Temperature-dependent local correlations from diffuse x-ray diffraction in the relaxor ferroelectric Cd₂Nb₂O₇

Relaxor ferroelectrics (FE) exhibit a broad peak in the temperature dependent dielectric susceptibility, typically as a result of compositional disorder that produces a wide range of local environments and thereby a broad distribution in the local dielectric response. Cd₂Nb₂O₇ (CNO) exhibits such relaxor FE behavior despite its chemical stoichiometry and apparent lack of compositional disorder [1], prompting the question of what is responsible for relaxor behavior in CNO. A common explanation in the literature is that the Cd ions are underbonded, tending to sit at one of several sites slightly displaced from their average-structure positions [2]; local disorder of the Cd ions may couple to the Nb ions and result in relaxor FE behavior. We use single-crystal hard x-ray diffraction to study diffuse scattering in CNO and 3D differential pair distribution function (3D-ΔPDF) analysis to extract local structural correlations. Our data show that a strong component of the local correlations have the same temperature dependence as the dielectric susceptibility, indicating a direct link between these correlations and the relaxor-FE behavior. I will discuss our 3D-ΔPDF results and the implications for the local correlations and electronic physics in CNO.

[1]: C. Ang, R. Guo, A. S. Bhalla, and L. E. Cross, J. Appl. Phys. 87, 7452 (2000).

[2]: M. Tachibana, K. Fritsch, and B. D. Gaulin, J. Phys. Condens. Matter 25, 435902 (2013).