Effect of yttrium doping on the formation and stability of β‑tungsten powder

Abstract Yttrium oxide doped tungsten powders were produced by spray-drying solutions of ammonium meta-tungstate (AMT) and yttrium nitrate, calcining the spray dried powder, and reducing with hydrogen. During the reduction process, the formation of metastable β‑tungsten (β-W) was observed; this phase was still present after being reduced at 950 °C whereas β-W was not found upon reducing pure tungsten oxide at the same conditions. The effect of Y-doping on the synthesis and stability of β-W was investigated by using density functional theory simulation. Our calculation results indicate that the formation energy of Y doped β-W is lower than that of undoped β-W. Charge density analysis further revealed the formation of a covalent structure of Y-O-W between substitutional Y, interstitial O and adjacent W in β-W, which traps the oxygen atom at an interstitial site in the β-W instead of being desorbed. This structure improves the stability of β-W substantially.