Dislocation‐tuned electrical conductivity in solid electrolytes (9YSZ): A micro‐mechanical approach

Tailoring the electrical conductivity of functional ceramics by introducing dislocations is a comparatively recent research focus, and its merits were demonstrated through mechanical means. Especially bulk deformation at high temperatures is suggested to be a promising method to introduce a high dislocation density. So far, however, controlling dislocation generation and their annihilation remains difficult. Although deforming ceramics generate dislocations on multiple length scales, dislocation annihilation at the same time appears to be the bottleneck to use the full potential of dislocations‐tailoring the electrical conductivity. Here, we demonstrate the control over these aspects using a micromechanical approach on yttria‐stabilized zirconia ‐ YSZ. Targeted indentation well below the dislocation annihilation temperature resulted in extremely dense dislocation networks, visualized by chemical etching and electron channeling contrast imaging. Microcontact‐impedance measurements helped evaluate the electrical response of operating individual slip systems. A significant conductivity enhancement is revealed in dislocation‐rich regions compared to pristine ones in fully stabilized YSZ. This enhancement is mainly attributed to oxygen ionic conductivity. Thus, the possibility of increasing the conductivity is illustrated and provides a prospect to transfer the merits of dislocation‐tuned electrical conductivity to solid oxygen electrolytes

Microelectrodes for local conductivity and degradation measurements on Al stabilized Li7La3Zr2O12 garnets

The attractiveness of Li7La3Zr2O12 (LLZO) cubic based garnets lies in their high ionic conductivity and the combination of thermal and electrochemical stability. However, relations between composition and conductivity as well as degradation effects are still not completely understood. In this contribution we demonstrate the applicability of microelectrodes (Ø = 20–300 μm) for electrochemical impedance spectroscopy (EIS) studies on LLZO garnets. Microelectrodes allow to obtain local information on the ionic conductivity. A comparison between the overall performance of the sample (3.3 × 10−4 S cm−1) and local measurements revealed differences in conductivity with a maximum of the locally measured values of 6.3 × 10−4 S cm−1 and a minimum of 2.6 × 10−4 S cm−1. One reason behind these conductivity variations is most probably a compositional gradient in the sample. In addition, microelectrodes are very sensitive to conductivity changes near to the surface. This was used to investigate the effect of moisture in ambient air on the conductivity variations of LLZO. Substantial changes of the measured Li-ion transport resistance were found, particularly for smaller microelectrodes which probe sample volumes close to the surface.The Austrian Research Promotion Agency (FFG)176181

Local Li-ion conductivity changes within Al stabilized Li7La3Zr2O12 and their relationship to three-dimensional variations of the bulk composition

The attractiveness of cubic Li7La3Zr2O12 (LLZO) based garnets lies in their high ionic conductivity and the combination of thermal and electrochemical stability. However, relationships between the exact chemical composition and ionic conductivity are still not well understood and samples of very similar composition and processing may show very different properties. In this contribution, we investigated Al stabilized LLZO by employing a combination of local conductivity measurements and 3D local chemical analysis using laser ablation inductively coupled plasma optical emission spectroscopy (LA-ICP-OES). These measurements revealed significant conductivity variations across some samples, with variations up to almost one order of magnitude, as well as an inhomogeneous elemental distribution of Al and Li, largely along the samples. Surprisingly, neither the local Al content nor the local Li content showed a clear correlation with the local Li-ion conductivity. Accordingly, an in-depth understanding of the conduction properties of Al stabilized LLZO has to concentrate on aspects beyond the simple chemical composition. Yet unknown factors (e.g. oxygen vacancies or local cation site occupancies) seem to have a much higher impact on the ionic conductivity than the exact stoichiometry.W1243-N16(VLID)354652

Dislocation-tuned electrical conductivity in solid electrolytes (9YSZ): a micro-mechanical approach

