Structural, magnetic, and transport properties in the Pr -doped manganites La 0.9-x Pr x Te 0.1 MnO 3 ( 0⩽x⩽0.9 )

The effect of $\mathrm{Pr}$-doping on structural, magnetic and transport properties in electron-doped manganites ${\mathrm{La}}_{0.9\ensuremath{-}x}{\mathrm{Pr}}_{x}{\mathrm{Te}}_{0.1}{\mathrm{MnO}}_{3}\phantom{\rule{0.3em}{0ex}}(0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.9)$ with fixed carrier concentration is investigated. The room temperature structural transition from rhombohedral $(R\overline{3}C)$ to orthorhombic $(Pbnm)$ symmetry is found in the samples with $x\ensuremath{\geqslant}0.36$ 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 $x\ensuremath{\leqslant}0.36$, there exist insulator-metal $(\mathrm{I}\text{\ensuremath{-}}\mathrm{M})$ transition. And the low-temperature $\mathrm{I}\text{\ensuremath{-}}\mathrm{M}$ transition is observed at about $66\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for the sample with $x=0.36$, which may be related to the opening of a new percolation channel. For the samples with $x\ensuremath{\geqslant}0.54$, $\ensuremath{\rho}(T)$ curves display the semiconducting behavior $(d\ensuremath{\rho}∕dTl0)$ in both the high-temperature PM phase and low-temperature FM phase. The results are discussed in terms of the increased bending of the $\mathrm{Mn}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}\mathrm{Mn}$ 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.