Dielectric maximum temperature non-monotonic behavior in unaxial Sr _0.75Ba_0.25Nb₂O₆ relaxor seen via acoustic emission

[100] oriented Sr_0.75Ba_0.25Nb₂O ₆ relaxor crystals have been studied by means of acoustic emission (AE) over a wide 20-400° C temperature range. Both the Burns temperature, Td = 350° C, and the intermediate temperature, T^* = 183°C, and the susceptibility maximum temperature, Tm (59° C on heating and 47° C on cooling), have been successfully detected. Dependent upon the external electric field, the T_m exhibits a local minimum near 0.25 kV=cm accompanied by pronounced AE maximum in a manner which had recently been detected in Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO ₃ by Dul-kin et al. [Appl. Phys. Lett. 94, 252904 (2009)] and in Pb(Sc_1/2Ta_1/2)O₃ by Dul-kin et al. [Phys. Rev. B 82, 180101(R) (2010)], whereas the T^* increases monotonically, similar to that which had recently been revealed in BaTiO3 by Dul-kin et al. [Appl. Phys. Lett. 97, 032903 (2010)] with a rate of 7.5 K cm/kV. An observed T_m behavior is discussed from the point of view of the existence of the random electric field components along the [100] direction in Sr_0.75Ba_0.25Nb₂O₆ crystals.