Amorphization of cuprite, Cu$_2$O, due to chemical decomposition under high pressure

Using synchrotron radiation and a diamond-anvil cell, a structural study of the phase transformations in Cu$_{2}$O is carried out from diffraction data obtained in-situ while heating at a pressure of 30 GPa. Around 140 $^\circ$C we observe a transition of Cu$_{2}$O to an amorphous state, with the amorphous state persisting to about 260 $^\circ$C. Further heating up to 400 $^\circ$C yields at first a nanocrystalline two-phase mixture of Cu+CuO; then with prolonged heating at 400 $^\circ$C full crystallization of this mixture. The present structural data are the first experimental evidence of solid state amorphization under high pressure as an intermediate stage of the high-pressure decomposition of complex compounds.