Electric Field Gradients at Hf and Fe Sites in Hf 2 Fe Recalculated J. BELOS ˇ EVIC ´ -C ˇ AVOR, B. CEKIC ´ *, N. NOVAKOVIC ´ , V. KOTESKI and Z. MILOS ˇ EVIC ´ Institute of Nuclear Sciences Vinca, Belgrade, Serbia and Montenegro; e-mail: cjeca@vin.bg.ac.yu Abstract. The electric field gradients (EFG) of the Hf 2 Fe intermetallic compound were calculated using the full-potential linearized augmented plain-wave (FP-LAPW) method as embodied in the WIEN 97 code. The obtained values are compared with other ab-initio calculations and on a qualitative basis with the previously reported experimental data obtained from TDPAC. The cal- culated results, j23.1I10 21 V/m 2 and 2.7I10 21 V/m 2 for Hf 48f and Fe 32e position, respectively, are in excellent agreement with experimental data (23.4I10 21 V/m 2 and 2.7I10 21 V/m 2 ), better than those reported in earlier calculations. The calculated EFG for Hf 16c position (4.2I10 21 V/m 2 ) is stronger than the experimental one (1.1I10 21 V/m 2 ). Key Words: Hf 2 Fe, electric field gradient, FLAPW, WIEN 97. 1. Introduction Electric field gradient (EFG) can be used as a powerful tool to provide structural information of solids on the atomic scale. It arises from the interaction of a nucleus and the electric field created by its chemical environment. Since the EFG varies from site to site, it can be regarded as a way to label non-equivalent sites in an investigated solid [1]. The Hf 2 Fe has attracted much attention in the past, mostly because of its ability to absorb a large amount of hydrogen [2]. It crystallizes in the cubic Ti 2 Ni structure, with 96 atoms per unit cell. The 32 Fe atoms are in positions 32e, the 64 Hf atoms are distributed on positions, 16c (Hf1) and 48f (Hf2) [3]. The striking feature of the EFG observed at the 48f site is its high value, probably the largest ever observed for the 181 Ta probe ion in any metallic medium. The value of the EFG at the 16c site is about one order of magnitude smaller thus approaching the usual values in most metallic systems [4]. These interesting properties, along with the existence of high quality experimental data concerning the EFG problem in this compound, stimulated us to treat Hf 2 Fe theoretically. * Author for correspondence. Hyperfine Interactions (2004) 158:47–51 DOI 10.1007/s10751-005-9010-x # Springer 2005