THE MAGNETIC-PROPERTIES OF THE OXYGEN-HOLE ALUMINUM CENTERS IN CRYSTALLINE SIO2 .5. O-17-ENRICHED [ALO4 LI](+) AND DYNAMICS THEREOF/

The O-17 electron paramagnetic resonance (EPR) hyperfine structure of the S = 1/2 centre [AlO4/Li](+) in an isotopically enriched single cry stal of alpha-quartz has been studied by 9-10 GHz EPR (at ca. 55 K) an d is found to be highly anisotropic. The hyperfine matrix A(O-17) has been determined via a least-squares minimization technique that uses e xact diagonalization of the spin Hamiltonian. Analysis of the principa l directions for A confirms earlier theoretical predictions that the e lectronic hole resides in ap orbital on a ''short-bonded'' oxygen adja cent to the A(3+) ion. The location of the Li+ ion within the centre h as been estimated from A(Li-7) and the known electron-spin distributio n. A thermal linewidth study (55-130 K) discloses that, below 75 K, EP R effects due to (i) hole hopping between oxygens and (ii) lithium ion motion are quenched. Above this temperature, such effects become obse rvable, with an activation energy found to be 52(15) meV.