Colossal dielectric constant, electric modulus and electrical conductivity of nanocrystalline SnO2: Role of Zr/Mn, Fe or Co dopants

Abstract

New dielectric compositions composed of SnO2, Sn0.97Zr0.03O2, Sn0.95Zr0.03Mn0.02O2, Sn0.95Zr0.03Fe0.02O2 and Sn0.95Zr0.03Co0.02O2 nanoparticles were synthesized via coprecipitation method. Single phase of SnO2 tetragonal rutile structure was detected in the XRD patterns and the changes of the lattice parameters suggest the substitution of Sn4+ sites by Zr4+, Mn2+, Fe2+ or Co2+ ions. The TEM images show the formation of nano-sized particle of clear crystalline facets within 15–25 ​nm and the HR-TEM image displays identical fringes with lattice spacing close to 0.32 ​nm which can be assigned to (110) crystallographic plane of SnO2 phase. The EDX pattern of Sn0.95Zr0.03Co0.02O2 sample revealed the existence of Sn, O, Zr and Co elements without any other impurities elements. Nanocrystalline SnO2, Sn0.97Zr0.03O2, Sn0.95Zr0.03Mn0.02O2, Sn0.95Zr0.03Fe0.02O2 and Sn0.95Zr0.03Co0.02O2 compositions exhibit band gap energies of 3.4 ​eV, 3.42 ​eV, 3.4 ​eV, 3.45 ​eV and 3.42 ​eV. Undoped SnO2 exhibits a high dielectric constant value of 4014 ​at 42 ​Hz. Interestingly, the Zr monodoping and Zr based Mn, Fe or Co codoping have the ability to increase the dielectric constant of SnO2 by nearly two, three or four-fold to reach to 14321 for Sn0.95Zr0.03Fe0.02O2. The dielectric properties were explained by means of electric modulus formalism. The electrical conductivity of the synthesized powders exhibited semiconducting behavior with temperature. The electrical conductivity of pure, Zr-monodoped and Zr/Mn, Fe or Co codoped SnO2 was increased with increasing the frequency due to the charge-hopping mechanism.