## 2 Materials and Methods  
The work here described comprises the following experimental steps: preparation of a stable suspension of TiTe\({}_{3}\)O\({}_{8}\) particles synthesised by solid state reaction, carbon coating of the nonconducting Al\({}_{2}\)O\({}_{3}\) substrates, EPD of green TiTe\({}_{3}\)O\({}_{8}\) thick films on carbon coated Al\({}_{2}\)O\({}_{3}\) substrates and their sintering, as well as electrical characterization of TiTe\({}_{3}\)O\({}_{8}\) thick films on Al\({}_{2}\)O\({}_{3}\) at microwave frequencies. TiTe\({}_{3}\)O\({}_{8}\) powders were synthesized from reagent-grade TeO\({}_{2}\) (>99%, Sigma-Aldrich, Saint Louis, MO, USA) and TiO\({}_{2}\) (>99%, Merck KGaA, Darmstadt, Germany) via a conventional solid-state-reaction method, as per [30]. The starting precursors were weighed according to the molar ratio of 3:1, ball mixed with ethanol and dried at 70 \({}^{\circ}\)C for 5 h. The mixed powders were calcined at 620 \({}^{\circ}\)C for 50 h and milled for 5 h in a planetary ball mill at 200 rpm using Teflon pots and zirconia balls. Milled TiTe\({}_{3}\)O\({}_{8}\) powders with particle size below 10 \(\upmu\)m were ultrasonically dispersed in acetone (>99.5%, Panreac Quimica SLU, Castellar del Valles, Spain) with a concentration of 10 g/l. Triethanolamine (TEA) (>99%, Merck KGaA, Darmstadt, Germany) was added as a suspension stabilizer to favour the EPD process [31]. The addition of TEA increased considerably the zeta potential of the suspension to 46.5 mV at pH of 8.1 that guaranteed the fabrication of crack free and homogeneous films. The suspensions were magnetically stirred for 5 h at room temperature. The stability of the suspensions was analysed by transmittance of the UV light (UV-2101/3101 PC, Shimadzu Corporation, Kyoto, Japan), particle size distribution and zeta potential techniques (Malvern Zeta sizer Nano ZS, Malvern, Worcestershire, UK). Non-conducting alumina substrates were coated with a sacrificial conducting carbon film that acts as a temporary electrode being burned at high sintering temperatures without leaving any residual contaminations, as mentioned before. Following our previous work [13], a radio frequency (RF) magnetron sputtering (CRIOLAB, Porto, Portugal) was used to perform the deposition of the carbon layer from the corresponding target (purity > 99.9%, Sofacel Inc., Madrid, Spain) of 55 mm in diameter and 3 mm in thickness on 25.4 \(\times\) 25.4 \(\times\) 0.0254 mm\({}^{3}\) polycrystalline Al\({}_{2}\)O\({}_{3}\) substrates (99.6%, Coors Ceramics U.K., Glenrothes, Fife, Scotland, UK, with the remaining 0.4 wt. % assumed to be a silicate based sintering aid). The carbon coatings were prepared at a substrate-magnetron distance of 120 mm under Ar pressure of 5.8 \(\times\) 10\({}^{-3}\) mbar, with a magnetron current of 0.3 A and a substrate bias of 470 V. The thickness of the carbon layer was controlled by the deposition time. The carbon coated Al\({}_{2}\)O\({}_{3}\) was employed as a substrate for the deposition of TiTe\({}_{3}\)O\({}_{8}\) films and stainless steel was chosen as the counterpart electrode. EPD was carried out for 3 min under a dc voltage of 100 V from the voltage supply (Glassman High Voltage Inc., High Bridge, NJ, USA). The obtained films were dried for more than 24 h at room temperature and then sintered from 680 \({}^{\circ}\)C to 720 \({}^{\circ}\)C for 5 h in a closed alumina crucible together with TeO\({}_{2}\) powders, to avoid Te volatilization. The use of TeO\({}_{2}\) powder was reported to increase the partial pressure of TeO\({}_{2}\) and to suppress the evaporation from TiTe\({}_{3}\)O\({}_{8}\)[30]. The crystallographic structure and phase content of TiTe\({}_{3}\)O\({}_{8}\) films were analysed by X-ray diffraction (XRD, PANalytical X'Pert Pro diffractometer, Philips, Amsterdam, The Netherlands, Cu-K\(\alpha\) radiation, 45 kV and 40 mA), used from 10\({}^{\circ}\) to 80\({}^{\circ}\) 20 with a step size of 0.025\({}^{\circ}\).