Ceramics comprising (i) at least one of Nb.sub.2O.sub.5 or Ta.sub.2O.sub.5 and (ii) at least two of (a) Al.sub.2O.sub.3, (b) REO, or (c) at least one of ZrO.sub.2 or HfO.sub.2. Embodiments of ceramics according to the present invention can be made, formed as, or converted into optical waveguides, glass beads, articles (e.g., plates), fibers, particles (e.g., abrasive particles), and thin coatings.