Surface atomic and chemical structure of relaxor Sr_(0.63)Ba_(0.37)Nb_2O_6(001)

摘要

The surface atomic and chemical structures of a Sr_(0.63)Ba_(0.37)Nb_2O_6(001) single crystal are studied using the low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy. Sharp, well-defined LEED patterns are observed, consisting of the superposition of two surface reconstructions, (5~(1) ×5~(1))R26.6° and (2~(5) × 2~(1))R45°, probably due to long-range ordering of the alkaline earth metal vacancies in A1 or A2 sites. The Sr/Ba stoichiometry is determined by high-resolution X-ray photoelectron spectroscopy. The Sr 3d core level has 2 components corresponding to the 12- and 15-fold coordinated A1 and A2 sites. The Ba 3d core level has only one component, consistent with the A2 site occupancy. The long-range order of the cation vacancies implies that it is rather the Sr/Ba occupancy of the A2 sites which is responsible for the local random fields at the origin of the relaxor behavior.