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Dielectric properties of (100 − x)Li2B4O7–x(Ba5Li2Ti2Nb8O30) glasses and glass nanocrystal composites

Authors
Journal
Materials Science and Engineering B
0921-5107
Publisher
Elsevier
Publication Date
Volume
167
Issue
3
Identifiers
DOI: 10.1016/j.mseb.2010.02.016
Keywords
  • Tetragonal Tungsten Bronze
  • Transparent Ferroelectric Glass Ceramics
  • Modulus Spectroscopy
  • Borate Glasses
  • Nanocomposites

Abstract

Abstract Transparent glasses of various compositions in the system (100 − x)(Li 2B 4O 7)– x(Ba 5Li 2Ti 2Nb 8O 30) (5 ≤ x ≤ 20, in molar ratio) were fabricated by splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses (DTA). X-ray powder diffraction studies confirmed the as-quenched glasses to be amorphous and the heat-treated to be nanocrystalline. Controlled heat-treatment of the as-quenched glasses at 500 °C for 8 h yielded nanocrystallites embedded in the glass matrix. High Resolution Transmission Electron Microscopy (HRTEM) of these samples established the size of the crystallites to be in the nano-range and confirmed the phase to be that of Ba 5Li 2Ti 2Nb 8O 30 (BLTN) which was, initially, identified by X-ray powder diffraction. The frequency, temperature and compositional dependence of the dielectric constant and the electrical conductivity of the glasses and glass nanocrystal composites were investigated in the 100 Hz to 10 MHz frequency range. Electrical relaxations were analyzed using the electric modulus formalisms. The imaginary part of electric modulus spectra was modeled using an approximate solution of Kohlrausch–Williams–Watts relation. The frequency dependent electrical conductivity was rationalized using Jonscher's power law. The activation energy associated with the dc conductivity was ascribed to the motion of Li + ions in the glass matrix. The activation energy associated with dielectric relaxation was almost equal to that of the dc conductivity, indicating that the same species took part in both the processes.

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