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

Abstract

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 $\mathrm{Pb}({\mathrm{In}}_{1/2}{\mathrm{Nb}}_{1/2}){\mathrm{O}}_{3}$ (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 ${T}_{\mathrm{N}}$. Inelastic x-ray scattering analysis of the diffuse scattering shows that the transverse-acoustic (TA) and transverse-optic (TO) modes are dominant at high temperatures ($\ensuremath{\sim}800$ K), while the central peak (CP) and TA modes, which are coupled, contribute majorly to diffuse scattering near ${T}_{{}_{\mathrm{N}}}$ and show critical behavior at temperature close to ${T}_{{}_{\mathrm{N}}}$. The TO mode shows no anomaly at temperature close to ${T}_{{}_{\mathrm{N}}}$. 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 $\ensuremath{\sim}500$ 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.