Sitaraman, N. Arias, T. Baraissov, Z. Gaitan, G. Liepe, M. Muller, D.A. Oseroff, T.E. Sun, Z. JACoW Publishing Geneva, Switzerland 2673-5504 978-3-95450-234-9 10.18429/JACoW-SRF2023-TUPTB004 English 398-400 niobium ECR vacuum electron superconductivity Contribution to a conference proceedings 2023 2023-09 https://doi.org/10.18429/JACoW-SRF2023-TUPTB004 https://jacow.org/srf2023/papers/tuptb004.pdf The first experimental studies of zirconium-doped surfaces verified that zirconium can enhance the critical temperature of the surface, resulting in a lower BCS resistance than standard-recipe niobium. However, they also produced a disordered oxide layer, resulting in a higher residual resistance than standard-recipe niobium. Here, we show that zirconium-doped surfaces can grow well-behaved thin oxide layers, with a very thin ternary suboxide capped by a passivating ZrO2 surface. The elimination of niobium pentoxide may allow zirconium-doped surfaces to achieve low residual resistance.