Dielectric Properties of Cr<sup>3+</sup> Doped Al<sub>2</sub>O<sub>3</sub> of a Hierarchical Nanostructure Synthesized Using a Highly Porous Precursor of Tubular AlO(OH)⋅αH<sub>2</sub>O Fibers

Herein, we have developed a Cr 3+ doped Al 2 O 3 of a hierarchical nanostructure by a simple two-step synthesis. A pure AlO(OH)⋅αH 2 O, as synthesized in forms of small tubular fibers by hydrolysis of Al-metal sheets, is easily doped with selective Cr 3+ dosages up to 2.0 mol% using an aqueous CrO 3 . As-synthesized samples exhibit XRD of a single phase Cr 3 + : Al 2 O 3 of a rhombohedral crystal structure. Average pore-volume is decreased as 98.1, 89.8, and 61.5 cm 3 -g -1 in the 0.5, 1.0 and 2.0 % Cr% doped samples, with average pore radius of 1.70, 2.17 and 1.90 nm, respectively, as measure from BET specific surface area. Local Al-O vibrations exhibit IR bands of 400 to 1200 cm -1 intrinsic of oxygen polygons. At room temperature, a duly tailored dielectric permittivity of 480 is obtained in a 2.0 mol% Cr 3+ :Al 2 O 3 and that is enhanced progressively on heating it over 25 to 300 °C, showing a value 6700 at 300 °C in phonon induced dynamics of charge carriers, useful for solid-state electronics.