Average and Local Structure of (PbMg1/3Nb2/3O3)1-x-(PbTiO3)x around its Morphotropic Phase Boundary

Relaxor ferroelectrics are perovskites-based oxides that are of great interest because of their dielectric and electromechanical properties. The specific property coefficients are enhanced at the so-called Morphotropic Phase Boundary (MPB). (PbMg1/3Nb2/3O3)1-x-(PbTiO3)x (PMN-PT) is one of the most attractive MPB- systems, at x=0.3-0.4. Although many studies were carried out to determine the average and local crystal structures of PMN-PT around its MPB, many uncertainties about its fine structure remain. Specifically, the information about local structure and disorder parameters is still missing. Being overlooked by traditional X-ray crystallography, disorder can be addressed using total X-ray / neutron scattering / single crystal diffuse scattering experiment, aiming at producing of atomic Pair Distribution Function and eventually reveal the subtle local correlations.

The aim of the work is to obtain the highest quality information about the average and local structure of PMN-PT around its MPB using X-ray and neutron scattering.

Neutron scattering data were collected from polycrystalline PMN-PT (x=0.30, 0.35, and 0.40) at 300, 383, and 533 K at the POLARIS beamline at ISIS. Rietveld refinement was performed using TOPAS-academic version 7.1.

X-ray total scattering were measured of PMN-PT single crystal samples (x=0.29 and 0.35) were measured in ID28 at the ESRF. The scattering data were collected via a 2D detector stationed in positions of 2θ=19 and 48 degrees and within various temperatures (300-530K). The collective datasets for each sample and temperature were reconstructed into a 3D reciprocal space and refined via CrysAlis Pro. Rietveld refinement confirms a tetragonal (Pm3m) - cubic (P4mm) phase transition around 410K for x=0.29 sample and the phase transitions for the x=0.35 sample are yet to be fully determined.

In our next step, we will perform simultaneous fitting of the total scattering and single-crystal diffuse scattering data using the Reverse Monte Carlo method to understand the nature of interatomic correlations.