Mechanical properties of niobium disulfide and its hydrated sodium cation intercalation compound
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. Wypych Departamento de Quı´mica, Universidade Federal do Parana´, Caixa Postal 19081, 81531-990 Curitiba-PR, Brazil (Received 20 January 2000; accepted 12 July 2000)
Mechanical properties of 2H–NbS2 and its intercalation derivative Nax(H2O)yNbS2 were measured by using nanoindentation techniques. The intercalation chemical process was conducted in solution and the cation–hydrated derivative produced was [Nax(H2O)yNbS2]. It was observed that the intercalation process occurs through the crystal edges producing a wave intercalation’s front that moved as the reaction proceeded. The hardness and elastic modulus presented very low values in the intercalated region. The load × displacement curves from nanoindentation tests suggested that intercalation of hydrated sodium ions through the edges caused layer separation even in the nonintercalated region at the center of the crystal. It is important to emphasize that no similar studies were found in the literature about this theme. Intercalation process is very important in several areas, like solid-state batteries, and mechanical properties of these kinds of materials are not completely understood. This study is a new approach to understanding the mechanical behavior of layered materials submitted to an intercalation process.
Layered transition-metal dichalcogenides, MX2 (M ⳱ transition metal, X ⳱ S, Se, or Te) are part of a distinct class of materials with interesting anisotropic properties. These quasi-bidimensional properties are mainly related to the strong intralayer covalent bonding and weak interlayer Van der Waals interactions. The weak interlayer interactions and the transitionmetal reduction possibility allows intercalation of organic and inorganic cations, producing intercalation compounds such as Ax /mMX2 (A ⳱ intercalated ion with the charge “m”).1,2 If the intercalation process is conducted in solution on other polar solvent the cationhydrated derivatives produced are Ax /m(solvent)y MX2. The main processes to intercalate organic or inorganic cations between the layers are the chemical and electrochemical methods. These methods involve the reduction of the transition metals in the lattice, which then incorporate the solvated cations into the Van der Waals gaps in order to balance the charge. Using the electrochemical methods, intermediary reactions products can be detected and isolated until the
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 15, No. 10, Oct 2000
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stage associated with the reduction potential.3,4 Sodium ditionite has been found to be the most convenient reagent to perform reduction of layered materials in aqueous media. Niobium disulfide (2H–NbS2) is a member of the described family in which niobium atoms are linked covalently to six sulfur atoms in a trigonal prismatic coordination.1,2 These prisms are linked to each other by their corners, building slabs that are stacked along the c-axis direction. In this paper we describe the prepar
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