Abstract
In this paper we report the synthesis, structure and Li ion conductivity of a new tetragonal garnet phase Nd3Zr2Li7O12. In line with other tetragonal garnet systems, the Li is shown to be ordered in the tetrahedral and distorted octahedral sites, and the Li ion conductivity is consequently low. In an effort to improve the ionic conductivity of the parent material, we have also investigated Al doping to reduce the Li content, Nd3Zr2Li5.5Al0.5O12, and hence introduce disorder on the Li sublattice. This was found to be successful leading to a change in the unit cell symmetry from tetragonal to cubic, and an enhanced Li ion conductivity. Neutron diffraction studies showed that the Al was introduced onto the ideal tetrahedral garnet site, a site preference also supported by the results of computer modelling studies. The effect of moisture on the conductivity of these systems was also examined, showing significant changes at low temperatures consistent with a protonic contribution in humid atmospheres. In line with these observations, computational modelling suggests favourable exchange energy for the Li+/H+ exchange process.
Highlights
The recent portable electronics boom has been driven by advances made in Li ion battery technology
Initial structural studies using X-ray diffraction data led to different claims on the location of the Li sites.[17,18,19]. This can be explained by the fact that Li has a weak X-ray scattering factor, which severely hinders its effective location using X-ray diffraction. This problem can be solved through the use of neutron diffraction studies, with initial work in the area by Cussen et al on Li5La3M2O12, showing that the space group was Ia3d, with Li distributed over both the ideal tetrahedral garnet site and interstitial distorted octahedral sites.[2]
Cussen et al showed that the occupancy of the interstitial sites was only observed for Li contents per formula unit greater than 3, while in systems with ideal conventional garnet stoichiometry, such as Li3Ln3Te2O12 (Ln 1⁄4 rare earth), the Li was only present in the tetrahedral site
Summary
The recent portable electronics boom has been driven by advances made in Li ion battery technology.
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