ИСТИНА

In recent years, materials obtained using additive technologies are being actively studied. It is important to study a defect properties such structures. One of the effective methods of formation of additive samples is laser sintering. The materials formed in this process have interesting properties and a low cost in comparison with ones, obtained by another way of formation. It is known that titania based materials have unique properties and are characterized by the presence of a large number of point defects that are paramagnetic. Therefore electron paramagnetic resonance (EPR) spectroscopy is powerful technique for their investigation. Therefore, in order to identify these defects and to determine their main parameters both in dark and under illumination, we used this method and the technique developed on the basis of this method to diagnose the radicals formed in the process of various physicochemical effects in the "in situ" mode in the samples obtained with the help of additive technologies. We have made of the samples using laser sintering (Nd: YAG laser). The titania powder for laser sintering was formed using sol-gel method. Sintering of the titania powder was carried using a 15 W laser radiation power. The scanning speed of the laser beam was 3 cm/s. The EPR spectra were measured with an EPR spectrometer Bruker ELEXSYS-500 (operating frequency 9.5 GHz, sensitivity 5-10_10 spin/Gs). Illumination of the samples was carried out directly in the cavity of the spectrometer using a Bruker ER 202 UV mercury lamp (power of 50 W) in a wide spectral range (270-900 nm). To calculate the concentration of paramagnetic centers, we used a standard CuCl2(2H2O) with a known number of spins. The initial titania was characterized by the presence of Ti3+/oxygen vacancy centers. However, after the laser sintering process, the EPR signal from these defects disappeared and, instead of it, the signal from the electrons in the conduction band was recorded. The calculated concentrations of Ti3+/oxygen vacancy centers and conduction band electrons are equal (7.5*1017 cm-3). Therefore we suppose, that in the additive samples the oxygen vacancies are ionized, due to the movement of electrons to the conduction band, and therefore the vacancies are non-paramagnetic. Illumination of additive titania samples did not lead to a change in the EPR spectrum, which indicates that all oxygen vacancies are ionized (non-paramagnetic). These results can be useful for understanding the mechanism of defect trans-formation during laser sintering process and further practical applications of the TiO2 based additive materials.