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.