A comparative study of the lattice structure, optical band gap, electrical conductivity and polarization at different stages of the heat treatment of chemical routed Al(OH)3

Abstract

Aluminium hydroxide (Al(OH)3) was prepared by chemical reaction of the Al(NO3)3 in alkaline medium. The as-prepared powder was heated in the temperature range 250 °C to 1250 °C for studying the structural phase transformation at different stages of the heat treatment. The synchrotron x-ray diffraction patterns confirmed a structural transformation of Al(OH)3 through different (Boehmite, γ, θ, δ, and α) polymorphic phases of Al2O3 on increasing the heat treatment temperature. The samples in Boehmite (γ-AlOOH) and α- Al2O3 phases showed Raman active modes, whereas the intermediate (meta-stable) multi-phased structure showed weak Raman active peaks. The analysis of UV–visible spectra of the samples indicated two optical band gap energy values in the high energy range 4.50–4.73 eV and low energy range 3.06–3.84 eV. The voltage dependence of current, capacitance and electrical polarization were recorded to study electrical properties in heat treated samples. The capacitance value, derived from the polarization, showed a usual increasing trend on decreasing the measurement frequency (inverse of the time) of driving electric voltage. The measured electrical polarization in the samples was found to be highly correlated to their electrical conductivity and the results are helpful to understand the role of electrical conductivity on exhibiting the apparently ferroelectric properties in high conductive and low polarizable dielectric oxides.