THE STRUCTURE OF MOLTEN ALKALI CARBONATES STUDIED BY NEUTRON-DIFFRACTION AND AB-INITIO CALCULATIONS

The total structure factors, S(Q), of pure molten Li2CO3 and an equimo lar mixture with K2CO3. LiKCO3, were measured by neutron diffraction a t 1013 it and 923 K, respectively. The results are generally consisten t with the findings of previous MD simulations. The CO32- ion remains essentially unperturbed in the mixture. The real-space pair correlatio n functions are consistent with a close-packed, regular, planar, trigo nal geometry for the CO32- ion in both Li2CO3 and LiKCO3. There is som e indication, also consistent with the findings of MD simulation, of a possible tightening of the local coordination of CO32- ions around Li + in the presence of the larger, more weakly polarizing K+ cation. Mod elling the S(Q) data using structure factors calculated from monomer a nd dimer structures derived from ab initio quantum chemical calculatio ns suggests that larger clusters are needed to realistically describe the melt local structure.