Structural, magnetic and Mossbauer spectroscopic investigations of the magnetoelectric relaxor Pb(Fe_(0.6)W_(0.2)Nb_(0.2))O_3

摘要

The complex perovskite lead iron tungsten niobium oxide, Pb(Fe_(0.6)W_(0.2)Nb_(0.2))O_3 (PFWN) which belongs to the class of disordered magne-toelectrics, has been studied by X-ray and neutron powder diffraction, magnetic and Mossbauer spectroscopic measurements. Structural, dielectric and magnetic properties of PFWN are presented and reviewed. Magnetic measurements indicate that the most important interactions are of antiferromagnetic nature yielding T_N = 300 K, however, with indications of a reentrant spin glass behaviour below 20 K. The parameters of Mossbauer spectra also support the existence of the magnetic order and are consistent with the presence of high-spin Fe~(3+) cations located in the octahedral B-site. Rietveld refinements of diffraction data at different temperatures between 10 and 700 K have been carried out. The long-range structure of PFWN is cubic (space group Pm-3m) over the whole temperature interval. The Fe, W and Nb cations were found to be disordered over the perovskite B-sites. The Pb cations show a position disorder along the <111> direction shifting from their high-symmetry position. At the temperatures below T_N, an antiferromagnetic arrangement of the magnetic moments of Fe~(3+) cations in the B-site is proposed in accordance with the antiferromagnetic properties of PFWN. The factors governing the observed nuclear and magnetic structures of PFWN are discussed and compared with those of pure Pb(Fe_(0.67)W_(0.33))O_3, Pb(Fe_(0.5)Nb_(0.5))O_3 and other quaternary Pb-based perovskites containing iron.