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Register a new userRevised crystal structure and electronic properties of Ba(Fe$_{1/2}$Nb$_{1/2}$)O$_{3}$ ceramics
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Ba(Fe$_{1/2}$Nb$_{1/2}$)O$_{3}$ (BFN) ceramics are considered to be a potential candidate for technological applications owing to their high dielectric constant over a wide range of temperature values. However, there exists considerable discrepancy over the structural details. We address this discrepancy through a comparative analysis of the earlier reported structures and combined X-Ray Diffraction (XRD) at room temperature and Neutron Powder Diffraction (NPD) measurements in the range of 5K up to room temperature. Our study reveals a cubic structure with space group $Pmbar{3}m$ at all measured temperatures. The local environment of the Fe ions is investigated using X-ray Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) technique. A detailed investigation of the electronic properties of the synthesized BFN ceramics is carried out by combination of theoretical and experimental tools: X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and density functional theory (DFT) within GGA$+U$. The bandgap is estimated using the diffuse reflectance measurements in the UV-Vis-NIR range and an appropriate value of the electron-electron correlation strength $U$ is estimated based on the UV-Vis-NIR and the XAS spectra.
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PbFe$_{1/2}$Ta$_{1/2}$O$_{3}$ (PFT) belongs to the family of PbB$_{x}$B$_{1-x}$O$_{3}$ which have inherent chemical disorder at the B-site. Due to this disorder, a complex magnetic phase diagram is expected in the material. In this paper, we report experimental results of magnetic properties in PFT through macroscopic characterization, neutron scattering and M{o}ssbauer spectroscopy techniques. With these results we show for the first time that PbFe$_{1/2}$Ta$_{1/2}$O$_{3}$ behaves very similar to PbFe$_{1/2}$Nb$_{1/2}$O$_{3}$, i.e, it undergoes AF transition at 153 K and has a spinglass transition at 10 K, below which the antiferromagnetism coexists with spinglass. We suggest that the mechanism which is responsible for such a non-trivial ground state can be explained by a speromagnet-like spin arrangement similar to the one proposed for PbFe$_{1/2}$Nb$_{1/2}$O$_{3}$.
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