PREPARATION AND STRUCTURAL CHARACTERIZATION OF ALKALINE-EARTH SHEET SILICATES CONTAINING COPPER BY POWDER NEUTRON-DIFFRACTION, EXAFS AND UVVISIBLE SPECTROSCOPY

The layered copper silicates, MCuSi4O10, M = Ca, Sr and Ba, have been prepared from the constituent oxides using conventional solid state sy nthesis. Their structures have been elucidated from the Rietveld refin ement of powder neutron diffraction data; all crystallise in the space group P4/ncc with a square-planar geometry around the copper site. Ch anges in the local environment, which occur as a function of the alkal i-earth metal cations, were also investigated using Cu K-edge EXAFS. T he effect of changing alkali-earth cation on the local copper geometry , and therefore the crystal field, was also investigated using diffuse reflectance UV-visible spectroscopy. When M=Ca the complex silicate i s well known as the pigment Egyptian Blue, and the possible use of the other materials with M=Sr, Ba as pigments is also discussed.