Optical and dielectric properties of Sillén Bi2Y1-xMxO4Cl (M = Cu, Cd)

Abstract

Mixed-anion solids with reduced dimensionality and layered (2D) structures exhibit a range of advantages arising from their tunable bonding environments and structural flexibility. Studies involving cationic substitution in the Sillen family of bismuth oxychloride-containing triple fluorite blocks, Bi2YO4Cl, to impart new functions are scarce and require further investigation. In this study, we examined the optical and dielectric property changes of Bi2YO4Cl by introducing Cu2+ and Cd2+ at the Y3+site. Up to 20 mol% of Y3+ in Bi2YO4Cl could be substituted with Cu2+ and Cd2+, while retaining the layered tetragonal structure (S.G. P4/mmm). The inclusion of these two divalent ions increased the unit-cell volume. Doping with Cu2+ and Cd2+ ions produced nearly equivalent amounts of Bi5+ ions, as confirmed by XPS analysis and iodometric redox titration. The EPR spectra of Bi2Y0.80Cu0.20O4Cl indicated a pseudo-octahedral environment around Cu2+. The absorption edge in the UV-visible spectra of the Cu2+ and Cd2+ doped Bi2YO4Cl samples was redshifted, leading to a reduction in the optical bandgap. For the Cu2+ doped sample, the CIE 1976 a* coordinate became more negative, indicating the enrichment of the green shade. The a* value became positive with the addition of Cd2+, imparting a reddish tinge to the sample. Temperature-dependent dielectric measurements of Cu2+ and Cd2+-doped samples in the frequency range of 1-104 Hz revealed Maxwell-Wagner-type polarization and pseudo-Debye-type behavior, respectively.