Weak-relaxor behaviour in Bi/Yb-doped KNbO3 ceramics

Weak-relaxor behaviour was observed in K1−xBixNb1−xYbxO3 ceramics with x = 0.20 and x = 0.30. According to x-ray diffraction analysis, the crystal structure of these ceramics can be described by the cubic centrosymmetric Pmm space group; however Raman spectroscopy reveals both the occurrence of local lattice distortions and the disruption of the long-range ferroelectric order. The local lattice strain caused by the larger Yb3+ combined with the presence of Bi3+, which lone-pair of electrons induces further local distortions, gives rise to polar nanoregions (PNRs). Nevertheless, the interaction between the PNRs appears weak and proper relaxor behaviour does not develop.