Nuclear quadrupole interaction at Sc in the anatase and rutile modifications of TiO2: Time- differential perturbed-angular-correlation measurements and ab initio calculations

The nuclear quadrupole interaction of the first excited I=1 state of Sc in the anatase and rutile modifications of bulk TiO2 was determined by time-differential perturbed-angular correlation of rays. New LaBr3 Ce scintillators with excellent energy resolution allowed us to separate the 68 and 78 keV lines of the cascade. For anatase, an almost axially symmetric electric field gradient EFG with an asymmetry parameter of =0.10 1 and a nuclear quadrupole frequency of Q=9.29 3 Mrad /s was obtained. For rutile, an almost antiaxial EFG with =0.94 1 and Q=16.14 6 Mrad /s was obtained, which contradicts literature values. Ab initio calculations of the EFG using the WIEN2K code were performed for anatase and rutile for pure systems as well as for relevant impurities, such as Sc and Cd on Ti sites. The nuclear quadrupole moment of the I=1 state in Sc is redetermined with a sevenfold improved accuracy to be Q= 0.214 3 b.