Structural and magnetic properties of pure and Ca-doped LaCoO3 nanopowders obtained by a sol-gel route.
Pure and Ca-doped LaCoO3 nanopowders were prepared by a non-alkoxidic sol-gel route using cobalt(II) acetate, lanthanum(III) nitrate and calcium(II) acetate as oxide precursors. The structural evolution and magnetic properties of the samples were studied as a function of thermal treatments in air up to 1273 K. In particular, the microstructure and composition of the systems were analyzed by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), and X-ray Photoelectron Spectroscopy (XPS). Both pure and calcium-doped samples annealing at 973 K resulted in the formation of cubic LaCoO3 (average crystallite size <30 nm). This phase was fully retained in the calcium-doped materials even after annealing at higher temperatures, whereas a transition to the rhomboedral polymorph was detected in the pure samples at 1073 K. The magnetic behavior of the nanopowders was investigated as a function of temperature and applied field using both dynamic and static susceptibility measurements. Pure lanthanum cobaltite samples underwent a transition to an ordered state at 88 K, and their magnetic properties changed as a function of thermal treatments. As concerns calcium-doped samples, they ordered ferromagnetically at 171 and 185 K depending on the annealing temperature and displayed open hysteresis loops with coercive fields as large as 1.75 T at low temperatures.
Armelao
Lidia
L
ISTM-CNR and INSTM, Department of Chemistry, University of Padova, Italy.
Barreca
Davide
D
Bottaro
Gregorio
G
Maragno
Cinzia
C
Tondello
Eugenio
E
Caneschi
Andrea
A
Sangregorio
Claudio
C
Gialanella
Stefano
S
D002118:Calcium / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D003460:Crystallization / Q000379:methods*; D005782:Gels / Q000737:chemistry; D007811:Lanthanum / Q000737:chemistry*; D008280:Magnetics; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods; D010087:Oxides / Q000737:chemistry*; D010316:Particle Size; D044367:Phase Transition; D011208:Powders
D005782:Gels; D010087:Oxides; D011208:Powders; D003035:Cobalt; D007811:Lanthanum; D002118:Calcium; C060728:cobalt oxide