Calculation of Crystal Growth and Morphology.

Simulation is well suited to the calculation of surface strcuture and energy, but from this information it is also possible to make predictions about crystal morphology and growth. Some of these relate to the equilibrium form of a crystal such as morphologies generated directly from surface energies while others attempt to introduced kintic factors such as growth rate (e.g. attachment energies).

Computer Simulation of the crystal morphology of NiO

NiO is isostructural with MgO and whilst the crystal morphology of MgO is cubic NiO is not. The surface energies for the {100}, {110} and {111} surfaces of NiO were calculated but the ulting equilibrium orphology (using a Wulff construction) was dominated by the {100} ie cubic. However, the discrepancy can be explained by appreciating that NiO is easily oxidised and hence the surface energy as a function of surface oxidation was calculated for all three surfaces. It was found that at 75% oxidation of the surface the calculated morphology agreed well with the experimentally observed morphologies. Thus we have shown that oxidation can stabilise an otherwise unstable surface ie the {111} surface.

Experimental Morphology

Unoxidised

75 % Oxidised

100% Oxidised

Click here for a java applet allowing rotation of the above morphologies of NiO.

related references:

  1. Parker S.C., Kelsey E.T., Oliver P.M. and Titiloye J.O.
    'Computer modelling of inorganic solids and surfaces'
    Faraday Discuss. 95 75-84 (1993)

  2. Oliver P.M., Parker S.C. and Mackrodt W.C.
    'Computer simulation of the morphology of NiO' Modelling and Simulation in Materials
    Science and Eng. 1 755-760 (1993)

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Send your comments and questions to s.c.parker@bath.ac.uk.