Materials Chemistry and Physics 129 (2011) 1233–1239 Contents lists available at ScienceDirect Materials Chemistry and Physics j ourna l ho me pag e: www.elsevier.com/locate/matchemphys Effect of heat-treatment on the electrical and dielectric properties of a TiO 2 -containing lithia–calcia–silica glass and glass ceramics Reham M.M. Morsi a,∗ , Mohammad A.F. Basha b a Physical Chemistry Dept, Inorganic Chemical Industries & Mineral Wealth Division, National Research Centre-Cairo, ElTahreer St, Cairo 12622, Egypt b Physics Dept, Faculty of Science, Cairo University, Giza, Egypt h i g h l i g h t s • Lithia calcium silicate glass with and without TiO 2 . • Glass ceramic. • Heat treatment. • DTA, XRD and IR measurements and discussions. • Dielectric constant (ε ′ ), dielectric loss (ε ′′ ) and conductivity  ac measurements and discussions. a r t i c l e i n f o Article history: Received 3 February 2011 Received in revised form 5 May 2011 Accepted 12 June 2011 Keywords: Electrical conductivity Dielectric properties Glass Glass ceramics a b s t r a c t The glass 65 SiO 2 , 20 CaO, 15 Li 2 O (mol%) containing 4 g TiO 2 /100 g glass was prepared. Samples of this glass were heat treated at temperatures pre-determined by DTA to produce crystalline samples which were characterized by IR, XRD and SEM. The dielectric constant (ε ′ ), dielectric loss (ε ′′ ) and conductivity  ac over a wide range of frequency and temperatures were measured. Optical absorption and values of the absorption edge were also determined for the transparent samples. Li–calcium silicate was found to crystallize at 964 ◦ C as the main phase with lithium disilicate and quartz as minor phases. An enhancement in conductivity of about 1–3 orders of magnitude was obtained in the heat treated samples as compared to parent glass. Conduction takes place through an electronic mechanism in the low temperature region. In crystalline samples, the electronic conduction is extended to high temperature regions. Crystallized samples show high ε ′ values, particularly at low frequencies. The values of (ε ′ ) reached 60–300 at 300 ◦ C. The capacitance results indicated that these materials can be used in capacitors. Dielectric loss bands appeared in the range 0.32–5 MHz and the conduction relaxation times were calculated. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Lithia silicate glasses showed marked effect as sealing materi- als of filament lamps due to their high electrical resistivity of the formed meta-stable immiscibility when heat-treated [1]. Certain lithium silicate glass–ceramics could also be applied for sealing to metal substrates in the electrical industry [2]. The rates of nucleation and crystal growth can be controlled during the heat- treatment process of these materials. During this process, the base glass is converted into a glass–ceramic, the properties of which are affected by the presence of nucleating agents. Among the nucleating agents, which trigger the controlled nucleation and subsequent crystal growth, and widely used in glasses for glass–ceramics preparation is TiO 2 [3–7]. It is reported in the lit- ∗ Corresponding author. Tel.: +20 123733794; fax: +20 233370931. E-mail address: morsi reham@yahoo.com (R.M.M. Morsi). eratures [5–7] that this oxide is greatly dissolved in glass melts; however, due to its high ionic field strength, it encourages the liquid–liquid phase separation phenomenon during subsequent heat treatment of solid glass. During cooling it can precipitate in the forms of titanium oxide or titanium compounds and facilitate development of main crystalline phases by acting as a nucleating agent. The coordination studies of Ti-ion in TiO 2 –SiO 2 glass determined by the electron energy loss showed that Ti-ions substitute Si-ions in the tetrahedral structure of the glass to form the glass network [8]. In sodium silicate titania glass, high values for the refrac- tive index and dispersion were recorded, which were attributed to the high polarizability feature of Ti and the low preference of 4-coordination for titanium ion [9]. It has been noticed that titanium ions of low co-ordinate states can be changed to the six co- ordinate state upon crystallization [10]. These features are expected to be reflected on the dielectric properties of glasses containing Ti-ions. 0254-0584/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2011.06.017