Local structure in the paraelectric phase of Cd2Nb2O7 determined from x-ray diffuse scattering, by means of ab initio molecular dynamics and Monte Carlo modeling

X-ray diffuse scattering in the paraelectric phase of Cd2Nb2O7 is measured and structurally interpreted using atomistic methods. Ab initio molecular-dynamics simulations show dynamic disorder in both sublattices with average displacements of Cd ions significantly larger than for Nb. Within octahedral NbO6 and zigzag CdO chains along < 110 > rather strong longitudinal correlations of ion displacements are found whereas the transverse component is weakly correlated. Local distortions lead to shifts of valence bond sums for cations toward nominal values. In combination with Monte Carlo simulations, excellent agreement of calculated and experimental diffuse scattering patterns is achieved.