Experimental materials physics

Zn₁₋ₓMgₓFe₂O₄ spinel ferrites

Combustion synthesis and structural and optical characterization of Zn₁₋ₓMgₓFe₂O₄ (x = 0, 0.5, 1.0), correlated with DFT calculations.

Bachelor's thesis (trabajo de grado) · Universidad Nacional de Colombia · 2026 · 152 pp · advisor D. A. Landínez Téllez

Laboratory work: synthesis of the series by glycine-assisted combustion, and characterization by X-ray diffraction with Rietveld refinement, SEM/EDX and UV-Vis diffuse reflectance. Electronic structure: GGA+U band structures, with the treatment proposed and analysed in the thesis and the calculations run within the research group.

Thesis PDF (Spanish, 3.5 MB)

Main results

Single-phase Fd3̄m solid solution across the series; Rietveld refinement tracks the lattice parameter with composition.
Coherent domains of 20–26 nm (Scherrer; Williamson–Hall used only as a diagnostic). SEM grain size ~65 → ~81 nm.
Direct optical gap of 1.88–1.91 eV, nearly independent of composition.
GGA+U band structures place the gap in the Fe–O subsystem, which explains why replacing Zn with Mg barely moves it.

Analysis of the diffraction data continues with whole-pattern simulation (GSAS-II).

Synthesis

Precursor gel before combustion — Precursor gel just before ignition.

Expanded solid product after combustion — Expanded solid after combustion.

Structure and microstructure

Rietveld refinement of the mixed Zn–Mg ferrite — Rietveld refinement, mixed ferrite (x = 0.5), space group Fd3̄m.

Refined lattice parameter across the series with the Vegard trend — Refined lattice parameter across the series, with the Vegard trend (axis labels in Spanish).

SEM micrograph of the mixed ferrite — SEM of the mixed ferrite: grain morphology.

Ordered Zn–Mg superstructure drawn in VESTA — Ordered Zn–Mg superstructure for x = 0.5 (VESTA).

Williamson–Hall analysis of the mixed ferrite — Williamson–Hall, used as a diagnostic; crystallite size is quoted from Scherrer.

EDX spectrum of the mixed ferrite — EDX of the mixed ferrite.

Optical gap

Tauc plots of the three ferrites with linear fits and gap values — Diffuse reflectance converted with Kubelka–Munk and plotted for a direct transition; dashed lines are the linear fits whose intercepts give the gaps reported in the thesis. Regenerated for this site from the measured spectra.

The thesis is written in Spanish, and so are some figure labels on this page. The PDF linked above is a compressed copy for the web; the full-resolution file is available on request.