Studies of the Structure and Optical Properties of BaSrMgWO6 Thin Films Deposited by a Spin-Coating Method
Luciana Punga, A. Abbassi, Mihaela Toma, Teodor Alupului, Corneliu Doroftei, Marius Dobromir, Daniel Ţîmpu, Florica Doroftei, Laura Hrostea, George G. Rusu, A. Razouk, Felicia Iacomi
Abstract
Highly transparent thin films with the chemical formula BaSrMgWO6 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 BaO2, SrO2, and MgO, and an under-stoichiometric phase (24.4%) with the chemical formula Ba2−(x+y) SrxMgyWO5. From transmittance measurements, the values of the optical band gap were estimated for the amorphous (Egdir = 5.21 eV, Egind = 3.85 eV) and nanocrystalline (Egdir = 4.69 eV, Egind = 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.