Papers by Keyword: Double Perovskite

Abstract: The magnetic properties of Ba₂FeMoO₆ (BFMO) double perovskite are investigated. BFMO samples were prepared by solid state reaction method through compression. Magnetic properties are influenced by electron environments of the Fe³⁺ and Mo⁵⁺ ions within the perovskite structure. BFMO sintered at 800 oC exhibited the largest hysteresis loop at 50 K. In addition, the values of Ms and Mr indicate ferromagnetic behaviour in BFMO ceramics sintered at 800 oC for different times up to 10 hours. Using the Curie-Weiss law fitting to investigate μeff~30μ_B high spin of Fe and Mo, and negative θ present the antiferromagnetic characteristics of the BFMO sample.

Abstract: In this work were synthesized new catalysts of stoichiometries Sr_0.8K_0.2TiCu_0.10O₃, Sr_0.7K_0.3TiCu_0.15O₃ and Sr_0.5K_0.5TiCu_0.25O₃ by spray pyrolysis method. The synthesis conditions were optimized to obtain single phase powder of titanates of double perovskite structure, with an ultrasound vibration frequency of 1.3 MHz at 700 °C under air flow. The average crystallite size of the powders, determined by the Scherrer equation and using the Jade Plus 8 software, was at around 9 nm. The powder morphology was analyzed by scanning electron microscopy (SEM). The Sr_0.5K_0.5TiCu_0.25O₃ system showed particles with smooth surfaces, spherical and with smaller agglomerates than Sr_0.8K_0.2TiCu_0.10O₃, Sr_0.7K_0.3TiCu_0.15O₃ systems. This phenomenon suggests that the stoichiometry changes the aspect of the particle surface, which may influence in the catalytic activity. Thus, particles without roughening and smaller size can act as promising catalysts.

Abstract: In this work was investigated the catalytic potential of a new heterogeneous catalyst of stoichiometry Ca_0.5K_0.5TiCu_0.25O₃ , with double perovskite structure, in the preparation of biodiesel via ethylic route. The catalyst was synthesized by the Polyol Modified method and characterized by X-ray diffraction, scanning electron microscopy, infrared spectroscopy and gas chromatography coupled to mass spectrometry. The investigation of the catalytic activity was carried out from transesterification reaction of commercial soybean oil with ethyl alcohol. Single-phase and crystalline powders related to the CaTiO₃ phase were obtained with an average crystallite size at around 17.25 nm. The new catalyst showed high efficiency for the production of biodiesel via heterogeneous catalysis with a yield at around 97%, with reaction time of 8 hours at 78°C and 15% of catalyst mass in relation to the soybean oil mass.

Abstract: We report on the magnetoelectric properties of Er₂CoMnO₆. This compound adopts the structure of a double perovskite with a strong monoclinic distortion. Our specimen exhibits a nearly perfect Co-Mn order. It undergoes a ferromagnetic transition at T_C~70 K due to the Co²⁺-O-Mn⁴⁺ ferromagnetic superexchange interaction. Below 30 K, the Er³⁺ moments start to order antiferromagnetically to the Co/Mn sublattice. Pyroelectric measurements reveal electrical polarization at low temperature but its strong dependence on the heating rate indicates the lack of a spontaneous ferroelectricity. Instead, electric polarization is derived from thermally stimulated depolarization currents.

Abstract: In this work we demonstrate that La₂NiMnO₆ exhibits a colossal magneto-dielectric (MD) effect (5%-55%) over a broad range of temperatures (100–270 K), when compared to other Rare Earth (RE = Pr, Sm, and Tb) containing Ni-Mn double perovskites. The noticeable magneto-dielectric effect in RE₂NiMnO₆ signals the influence of spin orientations in the two magnetic sublattices on the spin-lattice coupling. Finally with the help of Raman spectroscopy we clarify that the presence of spin-phonon coupling alone is not the cause for the observed colossal MD effect in RE₂NiMnO₆.

Abstract: We have investigated temperature-dependent magnetic hysteresis loop behavior of Ba_2-xLa_xFeMoO₆ with double perovskite structure by means of a vibrating sample magnetometer (VSM). As partial substitution of Ba²⁺ by La³⁺ is varied from x = 0.1 to 0.3, T_C is found to increase from 324 to 345 K. Interestingly, however, hysteresis loop area, remanent magnetization, and coercivity are found to follow a universal behavior with respect to a temperature variation regardless of the Ba²⁺ substitution.

Abstract: The powder of (La_0.8Sr_0.2)₂FeNiO_6-δ (LSFN) oxide with double-perovskite structure was synthesized by polymeric precursor method. Then the YSZ-based NO sensors with LSFN sintered at different temperatures (1000, 1100, 1200 and 1300 °C) as sensitive electrode (SE) were fabricated. All samples were characterized by XRD. The morphologies of the LSFN-SEs were observed with ESEM. The NO sensing properties of the sensors were investigated in the operating temperature range of 350-650 °C in 10 vol. % O₂. Results demonstrated that the sensor with LSFN-SE sintered at 1300 °C exhibited highest response to 500 ppm NO at 400 °C, which was about 85 mV. A linear relationship was obtained between the emf and the logarithm of NO concentration from 500 to 800 ppm at 400 and 500 °C. Moreover, both magnitude and slope to NO response decreased as operating temperature increased. And both the response time and recovery time shortened as temperature increased. But the recovery rate was slower than the response rate, especially at and below 450 °C. The optimal sensor response was obtained at 500-550 °C.

Abstract: Hole doped compounds (Sr, Na)₂FeMoO₆ with the Na content of x = 0, 0.02, 0.03, 0.07 and 0.17 have been synthesized by sol-gel method. Effects of hole doping on the crystal structure and magnetic properties of Sr₂FeMoO₆ have been investigated. XRD pattern indicates that all the samples are of single phase and belong to the space group I4/m. The degree of cation ordering in the Na-doped Sr₂FeMoO₆ compounds shows a non-monotonic variation with the doping level. The saturation magnetization of the compound increases with x for x<0.17. Provided that the doped hole enters selectively the spin-down band, the variation of the saturation magnetization can be explained in light of the ferrimagnetic model (FIM), which is Similar to the electron doped Sr₂FeMoO₆.

Abstract: The compounds of Fe substitution of Al in nanotructured Sr₂Fe_1-x Al _xMoO₆ (0≤x≤0.2) double perovskite have been prepared by sol-gel method. The x-ray diffraction patterns of the samples show that the samples are in nanometer range. The Curie temperature and thesaturation magnetization of the samples decrease with the increasing of Al substitution. And the magnetoresistance of the samples increase with the increasing of x.

Abstract: The compounds of Fe substitution of Cr in nanotructured Sr2Fe1-xCrxMoO6 (0≤x≤0.2) double perovskite have been prepared by sol-gel method. And the x-ray diffraction patterns of the samples show that the samples are in nanometer range. All the samples show a paramagnetic to ferromagnetic transition with temperature, and the Curie temprature increase with the increasing of x. The resistivity of the samples decrease with the increasing of temprature, and increase with the increasing of x.