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End date: 2024 × Start date: 2020 × End date: 2024 × Start date: 2020 × Publisher: Weinheim : Wiley-VCH × Subject: single crystals × WGL Institute: IKZ ×

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    The Electronic Conductivity of Single Crystalline Ga-Stabilized Cubic Li7La3Zr2O12: A Technologically Relevant Parameter for All-Solid-State Batteries
    (Weinheim : Wiley-VCH, 2020) Philipp, Martin; Gadermaier, Bernhard; Posch, Patrick; Hanzu, Ilie; Ganschow, Steffen; Meven, Martin; Rettenwander, Daniel; Redhammer, Günther J.; Wilkening, H. Martin R.
    The next-generation of all-solid-state lithium batteries need ceramic electrolytes with very high ionic conductivities. At the same time a negligible electronic conductivity σeon is required to eliminate self-discharge in such systems. A non-negligible electronic conductivity may also promote the unintentional formation of Li dendrites, being currently one of the key issues hindering the development of long-lasting all-solid-state batteries. This interplay is suggested recently for garnet-type Li7La3Zr2O12 (LLZO). It is, however, well known that the overall macroscopic electronic conductivity may be governed by a range of extrinsic factors such as impurities, chemical inhomogeneities, grain boundaries, morphology, and size effects. Here, advantage of Czochralski-grown single crystals, which offer the unique opportunity to evaluate intrinsic properties of a chemically homogeneous matrix, is taken to measure the electronic conductivity σeon. Via long-time, high-precision potentiostatic polarization experiments an upper limit of σeon in the order of 5 × 10−10 S cm−1 (293 K) is estimated. This value is by six orders of magnitude lower than the corresponding total conductivity σtotal = 10−3 S cm−1 of Ga-LLZO. Thus, it is concluded that the high values of σeon recently reported for similar systems do not necessarily mirror intragrain bulk properties of chemically homogenous systems but may originate from chemically inhomogeneous interfacial areas. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Melt Growth and Physical Properties of Bulk LaInO3 Single Crystals
    (Weinheim : Wiley-VCH, 2021) Galazka, Zbigniew; Irmscher, Klaus; Ganschow, Steffen; Zupancic, Martina; Aggoune, Wahib; Draxl, Claudia; Albrecht, Martin; Klimm, Detlef; Kwasniewski, Albert; Schulz, Tobias; Pietsch, Mike; Dittmar, Andrea; Grueneberg, Raimund; Juda, Uta; Schewski, Robert; Bergmann, Sabine; Cho, Hyeongmin; Char, Kookrin; Schroeder, Thomas; Bickermann, Matthias
    Large bulk LaInO3 single crystals are grown from the melt contained within iridium crucibles by the vertical gradient freeze (VGF) method. The obtained crystals are undoped or intentionally doped with Ba or Ce, and enabled wafer fabrication of size 10 × 10 mm2. High melting point of LaInO3 (≈1880 °C) and thermal instability at high temperatures require specific conditions for bulk crystal growth. The crystals do not undergo any phase transition up to 1300 °C, above which a noticeable thermal decomposition takes place. The good structural quality of the crystals makes them suitable for epitaxy. The onset of strong optical absorption shows orientation-dependent behavior due to the orthorhombic symmetry of the LaInO3 crystals. Assuming direct transitions, optical bandgaps of 4.35 and 4.39 eV are obtained for polarizations along the [010] and the [100], [001] crystallographic directions, respectively. There is an additional weak absorption in the range between 2.8 and 4 eV due to oxygen vacancies. Density-functional-theory calculations support the interpretation of the optical absorption data. Cathodoluminescence spectra show a broad, structured emission band peaking at ≈2.2 eV. All bulk crystals are electrically insulating. The relative static dielectric constant is determined at a value of 24.6 along the [001] direction.