Volume 157, number 8,9 PHYSICS LETTERS A 12 August 1991 Scaling of the electric field gradient of “Cd impurities in the bixbyite oxides of Y, Sc, Dy and Yb * A. Bartos, K.P. Lieb, A.F. Pasquevich ‘, M. Uhrmacher and ISOLDE Collaboration II. Physikalisches Instilut, Universität Gottingen, W-3400 Gottingen, Germany Received 25 February 1991; revised manuscript received 17 May 1991; accepted for publication 12 June 1991 Communicated by J. Flouquet The quadrupole hyperfine interaction of” ‘Cd in the cubic C-form sesquioxides of Sc, Y, Dy and Yb has been investigated over the temperature range 295—8 50 K with perturbed angular correlation (PAC) spectroscopy. The “Cd probe nuclei were either produced in the EC-decay of “In or in the y-decay of the “Cd isomeric state and introduced via ion implantation into the oxide matrices. A simple scaling of the components of the electric field gradient with the lattice constant has been observed on both substitutional octahedral sites. The perturbed angular correlation (PAC) method reported [71. All rare earth metal oxides can be ob- is a powerful tool for investigating lattice defects, tamed in the cubic C-form (bixbyite) which belongs solid state reactions and phase transitions on a mi- to the 1a3 (T~) space group. A unit cell contains 8 croscopic scale [1]. PAC measurements require a ra- cations at position 8b having D3d point group sym- dioactive probe with a sensitive nuclear state the metry, 24 cations at position 24d with C 2 point group electric quadrupole moment Q of which interacts with symmetry and 48 oxygen ions in position 48e [8]. the electric field gradient(s) (efg) generated by ionic Consequently, there exist two possible substitutional and electronic contributions of the nearest neigh- sites referred to as site “C” (asymmetric site) and borhood. In the past, we have extensively used this “D” (regular or symmetric site), to be occupied by method to study hyperfine interactions between “Cd a probe atom with relative fractions in the ratio 3:1. probe nuclei and oxygen during oxidation of fcc met- Besides the rare earth elements, also 1n203, Sc203 and als [2] as well as structural, antiferromagnetic and Y203 share the cubic C-form. A comparison of the oxidation phase transitions in many oxides [3—6]. efg in Sc203 (lattice constant a=0.9857 nm), Y203 Recently, Kesten et al. [3] discovered a pro- (1.0621 nm), 1n203 (1.0116 nm), Yb203 (1.0433 nounced, but so far unexplained correlation of the nm) and Dy203 (1.0665 nm) thus offers the pos- efg for substitutional “Cd with the crystal structure sibility to compare the 4f rare earth oxides and the and the nearest-neighbor oxygen coordination. d-element oxides of In [9], Y and Sc and to study The subject of the present PAC study is to inves- the variation of the efg over quite a large range of the tigate the scaling of the efg for substitutional “Cd lattice constant. atoms in several rare earth oxides of bixbyite struc- The oxide powder targets (Johnson Matthey; Y203: ture. Under suitable conditions, all rare earth ele- ultrapure, Sc203, Yb203, Dy203: 99.999%) were ments form a sesquioxide RE203, but polymorphism rolled onto Ag backings. About 1013 “ 11n + ions were is common and up to five crystalline types have been implanted at 400 keY using the Gottingen ion im- planter IONAS [10]. After implantation, the sam- ples were annealed for 1A= 1 h at TA= 1075 K under * Supported by Deutsche Forschungsgemeinschaft (L,325/2-l) 5 and Stiftung Volkswagenwerk. vacuum (p~ 10— mbar) to remove radiation dam- Permanent address: Facvltad de Ciencias, Universidad Na- age. About 10” ions of hhlmCd+ were implanted with cional de La Plata, La Plata, Argentina. an energy of 60 keY at ISOLDE/CERN, followed by 0375-9601/91/S 03.50 © 1991 — Elsevier Science Publishers B.V. (North-Holland) 513