High-pressure tuning of d-d crystal-field electronic transitions and electronic band gap in Co(IO3)2

High-pressure optical-absorption measurements performed on polycrystalline Co(IO3)(2) samples were used to characterize the influence of pressure on the electronic d-d transitions associated with Co2+ and the fundamental band gap of Co(IO3)(2). The results shed light on the electron-lattice coupling and show that Co(IO3)(2) exhibits an unusual behavior because the compression of Co-O bond distances is not coupled to pressure-induced changes induced in the unit-cell volume. Experimental results on the internal d-d transitions of Co2+ have been explained based on changes in the constituent CoO6 octahedral units using the semiempirical Tanabe-Sugano diagram. Our findings support that the high-spin ground state (T-4(1)) is very stable in Co(IO3)(2). We have also determined the band-gap energy of Co(IO3)(2) and its pressure dependence which is highly nonlinear. According to density-functional theory band-structure calculations, this nonlinearity occurs because the bottom of the conduction band is dominated by I-5p orbitals and the top of the valence band by Co-3d and O-2p orbitals, and because the Co-O and I-O bond lengths exhibit different pressure dependences.

Automated summary

High-pressure optical-absorption measurements were conducted on polycrystalline Co(IO3)(2) samples to investigate the influence of pressure on the electronic properties and fundamental band gap of Co(IO3)(2). The results revealed unusual behavior in the electron-lattice coupling of Co(IO3)(2), and the d-d transitions were explained by changes in the CoO6 octahedral units.