La³⁺ ion doped Mg-Zn aluminates spinel nanoparticles: A gateway to high-frequency dielectric applications

In this paper, the sol-gel auto combustion, an environmentally friendly and economically cheap technique, was utilized for the synthesis of La³⁺ doped Mg-Zn aluminates with compositional formula of Zn_0.5Mg_0.5La_2-xAl_2-xO₄ and concentration from x = 0.00 to 0.10 with step size of 0.02. Synthesized samples were further annealed for 3 h at 800 °C. X-Ray diffractometry (XRD) was applied that confirmed the spinel structure of La³⁺ doped Mg-Zn Aluminate nanoparticles. XRD analysis shows that the crystal size was found from 6.35 nm to 7.54 nm with average of 6.95 nm. The increasing trend in lattice constant and crystalline size was observed by an increase in the doping concentrations of La³⁺. TEM was utilized to study morphology and confirm the structural parameters of the samples. EDX was used to confirm the present elements and their weights % in the sample. Furrier transformed infrared spectroscopy) FTIR) in the range of 400 to 1000 cm^-1 was used to study the absorption bands for octahedral sites and tetrahedral sites. Energy bands for both sites were observed to confirm the spinel structure. Using impedance analyzers at room temperature in the range of 1 MHz to 3 GHz was utilized to study impedance, dielectric constant, dielectric loss, electric modulus, tangent loss and AC conductivity of the samples. In the intermediate region of frequencies, the dielectric constant and loss ware found constant and stable. The variation in dielectric constant, dielectric loss, and impedance, due to change in doping concentration, polarization phenomena and conductivity mechanisms have been studied and discussed. AC conductivity with applied frequencies was also studied. A very low dielectric loss and a peak in dielectric constant was found at high frequencies in MHz range, it means that La³⁺ doped Mg-Zn aluminates nanoparticles can be used as dielectric materials in the high frequency energy devices.