Role of bond coordination and molecular volume on the dielectric constant of mixed-oxide compounds

First-principles calculations have been employed to study clusters of Zr embedded in SiO2. Stable complexes are found with four, six, and seven oxygens coordinated to the Zr atom. Consistent with experiment, the higher coordinated complexes are the most stable. These also have a higher density, and hence, smaller molar volume. This smaller molar volume provides an explanation of the increased dielectric constant of ZrxSi1-xO2 mixed-oxide systems for small amounts of Zr (x <0.3). An unusual sevenfold coordinated structure is described. (C) 2001 American Institute of Physics.