  We report on the study of insulator-to-metal transition in post-perovskite
compound CaIrO3. It is discovered that a gradual chemical substitution of
calcium by yttrium leads to the onset of strong metallic behavior in this
compound. This observation is in stark contrast to BaIrO3, which preserves its
Mott insulating behavior despite excess of charge carriers due to yttrium
doping. Magnetic measurements reveal that both compounds tend to exhibit
magnetic character irrespective of the chemical substitution of Ca or Ba. We
analyze these unusual observations in light of recent researches that suggest
that unlike BaIrO3, CaIrO3 does not necessarily possess j = 1/2 ground state
due to structural distortion. The insulator-to-metal transition in CaIrO3 will
spur new researches to explore more exotic ground state, including
superconductivity, in post-perovskite Mott insulators.
