A study of structural phase transition, vibration, optical, and magnetic properties of Fe-doped PbTiO3 nanostructured powders

Abstract

Crystal structure, surface morphology, vibration, optical, and magnetic properties of PbTi1−x Fe x O3 (x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10) nanoparticles prepared by sol–gel method have been investigated using X-ray diffraction (XRD) analysis, scanning electron microscopy, Raman scattering, ultraviolet–visible (UV–Vis) absorption spectroscopy, and magnetization measurements. PbTi1−x Fe x O3 nanoparticles exhibit a structural phase transition from tetragonal to cubic structure as Fe concentration increases from 0 to 10 %mol. This leads to the reduction in tetragonal c/a ratio from 1.052 for un-doped PbTiO3 to 1.017 for PbTi0.9Fe0.1O3 sample. Grain size of the PbTi1−x Fe x O3 nanoparticles decreases with increasing Fe content and obviously increases with increasing calcination temperature. Raman spectra not only indicate the structural phase transition, but also confirm the replacement of Ti cations by Fe in the host PbTiO3 crystal lattice. Moreover, PbTi1−x Fe x O3 presents a narrowed band gap, much smaller than that of pure PbTiO3, which even remarkably reduces with increasing calcination temperature. PbTi1−x Fe x O3 shows a decrease in room temperature ferromagnetism as calcination temperature increases which can be explained by the decrease in surface oxygen vacancy. Furthermore, high tetragonality PbTi1−x Fe x O3 nanocrystals calcined at 900 °C exhibit a rapid increase in saturation magnetization M s when Fe concentration exceeds 4 %mol. This reveals the major role of magnetic-polaron interaction in magnetism of high tetragonality PbTi1−x Fe x O3 nanocrystals.