A trioxide is a compound with three oxygen atoms. For metals with the M2O3 formula there are several common structures. Al2O3, Cr2O3, Fe2O3, and V2O3 adopt the corundum structure. Many rare earth oxides adopt the "A-type rare earth structure" which is hexagonal. Several others plus indium oxide adopt the "C-type rare earth structure", also called "bixbyite", which is cubic and related to the fluorite structure. List of trioxides MO3 Carbon trioxide, CO3 Chromium trioxide, CrO3 Molybdenum trioxide, MoO3 Rhenium trioxide, ReO3 Selenium trioxide, SeO3 Sulfur trioxide, SO3 Tellurium trioxide, TeO3 Tungsten trioxide, WO3 Uranium trioxide, UO3 Xenon trioxide, XeO3 M2O3 Antimony trioxide, Sb2O3 Arsenic trioxide, As2O3 Bismuth(III) oxide, Bi2O3 Boron trioxide, B2O3 Cobalt(III) oxide, Co2O3 Dichlorine trioxide, Cl2O3 Dinitrogen trioxide, N2O3 Gadolinium oxide, Gd2O3 Gallium(III) oxide, Ga2O3 Gold trioxide, Au2O3 Indium(III) oxide, In2O3 Iron(III) oxide, Fe2O3 Manganese(III) oxide, Mn2O3 Nickel(III) oxide, Ni2O3 Phosphorus trioxide, P4O6 (named before the true formula known) Thallium(III) oxide, Tl2O3 Terbium(III) oxide, Tb2O3 Trioxidane, H2O3 Vanadium trioxide, V2O3 Ytterbium(III) oxide, Yb2O3 Yttrium(III) oxide, Y2O3 Other trioxides Mineral trioxide aggregate Sulfur trioxide pyridine complex, SO3(py) References