NATURE OF STRUCTURAL DISORDER IN NATURAL KAOLINITES - A NEW MODEL-BASED ON COMPUTER-SIMULATION OF POWDER DIFFRACTION DATA AND ELECTROSTATICENERGY CALCULATION

A new model for the description of the structural disorder in natural kaolinite materials is proposed, based on the stacking of two 1:1 laye rs and their enantiomorphs, and encompassing previously proposed model s. The layers, where randomly stacked along the c axis (using probabil istic functions nested in recursive algorithms), correctly describe th e observed powder diffraction patterns of natural kaolinites with any density of structural faults. The proposed model was evaluated using e lectrostatic energy calculations against earlier models of disorder ba sed on layer shift, layer rotation, statistical occupancy of the Al oc tahedra, or enantiomorphic layers. The present 4-layer model has a min imum of potential energy with respect to the previous models. As expec ted, the fully ordered triclinic structure of kaolinite possesses the absolute minimum of potential energy.