Effect of the Local Atomic Ordering on the Stability of ß-Spodumene.

This study focuses on the relative energetic stability of ß-spodumene configurations with different atomic ordering, evaluated using electronic structure methods based on static periodic density functional theory. We found that ß-spodumene configurations with a framework containing exclusively Al-O-Si linkages are energetically the most stable, consistent with the aluminum avoidance principle. A correlation between the interstitial sites occupied by lithium and the stability of the configuration was established: highly stable configurations contain greater proportions of lithium associated with the edges of AlO4 tetrahedrons. The identified low-energy configurations have a band gap of ∼4.8 eV, and similar electronic band structures and densities of states. Both the PBE and PBEsol functionals predict small differences in the relative stabilities of the different configurations of ß-spodumene. However, only PBEsol is able to reproduce the experimentally observed stability differences between α-spodumene and ß-spodumene. ß-Spodumene is the preferred polymorph at high temperatures, with the PBEsol inversion temperature from α- to ß-spodumene predicted to occur at 1070 K.