Thesis (Ph. D.)--University of Wisconsin--Madison, 1968. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

No description available.

No description available.

The study of solids at high pressure and variable temperature enables development of accurate interatomic potential functions over wide ranges of interatomic distances. A review of the main models used in the determination of these potentials is given in Chapter one. A discussion of phonon frequency as a variable physical parameter reflecting the interatomic potential is given. A high pressure Raman study of inorganic salts of the types MSCN, (M = K,Rb,Cs & NH4+) and MNO2, (M = K,Na) has been completed. The studies have revealed two new phases in KNO2 and one new phase in NaNO2 at high pressure. The accurate phonon shift data have enabled the determination of the pure and biphasic stability regions of the phases of KNO2. A discussion of the B1, B2 relationship of univalent nitrites is also given. In the series of thiocyanates studied new phases have been found in all four materials. In both the potassium and rubidium salts two new phases have been detected, and in the ceasium salt one new phase has been detected, all at high pressure, from accurate phonon shift data. These transitions are discussed in terms of second-order mechanisms with space groups suggested for all phases, based on Landau's theory of second-order phase transitions. In the ammonium salt one new phase has been detected. This new phase transition has been interpreted as a second-order transition. The series of molecular crystals CH3HgX, (X = Cl,Br & I) has been studied at high pressure and at variable temperature. In Chapter five, their phase behaviour at high pressure is detailed along with the pressure dependencies of their phonon frequencies. In the chloride and the bromide two new phases have been detected. In the bromide one has been detected at high temperature and one at high pressure, the latter being interpreted as the stopping of the methyl rotation. In the chloride one phase has been found at both low temperature as well as high pressure, and the other only at high pressure, the latter again associated with the stopping of methyl rotation. The iodide displays two high pressure transitions. A Raman-active soft-mode has been observed in all three analogues, at both high pressure and variable temperature. For the chloride and bromide analogues there is a discussion of the nature of the soft-mode along with the mechanism associated with the I/II transition. The results of the X-ray crystal structure determination of CH3HgBr at ambient temperature and pressure are given.

This thesis is concerned with three aspects of magnetic properties in solids. 1. The mean square value <I(I + 1)> of the proton angular momentum per molecule has been measured to be 3.73 ± 0.18 in solid CH₄ at 4.2 K . The experiment was done by measuring the ratio of the proton magnetic resonance free induction decay signal to that of ¹³C at the same frequency in a sample containing 53% ¹³CH₄ . The measured value of <I(I + 1)> differs appreciably from the high temperature value of <I(I + 1)> =3 and from the value of <I(I + 1)> = 6 when all the molecules are converted into the A spin symmetry species. Experiments at lower temperatures using a sample containing 0.002% O₂ impurity indicated that there may be a slight increase in the value of <I(I + 1)> between 4.2 K and 2.45 K . The presence of 0.05% O₂ impurity shortened the time constant for conversion of CH₄ between different symmetry species. The interpretation of measurements of <I(I + 1)> in the presence of large amounts of O₂ impurities is complicated by changes in the NMR line shapes. These complications are discussed in terms of the theoretical results obtained in the second part of the thesis. 2. The NMR line shape inhomogeneously broadened by paramagnetic impurities in solids was investigated theoretically using the statistical method of Margenau. The general expression for the Fourier transform of the line shape function was derived. The lattice can be divided into an inner spherical cut-off region and its complement. Impurities inside the cut-off region give rise to satellite lines and impurities outside determine the shape of the main line and satellite lines. Detailed numerical calculations were performed for a f.c.c. lattice when the impurities are (a) classical magnetic dipoles, (b) spin 1/2 systems and (c) spin 1 systems. An asymmetry in the line shape is predicted at finite temperatures. The peak intensity is shifted from the centre by an amount linear in the impurity concentration and in the magnitude of the magnetic moment and the overall line shape adjusts itself in such a way to give a vanishing first moment about the centre. The line shape is always Lorentzian at the centre and Gaussian in the wings. It depends on the impurity concentration. At low concentrations, the main line and the satellite lines have the same shape which is predominantly Lorentzian. The shape of a powdered sample is also discussed. 3. General expressions are derived for the first two terms in the expansion of the specific heat of a paramagnetic salt in powers of T⁻¹. It is assumed that the interaction between the paramagnetic ions consists of magnetic dipole and isotropic exchange interactions, and that the g-tensor of each ion is axial and has the same orientation for all ions. The general formulae are evaluated numerically for cerium magnesium nitrate. Comparison with the experimental data of Mess and coworkers indicated that the exchange parameter corresponds to a ferromagnetic interaction. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Paramagnetic impurities containing oxygen were produced in the reactions of KBr, KCl, NaCl and SrCl(2) with fluorine. Molecular oxygen, FOO･ radical and C10(2) were identified by ESR as reaction by-products. The spectra assigned to CIO(2) have predominant powder character even in single crystals of halides. The results are correlated with previous work in this laboratory. The origin of oxygen impurity is suggested to be surface hydroxide ions in KBr and KC1, and entrapped water in NaCl and SrCl(2). Nucleation processes and other anomalous features observed in these reactions by previous workers are explained by the presence of impurities. Oxygen was found to be incorporated into the SrCl(2) crystals by recrystallisation from the melt in the presence of oxygen. It exists in the form of superoxide ion O(2)¯ which occupies an interstitial position between two lattice anions and is associated with two anion vacancies. The molecular axis lies in a [00l] direction of the crystal and the degeneracy of the 2pπ(g) -molecular orbital is lifted by the crystal field. The bonding between the O(2)¯ ion and its neighbouring cations and anions is discussed in terms of a Cl(6)Sr･O(2)¯･SrCl(6) "complex". The orbital angular momentum reduction factor for O(2)¯ in SrCl(2) has been calculated from the experimental g-factors and found to be anomalously large. A survey was made on impurities incorporated into strontium compounds through processes of recrystallisation from melts or from aqueous solutions. Strontium carbonate was identified in melt-recrystallised Sr(NO3)(2) by Infrared Spectroscopy and X-ray powder method. It was produced by partial decomposition of the nitrate in the presence of atmospheric CO(2). NO(3)²¯ ion was identified in the recrystallised material by ESR. ESR and infrared studies suggest that the NO(3)²¯ ion substitutes a carbonate ion in the SrCO(3) lattice. Results from a similar study on Ba(NO3)(2) also support this conclusion. / Science, Faculty of / Chemistry, Department of / Graduate

No description available.

No description available.

No description available.

No description available.