The Chemical vapour transport (CVT) reactions summarize a variety of reactions during which a solid is volatilised in the presence of a transport agent, a gaseous reactant, and deposits elsewhere when a temperature gradient is applied. The transport reaction can be described in three steps: i) the forward reaction at the source where the solid stays at the beginning of the CVT process, ii) the gas motion proceeding mainly by diffusion, and iii) the back reaction leading to the formation of the solid at the sink. Thousands of compounds can be grown by CVT. However, CVT growth have never been studied in-situ. So many mechanistic questions remain unanswered. The In-situ XRD and XAS measurements proposed here will pioneer the examination of the CVT growth process at the atomic level.