A DSC/TGA and XRD study on the thermal stability of yttria-stabilized zirconia TBC (thermal barrier coatings) obtained by atmosphere- and temperature-controlled plasma spray, was carried out. As-sprayed zirconica coatings were under-stoichiometric and highly disordered. The thermal analysis showed that several endo- and exothermic phenomena take place on heating the ceramic. TGA clearly showed weight gains associated with the oxygen recovery, whereas DSC also detected the structural relaxation and transformations found by XRD. The activation energies, reaction order and mechanism are also discussed.