The peculiarities of the synthesis and crystallization of complex oxides (B4Ti3O12 as an example) from the decay products in magnetron sputtering are discussed. The processes of complex oxide sputtering by ion bombardment, transfer of the products through the plasma to the substrate, the surface processes on the substrate and oxidation-reduction processes are considered. The dynamics of the layer formation is investigated by measuring the spectral line intensities (λBi=472.25 nm and λTi=498.1 nm) of the sputtered atoms at the target surface. The film deposition mechanism is shown to change with distance between substrate and target. A critical distance of hcrit=7 nm is found. At h<hcrit atoms are deposited, while at h>hcrit molecules condense. The degree of crystallization depends on oxygen pressure. Thermal activation strongly affects the deposition rate. In the case of molecular deposition at temperatures of ≥900∘C the high-temperature phase of γ-Bi2O3 forms along with Bi2O3 and TiO2. The dielectric loss tangent of Bi4Ti3O12 films depends on the bias potential of the substrate