Impact of aluminum substitution on lithium oxide (Li₂Ni₆Al_xCo_2-xO₁₀) nanomaterials synthesized via sol-gel auto-combustion route

The lithium transition metal oxide materials have got attention due to attractive physical and chemical properties applicable for energy storage devices such as batteries and supercapacitor. In this paper, five samples of Li₂Ni₆Al_xCo_2-xO₁₀ with different Al³⁺ concentrations (x = 0.0, 0.5, 1.0,1.5 and 2.0) were successfully synthesized via sol-gel auto-combustion method. Structural properties were studied using X-ray diffraction analysis confirmed that the prepared nanomaterials are hexagonal in structure. Scherrer's formula was used for the determination of crystallite size found in the range from 18 to 25 nm. Electrical properties including real part of relative permittivity, tangent loss, real and imaginary part of impedance, electric modulus and AC conductivity were studied in the applied frequency ranging from 1 MHz to 3 GHz as well as effect of Al³⁺ concentrations at room temperature. The significant change in relative permittivity was examined with increasing frequency as well as aluminum concentration. The maximum value of relative permittivity was found 66.37 at frequency of 1 MHz and aluminum concentrations of x = 0.05. Furthermore, the polarization mechanisms were also discussed with applied frequency to study the relaxation behavior. The relaxation behavior at high frequency is responsible due to deviation in valency of both cobalt and aluminum ions. Magnetic properties were analyzed through vibrating sample magnetometer (VSM) and the results revealed that the saturation magnetization decreased while coercivity increased with increasing the concentrations of aluminum. The obtained high value of relative permittivity confirmed that the prepared nanomaterials are suitable for high energy storage device applications. Further, the soft magnetic nature of prepared nanomaterials is suitable for soft magnetic applications.