Nanoparticles: Synthesis, Characterization, and Dielectric Properties

M n 3 O 4 nanoparticles were prepared by a simple chemical route using cetyltetramethylammonium bromide (CTAB) as a template agent. M n 3 O 4 nanocrystals present an octahedral shape, and their crystallite size varies between 20 and 80？nm. They were characterized by XRD, SEM, DTA/TG, and IR spectroscopy. XRD studies confirm the presence of a highly crystalline M n 3 O 4 phase. The Rietveld refinement of the X-ray diffraction data confirms that M n 3 O 4 nanoparticles crystallize in the tetragonal system with space group I41/amd. DTA/TG and XRD measurements demonstrate the phase transition toward a spinel structure between 25 and 7 0 0 ° C . The electrical conductivity increases between 80 and 3 0 0 ° C , suggesting a semiconducting behaviour of M n 3 O 4 . Both dielectric dispersion (ε′) and dielectric loss (ε′′) were investigated from 80 and 3 0 0 ° C in the frequency range of 10？Hz–13？MHz. The dielectric properties showed typical dielectric dispersion based on the Maxwell-Wagner model. 1. Introduction Metal oxide nanocrystals are widely applied in catalysis, energy storage, magnetic data storage, sensors, and ferrofluids [1–4]. Tetramanganese oxides (Mn3O4) are particularly used as main sources of ferrite materials [5] and applied in numerous industrial fields such as magnetic [6], electrochemical [7], and catalysis [8, 9]. The particle size and morphology may be controlled by using various methods including solvothermal/hydrothermal [10, 11], vapor phase growth [12], vacuum calcining precursors [13], thermal decomposition [14], ultrasonic, gamma, and microwave irradiation [15–17], and chemical liquid homogeneous precipitation [18]. Therefore, Mn3O4 compounds show distinct shapes including nanoparticles [19], nanorods [20], nanowires [21], and tetragonal particles [22]. The electrical and magnetic properties of numerous nanomaterials are completely different from those of their bulk counterparts. Changes in dielectric properties were attributed to changes in particle size, shape, and boundaries [23, 24]. The modified dielectric properties were used as capacitors, electronic memories, and optical filters. Materials exhibiting a giant dielectric constant were already reported elsewhere [25–27]. The high dielectric permittivity and the low loss factors over a wide frequency range are always of a great interest [28]. In a previous work, we synthesized Mn3O4 nanomaterials with lozenge morphology under hydrothermal treatment [29]. The temperature dependence of the conductivity between 25 and 220°C obeys the Arrhenius law with activation energy of 0.48？eV.