Study on structural and transport properties of nonstoichiometric La0.67Sr0.33-x□xMnO3

Abstract

In this article，hole-doped nonstoichiometric manganites La0.67Sr0.33-x□xMnO3 (x=0，0.05，0.1，0.15，0.2，0.25，0.3，0.33) with A-site vacancy were synthesized using the solid-state reaction technique and the effect of A-site vacancy on structure and transport properties were studied. Results from Rietveld refinement of powder X-ray diffraction patterns showed that all samples were single phase with space group R3c and there were no structural phase transition for vacancy content x ranging from 0 to 0.33. The lattice parameters and volume of unit cell vary distinctly with x. These variations maybe result from the uncertain occupation ratio of vacancies at A-sites and Mn-sites. The bond angle of Mn—O—Mn decreases with increasing x，which indicates the presence of further distortion of MnO6 octahedron. Electrical measurements of La0.67Sr0.33-x□xMnO3 showed that the samples exhibited a metallic-insulator phase transition for xTMI towards higher temperature. In the range of 0.25≤x≤0.33，the samples exhibit insulating behavior without metallic-insulator transition，and also the effect of the magnetic field is to lower the resistivity.