ORIGIN OF SPURIOUS BANDS IN THE INFRARED-SPECTRUM OF BA2TIO4

The IR spectrum of Ba2TiO4 synthesized from ''pure'' commercial sample s of TiO2 and BaCO3 exhibits between 1200 and 950 cm-1 a more-or-less complex pattern of sharp, very weak bands whose intensity depends on t he origin of the reagents, and which disappear completely if very pure reagents are used for the synthesis. It is shown that most of these b ands are due to a small quantity (e.g. 0.5 mole % or less) of phosphat e and/or sulfate ions (brought by the reagents) replacing the TiO4 tet rahedra in the Ba2TiO4 structure and thus forming a ''dilute'' solid s olution. This is responsible for the sharpness of the IR bands and for their easy observation, even at fairly low concentrations [e.g. 0.1 m ole % for the (PO4)3- ion]. The four investigated TiO2 samples are fre e from sulfate, but all of them (including pro analysi samples) contai n a small amount (0.5-0.1%) of phosphate, not disclosed in TiO2 itself , but easily evidenced after transformation into Ba2TiO4.