Steric effects in the metallic-mirror to transparent-insulator transition in YHx

We have exploited the switchable mirror transition, from metallic mirror to transparent insulator, in YHx to study steric effects due to scandium (Sc) substitution into the Y lattice. The reduction of lattice dimension upon Y replacement with Sc lends insight into the dynamics of this dramatic phase transition. Electron-beam evaporation was used to deposit 100 nm thick films of Y1−xScx alloys for 0.00 ≤ x ≤ 1.00. The films are capped with a protective, 10 nm overlayer of palladium (Pd) to prevent oxidation and to catalyze hydrogen absorption. Despite a significant decrease in the unit cell volume of approximately 30%, optical spectral transmission and resistivity measurements reveal that a transition persists far into the alloy phase diagram. The optical transmittance behavior smoothly transitions from trihydride behavior to dihydride behavior with a total decrease in optical transmittance by a factor of 12. Electrical resistivity measurements indicate a similar reduction in the metal to insulator transition with Sc concentration. In addition, large disorder of ρdo ≈ 120 µΩ·cm is introduced due to alloying. Details of structural analysis, spectroscopy, and electrical transport are discussed.Physic