Partial cation ordering, relaxor ferroelectricity, and ferrimagnetism in Pb(Fe_(1-x)Yb_x)_(2/3)W_(1/3)O_3 solid solutions

摘要

The structural, magnetic, and dielectric properties of ceramic samples of Yb-doped PbFe_(2/3)W_(1/3)O_3 have been investigated by a variety of methods including x-ray powder diffraction, magnetometry, and dielectric spectroscopy. In addition, theoretical investigations were made using first-principles density functional calculations. All the doped samples Pb(Fe_(1-x)Yb_x)_(2/3)W_(1/3)O_3 (PFYWO) (0.1 ≤ x ≤ 0.5) were found to crystallize in an ordered cubic (Fm3m) structure with partial ordering in the B-perovskite sites. Observed changes in the cationic order were accompanied by differences in the dielectric and magnetic responses of the system. While pure PbFe_(2/3)W_(1/3)O_3 is antiferromagnetic, the doped Pb(Fe_(1-x)Yb_x)_(1/3)W_(1/3)O_3 PFYWO samples display excess moments and ferrimagnetic-like behavior, associated with differences in B' and B" site occupancies of the magnetic Fe~(3+) cations. The magnetic transition temperature of the ferrimagnetic phase is found to decrease with increasing Yb content, from T_N ～350 K of the undoped sample down to 137 K for x = 0.5. All PFYWO compounds display a ferroelectric relaxor behavior akin to that of PbFe_(2/3)W_(1/3)O_3, albeit our results show significant changes of the frequency and temperature dependence of the dielectric properties. The changes of the properties of PFYWO with increasing Yb substitution can be explained by the changes in the cation size/charge mismatch and the size difference of the two ordered positions.