First-principles calculations of structural and electronic properties of monoclinic hafnia surfaces

Abstract

We have carried out a systematic theoretical study of the surfaces of monoclinic hafnia ͑HfO 2 ͒ using plane waves and density functional theory based on the generalized gradient approximation. The fully relaxed structures of the bulk phases of HfO 2 are found to be in excellent agreement with experimental data, the monoclinic phase being the most stable. Simulations of the monoclinic phase surfaces indicate a large relaxation which reduces the total surface energy of all nine faces considered by between 23% and 36%, with a strong correlation between the unrelaxed and relaxed surface energies. Our calculations predict that the ͑111͒ and ͑111͒ faces of the monoclinic phase have the lowest surface energies and are hence the most stable faces. An analysis of the total and partial electronic density of states of bulk monoclinic HfO 2 reveals that the outer valence band significantly mixes the O 2p and Hf 5d atomic states indicating some covalency of the Hf-O bonds. The total density and partial density of states of the monoclinic surfaces exhibit a surface state corresponding to the surface O 2s states in the inner valence band region.

Impurity Centers in Oxides Investigated by γ-γ Perturbed Angular Correlation Spectroscopy and <i>Ab Initio</i> Calculations

“…This condition is met in the elements Cd, In, Sn, Zn and Ga, all of which still have filled d-bands after reaction with oxygen [83]. In the context on hyperfine interactions studies of binary oxides using PAC and 111 In(EC) 111 Cd as probe, In 2 O 3 becomes very special because the starting probe is not an impurity in the compound. The hyperfine interactions can be studied without taking into account the binding of structural or electronic defects to the probe site, at least before de EC decay of 111 In to 111 Cd.…”

“…In the context on hyperfine interactions studies of binary oxides using PAC and 111 In(EC) 111 Cd as probe, In 2 O 3 becomes very special because the starting probe is not an impurity in the compound. The hyperfine interactions can be studied without taking into account the binding of structural or electronic defects to the probe site, at least before de EC decay of 111 In to 111 Cd. While the local structure of the In site is well-known and the structural relaxations produced by the 111 Cd atom has been understood completely [30,32], open questions remain concerning the electronic configuration of the impurity center after the EC decay.…”

“…The hyperfine interactions can be studied without taking into account the binding of structural or electronic defects to the probe site, at least before de EC decay of 111 In to 111 Cd. While the local structure of the In site is well-known and the structural relaxations produced by the 111 Cd atom has been understood completely [30,32], open questions remain concerning the electronic configuration of the impurity center after the EC decay. In 1956, Lehmann and Miller carried out the first PAC investigation on In 2 O 3 doped with 111 In(EC) 111 Cd [84].…”

“…While the local structure of the In site is well-known and the structural relaxations produced by the 111 Cd atom has been understood completely [30,32], open questions remain concerning the electronic configuration of the impurity center after the EC decay. In 1956, Lehmann and Miller carried out the first PAC investigation on In 2 O 3 doped with 111 In(EC) 111 Cd [84]. Measuring at room temperature the angular correlations of the 111 Cd γ radiation, they found a PAC spectrum dramatically attenuated.…”

“…In this sense the PAC technique, having its tracers located at the "eye of the storm", can supply unique and valuable information about the impurity center configuration and the properties of the doped systems. In this chapter a review of the PAC studies performed on binary oxides using 111 Cd and 181 Ta impurities as probe-atoms is given. Results of selected experiments that have given by themselves important information are described, as well as cases in which ab initio calculations were necessary to explain more complicated scenarios.…”