La 0.7 Sr 0.3 Fe x Mn 1- x O 3 compounds (0 05≤ x ≤0 18) were prepared by the sol gel technique. The effects of Fe doping on the magnetic properties, conductivity and magnetoresistance for L...La 0.7 Sr 0.3 Fe x Mn 1- x O 3 compounds (0 05≤ x ≤0 18) were prepared by the sol gel technique. The effects of Fe doping on the magnetic properties, conductivity and magnetoresistance for La 0.7 Sr 0.3 MnO 3 was investigated. Experimental results indicate that the Fe doping leads to a decrease in the ferromagnetic ordering temperature, an increase in the resistance and magnetoresistance effect. For samples of x =0 05 and x =0 08 two peaks are observed in their ρ T curve. Magnetic resistivity ( MR ) of La 0.7 Sr 0.3 Fe 0.08 Mn 0.92 O 3 sample is capable of reaching 18%(8×10 5A·m -1 , 293 K). At x ≥0 1, metal insulator (M I) transition temperature ( T p) is lower than ferromagnetic Curie temperature ( T C) by about 50～80 K.展开更多
Colloidal silica sol is formed by a novel hydrolyzing procedure of tetraethyl orthosilicate(TEOS) catalyzing with NH 3 ·H 2 O in aqueous mediums. Glycerol, combining with the hydrolyzed intermediates of ...Colloidal silica sol is formed by a novel hydrolyzing procedure of tetraethyl orthosilicate(TEOS) catalyzing with NH 3 ·H 2 O in aqueous mediums. Glycerol, combining with the hydrolyzed intermediates of TEOS, controls growing of the silica particles; poly(vinyl vinyl alcohol makes the colloidal silica sol with polymeric structure and spinning, thermal strain makes the gel silica film changed into a nanoporous structure with diameter ranging 50-150 nm. Morphologies of the nanoporous silica film have been characterized; the porosities (%) is 32-64; the average dielectric constant at 1MHz region is 2.0 and 2.1; the thermal conductivity is less than 0.8. Chemical mechanism of the sol gel process is discussed.展开更多
文摘La 0.7 Sr 0.3 Fe x Mn 1- x O 3 compounds (0 05≤ x ≤0 18) were prepared by the sol gel technique. The effects of Fe doping on the magnetic properties, conductivity and magnetoresistance for La 0.7 Sr 0.3 MnO 3 was investigated. Experimental results indicate that the Fe doping leads to a decrease in the ferromagnetic ordering temperature, an increase in the resistance and magnetoresistance effect. For samples of x =0 05 and x =0 08 two peaks are observed in their ρ T curve. Magnetic resistivity ( MR ) of La 0.7 Sr 0.3 Fe 0.08 Mn 0.92 O 3 sample is capable of reaching 18%(8×10 5A·m -1 , 293 K). At x ≥0 1, metal insulator (M I) transition temperature ( T p) is lower than ferromagnetic Curie temperature ( T C) by about 50～80 K.
文摘Colloidal silica sol is formed by a novel hydrolyzing procedure of tetraethyl orthosilicate(TEOS) catalyzing with NH 3 ·H 2 O in aqueous mediums. Glycerol, combining with the hydrolyzed intermediates of TEOS, controls growing of the silica particles; poly(vinyl vinyl alcohol makes the colloidal silica sol with polymeric structure and spinning, thermal strain makes the gel silica film changed into a nanoporous structure with diameter ranging 50-150 nm. Morphologies of the nanoporous silica film have been characterized; the porosities (%) is 32-64; the average dielectric constant at 1MHz region is 2.0 and 2.1; the thermal conductivity is less than 0.8. Chemical mechanism of the sol gel process is discussed.
