We successfully demonstrated the applicability of microcontact impedance spectroscopy (MC IS) on Li+conducting solid electrolytes and measured the Li+bulk conductivity (σb) of LiTi2(PO4)3(LTP) and Li1+xAlxTi2−x(PO4)3(LATP) single crystals independent of microstructural effects (e.g., grain boundaries, pores, and density).
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.
Mass and charge transport properties of slightly Fe-doped SrTiO3 (Fe:STO) thin films on a conducting substrate were investigated by means of impedance spectroscopy under different bias voltages and I-V measurements with varying scan rates. At measurement temperatures between 325 °C and 700 °C the applied bias voltage caused an unusual "inductive loop" in the low frequency range of impedance spectra. DC measurements showed that current-voltage curves strongly depend on the scan rate, indicating that different states of the sample became accessible to probe. Both findings can be understood in terms of bias induced ion motion, i.e. by stoichiometry polarization within the Fe:STO thin films upon voltage. Hence, the appearance of an "inductive loop" in the impedance spectra is considered a very general feature that might exist for many materials, particularly in oxide thin films. It may indicate ion motion and stoichiometry variations taking place in the corresponding frequency range.
Investigating conductivity variations in Al stabilized LLZO by combining microelectrode impedance spectroscopy with spatially resolved chemical analysis.
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