Effect of B-site Randomness on the Antiferroelectric/Relaxor Nature of the Ground State: Inelastic X-ray Scattering Study of Pb(In1/2Nb1/2)O3

Pb(In1/2Nb1/2)O-3 (PIN) can be antiferroelectric (AFE), ferroelectric (FE) or a relaxor depending upon the perovskite B-site randomness. In order to clarify the effect of B-site randomness, we studied the dynamics of ordered PIN without B-site randomness (O-PIN, AFE), which will give us a clear picture of the AFE/relaxor nature of the ground state due to B-site randomness. The quasielastic (QE) scattering shows a critical slowing down near the Gamma-point and the transverse acoustic (TA) mode shows a softening trend at a finite wavenumber position (not at the Gamma-point) towards. the AFE phase transition temperature (T-N similar to 450 K). On the other hand, the transverse optic (TO) mode shows a softening near the Gamma-point toward low temperature with no clear anomaly at T-N These results indicate that the AFE phase transition is associated with the TA mode and the origin of the QE scattering while a ferroelectric correlation exists behind the AFE ordering. The effect of B-site randomness is finally discussed on the basis of the results.