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

In this article, hole-doped nonstoichiometric manganites La0.67Sr0.33-x square 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 R (3) over barc 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 square xMnO3 Showed that the samples exhibited a metallic-insulator phase transition for x < 0.25, and the effect of the magnetic field is to lower the resistivity and to shift T-MI 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.