In this work, the syntheses and characterization of oxygen deficient perovskite cobalt oxides prepared under ambient pressure conditions with different “x” in the Co(Sr1-xYx)O3–δ;0.05 ≤ x ≤ 0.4 series are report...In this work, the syntheses and characterization of oxygen deficient perovskite cobalt oxides prepared under ambient pressure conditions with different “x” in the Co(Sr1-xYx)O3–δ;0.05 ≤ x ≤ 0.4 series are reported. The system studied in the present investigation undergoes structural phase transition at room temperature from cubic to tetragonal symmetry. The samples with x ≥ 0.2 show a tetragonal structure with I4/mmm space group, while the samples with 0.05 ≤ x ≤ 0.15 reveal cubic with pm3m group symmetry. Quite similar to Ho-substituted system [J. Appl. Phys. 103, 07B903 (2008)], the present Y-doped magnetization data clearly show the appearance of an enhanced ferromagnetic component at ~350 K for 0.15 ≤ x ≤ 0.225. Unlike the Ho-substituted system, the present narrow compositions behave as hard ferromagnet with quite high coercive field, Hc = 11.02, 12.25 and 14.0 kOe for x = 0.15, 0.2 and 0.225 compositions, respectively at T = 10 K. All the compositions show a semiconducting-like behaviour and some interesting features of temperature dependence of magnetoresistance (MR) are observed. The Co(Sr1-xYx)O3–δ samples seemly to obey variable range hopping conduction model showing a linear ln ρ versus T–1/4 dependence at the temperature range 80 K ≤ T ≤ 300 K.展开更多
A series of Ni modified hexaaluminates LaNi y Al 12- y O 19- δ ( y =0 3, 0 6, 0 9, 1 0) were prepared by decomposition of nitrates and calcination at high temperature. The crystalline structure and catalytic properti...A series of Ni modified hexaaluminates LaNi y Al 12- y O 19- δ ( y =0 3, 0 6, 0 9, 1 0) were prepared by decomposition of nitrates and calcination at high temperature. The crystalline structure and catalytic properties for CO 2 reforming of methane to synthesis gas were investigated by using XRD, XPS, TPR and TGA techniques. The results showed that a pure hexaaluminate LaNi y Al 12- y O 19- δ phase is formed only when y value is in 0< y ≤1. The reduced hexaaluminates LaNi y Al 12- y O 19- δ exhibit significant catalytic activity and stability for the reaction of CO 2 reforming of methane to synthesis gas at 780 ℃, and no deactivation resulting from carbon deposition is found. In the meantime, the catalytic activity is obviously affected by the modifier Ni in the hexaaluminate lattices. Under the same reaction conditions, the conversion of CH 4 and CO 2 increase with increase in the amount ( y value) of the modifier Ni.展开更多
文摘In this work, the syntheses and characterization of oxygen deficient perovskite cobalt oxides prepared under ambient pressure conditions with different “x” in the Co(Sr1-xYx)O3–δ;0.05 ≤ x ≤ 0.4 series are reported. The system studied in the present investigation undergoes structural phase transition at room temperature from cubic to tetragonal symmetry. The samples with x ≥ 0.2 show a tetragonal structure with I4/mmm space group, while the samples with 0.05 ≤ x ≤ 0.15 reveal cubic with pm3m group symmetry. Quite similar to Ho-substituted system [J. Appl. Phys. 103, 07B903 (2008)], the present Y-doped magnetization data clearly show the appearance of an enhanced ferromagnetic component at ~350 K for 0.15 ≤ x ≤ 0.225. Unlike the Ho-substituted system, the present narrow compositions behave as hard ferromagnet with quite high coercive field, Hc = 11.02, 12.25 and 14.0 kOe for x = 0.15, 0.2 and 0.225 compositions, respectively at T = 10 K. All the compositions show a semiconducting-like behaviour and some interesting features of temperature dependence of magnetoresistance (MR) are observed. The Co(Sr1-xYx)O3–δ samples seemly to obey variable range hopping conduction model showing a linear ln ρ versus T–1/4 dependence at the temperature range 80 K ≤ T ≤ 300 K.
文摘A series of Ni modified hexaaluminates LaNi y Al 12- y O 19- δ ( y =0 3, 0 6, 0 9, 1 0) were prepared by decomposition of nitrates and calcination at high temperature. The crystalline structure and catalytic properties for CO 2 reforming of methane to synthesis gas were investigated by using XRD, XPS, TPR and TGA techniques. The results showed that a pure hexaaluminate LaNi y Al 12- y O 19- δ phase is formed only when y value is in 0< y ≤1. The reduced hexaaluminates LaNi y Al 12- y O 19- δ exhibit significant catalytic activity and stability for the reaction of CO 2 reforming of methane to synthesis gas at 780 ℃, and no deactivation resulting from carbon deposition is found. In the meantime, the catalytic activity is obviously affected by the modifier Ni in the hexaaluminate lattices. Under the same reaction conditions, the conversion of CH 4 and CO 2 increase with increase in the amount ( y value) of the modifier Ni.
