²⁷Al Hyperfine and Quadrupole Interactions for the [A10₄]⁰ Center in Quartz

Abstract

An electron-nuclear double resonance (ENDOR) study at 20 K of the [AlO,]O trapped-hole center i n u-quartz gives the principal axes and principal values of the 27Al hyperfine and quadrupole matrices. These are in substantial agreement with previous ESR results obtained by Nuttall and Weil. A model involving both dipole-dipole interactions and the admixing of unpaired spin into aluminum 3p-type orbitals is used t o explain the small anisotropic 27Al hyperfine matrix components. The "best fit" with this model results in 3.7% of an unpaired spin in aluminum 3p-type orbitals and a 0.188 nm distance from the aluminum ion to the oxygen ion containing the trapped hole.Eine Elektronen-Kern-Doppelresonanz (ENDOR) Untersuchung bei 20 K des [A1OJO-Zentrums mit eingefangenem Loch in a-Quartz ergibt die Hauptachsen und -werte der 27Al-Hyperfeinund Quadrupolmatrizen. Sie sind in wesentlicher Ubereinstimnng mit friiheren ESR-Ergebnissen von Nuttall und Weil. Ein Modell, das sowohl Dipol-Dipol-Wechselwirkung als auch die Beimiscliung von ungepaartem Spin in Aluinmium-3p-Orbitale einschlieBt, wird zur ErklLrung der geringen anisotropen 27Al-Hyperfeinmatrixkomponenten herangezogen. Die ,,beste Anpassung" an dieses Modell fiihrt zu 3,7% eines ungepaarten Spins in den Aluminium-3p-Orbitalen und zu einem Abstand von 0,188 nm des Aluminiumions vom Sauerstoffion, das das eingefangene Loch enthLlt .

The Structures of Two Hole Centers in the Mineral Brasilianite NaAl3(PO4)2(OH)4

“…The detailed determination of the structure of such radiation defects largely rests on the evaluation of the hyperfine splitting (hfs) of the neighboring atoms. The best known example of this kind is the smoky quartz center with dominating hfs due to an Al impurity [1][2][3]. In brazilianite hf interaction with the nucleus of at least one structural atom, either Al or P, can be expected, and in a previous study [4] an CT adjacent to one Al and one P was postulated suggesting substitution of the second Al by a divalent impurity.…”

An Electrolytically Generated, Localized Hole Center in Quartz

“…Considering first the 2 Al hyperfine splitting, it is evidently much smaller than in the smoky quartz cen ter [3,4] as the basic center of this type without modi fication by an additional defect in the neighborhood. Decomposition of the principal values into their iso tropic (/liso), dipolar (B) and rhombic (C) components for these as well as the A l... O ~-P [15] and three localized centers observed in the natural quartz variety citrine [14] in Table 2 shows that for all centers with localized holes the isotropic part is much smaller than in the smoky quartz center.…”

“…Smoky quartz is the most thoroughly studied example of such a mineral with a hole on one of the oxygens adjacent to an Al impurity [1][2][3][4]. Since complementary electron and hole centers are simultaneously formed in this photochemical process, assignment of optical absorp tion bands to one of them is always a problem that is still largely unsolved in most cases since even correla tion of the band intensity with the concentration of a certain center (measured, e.g.…”