ELECTRIC QUADRUPOLE INTERACTIONS OF THE SHORT-LIVED BETA-EMITTER N-12IN INSULATOR CRYSTALS (N-12 IMPLANTED IN SINGLE-CRYSTAL TIO2)

The electronic structure of nitrogen atoms as impurities in an ionic T iO2 crystal has been investigated by analyzing electric field gradient s (EFGs) measured by use of short-lived beta-emitting N-12 implanted f ollowing nuclear reactions. Conventional beta-NMR and its modification , suitable for the detection of quadrupole effects in the NMR spectra, were used for the investigation of hyperfine interactions of N-12 loc ated in substitutional sites of O atoms and interstitial sites in the crystal. In order to deduce absolute values of the EFGs from the obtai ned eqQ/h, the quadrupole moment of N-12 has been determined from the NMR detection of N-12 implanted in BN(hexagonal) crystal. Here the EFG at the N atom in BN was measured by detecting the FT-NMR of N-14 in t he crystal. The EFGs in TiO2 are compared with the theoretical predict ions based on the nb initio band-structure calculation in the framewor k of the KKR method.