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A study of the vanadium oxide bronze 0-VOB, and vanadium oxides V2O5 and VO2, using hyperfine interaction techniques.Naicker, Vishnu Visvanathan. January 1999 (has links)
One of the main interests in the vanadium oxides V2O5 and VO2 is that, when doped with a
metal such as Fe, these oxides display semiconductor-to-metal transitions at certain critical
temperatures. These transitions are also accompanied with changes in the crystallographic
phases of the oxides. This thesis describes the use of hyperfine interactions at dopant sites
in the vanadium oxides V2O5 and VO2 to infer information on the phase transitions that
take place in these oxides.
The hyperfine interaction techniques of Mossbauer Spectroscopy and Time Differential
Perturbed Angular Correlation (TDPAC) are used to study the hyperfine parameters in the
Fe - V2O5 system and Cd - V2O5 system, respectively. X-ray powder diffraction
spectroscopy were also conducted on the samples to establish the phases created.
A large part of this project was spent in the design of apparatus. The apparatus constructed
were (i) a furnace to perform a solid state reaction in order to introduce Fe into V2O5, the
maximum operating temperature of the furnace being 1473 K, (ii) a Mossbauer sample
chamber and sample holder which enabled the sample to be heated up to a temperature of
873 K, and (iii) a device constructed to determine the electrical conductivities of powder
samples at temperatures ranging from 773 K to room temperature.
For the Mossbauer studies, the Fe-V2O5 system was studied as a function of the Fe
concentration. Six symmetric doublets, with intensities changing as the Fe concentration
changed, were observed. Correlating the Mossbauer components of the individual spectra
with the phases identified using powder x-ray diffraction patterns in terms of the reflection
intensities, allowed two of the doublets to be assigned to lattice sites in the vanadium oxide
bronze system, θ-YOB, a further two doublets to substitutional and interstitial sites in the
Fe doped V2O5 system, respectively, and the fifth doublet to the super-paramagnetic Fe2O3
phase. The sixth doublet observed was attributed to an unresolved crystallographic phase
observed in the x-ray diffraction spectra at large Fe concentrations.
The magnitude of the quadrupole splittings of the doublets assigned to the vanadium oxide
bronze and the Fe-V2O5 systems indicate that the electronic environment of the Fe atoms in
the bronze phase displays a greater symmetry than those in the V2O5 phase.
In order to gain insight on the semiconducting nature of the Fe doped V2O5 and the θ-VOB
phases, temperature dependent Mossbauer measurements ranging from 300 K to 573 K,
together with electrical conductivity measurements, were performed on a few samples. The
temperature dependent Mossbauer spectra displayed the usual second order Doppler shift
of the isomer shifts for the various components as a function of temperature, but no
significant change in the magnitude of the quadrupole splittings. From this result, on the
basis of the Duncan-Golding correlation diagram, the valence state of the Fe ions was
inferred to be 3+. No components were observed (with increasing temperature) that could
be correlated with the population of Fe2+ states. This therefore suggests that the
semiconducting properties of the Fe doped V2O5 phase and the θ-VOB phase are associated
with electron hopping between V4+ - V5+ valence sites rather than Fe3+ - Fe2+ valence sites.
111In-TDPAC measurements were made on V2Os and VO2. For V2O5, the measurements
yielded one distinct substitutional cation site for the 1llCd ions, with quadrupole coupling
constant vQ =88,1(3) MHz, and asymmetry η =0,619(3)
In VO2, temperature dependent TDPAC measurements yielded two well defined
quadrupole coupling frequencies for the 1llCd probe nuclei, the first, vQ =43,0(7) MHz,
observed at room temperature, corresponding to a monoclinic or triclinic phase of VO2, and
the second, vQ =89,1(1) MHz, observed at 423 K and above, corresponding to the rutile
phase of VO2. / Thesis (Ph.D.)-University of Durban-Westville, 1999.
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Real-time terahertz imaging using a quantum cascade laser and uncooled microbolometer focal plane arrayBehnken, Barry N. January 2008 (has links) (PDF)
Dissertation (Ph.D. in Physics)--Naval Postgraduate School, June 2008. / Dissertation Advisor(s): Karunasiri, Gamani. "June 2008." Description based on title screen as viewed on August 28, 2008. Includes bibliographical references (p. 75-80). Also available in print.
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Intermediate oxides of vanadium and titaniumKhan, A. S. January 1968 (has links)
No description available.
