In order to elucidate room-temperature ͑RT͒ ferromagnetism ͑FM͒ in ZnO, we have analyzed a multitude of experimental publications with respect to the ratio of grain-boundary ͑GB͒ area to grain volume. FM only appears if this ratio exceeds a certain threshold value s th . Based on these important results nanograined pure and Mn-doped ZnO films have been prepared, which reveal reproducible RT FM and magnetization proportional to the film thickness, even for pure ZnO films. Our findings strongly suggest that grain boundaries and related vacancies are the intrinsic origin for RT ferromagnetism.

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All-inorganic solid-state batteries (SSBs) currently attract much attention as nextgeneration high-density energy storage technology. However, to make SSBs competitive with conventional Li-ion batteries, several obstacles and challenges must be overcome, many of which are related to interface stability issues. Protective coatings can be applied to the electrode materials to mitigate side reactions with the solid electrolyte, with lithium transition metal oxides, such as LiNbO3 or Li2ZrO3, being well established in research. In addition, it has been recognized lately that carbonates incorporated into the coating may also positively affect the interface stability. In this work, we studied the effect that surface carbonates in case of Li2ZrO3-coated Li1+x(Ni0.6Co0.2Mn0.2)1−xO2 (NCM622) cathode material have on the cyclability of pellet stack SSB cells with Li6PS5Cl and Li4Ti5O12 as solid electrolyte and anode, respectively. Both carbonate-rich and carbonate-poor hybrid coatings were produced by altering the synthesis conditions. The best cycling performance was achieved for the carbonate-deficient Li2ZrO3-coated NCM622, due to decreased degradation of the argyrodite solid electrolyte at the interfaces, as determined by ex situ X-ray photoelectron spectroscopy and in situ differential electrochemical mass spectrometry. The results emphasize the importance of tailoring the composition and nature of protective coatings to improve the cyclability of bulk SSBs.

Dense nanograined pure and Mn-doped Zn1−xMnxO polycrystals with x ranging between 0.1–34 at. % were synthesized by the wet chemistry method from butanoate precursors. Pure and Mn-doped ZnO possesses ferromagnetic properties only if the ratio of grain boundary (GB) area to grain volume sGB exceeds a certain threshold value sth. The polycrystals in this work satisfy these conditions and, therefore, reveal ferromagnetic properties. The observed dependence of saturation magnetization on the Mn concentration shows an unexpected nonmonotonous behavior. The increase in saturation magnetization at low Mn concentration is explained by the injection of divalent Mn2+ ions and charge carriers into pure ZnO. The decrease in saturation magnetization between 0.1 and 5 at. % Mn can be explained by the increase in the portion of Mn3+ and Mn4+ ions. The second increase in saturation magnetization above 5 at. % Mn is explained by the formation of multilayer Mn segregation layer in ZnO GBs. The shape of the dependence of saturation magnetization on Mn concentration is different for the Mn-doped nanograined ZnO manufactured by different methods. It is most probably controlled by the topology of GB network (ferromagnetic GB foam) in the ZnO polycrystals.

Printed thermoelectrics (TE) could significantly reduce the production cost of energy harvesting devices by large-scale manufacturing. However, developing a high-performance printable TE material is a substantial challenge. In this work,...

Conformal coating of nm-thick Al 2 O 3 layers on electrode material is an effective strategy for improving the longevity of rechargeable batteries. However, solid understanding of how and why surface coatings work the way they do has yet to be established. In this article, we report on low-temperature atomic layer deposition (ALD) of Al 2 O 3 on practical, ready-to-use composite cathodes of NCM622 (60% Ni), a technologically important material for lithium-ion battery applications. Capacity retention and performance of Al 2 O 3 -coated cathodes (≤10 ALD growth cycles) are significantly improved over uncoated NCM622 reference cathodes, even under moderate cycling conditions. Notably, the Al 2 O 3 surface shell is preserved after cycling in full-cell configuration for 1400 cycles as revealed by advanced electron microscopy and elemental mapping. While there are no significant differences in terms of bulk lattice structure and transition-metal leaching among the coated and uncoated NCM622 materials, the surface of the latter is found to be corroded to a much greater extent. In particular, detachment of active material from the secondary particles and side reactions with the electrolyte appear to lower the electrochemical activity, thereby leading to accelerated capacity degradation.

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