Structure-property correlations in lithium zinc cobalt metaphosphate glasses and glass-ceramics

Abstract

The main goal of this work is to study the physical, structural, optical, and electrical properties of alkali zinc phosphate glasses doped with CoO oxide with the general formula 10Li2O-xCoO-(40-x)ZnO–50P2O5. Using the standard melt-quench technique, a large glass-forming region is obtained, and up to 40 mol% CoO doped glasses are prepared. XRD diffraction confirmed the amorphous nature of these materials. Density, molar volume, and the glass transition temperature (Tg) are composition-dependent. Infrared (IR) spectroscopy is performed to study the structural approach. It is observed that the substitution of ZnO by CoO oxide in the glassy framework induces some structural modifications. The UV–Visible spectra of the CoO-doped glasses show visible absorption bands in the region 400–700 nm which are related to the coexistence of cobalt in divalent and trivalent states. The crystallization behaviour of the samples is performed by submitting the glasses to controlled heat treatments and the crystalline phases obtained are identified by X-Ray diffraction (XRD). The kinetic of the crystallization is carried out by employing the thermal analysis (DSC) technique. The crystallization process is discussed regarding the obtained activation energy (Ec) and Avrami parameter (n). The Vickers hardness values of the glasses and the glass-ceramics are determined and discussed according to the bond strengths. The electrical conductivity of these materials is investigated over a large frequency domain at various temperatures. It is found that the electric conductivity decreases with increasing cobalt content. It is also noted that the conductivity of each glass-ceramic is reduced in comparison with that of its mother glass. The frequency-dependent of the conductivity follows Jonscher's power law and the correlated barrier hopping mechanisms (CBH) was appropriate for the conduction process inside the glasses. The electrical modulus formalism is applied to the electric data in order to study their dielectric relaxation. The results show that this latter is non-Debye type in agreement with the well-known universal responses of amorphous materials.