Measurements of the low-frequency $(f⩽100\mathrm{kHz})$ permittivity $\left(\epsilon \right)$ and conductivity $\left(\sigma \right)$ at $T\lesssim 150\mathrm{K}$ are reported for ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x\mathrm{Mn}{\mathrm{O}}_3$ $(0⩽x⩽1)$ and ${\mathrm{Ca}}_{1-y}{\mathrm{Sr}}_y\mathrm{Mn}{\mathrm{O}}_3$ $(0⩽y⩽0.75)$ having antiferromagnetic, insulating ground states covering a broad range of Mn valencies from ${\mathrm{Mn}}^{3+}$ to ${\mathrm{Mn}}^{4+}$. Static dielectric constants are determined from the low-$T$ limiting behavior. With increasing $T$, relaxation peaks associated with charge-carrier hopping are observed in the real part of the permittivities and analyzed to determine dopant binding energies. The data are consistent with a simple model of hydrogenic impurity levels and imply effective masses $m^{*}∕m_e\sim 3$ for the ${\mathrm{Mn}}^{4+}$ compounds. Particularly interesting is a large dielectric constant $\left({\epsilon }_0\sim 100\right)$ associated with the $\mathrm{C}$-type antiferromagnetic state near the composition ${\mathrm{La}}_{0.2}{\mathrm{Ca}}_{0.8}\mathrm{Mn}{\mathrm{O}}_3$.

• Received 30 July 2004

DOI:https://doi.org/10.1103/PhysRevB.70.214433