High-pressure study of X-ray diffuse scattering in ferroelectric perovskites

TL;DR

This study investigates how high pressure affects x-ray diffuse scattering in ferroelectric perovskites BaTiO3 and KNbO3, revealing differences in diffuse line behavior and their relation to atomic off-centering.

Contribution

It provides new insights into the pressure dependence of diffuse scattering and atomic disorder in ferroelectric perovskites, linking diffuse lines to B atom off-centering.

Findings

Diffuse lines persist in all phases studied.

Diffuse line intensity decreases with pressure in BaTiO3.

Diffuse lines in KNbO3 remain up to 21.8 GPa with constant width.

Abstract

We present a high-pressure x-ray diffuse scattering study of the ABO$_3$ ferroelectric perovskites BaTiO_3 and KNbO_3. The well-known diffuse lines are observed in all the phases studied. In KNbO_3, we show that the lines are present up to 21.8 GPa, with constant width and a slightly decreasing intensity. At variance, the intensity of the diffuse lines observed in the cubic phase of BaTiO_3 linearly decreases to zero at $\sim 11$ GPa. These results are discussed with respect to x-ray absorption measurements, which leads to the conclusion that the diffuse lines are only observed when the B atom is off the center of the oxygen tetrahedron. The role of such disorder on the ferroelectric instability of perovskites is discussed.