Síntesis y propiedades ópticas y magnéticas del ycro3 preparado por los métodos precursor polimérico modificado y reacción de combustión
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2014-04-23
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Universidade Federal de Goiás
Resumo
This work describes the synthesis of yttrium orthochromite polycrystalline YCrO3
by two different methods: modified polymeric precursor (MPP) and solution
combustion (SC) and with additional heat treatment at 1300 °C. Were analyzed the
effect of these two methods as well as the effect of additional thermal treatment of the
samples prepared by the combustion method, on the physical properties of YCrO3 by
several spectroscopic and structural techniques: X-ray diffraction (XRD), scanning
electron microscopy and transmission (SEM and TEM), Fourier transform spectroscopy
and infrared, diffuse reflectance, susceptibility and electron paramagnetic resonance
(EPR). Images (SEM) show that the powders YCrO3 synthesized by the two methods of
synthesis have similar morphologies, with average grain size of approximately 160 nm.
Through the images was found that applying heat treatment to the sample obtained by
combustion synthesis at the same temperature as the precursor obtained by the
polymeric precursor method, the structural characteristics of the material are similar.
The spectra diffuse reflectance of the different samples exhibit two intense
bands, which correspond to electronic transitions of ion Cr3+ from the ground state 4A2g
to the excited states, 4A2g → 4T2g and 4A2g → 4T1g two minor bands corresponding to the
transitions 4A2g → 2Eg and 4A2g → 2T1g were observed in the spectra. Were calculated
from the spectra the crystal field parameters Dq and Racah, B and C for all samples,
with average values of 3.03 for Dq, 542 cm-1 and 3,144 cm-1 for B and C respectively.
Even with these spectra and the theory of Kubelka-Munk was calculate the optical gap
Eg, with a mean value of 3.7 eV, coinciding with those reported in the literature for
YCrO3 prepared by other methods.
The dependence of the spectrum parameters (EPR), factor g, intensity, and line
width as a function of temperature was also studied from 100 K to 300 K. The results
show that, near 140 K, the Néel temperature for the material, a magnetic phase
transition occurs from the antiferromagnetic phase to the paramagnetic phase, in full
agreement with the results obtained from measurements of susceptibility.
Our results are discussed and compared with other reported in the literature.
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Citação
JARA, A. N. L. Síntesis y propiedades ópticas y magnéticas del ycro3 preparado por los métodos precursor polimérico modificado y reacción de combustión. 2014. 67 f. Tese (Doutorado em Fisica) - Universidade Federal de Goiás, Goiânia, 2014.