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Superconductivity in the α-Form Layer Structured Metal Nitride Halide

by Masashi Tanaka, Noriyuki Kataoka and Takayoshi Yokoya

Condens. Matter 2022, 7(2), 33; https://doi.org/10.3390/condmat7020033 - 1 Apr 2022

Cited by 11 | Viewed by 4188

Layered metal nitride halides MNX (M = Ti, Zr, Hf; X = Cl, Br, I) have two polymorphs, including α- and β-forms, which have the FeOCl and SmSI structures, respectively. These compounds are band insulators and become metals and show superconductivity after electron doping by intercalating alkali metals between the layers. The superconductivity of β-form had been extensively characterized from decades ago, but it is not easy to consistently interpret all experimental results using conventional phonon-mediated Bardeen–Cooper–Schriefer mechanisms. The titanium compound TiNCl crystallizes only in the α-form structure. TiNCl also exhibits superconductivity as high as ~16 K after electron doping by intercalating metals and/or organic basis. It is important to compare the superconductivity of different M–N networks. However, α-form compounds are vulnerable to moisture, unlike β-form ones. The intercalation compounds are even more sensitive to humid air. Thus, there are few experimental studies on the superconducting mechanism of α-form, although it has been discussed for exotic Cooper-pairing mechanisms. This short review gathers the recent progress in experimental studies of TiNCl. Full article

(This article belongs to the Special Issue Layered Superconductors III)

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12 pages, 1801 KiB

Open AccessArticle

Theoretical Study of Aluminum Hydroxide as a Hydrogen-Bonded Layered Material

by Dongwook Kim, Jong Hyun Jung and Jisoon Ihm

Nanomaterials 2018, 8(6), 375; https://doi.org/10.3390/nano8060375 - 28 May 2018

Cited by 32 | Viewed by 6246

Abstract

In many layer-structured materials, constituent layers are bound through van der Waals (vdW) interactions. However, hydrogen bonding is another type of weak interaction which can contribute to the formation of multi-layered materials. In this work, we investigate aluminum hydroxide [Al(OH)

_{3}

] having [...] Read more.

_{3}

] having hydrogen bonding as an interlayer binding mechanism. We study the crystal structures and electronic band structures of bulk, single-layer, and multi-layer Al(OH)

_{3}

using density functional theory calculations. We find that hydrogen bonds across the constituent layers indeed give rise to interlayer binding stronger than vdW interactions, and a reduction of the band gap occurs for an isolated layer as compared to bulk Al(OH)

_{3}

which is attributed to the emergence of surface states. We also consider the alkali-halide intercalation between layers and examine how the intercalated atoms affect the atomic and electronic structures of Al(OH)

_{3}

. Full article

(This article belongs to the Special Issue Hybrid Nanomaterials for Future Technologies)

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