3 years ago

A review of the oxidation–pressure concept (OPC) and extended Zintl–Klemm concept (EZKC), and the emergence of the high-pressure Ni2In-type phase of lithium sulfide (Li2S) rationalized by reference to a newly defined stability enhancement ratio (S)

A review of the oxidation–pressure concept (OPC) and extended Zintl–Klemm concept (EZKC), and the emergence of the high-pressure Ni2In-type phase of lithium sulfide (Li2S) rationalized by reference to a newly defined stability enhancement ratio (S)
H. Donald Brooke Jenkins, Angel Vegas
Taking into account new experimental data [Barkalov et al. (2016). Solid State Sci.61, 220–224] on the pressure-induced Ni2In phase of Li2S, at 30 GPa, three concepts related to high-pressure phase transitions are reviewed here. This paper firstly reviews evidence that chemical oxidation (by inclusion of oxygen atoms) can produce a similar effect to the application of physical high pressure and temperature, in an effect labelled as the oxidation–pressure concept. Secondly, the pressure-induced Ni2In phase of Li2S is the final phase in the double transition antifluorite anticotunnite Ni2In, as is observed in other alkali metal sulfides. This new phase for Li2S could be expected after knowledge of the high-pressure Cmcm phase of Li2SO4, which is a distortion of the hexagonal I-Na2SO4 phase, both having M2S subarrays of the Ni2In-type. Thirdly, in order to clarify these links, a simple methodology is proposed for gauging the level of increased stability (by defining a stability enhancement ratio, S) when the extended Zintl–Klemm concept (EZKC) has been applied. The method uses relative values of the lattice potential energies estimated for Li2S and for the pseudo-lattice Ψ-BeS derived by applying the EZKC to Li2S, after which, Li2S can be reformulated as Li+[LiS]− ≡ Li+[Ψ-BeS].The Ni2In phase of Li2S (P63/mmc), recently observed at 30 GPa as the final step in the transition antifluoriteanticotunniteNi2In, provides evidence of the oxidation–pressure concept, since the [Li2S] subarray of the high-pressure phase of Li2SO4 (Cmcm) is a distortion of the new Li2S phase. Following the extended Zintl–Klemm concept (EZKC), Li2S can be formulated as Li+[LiS]– ≡ Li+[Ψ-BeS] and its usefulness has been enhanced by calculating the values of the ionic strength I. The enhancement factor, S = I[Ψ-BeS]/I[Li2S] = 1.16, denotes increased stability in [Ψ-BeS] as brought about by the EKZC.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1107/S2052520617011131

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