In the present work the barium titanate (BT) fabricated via mechanochemical treatment (MChT) have been investigated. Powders consisting of BT nanoparticles were synthesized by decomposition of barium titanyl oxalate BTO (BT-ox) and interaction of BaO and TiO2 (BT-o) during MChT for 5-10 h in air. In addition, the matrix samples of BT nanoparticles were prepared by means of BTO thermal decomposition in silica pores. It was shown (XRD data) that nanoparticles of pure tetragonal BaTiO3 were obtained. They have the specific surface area SSA 20-70 m2/g and crystallite size D 10-30 nm. The BT-o particles demonstrate the paraelectric – ferroelectric phase transition at 132oC (DSC data). The real ε1 and imaginery ε2 permittivity of BT-ox were about 4-5 and 0.5-1.5 accordingly and for BT-o ε1=18 and ε2= 6 in the temperature interval of 25-170oC. After annealing at 650oC which is accompanied by the mass loss the permittivity of both samples lowers and at 800-850oC the ε1 and ε2 increase to values about 14-17 and 1-2 in BT-ox and ε1 =26, ε2 =10-12 in BT-o. Moreover, the BT-ox particles display the phase transition at about 120-130oC. The annealing at 1100oC do not change essentially the permittivity and transition temperature of both samples. The BT-ox/SiO2 (25 % w/w BT) composite has SSA 140 m2/g, pore volume V=0.77 cm3/g and D~12 nm. Heating at 850 - 1100oC does not influence on D while the SSA and V slightly decrease. The milled BT-o possesses the photocatalytic activity while the BT-ox is photocatalytically non-active. However, in BT-ox annealed at 600-800˚C the destruction of safranin T with the rate constant Kd = 4-5•10-5 s-1 under UV-irradiation for power 30 W enhances (in BT-o Kd is 4-8•10-5 s-1). On the contrary, the annealing of BT-o leads to the loss of the photocatalytic activity. Thus, the mechanochemical treatment allows to obtain the ferroelectric particles of BT with ε1 = 18-26 for 8-12 GHz and change their photocatalitical properties.

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