Structure, Morphology, and Resistance Properties of Non-Stoichiometric Sodium Manganite Nanoparticles with Superstoichiometric Manganese

Structure, morphology, chemical and phase composition, as well as transport of the manganite
$\text{La}_{0.8-x}\text{Na}_{0.2}\text{Mn}_{1+x}\mathrm{O}_{3}$
nanoparticles have been studied by means of X-ray diffraction, high-resolution transmission electron microscopy, transmission electron microscopy, and resistance methods. The samples have been synthesized using a sol-gel method at
$850\ ^{0}\mathrm{C}$
(20 h) in an air atmosphere. According to the X-ray diffraction and transmission electron microscopy data, the average size of spherical-like nanoparticles is in the range of 48–73 nm. Rietveld refinement of X-ray data indicates a slight decrease in the volume of a rhombohedral
$R$
-3
$c$
perovskite structure for all compositions with an increase in the
$x$
. Based on the analysis of resistance data, the metal-semiconductor phase transition has been detected at a temperature of
$T_{\text{ms}}$
, which reduces with increasing the
$x$
. The temperature dependence of resistivity has been fitted successfully by the different models within a large temperature region from 2K to 360K. The transport parameters have been obtained.