First-Principles Analyses of Electronic Structure of Multiferroic Nd Doped BiFeO3Solid Solution

摘要

BiFeOn3n(BFO) and Bin0.95nNdn0.05nFeOn3n(B-Nd) ceramics were prepared by solid state reaction method[1]. In the perovskite type structure ABOn3n, the substitution ofn$text{Bi}^{3+}$nbyn$text{Nd}^{3+}$nwas identified on the A-site[2]. Crystal refinememts(from XRD in Fig. 1(a)) and STEM in Fig. 1(b)/HRTEM(Scanning and High-resolution transmission electron microscopy)with the multislice methods reveal a R3c space group with lattice parameters ofn$mathrm{a}_{mathrm{B}mathrm{F}mathrm{O}}= 5.48$nÅ,n$alpha_{mathrm{B}mathrm{F}mathrm{O}}$n= 59.90°, andn$mathrm{a}_{mathrm{B}-mathrm{N}mathrm{d}}$n== 5.64 Å,n$alpha_{mathrm{B}-mathrm{N}mathrm{d}}$n: =59.82° for BFO and B-Nd, respectively. For Nd doped BFO, the photovoltaic effect was markedly improved, where the maximum power-conversion efficiency increased around 2 order due to the reduced optical band gap, and, reduced leakage current density as Nd substitutes the Bi sites, resulting in a structural distortion, reducing the Bi deficiency [3]. The optically measured band gap are 2.24eV and 2.204eVfor BFO and B-Nd, which are consistent reasonably well with the calculated results based on Vienna ab initio simulation package(V ASP) [4], [5] following L(S)DA +U methods. In Figs. 1(c) and (d), the calculated band gap of B-Nd is 2.091eV which is smaller than the simulated value 2.271eV of BFO.