Synthesis of nano- and microstructured materials is a field of high activity in material science. Plasma-chemical processes are effective and versatile tools for this purpose. Plasma can be generated in different ways, in this work we use pulses of high-power gyrotron (75 GHz/550 kW) to initiate a discharge in mixtures of metal and dielectric powders. Depending on the starting composition of mixture it is possible to obtain new materials. It was shown earlier that MgAl2O4 can be prepared from Mg/Al2O3 mixture. Now we demonstrate that organic compounds can also be introduced into the mixture. Using melamine as a source of nitrogen we prepared aluminum oxynitrides (Al11O15N, Al27O39N) starting from Al/Al2O3. An addition of small amount of carborane C2B10H12 makes the process even more intensive, since in this case hydrogen is involved. Proposals on possible mechanism was made basing on observations during the process and composition and morphology of final products.