## 1 Introduction  
The application of titanium oxide materials is a well-researched subject, especially the application of titanium dioxide (TiO\({}_{2}\)). Numerous non-stoichiometric phases can be formed [1; 2; 3], but their potential is still poorly defined. They can be prepared using various methods [4; 5; 6; 7; 8; 9]. One of these methods is magnetron sputtering, which can provide a wide variation in the amount of oxygen in the plasma, and has a high impact on the properties of the Ti-based coatings. It is known that an increase in the O\({}_{2}\) content results in higher transmittance (up to 80%) and a \"blue shift\" of the absorption edge, but decreases the sputtering rate [10]. What is more interesting is when the O\({}_{2}\) content in the plasma is low. Below 1% O\({}_{2}\) content, opaque coatings will be obtained due to the lack of sufficient titanium oxidation [5]. In some instances, transparent films are obtained at 2% oxygen content, but this was not enough for significant structural changes [5]. Modification of the crystal structure will be more observable at a higher oxygen content. For ca. 30% in O\({}_{2}\), we will be able to obtain stoichiometric materials, and any further increase in the amount of oxygen will result in the formation of more or less stable forms of TiO\({}_{2}\), i.e., rutile or anatase [7]. The analysis of the current state of knowledge does not allow for an unambiguous indication of the limit of oxygen content in the gas mixture, which would enable the preparation of non-stoichiometric TiOx films. The reports in the literature point to this value as being less than around 20%. For example, in the work of [PERSON] et al. [6], an abrupt decrease in the deposition rate was observed at approximately 6.2%. The presence of this critical point was confirmed by the significant change in resistivity. Moreover, the presence of metallic titanium was observed for films deposited with less than 5.8% oxygen, while fully amorphous films were obtained above this content. In the work of [PERSON] et al. [11], coatings deposited with an O\({}_{2}\) content in the range of 5% to 13% were amorphous; however, the increase in transmittance suggested partial oxidation at lower concentrations. Similar transitions between the metallic and oxide modes, along with a hysteresis effect, were also found in the works of [PERSON] et al. [8], [PERSON] et al. [1], [PERSON] et al. [10], and [PERSON] et al. [12]. It should be noted that a transition between the metallic and oxide modes can also be observed as a change in the supply parameters of the magnetron source, as shown in the work by [PERSON] et al. [13], where the critical oxygen content was around 12%. A similar effect was observed in the work by [PERSON] et al. [14], where the deposition rate decreased significantly above 15% of O\({}_{2}\) and was correlate with an increase in the resistivity of the films. In the case of non-stoichiometric films, the presence of crystalline forms of metallic titanium itself is often revealed. More often, metallic Ti is not found in coatings prepared with O\({}_{2}\) concentrations of greater than ca. 20% [14; 15]. Less oxygen will result in the presence of oxidation states such as Ti\({}^{0}\), Ti\({}^{2+}\), and Ti\({}^{3+}\). The relationship between the number of Ti\({}^{4+}\) ions at the expense of fewer Ti\({}^{0,2+,3+}\) has been highlighted by [PERSON] et al. [16]. However, for stoichiometric films, only Ti\({}^{4+}\) ions are observed. The degree of oxidation of titanium in thin films also influences changes in their structure as a result of high-temperature annealing. However, crystalline materials that do not change their structure further after annealing can be obtained [4; 17], in most cases, annealing above 400 \({}^{\circ}\)C in an oxygen-containing atmosphere will transform the structure to a crystalline and stoichiometric (TiO\({}_{2}\)) form. This can be either complete [18; 19; 20; 21; 22] or only partial recrystallisation (mixed phases) [23; 24].