Studies of the Structure and Optical Properties of BaSrMgWO(6) Thin Films Deposited by a Spin-Coating Method

Highly transparent thin films with the chemical formula BaSrMgWO(6) 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(2), SrO(2), and MgO, and an under-stoichiometric phase (24.4%) with the chemical formula Ba(2−(x+y)) Sr(x)Mg(y)WO(5). From transmittance measurements, the values of the optical band gap were estimated for the amorphous (E(gdir) = 5.21 eV, E(gind) = 3.85 eV) and nanocrystalline (E(gdir) = 4.69 eV, E(gind) = 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.