C Nmr

3β-Acetoxy-21,22-dioxo-18α,19βH-ursan-28,20β-olide (IIIa) reacts with acetic anhydride in pyridine under very mild conditions affording β-lactone IVa and γ-lactones Va and VIIa as condensation products. On reaction with pyridine, lactones Va and VIIa undergo elimination of acetic acid to give unsaturated lactones VIIIa and IXa, respectively. Similarly, the condensation of 20β,28-epoxy-21,22-dioxo-18α,19βH-ursan-3β-yl acetate (IIIb) with acetic anhydride leads to β-lactone IVb and γ-lactone Vb; the latter on heating with pyridine affords unsaturated lactone VIIIb and 21-methylene-22-ketone Xb. The structure of the obtained compounds was derived using spectral methods, particularly 1H and 13C NMR spectroscopy; structure of lactone IVa was confirmed by X-ray diffraction.

Reactivity of Sodium Hexaethyl-2,4-dicarba-nido-hexaborate(1-)

1999 ◽  
Vol 64 (6) ◽  
pp. 977-985 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Hans-Jörg Schanz ◽  
Wolfgang Milius ◽  
Catherine McCammon
Keyword(s):  
Mössbauer Spectroscopy ◽  
Nmr Spectroscopy ◽  
Structural Analysis ◽  
Hydrogen Atom ◽  
Mossbauer Spectroscopy ◽  
Sandwich Complex ◽  
X Ray ◽  
Bromo Derivative ◽  
Boron Tribromide ◽  
C Nmr

Sodium hexaethyl-2,4-dicarba-nido-hexaborate(1-) (6), available from hexaethyl-2,4-dicarba- nido-hexaborane(8) (4) by deprotonation, reacts with deuterated methanol, CD3OD, to give back 4 without H/D exchange of the B-H-B hydrogen atom. The reaction of 6 with diethylboron chloride, Et2BCl, affords hexaethyl-2,4-dicarba-closo-hexaborane(6) (7), the first example of a peralkylated carborane of this type. In contrast, the reaction of 6 with boron tribromide, BBr3, leads mainly to 2,3,4,5,6,7-hexaethyl-2,4-dicarba-closo-heptaborane(7) (8), together with the corresponding 1-bromo derivative (9) and the closo-carborane 7 as side products. The reaction of two equivalents of 6 with FeCl2 gives the air-stable sandwich complex bis[hexaethyl-2,4-dicarba-nido-hexaborate(1-)]iron 10 which was characterised by X-ray structural analysis. All products were characterised by 1H, 11B and 13C NMR spectroscopy, and 57Fe Mössbauer spectroscopy was used to study 10.

Unusual Rearrangement of Naphthalene in the Synthesis of a Novel B8-B8-Bridged Derivative in the [(1,2-C2B9H11)2-3-Co]- Series. X-Ray Structure and 11B NMR Spectra of [8,8'-μ-(CH2-C9H6)-(1,2-C2B9H10)2-3-Co]- (CH3)4N+

1997 ◽  
Vol 62 (5) ◽  
pp. 746-751 ◽  
Author(s):  
Andreas Franken ◽  
Jaromír Plešek ◽  
Christiane Nachtigal
Keyword(s):  
Nmr Spectroscopy ◽  
Single Crystal ◽  
Nucleophilic Substitution ◽  
Nmr Spectra ◽  
X Ray Diffraction ◽  
X Ray ◽  
Unusual Rearrangement ◽  
Multinuclear Nmr Spectroscopy ◽  
11B Nmr ◽  
Isolated Compound

On treatment of the [(1,2-C2B9H11)2Co]- ion with naphthalene in presence of AlCl3 a remarkably bridged [8,8'-μ-(CH2-C9H6)-(1,2-C2B9H10)2-3-Co]- ion is obtained as a single isolated compound. The triatomic -CH2-C9H6- bridge is derived from the rearranged naphthalene nucleus. The mechanism of this reaction is obscure but it does resemble the "Electrophile-Induced Nucleophilic Substitution" reported earlier. The structure of the compound was established by multinuclear NMR spectroscopy and by single crystal X-ray diffraction.

Sign in / Sign up

Export Citation Format

Share Document