Sol–gel synthesis, crystal structure, and characterization of Y x Bi2+x Cd4−3x O7 (0.05 ≤ x ≤ 0.35) nano-oxides

Abstract

Synthesis of the Bi2+x Y x Cd4−3x O7 (D1–D4: x = 0.05, 0.15, 0.25, and 0.35) nano-oxides was performed by sol–gel method via nitrate–citrate route. Analysis of the powder X-ray diffraction patterns shows a tetragonal unit cell with lattice parameters: a = 9.6874, 9.6919, 9.6909, and 9.6890 A, c = 5.9091, 5.4276, 5.4271, and 5.4268 A, respectively, in D1–D4, with space group P42/mcm and Z = 2 (number of molecules in unit cell). Average crystallite sizes determined by Scherrer’s relation are found to be in the range 53–83, 40–68, 23–85, and 51–88 nm in D1–D4, respectively, that shows the nanoparticles formation in the samples. On Rietveld refinement, the agreement factors are lowered to R p = 0.97, 0.97, 0.97, and 0.97; R wp = 0.98, 0.98, 0.98, and 0.98; and R exp = 0.001, 0.001, 0.002, and 0.002 in samples D1–D4, respectively. The calculated bond lengths in D1–D4 are as follows: Cd1–O1: 2.4348, 2.4359, 2.4361, and 2.4373 A; Bi2–O3: 2.3238, 2.3258, 2.3260, and 2.3272 A; and Bi3–O1: 2.2270, 2.2289, 2.2290, and 2.2302 A, respectively. The plane-wave density functional theory calculations on the unit cell crystal structure of D1–D4 show that the high density of states (DOS) of valence band located at −7.0 to 0.0 eV is due to the Y 4s, 4p; Bi 6s, 6p; Cd 4s, 4p; and O 2s, 2p orbitals. The DOS of conduction band located at ~0.0 to 2.2 eV is due to Y 4s, 4p; Bi 6s, 6p; Cd 4s, 4p; and O 2p orbitals. The optical absorbance spectra of the samples D1–D4 show the broad band of ~290 nm, which is commonly assigned to the Bi+3 (5d 10) 1S0 → 3P1 electronic transitions .