Nb-related perovskite oxides, such as NaNbO3, KNbO3, and AgNbO3, are the end members of novel ferroelectric materials. Although they have NbO6 octahedron, the phase transition mechanism changes depending on A-site ion. NaNbO3 and KNbO3 have rhombohedral structure at low temperature, and after the structural phase transition, orthorhombic structure appears. On the other hand, the monoclinic structure of AgNbO3 appeared as a disordered phase of rhombohedral structure. The rhombohedral structure is a highly ordered average structure, and the rhombohedral structure also tends to be subject to the influence of local randomness. We performed local structure analysis by using atomic pair-distribution function (PDF) and X-ray absorption fine structure (XAFS). Although these three materials have perovskite structures in which Nb occupies to B-site, local structures differ greatly. The Nb-O bond distribution appeared clearly in NaNbO3, but broaden in AgNbO3. The difference of local structures causes various phase transitions of Nb-related perovskite materials.
2014 The Materials Research Society of Japan