Tailoring the electrical conductivity of functional ceramics by introducing dislocations is a comparatively recent research focus, and its merits were demonstrated through mechanical means. Especially bulk deformation at high temperatures is suggested to be a promising method to introduce a high dislocation density. So far, however, controlling dislocation generation and their annihilation remains difficult. Although deforming ceramics generate dislocations on multiple length scales, dislocation annihilation at the same time appears to be the bottleneck to use the full potential of dislocationstailoring the electrical conductivity. Here, we demonstrate the control over these aspects using a micromechanical approach on yttria-stabilized zirconia-YSZ. Targeted indentation well below the dislocation annihilation temperature resulted in extremely dense dislocation networks, visualized by chemical etching and electron channeling contrast imaging. Microcontact-impedance measurements helped evaluate the electrical response of operating individual slip systems. A significant conductivity enhancement is revealed in dislocationrich regions compared to pristine ones in fully stabilized YSZ. This enhancement is mainly attributed to oxygen ionic conductivity. Thus, the possibility of increasing the conductivity is illustrated and provides a prospect to transfer the merits of dislocation-tuned electrical conductivity to solid oxygen electrolytes

Chemistry of Materials / Fast Li-Ion-conducting garnet-related Li73xFexLa3Zr2O12 with uncommon I43d structure

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 I43d. This structure can be derived by a symmetry reduction of the garnet-type Ia3d 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 I43d also for Li73xFexLa3Zr2O12. The crystal structure was characterized by X-ray powder diffraction, single-crystal X-ray diffraction, neutron powder diffraction, and Mößbauer spectroscopy. The crystalchemical 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 I43d. Electrochemical impedance spectroscopy measurements showed a Li-ion bulk conductivity of up to 1.38 103 S cm1 at room temperature, which is among the highest values reported for this group of materials.(VLID)239179

Fast Li-Ion-Conducting Garnet-Related Li_{7–3<i>x</i>}Fe_<i>x</i>La₃Zr₂O₁₂ with Uncommon <i>I</i>4̅3<i>d</i> Structure

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 <i>I</i>4̅3<i>d</i>. This structure can be derived by a symmetry reduction of the garnet-type <i>Ia</i>3̅<i>d</i> 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 <i>I</i>4̅3<i>d</i> also for Li_{7–3<i>x</i>}Fe_<i>x</i>La₃Zr₂O₁₂. 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 (12<i>a</i>) site of space group <i>I</i>4̅3<i>d</i>. 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

Unravelling the Origin of Ultra-Low Conductivity in SrTiO3 Thin Films: Sr Vacancies and Ti on A-Sites Cause Fermi Level Pinning

Different SrTiO3 thin films are investigated to unravel the nature of ultra-low conductivities recently found in SrTiO3 films prepared by pulsed laser deposition. Impedance spectroscopy reveals electronically pseudo-intrinsic conductivities for a broad range of different dopants (Fe, Al, Ni) and partly high dopant concentrations up to several percent. Using inductively-coupled plasma optical emission spectroscopy and reciprocal space mapping, a severe Sr deficiency is found and positron annihilation lifetime spectroscopy revealed Sr vacancies as predominant point defects. From synchrotron-based X-ray standing wave and X-ray absorption spectroscopy measurements, a change in site occupation is deduced for Fe-doped SrTiO3 films, accompanied by a change in the dopant type. Based on these experiments, a model is deduced, which explains the almost ubiquitous pseudo-intrinsic conductivity of these films. Sr deficiency is suggested as key driver by introducing Sr vacancies and causing site changes (Fe-Sr and Ti-Sr) to accommodate nonstoichiometry. Sr vacancies act as mid-gap acceptor states, pinning the Fermi level, provided that additional donor states (most probably TiSr center dot center dot$${\rm{Ti}}_{{\rm{Sr}}}{ \bullet \bullet }$$) are present. Defect chemical modeling revealed that such a Fermi level pinning also causes a self-limitation of the Ti site change and leads to a very robust pseudo-intrinsic situation, irrespective of Sr/Ti ratios and doping.ISSN:1616-3028ISSN:1616-301