Raman scattering features of lead pyroantimonate compounds. Part I: XRD and Raman characterization of Pb2Sb2O7 doped with tin and zinc

The origin and use of lead antimonate yellows as a painting pigment is addressed in plenty by Renaissance ceramic production. In particular, modified forms of the cubic pyrochlore structure of the pigment were recently identified in ternary oxide lead antimonates in an Italian 17th century painting and a 16th century majolica. To clarify structures and properties of these coloured materials, yellow pyroantimonates, in binary and ternary oxide forms, Pb–Sb, Pb–Sb–Sn and Pb–Sb–Zn were synthesized by solid-state reactions at high temperature and characterized by X-ray diffraction and Raman spectroscopy. It has been found that the lattice size of cubic pyrochlores increases with Sn and Zn doping and with Pb overstoichiometry, indicating the replacement of Sb5+ by the larger cations. These observations permit the understanding of the corresponding Raman spectral modifications as a consequence of the changes in the local symmetry of the Sb–O polyhedra, justifying the exploitation of Raman spectroscopy to noninvasively identify structurally modified pyroantimonate pigments in artworks. The results demonstrates the high sensitivity of Raman spectroscopy for the identification of particular varieties of lead antimonate yellow pigments. The availability of a fiber-optic portable spectrometer allowed us to successfully apply the knowledge acquired from laboratory synthesized compounds for the interpretation of spectra collected from lead–antimony yellow pigments of Renaissance majolica directly in museums. These last data will be discussed in the part II of this paper.