## 3 Results  
Before alumina substrates are used for EPD, the essential step is to sputter a carbon layer upon it to make them conductive, as explained before. The carbon coatings certainly affect the EPD process and thereby the quality of TiTe\({}_{3}\)O\({}_{8}\) films and their final dielectric performance. According to our previous results, there is an optimum carbon layer thickness in the range between 200 and 400 nm that guarantees a continuous uniform high quality film deposition [13]. Carbon layers with thickness below 100 nm cannot be used as temporary electrodes for EPD since the formed layer is not sufficiently conductive to permit the deposition of a continuous film. On the other hand, with too thick (>500 nm) carbon layers, non-conformal and non-uniform films are obtained after sintering, because thick carbon layers restrict the final film adhesion to the substrate. Therefore, \(\sim\)300 nm thick carbon layer was selected to be used in the present work. The surface of the green (non-sintered) TiTe\({}_{3}\)O\({}_{8}\) thick films deposited by EPD under 100 V for 3 min on carbon coated alumina substrate is presented in Figure 1a. Very uniform and crack free TiTe\({}_{3}\)O\({}_{8}\) film with circular shape is seen on the background of the black carbon layer with square shape. The cross-section microstructure of these green films is illustrated in Figure 1 b,d. The low magnification SEM micrograph depicts a very uniform, compact and conformal \(\sim\)50 \(\upmu\)m thick TiTe\({}_{3}\)O\({}_{8}\) film on the carbon coated alumina substrate (Figure 1b,c). TiTe\({}_{3}\)O\({}_{8}\) particles are densely packed and deposited on the substrate thanks to the carbon coating conductive surface. The uniform continuous conformal carbon layer with thickness of \(\sim\)300 nm can be easily observed from the high magnification micrographs (Figure 1c,d). Figure 1: A surface optical image (**a**) and cross section SEM micrographs (**b–d**) of a green TiTe\({}_{3}\)O\({}_{8}\) thick film deposited by EPD under 100 V for 3 min on carbon coated 25.4 \(\times\) 25.4 \(\times\) 0.0254 mm\({}^{3}\) alumina substrate: very uniform and crack free TiTe\({}_{3}\)O\({}_{8}\) film with a circular shape on a background of a black carbon layer (**a**), average film thickness of \(\sim\)50 \(\upmu\)m (**b**) and compact microstructure of the film (**c**) on a continuous \(\sim\)300 nm carbon layer (**d**) are visible. The optical images of TiTe\({}_{3}\)O\({}_{8}\) films deposited on carbon coated alumina substrates sintered for 5 h in air at 680 (a), 700 (b) and 720 \({}^{\circ}\)C (c), respectively, are presented in Figure 2. Sintered TiTe\({}_{3}\)O\({}_{8}\) films exhibit the yellow colour characteristic of polycrystalline TiTe\({}_{3}\)O\({}_{8}\) and the alumina substrates present the original white colour. For films sintered at 680 \({}^{\circ}\)C (Figure 2a), the substrate is slightly darker than for the other sintered films. This is possibly due to an incomplete burn out of the sacrificial carbon layer, although thermal analysis (see Appendix A Figure A1) clearly indicates that the carbon layer oxidizes in air below 660 \({}^{\circ}\)C and thus below the sintering temperature of TiTe\({}_{3}\)O\({}_{8}\) films. After sintering at 680 \({}^{\circ}\)C, films still present a powder-like aspect, similar to the green ones, and do not have good adhesion to the alumina substrates, being easily detached. Therefore, under the present conditions, the sintering temperature of 680 \({}^{\circ}\)C is not enough to fully densify TiTe\({}_{3}\)O\({}_{8}\) thick films on Al\({}_{2}\)O\({}_{3}\). Films sintered at higher temperatures, 700 \({}^{\circ}\)C and 720 \({}^{\circ}\)C, are denser and do not detach from the substrate. However, films sintered at 720 \({}^{\circ}\)C exhibit areas with an irregular surface and a reddish colour, as seen from Figure 2c. For films sintered at 700 \({}^{\circ}\)C, (Figure 2b) only some reddish vestiges at the edges may be seen.