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 similar 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 tau = tau(0) exp[E-0/(T - T-0)] with the freezing temperature of 48.1 K, whereas the corresponding value for the shortest relaxation time is similar to 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.