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

The unique propertiesof Egyptian blue, a cuprorivaite pigment,were herein studied through a holistic computational and experimentalapproach. A reliable model of the crystal of cuprorivaite was obtainedthrough periodic density functional theory calculations, allowingfor the elucidation of its lattice dynamics, including assessmentof structural, electronic, and vibrational properties. From this model,a sound assignment of the inelastic neutron scattering spectrum wasobtained, 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 transformspectroscopies provided enlightenment on the chemical surfaces ofthe pigment Egyptian blue Rwhich was missing hitherto and iscritical for potential applications of the pigment, such as thoseinvolving host-matrix interactions or requiring surface derivatization Rwhileconfirming the simulation results. On that account, it was found thatthe intensity of the dangling & nu;SiOd mode is ca. 8-13%of the total & nu;SiO modes. Moreover, and regarding the electronicproperties, the band structure confirmed that CaCuSi4O(10) is a direct band-gap semiconductor, with the valence band maximumand the conduction band minimum located at the & UGamma;-point, in boththe alpha (spin-up) and beta (spin-down) density bands. A reliable model of the crystal of cuprorivaitewas achievedvia periodic TDF calculations, which enabled the elucidation of itslattice dynamics, including the evaluation of its structural, electronic,and vibrational properties with implications for its surface chemistryanalysis assessment.