46 Ana-Maria Ungureanu, Ioana Jitaru, Florinela Gosnea gathered through TG/DSC analysis, the gels were thermally treated at 500 0 C for 2 hours with a heating rate of 10 o C/minute. Fig. 2 - Thermograms of 2% (coloured line) and 6% (black line) Mn doped SnO 2 gels 3.2. X Ray Diffraction The XRD patterns recorded for the three doped tin dioxide samples are presented in Fig. 3, in comparison with an undoped SnO 2 sample. All diffractograms are characteristic to rutile type SnO 2 in accordance with ASTM 41-1445, and with our reference SnO 2 sample, obtained through the same synthesis route. For all three Mn concentrations, all peaks are clearly indexed to tetragonal SnO 2 . No secondary phases are observed, indicating a good Mn integration in the tin dioxide lattice. This suggests that through the ethylene-glycol assisted sol-gel synthesis the solubility limit of manganese ions into the tin dioxide lattice exceeds 6% at. in agreement with literature [9,15]. A slight displacement in 2 theta values is observed for all samples, suggesting that the dopant was successfully integrated in the host lattice.
Mn doped SnO 2 prepared by a sol-gel method 47 Fig. 3 - Mn doped tin dioxide XRD patterns in comparison with undoped sample Table I contains the structural and dimensional characteristics of all Mn doped samples, in comparison with an undoped tin dioxide nanopowder. The crystallite size was calculated using Scherrer’s equation. The difference between the crystallite size of the undoped sample and the crystallite size of the doped samples is less than 0.5nm. No size variations are observed with dopant concentration as all samples were calculated to have a size of 6 nm. Table I Crystallite size and cell parameters calculated for Mn doped tin dioxide in comparison with undoped tin dioxide Cell parameters of all doped samples have lower values than the undoped sample. All doped samples were calculated to have similar lattice parameters values. The minor differences that are observed may be associated with the distortions that occur during the incorporation of smaller manganese ions into the tin dioxide lattice. Mn concentration [%] Crystallite size [nm] Cell Parameters [Å] a c 0 5.6 4.73 3.19 2 6 4.70 3.17 4 6 4.70 3.17 6 6 4.70 3.17
48 Ana-Maria Ungureanu, Ioana Jitaru, Florinela Gosnea 3.3. UV-VIS spectroscopy UV-VIS spectra for all three doped samples are presented in Fig. 4. It can be clearly observed that all three samples have the typical spectrum of SnO 2 , with a large absorption band around 380 nm and a shoulder at 250nm. The broad shoulder from 600nm can be attributed to the manganese ions. Table II Band gap energies calculated with Tauc method Mn concentration [%] Eg [eV] 0 3.03 2 2.48 4 2.38 6 2.33 Fig. 4 - UV-VIS spectra obtained for 2%, 4% and 6% at. Mn doped SnO 2 nanoparticles