Yttrium oxide plasma-spray deposits show a metastable B phase together with the cubic stable form. This B form is prejudicial for thermal applications of these coatings (i.e. weakens mechanical properties, etc.). Attempts have been made to avoid the formation of this metastable phase during the plasma-spraying operation by use of an inhibitor, such as ZrO2. A large solid solution with cubic C phase was found to form between ZrO2 and Y2O3 (Y1-xZrxO1.5+x/2 square 0.5-x/2). A method is described for preparing powders suitable for plasma spraying. Several compositions were tested. B phase is no longer formed for ZrO2 additions as low as x = 0.03. The influence of ZrO2 addition on Y2O3 coatings properties is discussed.