| Popis: |
The IR spectrum of Ba 2 TiO 4 synthesized from “pure” commercial samples of TiO 2 and BaCO 3 exhibits between 1200 and 950 cm −1 a more-or-less complex pattern of sharp, very weak bands whose intensity depends on the origin of the reagents, and which disappear completely if very pure reagents are used for the synthesis. It is shown that most of these bands are due to a small quantity (e.g. 0.5 mole % or less) of phosphate and/or sulfate ions (brought by the reagents) replacing the TiO 4 tetrahedra in the Ba 2 TiO 4 structure and thus forming a “dilute” solid solution. This is responsible for the sharpness of the IR bands and for their easy observation, even at fairly low concentrations [e.g. 0.1 mole % for the (PO 4 ) 3− ion]. The four investigated TiO 2 samples are free from sulfate, but all of them (including pro analysi samples) contain a small amount (0.5-0.1%) of phosphate, not disclosed in TiO 2 itself, but easily evidenced after transformation into Ba 2 TiO 4 . |
