A Structural Study of 0.06LiNbO3-0.94K0.5Na0.5NbO3 from Neutron Total Scattering Analysis

The structure of ferroelectric 0.06LiNbO3-0.94K0.5Na0.5NbO3 (KNNL6) was investigated by the neutron total scattering method in the temperature range of 290–773 K. The Rietveld analysis using the powder neutron diffraction data in the range of 290–773 K indicates transition from a two-phase (monoclinic and tetragonal) mixture at room temperature to tetragonal and cubic phases at higher temperatures. However, characterization of the local structure by the pair distribution function (PDF) method indicates that the local structure (r ≲ 10 A) stays monoclinic over the same temperature range. Besides, the local oxygen octahedral distortion exhibits smaller changes with temperature than what is observed for the long-range average structure.