Why isn't lead tetroxide stable?

I have heated lead(II) oxide at about 450 °C and it changed to lead(II,IV) oxide, but as soon as I took it out from hot plate, it changed to $\ce{PbO}$ again. Why does it happen? Is there a better way to synthesize $\ce{Pb3O4}$ from $\ce{PbO}?$


I had the same problem when I wanted to change $\ce{Pb3O4}$ to $\ce{PbO}.$ When I heated $\ce{Pb3O4},$ it got dark. When I took it out, it became red again. I used straight flame to decompose it.




Heat is very different while conducting such type of reactions because at a specific range of temperature, you will get a different species of lead oxide. [The general scheme of lead oxide conversion is as follows:](https://chemistry.stackexchange.com/a/137042/17368)


$$\ce{PbO2 ->[\pu{293 ^\circ C}] Pb12O19 ->[\pu{351 ^\circ C}] Pb12O17 ->[\pu{375 ^\circ C}] Pb3O4 ->[\pu{605 ^\circ C}] PbO}$$


So, around 375 °C-450 °C, you will get lead(II,IV) oxide. As soon as you overshoot the temperature, it will convert to lead(II) oxide.


If you have lead(IV) oxide, then it can be converted to lead(II,IV) oxide at around 450 °C-480 °C but if you overshoot it, lead(II,IV) oxide will decompose back to lead(IV) oxide (reaction completes at 580 °C). Wikipedia took the reaction from [*Lead Compounds* by Dodd S. Carr, **2000**](https://onlinelibrary.wiley.com/doi/10.1002/14356007.a15_249)


$$
\begin{align}
\ce{6PbO + O2 &->[\pu{450 ^\circ C - 480 ^\circ C}] Pb + CO2}\\
\ce{2 Pb3O4 &->[>500 ^\circ C] 6PbO + O2}
\end{align}
$$


Lead(II,IV) oxide is relatively stable to atmospheric oxidation and insoluble in water and as such, it was used as a pigment for a long time until it was scraped off due to its toxicity. It is temperature resistant upto a certain point.


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