Anomaly in the dielectric response at the charge-orbital-ordering transition ofPr0.67Ca0.33MnO3

Abstract

The complex impedance of a ${\mathrm{Pr}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3$ crystal has been measured. The frequency dependence is studied for a wide range of temperatures (50–403 K) and is found to be characteristic of relaxation process with a single Debye time relaxation constant, which is interpreted as a dielectric constant of the material. A strong peak is observed in this dielectric constant (up to ${10}^6)$ at the charge ordering transition suggesting an interpretation in terms of ordering electric dipoles at $T_{\mathrm{CO}}$ or in term of phase separation. Comparison with ${\mathrm{Pr}}_{0.63}{\mathrm{Ca}}_{0.37}{\mathrm{MnO}}_3$—in which the phase separation is much smaller and the peak in the dielectric constant is absent—suggests an interpretation in term of phase separation between insulating and metallic states.