Crystal Structures And Properties Of Double Perovskites Sr-Ba-Fe-Mo-O-S System

In this paper, double perovskite Sr₂FeMoO_6-xS_x (x=0.3, 0.4, 0.5, 0.8, 1) series samples had been successfully synthesized by solid-state reaction processing. The crystal structures, magnetic and electric properties of these samples were researched by using x-ray powder diffraction (XRD), vibrating sample magnetometer and four-point probe method. The main results of this dissertation as follows:1) The crystal structures of double perovskite Sr₂FeMoO_6-xS_x (x=0.3, 0.4, 0.5, 0.8, 1) series samples all belong to tetragonal system. The space groups of these samples are all I4/mmm. The lattice volumes increase with the increasing content of S.2) The magnetic moment of double perovskite Sr₂FeMoO_6-xS_x (x=0.3, 0.4, 0.5, 0.8, 1) series samples increases gradually with the increase of magnetic field. To the same magnetic field, The magnetic moment increase at first and then decrease with the increasing content of S, which is the largest when x=0.8. It doesn't appear phase transition temperature between 80 K to 300 K, so we can infer the Curie temperatures of the series of samples are higher then 300 K.3) The electrical transmission properties of double perovskite Sr₂FeMoO_6-xS_x (x=0.3, 0.4, 0.5, 0.8, 1) series samples show the property from semiconductor to conductor. The transition is that when x=0.5. All the samples show the negative magnetoresistance effect obviously.Double perovskite Sr_2-yBa_yFeMoO_6-xS_x (x=0.3, 0.4, 0.5, 0.8, 1; y=y₃, y=y₄, y=y₅, y=y₈, y=y₁₀) (the value of y see table 4-1) series samples had been successfully synthesized by solid-state reaction processing. The crystal structures, magnetic and electric properties of these samples were researched by using x-ray powder diffraction (XRD), vibrating sample magnetometer and four-point probe method. The main results of this dissertation as follows:1) When x=1, y=y₁, double perovskite Sr_2-yBa_yFeMoO_6-xS_x sample show the different diffraction pattern with others. From the position and intensity of the peak, we can infer the sample contains much more molybdate. 2) The magnetic moment of double perovskite Sr_2-yBa_yFeMoO_6-xS_x series samples increases gradually with the increase of magnetic field until steady. To the same magnetic field, The magnetic moment increase at first and then decrease with the increase content of S, which is the largest when x=0.8. The magnetic moment of these samples decrease with the temperature which decrease by zero magnetic field. And it doesn't appear phase transition temperature between 80 K to 300 K, so we can infer the Curie temperatures of the series of samples are higher then 300 K.3) When x=0.3, y=y₃, the sample of Sr_2-yBa_yFeMoO_6-xS_x shows the property of semiconductor absolutely. When x=0.8, y=y₈, the sample of Sr_2-yBa_yFeMoO_6-xS_x shows the property of conductor absolutely. When x=1, y=y₁₀, the sample of Sr_2-yBa_yFeMoO_6-xS_x shows the property of semiconductor.