Sol-Gel Synthesis, Crystal Structure, Electronic and Magnetic Properties of AlxTi1-xBiO3 (0.0 ≤x≤ 0.33) Oxides

Abstract

Synthesis of Al_xTi_1-xBiO₃ (0.0 ≤x≤ 0.33) (S1-S4: x = 0.0, 0.11, 0.22, 0.33) oxides is performed by sol-gel method via nitrate-citrate route. Analysis of the powder X-ray diffraction (XRD) patterns show tetragonal unit cell with lattice parameters: a = 6.6377, 6.6398, 6.6370, 6.6366 Ã…; c = 6.5445, 6.5391, 6.5259, 6.6583 Ã…, respectively in S1-S4, with space group P42/mnm and Z=4. Average crystallite sizes determined by Scherrer relation are found to be in the range ~16-36, 18-50, 19-48 and 19-41 nm in S1-S4, respectively. On Rietveld refinement of unit cell structures the agreement factors are lowered to: R_p= 98.28, 97.65, 98.85, 94.29 %; R_wp= 97.11, 96.76, 97.92, 95.73 %; R_exp= 0.09, 0.09, 0.09, 0.09 % in S1-S4, respectively. Fourier electron density mapping show irregular contours around Bi³⁺, Ti³⁺ and O^2- ions due to significant ionic character in Ti-O and Bi-O bonds in the materials. Presence of hysteresis loops in the range -6 kG to +6 kG at 300 K with magnetic susceptibility values in the range 5.926 x 10^-8 - 6.461 x 10^-8 emu/gG in S1-S4 show soft ferromagnetic nature of the oxides. Density functional theory (DFT) calculations using CASTEP (Cambridge Serial Total Energy Package) programme package show energy band gap, E_g,  ~ 0.01-0.02 eV indicating weak semiconducting nature of the oxides. The valence band (VB) predominantly comprises O 2p, Ti 3d, Al 3p and Bi 6p orbitals, and the conduction band (CB) comprises mostly O 2p, Al 3p and Bi 6p orbitals with extension of band tails narrowing the energy band gap.