We measured phonon frequencies and linewidths in doped and undoped BaFe 2 As 2 single crystals by inelastic x-ray scattering and compared our results with density functional theory calculations. In agreement with previous work, the calculated frequencies of some phonons depended on whether the ground state was magnetic or not and, in the former case, whether phonon wave vector was parallel or perpendicular to the magnetic ordering wave vector. The experimental results agreed better with the magnetic calculation than with zero Fe moment calculations, except the peak splitting expected due to magnetic domain twinning was not observed. Furthermore, phonon frequencies were unaffected by the breakdown of the magnetic ground state due to either doping or increased temperature. Based on these results we propose that phonons strongly couple not to the static order, but to high frequency magnetic fluctuations.

We report the results of a neutron diffraction study of structural evolution in sodium niobate, NaNbO 3 , which is the parent compound for lead-free ferroelectric material, as a function of temperature from 15 to 930 K over six phases. The Rietveld analysis of the high resolution powder neutron diffraction data shows the variation in the structure from cubic to rhombohedral ferroelectric structures. However, the refinements on local structure by the PDF method indicates that there are only three basic patterns of the local structure, and the ground states of NaNbO 3 in the low-temperature antiferroelectric and ferroelectric phases have the R3c symmetry, even though in the long range the system shows the Pbcm symmetry or the coexistence of two phases. The origin of the complex phase behavior and its implications on the performance as lead-free ferroelectrics are discussed.