First published:1 September 1984
Introduction
very interesting group of materials. In these materials, the intralayer interaction is very strong in comparison to that of interlayer interaction and therefore these materials can be cleaved in very thin sheets. Keeping in view their technological and industrial applications these materials have been investigated for the determination of their various electronic, optical, and structural properties /1 to 5/. Gamble /6/ has classified these compounds on the basis of the Pauling ionicity and the ionic radii ratio while Madhukar /7/ gave a classification on the basis of Pauling ionicity and metal to chalcogen covalent radii ratio. As these materials are less ionic therefore the use of ionic radii is not justified. Pauling’ s definition of ionicity works well for molecular systems /8, 9/, in case of crystalline solids it does not work satisfactorily because of the fact that it is based on the molecular approach and bonding properties and not on band structure. Our view point is further supported by the fact that according to the Pauling definition the ionicity for Ti and Zr dichalcogenides comes out to be the same while they have different values of effective charges /lo/. On the other hand, ionicity by Phillips /9/ is based on band structure and therefore a more appropriate parameter. It is therefore worthwhile to investigate Phillips’ ionicity of these materials and to look into their classification on the basis of the Phillips definition of ionicity .
https://sci-hub.tw/https://doi.org/10.1002/pssb.2221250150
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