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Influence of mechanical activation on the structure of ultrafine BaTiO3 powders

“…Our EPR investigation pointed out an increase of this signal with mechanical activation. That is in accordance with the results of Hari and Kutty [22], which indicated that the intensity of the signal at g = 1.997 rises with decreasing of mean grain size in barium titanate ceramic. Kolodiazhnyi and Petric [28] observed an anomaly increase of the signal at g = 2.004 at the temperature of transition to the cubic phase.…”

“…Kolodiazhnyi and Petric [28] observed an anomaly increase of the signal at g = 2.004 at the temperature of transition to the cubic phase. Since mechanical activation leads to diminution of the mean particle size and so to potential approaching of the tetragonal cell to the pseudocubic one, the observation of Kolodiazhnyi and Petric [28] could be related to our results, as well as to the results of Hari and Kutty [22].…”

“…Dunbar et al [29] and Castro et al [30] considered just the doped ceramic. On the other hand, several authors reported that the EPR peak with g ≈ 1.97 may be caused by intrinsic Ti 3+ related defects in BaTiO 3 [16][17][18][19][20][21][22][23][24] . A few of them observed this peak just in reduced BaTiO 3 ceramic [20,25].…”

“…Some authors whose examinations included EPR spectra at room temperature and above, attributed a peak at g = 1.97 to the localized Ti 3+ states [16]. Others emphasized that this and similar values of the g-factor (g = 1.963-1.975) should be ascribed to the Ti 3+ -V O , that is Ti 3+ -F + centers, rather than exactly to Ti 3+ [21][22][23][24]. These observations of Ti 3+ and Ti 3+ -V O signals at room temperature and above strongly contradict the reports of a different group of authors, where manifestation of the Ti 3+ ion in EPR spectra was observed only at rather low temperatures (below 250 K [17], even mostly below 80 K [18][19][20]).…”

“…As reported in the literature, the assignment of this EPR signal is also not without controversy. Lee and Park [21], Hari and Kutty [22] and Jayanthi and Kutty [24] supposed that a singlet peak at g ≈ 2 could be ascribed to the structural defects probably associated with barium vacancies. The signal at g = 1.997-2.006 could also come from the vacancy pair of the V Ba -F + type, as Slipenyuk et al [17] and Jida and Miki [18] reported.…”