1. Departments of Chemistry and Materials Science, University of North Texas, P.O. Box 305070, Denton, Texas 76203, Advanced Materials Laboratories, Sandia National Laboratories, Albuquerque, New Mexico 87106, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, and Sandia National Laboratories, 4100 National Parks Highway, Carlsbad, New Mexico 88220