A divalent rare earth oxide semiconductor: Yttrium monoxide

Rare earth oxides are usually widegap insulators like Y₂O₃ with closed shell trivalent rare earth ions. In this study, solid phase rock salt structure yttrium monoxide, YO, with unusual valence of Y²⁺ (4d¹) was synthesized in a form of epitaxial thin film by pulsed laser deposition method. YO has been recognized as gaseous phase in previous studies. In contrast with Y₂O₃, YO was dark-brown colored and narrow gap semiconductor. The tunable electrical conductivity ranging from 10⁻¹ to 10³ Ω⁻¹cm⁻¹ was attributed to the presence of oxygen vacancies serving as electron donor. Weak antilocalization behavior observed in magnetoresistance indicated significant role of spin-orbit coupling as a manifestation of 4d electron carrier.