Synthesis, structural and transport properties of nanocrystalline $La_{1-x}Ba_{x}MnO_{3}$ (0.0leq x leq0.3) powders

摘要

Nanocrystalline $La_{1-x}Ba_{x}MnO_{3}$ (0.0leq x leq0.3) manganites have been prepared by a simple and instantaneous solution combustion method, which is a low temperature initiated synthetic route to obtain fine-grained powders with relatively high surface area. The phase purity and crystal structure of the combustion products are carried out by powder X-ray diffraction. The as-made nanopowders are in cubic phase. On calcination to 900 C, barium doped manganites retain cubic phase, whereas barium free manganite transformed to rhombohedral phase. The scanning electron microscope (SEM) results revealed that the combustion-derived compounds are agglomerated with fine primary particles. The doped manganites have surface area in the range 24-44 $m^{2}/g$. The surface area of the manganites increases with barium content, whereas it decreases on calcination. Both undoped and doped lanthanum manganites show two active IR vibrational modes at 400 and 600 cmK1. The low temperature resistivity measurements have been carried out by four-probe method down to 77 K. All the samples exhibit metal-insulator behaviour and metal-insulator transition temperature $(T_{M-I})$ in the range 184-228 K and it is interesting to note that, as the bariumcontent increases the $T_{M-I}$ shifts to lower temperature side. The maximum $T_{M-I}$ of 228 K is observed for $La_{0.9}Ba_{0.1}MnO_{3}$ sample.