Dielectric dispersion of irradiated BaTiO3 within the region of phase transition

Frequency dependence of the dielectric constant (ε') and tg δ up to 1.5 × 1010 c/s have been measured for polycrystalline BaTiO 3 irradiated with fast neutron integrated fluxes up to ϕ ≃ 5 x 1019 cm-2. The radiation induced phase transition takes place at ϕc ≃ 5 x 1018 cm-2 corresponding to a maximum in the ε vs ϕ dependence and a fairly sharp increase in the dispersion frequency f0. Qualitatively, changes of e' and f0 are analogous to these near the Curie point for non-irradiated BaTiO3. At ϕ < ϕc the Curie point shift to lower temperatures depends upon the frequency according to the law ΔTc(f) = ΔT0 ln(f'0/f), where ΔT0 = 4-5 °C and f'0 ≃ 1011 c/s.