Optical properties of ErH$_{2+x}$: First principles calculations and experimental measurements.

Rare earth and transition metal hydrides exhibit many interesting physical phenomena, from metal-semiconductor transitions to transparency changes at RT as a function of hydrogen content. Electrical resistivity measurements by P. Vajda (1) indicate that ErH$_{2+x}$ undergoes a metal-semiconductor transition between 240-290K and an antiferromagnetic transition between 1.75-2.3K depending on hydrogen content. These same transitions should also cause profound changes in the optical properties. This work will present first principles calculations of the optical properties of ErH$_{2+x}$ from 300-600K where x ranges from -0.2 to 0.2. The calculations will be compared to experimental results on thin films of ErH$_{2+x}$ which were obtained as a function of temperature from 10-600K and hydrogen content. \newline [1] P. Vajda and J.N. Daou, Phys. Rev. B., Vol. 49, p. 3275 (1994).