18. Ammonothermal Materials

Even more than fifty years after the first ammonothermal syntheses, the synthetic potential of this technique is still far from established. Even in the already commercialized crystal growth of GaN substrates, various technical obstacles remain, partly because of lack of materials for high pressure equipment sufficiently resistant against the aggressive medium and at the same time persistent at the process conditions, but clearly because of insufficient understanding of the chemical and physical processes in supercritical ammonia. Still, many novel nitrides already emerge from ammonothermal synthesis. This technique has already proven to hold great prospects in crystal growth of the other group III nitrides, AlN and InN, relevant from a technical point of view, and substitution variant among those nitrides with further trivalent ions. Huge potential was also demonstrated for synthesis of further hard to produce nitrides as nitridosilicates, nitridophosphates and similar compounds, or oxide nitride perovskites. With increasing understanding of the physiochemical background and concomitant extension of the accessible process parameters we definitely will see great advances in the ammonothermal synthesis of novel materials for future applications.