Effect of B-site randomness on the antiferroelectric/relaxor nature of the ground state: Diffuse and inelastic x-ray scattering study of Pb(In1/2Nb1/2)O3

We have investigated the effect of B-site randomness on the antiferroelectric/relaxor nature of the ground state by studying diffuse and inelastic x-ray scattering from ordered and disordered Pb(In1/2Nb1/2)O-3 (O- and D-PIN) single crystals. The diffuse scattering measurement of O-PIN, which is antiferroelectric at low temperatures, shows that the ferroelectrically interactive local polarization exists in the cubic phase, above the transition temperature T-N. Inelastic x-ray scattering analysis of the diffuse scattering shows that the transverse-acoustic (TA) and transverseoptic (TO) modes are dominant at high temperatures (similar to 800 K), while the central peak (CP) and TA modes, which are coupled, contribute majorly to diffuse scattering near T-N and show critical behavior at temperature close to T-N. The TO mode shows no anomaly at temperature close to T-N. Furthermore, the phonon spectra are broad, indicating that a strong damping mechanism exists even in the sample with weak chemical disordering, O-PIN. No clear difference between O- and D-PIN is observed at temperatures above similar to 500 K. Here, the major difference between them is the property of the CP mode, which shows no drop and increases rapidly with decreasing temperatures in D-PIN. The CP mode is thought to be directly related to the local polarization and to originate in a combination of Pb flipping and the TO mode. The B site is considered to control the antiferroelectric/ferroelectric instability of lead-based perovskite materials. Finally, the B-site randomness is discussed in terms of suppressing the antiferroelectric instability and enhancing the polarization fluctuation.