Magnetic resonance in solids

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:5565332

O'Connell, A J

In this thesis electron paramagnetic resonance (EPR) and electro-nuclear double resonance (ENDOR) experiments are reported on paramagnetic defects in two host materials: (a) Cr[sup 3+] in the ferroelectric lecontite and (b) color centres and the Fe[sup 3+] centre in lithium oxide. A. Lecontite. Lecontite, NaNH[sub 4]SO[sub 4][center dot]2H[sub 2]O, undergoes a phase transition to a ferroelectric phase below [Tc] = 101 K. Reported here are EPR measurements on doped Cr[sup 3+] ions at two distinct sites, made at a variety of temperatures in an attempt to ascertain the details of the structural changes occurring at [Tc]. The room temperature data are compared to various models for the two defects using the Newman superposition model. The results show that the Cr[sup 3+] ions are at Na[sup +] sites, highly distorted due to charge compensation of the trivalent dopant and therefore that the EPR of these defects is not representative of the bulk material. B. Lithium oxide. Investigations of three defect in lithium oxide, Li[sub 2]O are reported here. (i) The electronic F[sup +] -centre has been investigated using EPR and [sup 7]Li ENDOR to determine the transferred hyperfine structure (THFS) due to hyperfine interactions of the defect wavefunction with the ligand nuclei. Comparison with F-centres in other simple ionic hosts shows that the centre is highly localized and this observation is explained by the charge states of the ligands and the defect site. (ii) EPR and [sup 7]Li ENDOR of the interstitial neutral hydrogen centre H[sup 0] show a novel tunnelling effect. At low temperatures the defect has tetragonal symmetry but at higher temperatures there is evidence of tunnelling between six equivalent sites, leading to effective cubic symmetry. (iii) THFS of Fe[sup 3+] centres, measured using [sup 7]Li ENDOR, interpreted using the Newman superposition model, are used to determine the distortions of the neighboring ligands.

• Research Organization: Oxford Univ. (United Kingdom)
• OSTI ID: 5565332
• Country of Publication: United States
• Language: English

Related Subjects

665100* -- Nuclear Techniques in Condensed Matter Physics -- (1992-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALKALI METAL COMPOUNDS
AMMONIUM COMPOUNDS
AMMONIUM SULFATES
CHALCOGENIDES
CHARGE STATES
CHARGED PARTICLES
CHROMIUM IONS
COLOR CENTERS
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DEFECTS
DOPED MATERIALS
ELECTRON SPIN RESONANCE
ENDOR
FERROELECTRIC MATERIALS
HYPERFINE STRUCTURE
IONS
IRON IONS
LIGANDS
LITHIUM COMPOUNDS
LITHIUM OXIDES
MAGNETIC RESONANCE
MATERIALS
OXIDES
OXYGEN COMPOUNDS
POINT DEFECTS
RESONANCE
SODIUM COMPOUNDS
SODIUM SULFATES
SULFATES
SULFUR COMPOUNDS
SYMMETRY
TEMPERATURE DEPENDENCE
VACANCIES