Titanium effect on the structural, morphological and transport properties of La0.7Sr0.3Mn1-xTixO3 (x = 0.03, 0.06 and 0.12)

Abstract

A formidable amount of work has been devoted aiming towards the understanding of the structure and properties of colossal magnetoresistance (CMR) manganites. Mixed valent manganites with the general formula R1-xAxMnO3 (R = trivalent rare earth ion and A = divalent ion like Sr+2, Ba+2, Pb+2, Ca+2 etc.) are found to exhibit variety of phenomena such as charge, spin and orbit ordering, electronic, magnetic and structural transitions depending on the type and amount of doping (x). In this paper, doping dependent modifications in the microstructure polycrystalline La0.7Sr0.3Mn1-xTixO3 (LSMTO) (x = 0.03, 0.06 and 0.12) compounds synthesized by hybrid method (sol gel method + solid state reaction method) have been discussed in detail. In the present work, the powder X-ray diffraction patterns reveals that the samples are single phase in nature and the samples show a rhombohedral structure in hexagonal lattice with the space group R3-c. The Rietveld refinement was performed using FullProf software for the detailed structural investigation. In this context, the lattice parameters, unit cell volume and χ2 were obtained for LSMTO samples. On the substitution of Mn+4 by Ti+4, the structure does not undergo any phase transformation, but lattice parameters steadily increase as Ti+4 doping concentration increases. It can be related to the larger ionic radius of Ti+4 (rTi+4 = 0.605 Å) ion compared to that of Mn+4 (rMn+4 = 0.540 Å) ion. FT-IR spectra for LSMTO of different concentration show the four peaks around 400–500 cm−1 (Mn-O-Mn bending mode), 610–670 cm−1 (Mn-O stretching mode), 2330–2400 cm−1 (moisture contain) and 540 cm−1 (Ti-O stretching modes). Weight loss % versus temperature plot (TGA) for the x = 0.06 sample confirms that the precursor shows three step weight loss profiles and does not melt up to the temperature of 1050 °C. A quantitative analysis of the energy dispersive spectroscopy (EDS) data indicates that the observed concentration of elements is very close to the calculated values from its chemical formula. Typical SEM micrographs for all the three samples show that each sample possesses fine and clear grain boundaries (GBs). From the R-T measurements, an increase in resistivity and a decrease in metal to insulator transition temperature (TMI) were observed by increasing doping level of Ti for Mn. All the LSMTO samples show the resistivity suppression under applied magnetic field. The maximum MR % (89%) was observed for x = 0.12 at 5 T compare to other doped samples. This result suggests that the magnetoresistance behavior is improved by addition of Ti at Mn. These results prove that concentration Ti substitution at Mn site enhances the various properties of this manganite system.