RAMAN-SPECTRA OF PB1-3XBI2XMOO4 (X-LESS-THAN-OR-EQUAL-TO-0.06) AND THEIR O-18 SUBSTITUTED SYSTEMS

A new band at 896 cm-1 is ascribed to a local mode, v1, due to a molybdate ion occupying a cation vacancy. Local modes for v3 and v4 were also found at ca. 800 and 397 cm-1, respectively. The relative intensity for translational modes at 71 and 59 cm-1 varied considerably with x. This was explained in terms of a decrease in primitive cells with two Pb2+ ions. The band decomposition was carried out for the v1 region in O-18-substituted systems. The equilibrium distribution for isotopic species, [(MoO4-nOn)-O-16-O-18]2- (n = 0-4), was found approximately in the system with x = 0.01 after annealing, whereas the discrepancy between the observed and equilibrium distributions increased with increase in x. These observations show that a molybdate ion interacting strongly with a Bi3+ ion and a cation vacancy is inactive for O-18-substitution.