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

Glassy freezing dynamics was investigated in ${\mathrm{BaZr}}_{0.5}{\mathrm{Ti}}_{0.5}{\mathrm{O}}_{3}$ (BZT50) ceramic samples by means of dielectric spectroscopy in the frequency range 0.001 Hz--1 MHz at temperatures $10lTl300$ K. From measurements of the quasistatic dielectric polarization in bias electric fields up to $\ensuremath{\sim}28$ 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 $\ensuremath{\tau}={\ensuremath{\tau}}_{0}\phantom{\rule{0.16em}{0ex}}\mathrm{exp}[{E}_{0}/(T\ensuremath{-}{T}_{0})]$ with the freezing temperature of 48.1 K, whereas the corresponding value for the shortest relaxation time is $\ensuremath{\sim}0$ 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.