PAC study of the high-temperature phase of Gd2O3: Site identification and temperature dependence of the EFGs at 181Ta impurities

M. RENTERIA; L. A: ERRICO; A. G. BIBILONI; K. FREITAG

Utah

Conferencia; 12th International Conference on Hyperfine Interactions; 2001

We present here PAC results of the electric-nuclear-quadrupole interaction at 181Ta impurities located at the three 7-fold coordinated cation sites of the monoclinic phase of Gd-sesquioxide (B-Gd2O3). The PAC experiments were performed in air in the temperature range 300-1373 K on a 181Hf-implanted B-Gd2O3 pellet with the pure monoclinic structure. For the present investigations high-purity C-Gd2O3 powder (cubic phase, bixbyite structure) was treated in air during 4 h at 1973 K to achieve the total CB phase transformation (verified by XRD experiments). The ion accelerator of the ISKP (Bonn) was then used to implant 181Hf+ ions into the samples. As in the case of the structural isomorph B-Sm2O3, the three cationic lattice sites in the B-phase were not equally occupied by the implanted 181Hf ions in the investigated temperature range. The application of 181Ta and 111Cd empirical correlations found in binary oxides [1,2] allowed us to correlate the observed interactions with each crystallographic site and to identify the single Gd-site populated in 111In-implanted B-Gd2O3 experiments [3]. The preferential site occupation of Cd and Ta in B-Gd2O3 is discussed in terms of the coordination geometry of the probe-atoms. The temperature dependence of the observed hyperfine interactions in the monoclinic phase are compared to those previously found in the cubic bixbyite phase of Gd2O3 and discussed in terms of structural and electronic properties of the impurity-host system. This work was partially supported by Fundación Antorchas, and ANPCyT (PICT98 03-03727), Argentina. The neutron irradiation performed by the GKSS reactor FRG-1, Germany, is kindly acknowledged. Lic. N. Firpo, R. Martino (CINDECA, Argentina), and Dr. E. Aglietti (CETMIC, Argentina) are kindly acknowledged for XRD measurements and the high temperature calcinations, respectively. [1] M. Rentería, C.P. Massolo, and A.G. Bibiloni, Mod. Phys. Lett. B6, 1819 (1992); R. Weht, G. Fabricius, M. Weissmann, M. Rentería, C.P. Massolo, and A.G. Bibiloni, Phys. Rev.B 49, 14939 (1994). [2] M. Rentería, K. Freitag, and L.A. Errico, Hyp. Int. 120/121, 449, (1999). [3] D. Lupascu, M. Urhmacher, and K.P. Lieb, J. Phys.: Condens. Matter 6, 10445 (1994).