An effective partial charge model for bulk and surface properties of cubic ZrO2, Y2O3 and yttrium-stabilised zirconia

Novel interaction potentials using effective partial charges are derived, leading to a superior description of bulk and surface properties.

Complexation of Zr(IV) Precursors in Aqueous Solutions

ABSTRACTThe sol-gel synthesis of metal oxides can be performed via the hydroxylation and condensation of metal cations in aqueous solutions. The complexation of these ionic species by anions leads to the chemical modification of inorganic precursors at a molecular level. The whole process of hydrolysis and condensation can then be modified allowing a chemical control of the morphology, the structure and even the chemical composition of the resulting powder.The role of anions during the formation of condensed phases from inorganic precursors in aqueous solutions has to be taken into account. The complexing ability of these anions is described in the frame of the Partial Charge Model as a function of pH and the mean electronegativity of anionie and cationic chemical species. Experimental evidence for the complexation of zirconyl species in aqueous solutions will be given using multinuclear NMR of anions.

Electronegativity-Based Computation of 29Si Chemical Shifts

ABSTRACTThe Partial Charge Model has been modified to take into account the detailed structure of any molecular sol-gel precursors or inorganic solid networks. Starting from these structure-dependent partial charges, the classical theory of nuclear shielding is applied to compute the electronic cloud compacity <r-3>p, the population unbalance Pu and also the mean excitation energy ΔE. With these three parameters it is possible to explain the chemical shifts variations, spanning from +40 down to -140 ppm, of more than 50 precursors. Depending on the ligands, the well-known upside-down U-curves for series SiXnY4-n (n=0‥4) can be ascribed either to the population unbalance term Pu or to a competition between the two other terms <r-3>p and ΔE.