Design of NiO @ SiO2 core shell nanocomposites and unveiling their dielectric behavior under diverse frequency and temperature regime

•TEM results visualize the formation of core shell structures.•XPS study confirms Ni 2p peak exists as Ni 2p3/2 and Ni 2p1/2 states.•The cole–cole plot reveals that the material follows non-Debye type of relaxation.•The charge carriers have both long and short range order as validated from modulus analysis.•The conduction mechanism envisages the movement of oxygen vacancies and oxide ions.