| Summary: | Highly transparent thin films with the chemical formula BaSrMgWO<sub>6</sub> were deposited by spin coating using a solution of nitrates of Ba, Sr, and Mg and ammonium paratungstate in dimethylformamide with a Ba:Sr:Mg:W ratio = 1:1:1:1. XRD, SEM, EDX, and XPS investigations evidenced that annealing at 800 °C for 1 h results in an amorphous structure having a precipitate on its surface, and that supplementary annealing at 850 °C for 45 min forms a nanocrystalline structure and dissolves a portion of the precipitates. A textured double perovskite cubic structure (61.9%) was found, decorated with tetragonal and cubic impurity phases (12.7%), such as BaO<sub>2</sub>, SrO<sub>2</sub>, and MgO, and an under-stoichiometric phase (24.4%) with the chemical formula Ba<sub>2−(x+y)</sub> Sr<sub>x</sub>Mg<sub>y</sub>WO<sub>5</sub>. From transmittance measurements, the values of the optical band gap were estimated for the amorphous (<i>E<sub>gdir</sub></i> = 5.21 eV, <i>E<sub>gind</sub></i> = 3.85 eV) and nanocrystalline (<i>E<sub>gdir</sub></i> = 4.69 eV, <i>E<sub>gind</sub></i> = 3.77 eV) phases. The presence of a lattice disorder was indicated by the high Urbach energy values and weak absorption tail energies. A decrease in their values was observed and attributed to the crystallization process, lattice strain diminution, and cation redistribution.
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