Raman study of cations’ distribution in Zn _x Mg_1−x Fe₂O₄ nanoparticles

Abstract

In a complementary way, Raman and Mössbauer spectroscopy were successfully employed to assess the cations’ distribution among the tetrahedral (A-site) and octahedral (B-site) sites of nonosized Zn _x Mg_1−x Fe₂O₄ (0 ≤ x ≤ 1) cubic ferrite structure, synthesized by combustion reaction method. Nanoparticles with little change in size distributions, in the 40 nm (x = 0.0) up to 42 nm (x = 1.0) were obtained. Mössbauer data indicated that as the Zn-content (x) increases in the range 0 ≤ x ≤ 1, the Fe³⁺ ion monotonically increases (decreases) the A-site (B-site) occupancy up to nearly equal values at the highest end x value. Analysis of the Raman data, however, confirms that the three highest energy modes around 650, 668 and 710 cm⁻¹ are assigned to Zn–O (B-site), Fe–O (A-site) and Mg–O (A-site) vibrations, respectively. Additionally, in agreement with the Mössbauer data, the Raman data show that as the Zn-content (x) increases in the range 0 ≤ x ≤ 1, the occupancy of A-sites by Mg²⁺ ions monotonically reduces with concomitant increase of A- and B-sites occupancy by Fe³⁺ and Zn²⁺ ions, respectively. Indeed, combination of the two sets of spectroscopic data (Raman and Mössbauer) provides an effective protocol for assessing the cations’ distribution within the crystal structure of nanosized quaternary cubic ferrite samples running for instance from $\left[ {{\text{Fe}}_{0.42}^{3 + } {\text{Mg}}_{0.58}^{2 + } } \right]^{A} \left[ {{\text{Zn}}_{0.20}^{2 + } {\text{Mg}}_{0.22}^{2 + } {\text{Fe}}_{1.58}^{3 + } } \right]^{B} O_{4}^{2 - }$ at x = 0.2 up to $\left[ {{\text{Fe}}_{1.0}^{3 + } } \right]^{A} \left[ {{\text{Zn}}_{0.60}^{2 + } {\text{Mg}}_{0.40}^{2 + } {\text{Fe}}_{1.0}^{3 + } } \right]^{B} {\text{O}}_{4}^{2 - }$ at x = 0.6.