Oxygen-assisted spinodal structure achieves 1.5 GPa yield strength in a ductile refractory high-entropy alloy

•Oxygen doping induces spinodal structure in the TiVHfNb refractory high-entropy alloy (RHEA).•The thermodynamic calculations revealed that oxygen doping assists in spinodal decomposition by extending the spinodal gap.•The lattice mismatch of nanoscale spinodal structure and the solid solution of interstitial oxygen enhance the yield tensile strength by 59.3%.