Effects Of Doping Nd And Te On Structure And Magnetic Property Of The Two Phases Of Composition La 0.6Sr0.1MnO 3

Over the last ten years or more, many works have been devoted to understand the magnetic and transport properties of doped perovskite manganites R1-xMxMnO3 (R is a rare earth element and M a divalent alkaline-earth metal) for its potential applications. In these materials, the magneto-transport properties can be explained on the basis of the double exchange mechanism through electron hopping between manganese ions along Mn3+-O-Mn4+ bonds. In order to resolve some problems in the study of perovskite manganites A1-xMnO3, a physical model has been supposed by our group: in high temperature treatment process for samples, any ions should preferential occupy A site, because the distance ratio of AO and BO is 2 , namely, the space of the A site is bigger than that of the B site; the lack in A sites should be filled by B type ions; if vacancies exist in A1-xMnO3, those should be at the B sites not at the A sites; the vacancy content is related to the preparation conditions.Obviously, the manganite with normal composition La0.6Sr0.1MnO3 belongs to A1-xBO3 type perovskite materials, in which contains two phases with perovskite main phase and Mn3O4 second phase. In this paper, the effects of doping Nd and Te on structure and magnetic property of the two phases composition La0.6Sr0.1MnO3 have been studied. the relation between the average ion radius ?rA?, the doped ion radius and the content of Mn3O4 phase has been discussed, respectively.1. The powder samples with nominal composition La0.6-xNdxSr0.1MnO3 (x=0.0, 0.1, 0.2, 0.3 and 0.4) were prepared through the conventional solid-state reaction in air. X-ray diffraction (XRD) analysis of sample was carried out on a X'pert Pro X-ray diffractometer with Cu Kαradiation at room temperature. X-ray diffraction (XRD) spectra indicate that the materials possess two phases with the ABO3 perovskite being the dominant phase and Mn3O4 being the second phase. The content of Mn3O4 second phase decreases with the increase of Nd doped level x. The perovskite phase of the samples x=0.0 and 0.1 have the rhombohedral structure (space group R 3c , with Z=6), while the perovskite phase of the other samples (x≥0.2)possess the orthorhombic structure (space group Pbnm, with Z=4). The intensity of the highest peak of the perovskite phase and the Mn3O4 phase of the samples were performed using profile-fitted peak intensity, obtained by the X'Pert HighScore Plus software. It is found that the intensity ratios of the highest peak of the Mn3O4 phase to the perovskite phase in the samples decreases with increasing x. This interesting phenomenon was explained using the theories of crystallography and crystal defects: the ratio of Mn content to the sum of La3+ and Sr2+ ions is 1:0.7, furthermore, the effective ion radius of Mn2+ is smaller than that of La3+ or Sr2+ ion. as a result that a part of Mn2+ ions doped into A sites of the perovskite, and the others will be formed Mn3O4 second phase. the effective ion radius of Mn2+ is smaller than that of La3+ or Sr2+ ion. With the Nd ions substitute for La, the content of the Mn2+ ion at A sites of ABO3 perovskite phase, increases with the decrease of the the average ionic radius of the A site ?rA?, resulted from the effective ion radius of Nd3+ is smaller than that of La3+ or Sr2+ ion. Consequently,the content of Mn3O4 second phase will be decrease. Temperature dependencies of specific magnetization are detected in the field of 0.05T, all samples present a transition from the ferromagnetic to paramagnetic behaviour as the temperature increases. This transition zone moves toward the low temperatures with increasing x. Curie temperature decreases with decreasing the Mn-O-Mn bond angleΘ.2. Powder samples with nominal composition La0.6Sr0.1TexMnO3(x=0.00, 0.05, 0.10, 0.15, 0.20) were prepared using the sol-gel method with thermal treatment up to 1473 K. It is found that almost all of the Te and a few of the Mn ions were lost in the heat treatment process prepared the samples.The X-Ray diffraction spectrum showed that there are a perovskite phase, a Mn3O4 phase and a third phase(contain Te element) in the samples with x≥0.05, calcined at 1073 and 1273K. However, there are only two phases in the samples sintered at 1473K: the perovskite phase and the Mn3O4 phase. The diffraction peak intensities have been obtained by peak profile fitting using the X'Pert HighScore Plus software. The intensity ratios of the highest peak of the third phase (I3) and the Mn3O4 phase (IM) to the perovskite phase (IP) in the samples calcined at 1073, 1273 and 1473K have been calculated. The value of IM/IP remains approximately constant. In comparison, the value of I3/IP increases rapidly with increasing x in the two series of samples after calcination at 1073 and 1273K. However, after calcination at 1473 K, the value of I3/IP falls to zero, while the value of IM/IP still remained approximately constant. The Te content for the sample La0.6Sr0.1Te0.2MnO3was detected using X-ray energydispersive spectroscopy (EDS). Te element could be found in the EDS patterns of the samples calcined at 1273. However, sintered at 1473K, the spectrum intensity of the Te tends to zero. In addition, the EDS results show that the content ratio of Mn to La for the sample calcined at 1473K is smaller than that for the sample calcined at 1273K. A quantum-mechanical potential barrier model have been applied to estimate the number ratio of Te3+ cations in La0.6Sr0.1TexMnO3 compound, the calculated value of Te3+ content is less 1% in every sample. The XRD diffraction data were fitted using the Rietveld powder diffraction profile fitting technique. The final fitting parameters, goodness of fit indicator s, profile factor Rp and weighted profile factor Rwp are satisfactory. The lattice parameters a, c, cell volume V, Mn–O bond length, d, and Mn–O–Mn bond angle,Θ, have not changed in any significant way. Alike, the difference between the Curie temperatures is very small. The experimental results for the XRD, EDS, TGA and magnetic measurements, plus phase analysis and Rietveld fitting of the X-ray diffraction data for the samples, showed that almost all of the Te and a few of the Mn ions were lost in the sintering process at 1473 K.