Physical characteristics of PbO-ZrO2-SiO2:TiO2 glass ceramics embedded with Pb2Ti2O6 cubic pyrochlore crystal phase: Part-I electrical properties

摘要

This study is mainly focused on electrical characteristics of PbO-ZrO2-SiO2: TiO2 glass ceramics embedded with Pb2Ti2O6 cubic pyrochlore crystal phases. The samples were synthesized by usual melt quenching technique and subsequent heat treating at crystallization temperature for prolonged times. The samples were characterized by XRD, SEM and DSC, IR, EPR and optical absorption spectroscopy techniques. Later, dielectric properties viz., dielectric constant, loss tangent, electric moduli, electrical impedance and a.c. conductivity over wide ranges of frequency and temperature, have been measured as a function of TiO2 content. The results of characterization techniques viz., XRD, SEM and DSC, indicated that the samples are embedded with multiple crystal grains (with sizes varying from 0.1 to 1 mu m) cemented with residual glass phase. The volume fraction of the crystal grains is found to increase with increase of TiO2 content. The XRD studies on PbO-ZrO2-SiO2:TiO2 glass ceramics revealed that Pb2Ti2O6 cubic pyrochlore crystal phase is the principal phase present in the bulk samples. The studies have also confirmed that a small part of Pb(Zr Ti-0.5(0).(5))O-3 and Ti2O3 crystal grains are also present in the titled glass ceramics. The results of IR spectral studies have indicated that there is an increasing degree of polymerization of glass network with increasing TiO2 content up to 0.6 mol%. This is attributed to the presence of Ti ions predominantly in Ti4+ state (in this concentration range of TiO2) that take part in the network forming positions with TiO4 and also substitutionally positioned octahedral sites. The results of optical absorption and EPR spectral studies have pointed out that a part of the Ti ions were reduced to Ti3+ state and such ions were predicted to act as modifiers. These studies have also indicated that the concentration of Ti3+ ions is higher in the samples crystallized with 0.8 and 1.0 mol%. The values of dielectric parameters are decreased with increasing of crystallizing agent. The decrease is attributed to the participation of Ti ions in the formation of Pb2Ti2O6 cubic pyrochlore crystalline phases with TiO4 structural units. Quantitative analysis of the dielectric properties of PbO-ZrO2-SiO2:TiO2 glass ceramics together with the results of spectroscopic studies indicated that the electrical insulating strength is the highest for the glass crystallized with 0.6 mol% of TiO2. (C) 2017 Elsevier B.V. All rights reserved.