BaZr0.5Ti0.5O3: Lead-free relaxor ferroelectric or dipolar glass

Glassy freezing dynamics was investigated in BaZr0.5Ti0.5O3 (BZT50) ceramic samples by means of dielectric spectroscopy in the frequency range 0.001 Hz-1 MHz at temperatures 10 <T < 300 K. From measurements of the quasistatic dielectric polarization in bias electric fields up to ~28 kV/cm it has been found that a ferroelectric state cannot be induced, in contrast to the case of typical relaxors. This suggests that--at least for the above field amplitudes--BZT50 effectively behaves as a dipolar glass, which can be characterized by a negative value of the static third order nonlinear permittivity. The relaxation spectrum has been analyzed by means of the frequency-temperature plot, which shows that the longest relaxation time obeys the Vogel-Fulcher relation ? = ?0 exp[E0/(T - T0)] with the freezing temperature of 48.1 K, whereas the corresponding value for the shortest relaxation time is ~0 K, implying an Arrhenius type behavior. By applying a standard expression for the static linear permittivity of dipolar glasses and/or relaxors the value of the Edwards-Anderson order parameter q(T ) has been evaluated. It is further shown that q(T ) can be described by the spherical random bond-random field model of relaxors.