Structural, electrical, and magnetic properties of La0.7Ca0.3 − xNaxMnO3 ± γ solid solutions

La0.7Ca0.3 − xNaxMnO3 ± γ (LCNM) solid solutions with x = 0, 0.04, 0.06, 0.08, and 0.10 have been synthesized (rhombohedral structure, sp. gr. R\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \overline 3 $$\end{document}c). Sodium volatility during sintering is shown to lead to the formation of vacancies on the lanthanum and oxygen sites. Ca2+ → Na+ substitution does not increase the fraction of Mn4+ in LCNM, but the increase in the concentration of lanthanum vacancies with increasing sodium content leads to an increase in ferromagnetic ordering temperature TC and magnetoresistance, which depend, in addition, on heat-treatment conditions on account of the sodium volatility.