The role of reductive and oxidative annealing processes in the phase composition and electrical conductivity of molybdenum oxides

•Pure MoO2 samples were grown by chemically driven close space vapour transport.•Sequential oxidative annealings were carried out to modify phase or conductivity.•Reductive annealings were carried out for samples converted to MoO3.•Crystal structure and electrical properties were monitored after each annealing.•MoO2 rich MoO2/MoO3 composite originates the conductivity in mixed samples.