Influence of hydrogenation on properties of layered crystals of gallium and indium monoselenides
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INFLUENCE OF HYDROGENATION ON PROPERTIES OF LAYERED CRYSTALS OF GALLIUM AND INDIUM MONOSELENIDES O. O. Balyts’kyi
UDC [546.221.1:546:77](542.06+539.26)
It is established that hydrogen enhances the anisotropy of properties (including the mechanical ones) of layered crystals of gallium and indium monoselenides. Hydrogen intercalated into the interlayer space of these compounds is in the molecular state occupying translation-ordered sites. Exceeding a certain concentration is accompanied by the entry of hydrogen ions into the matrix layers of crystals. Keywords: strength, layered crystal, hydrogen intercalation, density, microhardness.
Layered crystals [1–5], primarily WS2 and MoS 2 [3], are promising as solid-body elements in hydrogen accumulating systems. It is known that its concentration may attain values close to x = 5 ( x is the number of introduced hydrogen atoms per formula unit of the crystal). Hydrogen “intercalation–deintercalation” processes (“introduction–removal” of impurities into (from) the interlayer space of a layered crystal) in the intercalated nanophases based on WS2 and MoS 2 layered nanostructures are thermodynamically reversible, but disordered layered intercalated H x WS2 and H x MoS 2 nanostructures [2] affect substantially the characteristics of hydrogen deintercalation. Crystals of InSe and GaSe also have a layered structure and attract practical interest in energy-transforming systems because heterostructures obtained based on them are light-sensitive and are used in solar cells [1, 2]. At the same time, due to the strong anisotropy of chemical bonds (strong ionic–covalent bond inside the layer and weak Van der Waals bond between layers) one manages to intercalate efficiently by hydrogen, i.e., to introduce molecules into the interlayer space (into the so-called “van der Waals gap,” which, in gallium and indium monoselenides, occupies from 40 to 45% of the whole volume of the crystal) [2]. In what follows, we analyze works on the influence of hydrogen on the properties of gallium and indium monoselenides (InSe and GaSe) and confirm experimentally the hydrogen intercalation–deintercalation processes in these layered crystals and their influence on the mechanical characteristics of the indicated materials. Experimental Technique Bulk GaSe monocrystals ( -modification and
D13h
space group) and InSe ( -modification,
5 ) C 3v
monocrystals were grown by the Bridgman method. For further investigations, we prepared prismatic specimens with a cross-sectional area of 16 to 160 mm 2 and a length of 7 to 70 mm [4]. The microstructure was investigated by the standard metallographic method with a Neophot microscope. The densities of the alloys were determined by hydrostatic weighing according to the Mohr technique using an analytic balance. The microhardness was tested with a P-3 and Gnehm 100 Digital instruments. The strength was measured on fivefold specimens using Alfred J. Amsler & Co. facilities. Franko National University, Lviv, Ukraine; e-mail: [email protected]. Tra
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