Influence of particle sizes on the electronic behavior of ZnxCo1−xFe2O4 spinels (x=0.2,0.3)

• Published in: Journal of alloys and compounds 2014-07, Vol.601, p.130-139
• Main Authors: Viñas, R., Álvarez-Serrano, I., López, M.L., Pico, C., Veiga, M.L., Mompeán, F., García-Hernández, M.
• Format: Article
• Language: English
• Subjects: Chemical synthesis; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Diamagnetism, paramagnetism and superparamagnetism; Dielectric properties of solids and liquids; Dielectric response; Dielectrics, piezoelectrics, and ferroelectrics and their properties; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport in multilayers, nanoscale materials and structures; Exact sciences and technology; Magnetic measurements; Magnetic properties and materials; Magnetic properties of nanostructures; Nanocrystalline materials; Permittivity (dielectric function); Physics; X-ray diffraction
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2014.02.016

Relaxor ferroelectric behavior and superparamagnetism in nanoparticles of ZnxCo1−xFe2O4 obtained in supercritical water. [Display omitted] •Title ferrites were prepared by hydrothermal techniques (sub and supercritical).•In supercritical (SCW) conditions highly monodispersive samples were obtained.•All samples are semiconductors; n-type or p-type response depends on the composition.•Superparamagnetic and relaxor ferroelectric response coexist in SCW samples. The effect of composition and particle size on the electrical and magnetic behavior of ZnxCo1−xFe2O4 spinels (x=0.2 and 0.3) has been studied. Powdered samples of these ferrites have been synthetized by the liquid mix technique and hydrothermal method (in sub and supercritical conditions), leading to average particle sizes of ca. 50 and 10nm, respectively. They have been characterized by means of X-ray diffraction, Thermogravimetric analysis, Energy-Dispersive X-ray Spectroscopy and impedance and magnetic measurements. Permittivity values up to ca. 500 were registered at 375K, which remained almost constant at moderate frequencies, between 103 and 106Hz. Stabilization of polarization phenomena is very sensitive to grain size and composition. Dielectric behavior evolves to a relaxor ferroelectric response when grain size becomes nanometric and, particularly, when the sample shows high monodispersion. The conduction mechanism and type of majority charge carriers have been established from Seebeck measurements. The x=0.3 sample, prepared in supercritical water for the first time, exhibits homogeneous particle size distribution, superparamagnetic behavior and Curie temperature lower than those corresponding to similar microsized samples. The electronic response of the ferrites obtained in supercritical conditions is interpreted considering the possible short scale polarization of nanodomains.