Refractory materials are provided which contain P.sub.2O.sub.5/R.sub.2O.sub.3 constituents, where R is Y, Sc, Er, Lu, Yb, Tm, Ho, Dy, Tb, Gd, or a combination thereof, and/or V.sub.2O.sub.5/R'.sub.2O.sub.3 constituents where R' is Y, Sc, one or more rare earth elements, or a combination thereof. In certain embodiments, the refractory materials are xenotime-type materials and/or xenotime-stabilized zircon-type materials. The refractory materials can be used in the manufacture of glass and glass-ceramics. For example, the refractory materials, especially those that contain P.sub.2O.sub.5/R.sub.2O.sub.3 constituents, can be used as forming structures ("isopipes") in the fusion process for making flat sheets of glass such as the glass sheets used as substrates in the manufacture of flat panel displays.