The effect of $\mathrm{Pr}$-doping on structural, magnetic and transport properties in electron-doped manganites ${\mathrm{La}}_{0.9-x}{\mathrm{Pr}}_x{\mathrm{Te}}_{0.1}{\mathrm{MnO}}_3\left(0⩽x⩽0.9\right)$ with fixed carrier concentration is investigated. The room temperature structural transition from rhombohedral $\left(R\overline{3}C\right)$ to orthorhombic $\left(Pbnm\right)$ symmetry is found in the samples with $x⩾0.36$ by the Rietveld refinement of x-ray powder diffraction patterns. The Curie temperature $T_C$ of samples decreases and the transition becomes broader with an increasing $\mathrm{Pr}$-doping level. For the samples with $x⩽0.36$, there exist insulator-metal $\left(\mathrm{I}\text{−}\mathrm{M}\right)$ transition. And the low-temperature $\mathrm{I}\text{−}\mathrm{M}$ transition is observed at about $66\mathrm{K}$ for the sample with $x=0.36$, which may be related to the opening of a new percolation channel. For the samples with $x⩾0.54$, $\rho \left(T\right)$ curves display the semiconducting behavior $\left(d\rho ∕dT<0\right)$ in both the high-temperature PM phase and low-temperature FM phase. The results are discussed in terms of the increased bending of the $\mathrm{Mn}\text{−}\mathrm{O}\text{−}\mathrm{Mn}$ bond with decreasing the average ionic radius of the A-site element $⟨r_A⟩$ and the tolerance factor $t$, resulting in the narrowing of the bandwidth, the decrease of the mobility of $e_g$ electrons and the weakening of DE interaction caused by the substitution of smaller ${\mathrm{Pr}}^{3+}$ ions for a larger ${\mathrm{La}}^{3+}$ ion.

• Received 8 March 2004

DOI:https://doi.org/10.1103/PhysRevB.70.144421