IrO2 (iridium oxide) synthesis
One elder reference is Brauer's Handbook of Preparative Inorganic Chemistry, which states for this compound

&quot;In the method of Wöhler and Streicher, $\ce{IrO2}$ is prepared from green $\ce{IrCl3}$ which can readily oxidized in a stream of $\ce{O2}$ at 600$^\circ$C giving blue-black  $\ce{IrO2}$.
The oxidation of fine iridium powder in a stream of air or oxygen does not give $\ce{IrO2}$ quantitatively. [...]&quot;

which is accessible in archive.org's public scanned version here, p. 1590 (book's counting) / p. 1636 (the website's counting) of the 1963-edition by Academic Press.  The age of the edition should neither defer you from using it as a reference, nor inhibit you to look up additional references.