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High resolution spectroscopy of niobium nitride and vanadium oxideHuang, Gejian January 1988 (has links)
This thesis reports the spectroscopic studies of two gaseous molecules, niobium nitride (NbN) and vanadium oxide (VO). The ³∏ — ³∆ electronic transition of NbN was recorded by laser-induced fluorescence at Doppler-limited resolution as well as at sub-Doppler resolution. Two almost identical branch features are observed in the ³∏₀ — ³∆₁ sub-band because the A-doubling in the ³∏₀ sub-state is large and almost J-independent. The ³∏₁ — ³∆₂ transition is shifted 600 cm⁻¹ to the red of its central first-order position as a result of very large second-order spin-orbit interaction effects. The shift is believed to be caused principally by the coupling of the ³∏₁ component with the ¹∏ state from the same electron configuration, with a smaller contribution from coupling of the ³∆₂ component
of the ground state with the low-lying ¹∆ state. The ³∏ and ¹∏ states are unusual in that their zero-order energies are calculated to be within 100 cm⁻¹, based on the newly observed ¹∏₁ - ³∆₂ (1,0) transition; this means that they form a very fine example of a "super-multiplet", where the spin-orbit effects within and between the states of a particular
electron configuration are larger than their separations. The spin-orbit interactions are so extensive that the fine structure can only be fitted using effective rotational and hyperfine Hamiltonians for the individual sub-states, as in case (c) coupling. From the determined hyperfine constants h and C⍳ for the three ³∏(v — 0) components, the Fermi contact constant b was found to be negative, which is consistent with the configuration πδ. Rotational analysis gave the ³∏ and ³∆ bond lengths as 1.6705 Å and 1.6622 Å, respectively.
The near-infrared electronic system of VO has been recorded in emission at Doppler-limited resolution with the 1-m FT spectrometer at Kitt Peak National Observatory. The spectrum in the 4000-14000 cm⁻¹ region consists of numerous transitions with most of them extensively analyzed. Two isolated sub-bands at 7200 cm⁻¹ have been assigned as the two spin components of a ²∏ — ²∆ transition and rotationally analyzed. The rotational constant for the lower state is found to be larger than that for the σδ² X ⁴∑⁻ ground state, indicating that the ²∆ state arises from the electron configuration σ²δ. The configuration assignment was confirmed by the derived spin-orbit coupling constant for the ²∆ state. Similar reasoning applied to the ²∏ upper state suggests that it may arise from the configuration σ²π, though the preliminary study of the hyperfine structure argues against this assignment. / Science, Faculty of / Chemistry, Department of / Graduate
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A mechanistic study of the protein photocleavage activities of vanadate(V) and vanadium(V)-peroxo complexes towards aldolaseLeung, Wing Chi 01 January 2011 (has links)
No description available.
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Vanadium oxide anion clusters their abundances, structures and reactions with SO₂ /Wyrwas, Richard Ben, January 2004 (has links) (PDF)
Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2005. / Whetten, Robert L., Committee Chair ; First, Phillip N, Committee Member ; Sherrill, C. David, Committee Member ; Wine, Paul H., Committee Member ; El-Sayed, Mostafa A, Committee Member. Includes bibliographical references.
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Magnetic Studies On Nano-scale Radical-containing Vanadium OxideHuang, Yi-Fen 24 June 2006 (has links)
Recently, controlling the shape of nanoparticles during their fabrication has become a new and interesting research area. In fact, the nanoparticle has been proven that its physical properties are strikingly related to the shape of itself. After finding the carbon nanotubes in 1911, more and more nanostructure materials have been synthesized. The radical nano-scale vanadium oxide VO2.24(C12H14N2)0.061 is synthesized by hydrothermal method.
VO2.24(C12H14N2)0.061 has various physical properties, and we would focus on it¡¦s magnetic properties in the thesis, including magnetic susceptibility and magnetization. The magnetic susceptibility measurements show that the antiferromagnetic transition occurs at T = 20K ~ 25K, and it has been found the specific transition at T = 265K ~ 275K in some samples. Based on the magnetization data, these materials are ferromagnetic, and the hysteresis loops exhibit unusual steps. Whenever these materials process thermal treatments or not, the steps still exist. In addition, we will analyze the impact of the production date, thermal treatment, and preserved environment to discover more colorful properties of these materials.
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Syntheses, characterizatons and DNA photocleavage activities of some vanadium(V)-peroxo complexesChan, Oi-yin 01 January 1997 (has links)
No description available.
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Predicting the temperature-strain phase diagram of VO$_2$ from first principlesKim, Chanul January 2018 (has links)
Predicting the temperature-strain phase diagram of VO$_2$, including the various structural allotropes, from first principles is a grand challenge of materials physics, and even the phase diagram remains unclear at T = 0K. The coexistence of Peierls and Mott physics suggests that a theory which can capture strong electronic correlations will be necessary to compute the total energies. In order to understand the complex nature of the first-order transition of VO$_2$, we build a minimal model of the structural energetics using the Peirels-Hubbard model and solve it exactly using the Density Matrix Renormalization Group (DMRG) methods demonstrating that the on-site interaction $U$ has a minimal effect on the structural energetics for physical parameters. These results explain the qualitative failures of Density Functional Theory (DFT) and DFT+$U$ for the structural energetics, in addition to the partial success of the unorthodox DFT+$U$ results (i.e. non-spin-polarized and small $U$). It also guides the creation of empirical corrections to the DFT+$U$ functional which allow us to semi-quantitatively capture the phase stability of the rutile and monoclinic phases as a function of temperature and strain. Our work demonstrates that VO$_2$ is better described as a Mott assisted Peierls transition.
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Vanadium(V)-peroxo complexes : a study of their specific DNA-photocleavage activities and NMR spectral propertiesShek, Lai Kuen 01 January 2001 (has links)
No description available.
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