Spectroscopic, elastic and dielectric properties of Ho3+ substituted Co-Zn ferrites synthesized by sol-gel method

Ho3+ substituted cobalt-zinc ferrite with a chemical formula Co0.7Zn0.3HoxFe2-xO4 (0 <= x <= 0.1) were synthesized by sol-gel method. Synthesized samples were characterized by using X-ray diffraction, field emission scanning electron microscopy, Raman, Infrared and UV-visible spectroscopy. X-ray diffraction patterns show the formation of cubic spinel structure of all the synthesized samples. The gradual changes in the Raman spectra of Co-Zn ferrite were observed at higher level of Ho3+ substitution. The Raman band shows that there is a strong electron-phonon coupling in the investigated ferrite system and is the highest for the T-2g(3) mode as compared to A(1g) and T-2g(2) modes. Fourier transform infrared spectroscopy shows that the vibration bands corresponding to Fe-O is slightly varied with the substitution of Ho3+ substitution. UV-visible spectra was studied by using the optical absorbance measurements in the wavelength ranges from 500 to 800 nm. The estimated energy band gap is found to increase from 1.72 to 1.84 eV with the increase in Ho3+ substitution. The elastic properties such as longitudinal velocity, shearing velocity, elastic constant, Poisson's ratio and Debye temperature were measured at room temperature by using the ultrasonic pulse transmission method. It is found that the elastic constant and Debye temperature decreased with the increase in Ho3+ substitution. A linear relationship between Debye temperature, elastic constant and average sound velocity with the Ho3+ substitution is observed and discussed in this manuscript. Dielectric properties have been investigated as function of frequency. The dispersion of the dielectric properties was discussed in the light of Koop's theory in accordance with the Maxwell-Wagner polarization. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.