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Ferroeleetric ceramics of the general formula x (Litl~ Latl~ Ties) (1-x) (LiNbOa) have been found to have tungsten bronze (TTB) and ilmenite type structure in the ranges 0' 8 ~ x ~ 1.0 and 0 ~-~ x ~ 0.2 respectively. The system is biphasie in the other ranges. All single phase materials exhibit dielectric anomalies in the temperature range 300-600 K. The high dielectric constant of the TTB phase is explained as due to the existence of localised rotational excitons arising from a large number of defect structural units and their coupling with one of the low frequency lattice modes. Information about the lattice modes to which the rotational excitons are coupled has been obtained from Raman spectra.

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