Scandium was substituted for yttrium to observe the effect of unit cell size on the optical metal-to-insulator (MIT) transition in the Y_(1-z)Sc_(z)H_(x) alloy system. The optical transmittance decreases significantly for z>0.10. Simultaneous electrical resistivity measurements confirm the transition from trihydride to dihydride behavior with increasing z. These observations imply a quenching of the MIT when the unit cell volume falls below a critical level that is consistent with the boundary between trihydride and non-trihydride forming rare-earth elements. A combinatoric model reveals this formation boundary corresponds to two or more Sc per unit cell.
@article{arxiv.cond-mat/0703521,
title = {Steric quenching of the switchable mirror effect Phys. Rev. B 75, 104109 (2007)},
author = {Troy C. Messina and Casey W. Miller and John T. Markert},
journal= {arXiv preprint arXiv:cond-mat/0703521},
year = {2007}
}