Thallium(I) oxide

Thallium(I) oxide is the inorganic compound of thallium and oxygen with the formula Tl₂O in which thallium is in its +1 oxidation state. It is black and produces a basic yellow solution of thallium(I) hydroxide (TlOH) when dissolved in water. It is formed by heating solid TlOH or Tl₂CO₃ in the absence of air. Thallium oxide is used to make special high refractive index glass. Thallium oxide is a component of several high temperature superconductors. Thallium(I) oxide reacts with acids to make thallium(I) salts.

Tl₂O adopts the anti-cadmium iodide structure in the solid state. In this way, the Tl(I) centers are pyrdamidal and the oxide centers are octahedral.

Thallium(I) oxide, like all thallium compounds, is highly toxic.