An ex situ STM study was carried out of the surface morphology of thallium oxide films (from 10 to 10000 effective monolayers) electrodeposited on Pt, and a tunnel-spectroscopic characterization of these materials is presented. Taking into account these results and data on the phase composition of products and the thermodynamic properties of the thallium oxide system, the deposition transients and corresponding chronocoulograms are analyzed. The formal kinetic parameters of two nucleation processes that take place during the oxide deposition have been determined. A model is proposed which makes it possible to describe the transient shape at the simultaneous crystallization of two phases on sites of different nature. Within the framework of the assumption on the additivity of partial transients, it is shown that such a model provides an adequate description of the overpotential and the surface pretreatment effects on the shape of transients of the thallium oxide deposition on an inert substrate.