Fast
Li-ion-conducting Li oxide garnets receive a great deal of
attention as they are suitable candidates for solid-state Li electrolytes.
It was recently shown that Ga-stabilized Li7La3Zr2O12 crystallizes in the acentric cubic space
group I4̅3d. This structure
can be derived by a symmetry reduction of the garnet-type Ia3̅d structure, which is the most
commonly found space group of Li oxide garnets and garnets in general.
In this study, single-crystal X-ray diffraction confirms the presence
of space group I4̅3d also
for Li7–3xFexLa3Zr2O12. The crystal structure
was characterized by X-ray powder diffraction, single-crystal X-ray
diffraction, neutron powder diffraction, and Mößbauer
spectroscopy. The crystal–chemical behavior of Fe3+ in Li7La3Zr2O12 is very
similar to that of Ga3+. The symmetry reduction seems to
be initiated by the ordering of Fe3+ onto the tetrahedral
Li1 (12a) site of space group I4̅3d. Electrochemical impedance spectroscopy measurements showed
a Li-ion bulk conductivity of up to 1.38 × 10–3 S cm–1 at room temperature, which is among the
highest values reported for this group of materials.
A total of 30 synthetic samples of the Ca 2 Fe 2-x Al x O 5 , 0.00 ≤ x ≤ 1.34 solid solution series have been investigated by single crystal X-ray diffraction at 25 °C. Pure Ca 2 Fe 2 O 5 and samples up to x = 0.56 have space group Pnma, Z = 4, whereas samples with x > 0.56 show I2mb symmetry, Z = 4. The substitution of Fe 3+ by the smaller Al 3+ cation decreases unit-cell parameters and average octahedral and tetrahedral bond lengths and induces distinct changes in the O-atom coordination of the interstitial Ca atom. Discontinuities in the structural parameters vs. the Al 3
Li oxide garnets
are among the most promising candidates for solid-state electrolytes
in novel Li ion and Li metal based battery concepts. Cubic Li7La3Zr2O12 stabilized by a
partial substitution of Zr4+ by Bi5+ has not
been the focus of research yet, despite the fact that Bi5+ would be a cost-effective alternative to other stabilizing cations
such as Nb5+ and Ta5+. In this study, Li7–xLa3Zr2–xBixO12 (x = 0.10, 0.20, ..., 1.00) was prepared by a low-temperature
solid-state synthesis route. The samples have been characterized by
a rich portfolio of techniques, including scanning electron microscopy,
X-ray powder diffraction, neutron powder diffraction, Raman spectroscopy,
and 7Li NMR spectroscopy. Pure-phase cubic garnet samples
were obtained for x ≥ 0.20. The introduction
of Bi5+ leads to an increase in the unit-cell parameters.
Samples are sensitive to air, which causes the formation of LiOH and
Li2CO3 and the protonation of the garnet phase,
leading to a further increase in the unit-cell parameters. The incorporation
of Bi5+ on the octahedral 16a site was
confirmed by Raman spectroscopy. 7Li NMR spectroscopy shows
that fast Li ion dynamics are only observed for samples with high
Bi5+ contents.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.