Shedding Light on Cuprorivaite, the Egyptian Blue Pigment: Joining Neutrons and Photons for a Computational Spectroscopy Study.

Abstract

The unique properties of Egyptian blue, a cuprorivaite pigment,were herein studied through a holistic computational and experimental approach. A reliable model of the crystal of cuprorivaite was obtained through periodic density functional theory calculations, allowing for the elucidation of its lattice dynamics, including assessment of structural, electronic, and vibrational properties. From this model,a sound assignment of the inelastic neutron scattering spectrum was obtained, along with estimated values of heat capacity and Debye temperature,band-gap values, and magnetic properties of the crystal. Inelasticneutron scattering and diffuse reflectance infrared Fourier transform spectroscopy provided enlightenment on the chemical surfaces of the pigment Egyptian blue which was missing hitherto and is critical for potential applications of the pigment, such as those involving host-matrix interactions or requiring surface derivatization while confirming the simulation results. On that account, it was found that the intensity of the dangling & nu;SiOd mode is ca. 8-13%of the total & nu;SiO modes. Moreover, and regarding the electronic properties, the band structure confirmed that CaCuSi4O(10) is a direct band-gap semiconductor, with the valence band maximum and the conduction band minimum located at the & UGamma;-point, in both the alpha (spin-up) and beta (spin-down) density bands. A reliable model of the crystal of cuprorivaite was achieved via periodic TDF calculations, which enabled the elucidation of its lattice dynamics, including the evaluation of its structural, electronic,and vibrational properties with implications for its surface chemistry analysis assessment.

Mariana M. Coimbra, Inês Martins, Sofia M. Bruno, Pedro D. Vaz, Paulo J. A. Ribeiro-Claro, Svemir Rudić, Mariela M. Nolasco. Cryst. Growth.