Study of inorganic transparent materials with near-infrared absorbing properties

Abstract

The pigments investigated in this thesis were synthesised and characterised in order to find promising candidates for near-infrared absorbers. The chemical systems were chosen due to their absorbing properties and also their chemical and thermal stability and non-toxicity as well as for economical reasons. Investigations were undertaken on several phosphates and silicates.Within the group of phosphates, first several known copper compounds, i.e.Cu2P2O7, Cu4P2O9, Cu5P2O10, Cu3(PO4)2, Cu(PO3)2 and Cu2P4O12, were tested and the most suitable were chosen for more detailed experiments. The structure types with the general formula M2P2O7 were found to be promising and the metals calcium, strontium and copper were investigated as a starting point. It was confirmed that M2P2O7 (with M = Ca or Sr) and Cu2P2O7 could only form a pigment material for the middle member e.g. MCuP2O7. Better candidates were found in the systems Mg/Cu and Zn/Cu. Here solid solutions occur and the absorption behaviour could be adjusted according to the ratio of the metal cations. A series of different cation ratio compounds were synthesised for both systems. As Zn/Cu shows more favourable absorption properties compared to Mg/Cu, a full investigation of structural parameters including neutron powder diffraction and EXAFS studies was undertaken and the influence of the shape of M–O coordination spheres on the near-infrared absorption properties is discussed in detail. After deriving the successful concept it was investigated in two further chemical systems. First, the cation Fe2+ was used into the Zn3(PO4)2 structure to form a solid solution (Zn,Fe)3(PO4)2 and then Cu2+ was introduced into the Mg2Si2O6 pyroxene structure. Resulting from the studies, three promising systems for transparent near-infrared absorbing pigment applications were isolated: (Zn,Cu)2P2O7, (Zn,Fe)3(PO4)2 and (Mg,Cu)2Si2O6 solid solution