Co3O4 nanostructures: the effect of synthesis conditions on particles size, magnetism and transport properties

Pierre Ferdinand P. Poudeu

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ppoudeup@umich.edu

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Pranati Sahoo, Honore Djieutedjeu, and Pierre FP Poudeu (2013)

Journal of Materials Chemistry A, 1(47):15022-15030.

Surfactant-free Co3O4 nanostructures with various particle size ranges were synthesized via the solution combustion method using cobalt nitrate solution as a cobalt precursor and urea as a combustion fuel. Control over average particles size range was achieved by tuning the reaction ignition temperature between 300 degrees C and 800 degrees C. X-ray diffraction (XRD) and helium gas pycnometry indicated the formation of single phase Co3O4 nanoparticles with a spinel structure. Transmission electron microscopy (TEM) studies revealed an increase of the size range from 5-8 nm to 200-400 nm for Co3O4 nanoparticles synthesized at 300 degrees C and 800 degrees C, respectively. The corresponding decrease in the specific surface area from 39 m(2) g(-1) to similar to 2 m(2) g(-1) was confirmed by gas adsorption analysis using BET techniques. Magnetic susceptibility measurements revealed a dominant antiferromagnetic (AFM) ordering and the Neel temperature decreases with a decreasing average particle size range from 31 K (200-400 nm) to 25 K (5-18 nm). Interestingly, effective magnetic moments (ranging from 4.12 mu(B) to 6.16 mu(B)) substantially larger than the value of 3.9 mu(B) expected for Co2+ ions in the normal spinel structure of Co3O4 were extracted from the inverse susceptibility data. This finding was rationalized by taking into account the disordered distribution of Co2+ and Co3+ ions in the Co3O4 inverse spinel structures ([(Co2+)(1-x)(Co3+)(x)](tet)[(Co2+)(x)(Co3+)(2-x)]O-oct(4)) where the inversion degree (x) depends on the synthesis temperature. Transport measurements using hot pressed pellets of Co3O4 nanoparticles indicated p-type semiconducting behavior and drastic reductions in the thermal conductivity with decreasing average particle size.

Times Cited: 3

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