Influence of BaTiO₃ nanoparticles/clusters on the structural and dielectric properties of glasses-nanocomposites

Abstract

Glass nanocomposite (GNCs) samples in the composition [(90-x) Li₂B₄O₇- xBaTiO₃- 10Nb₂O₅] with x = 5, 7.5, 10, 12.5 and 15 (in mol%) were prepared. Rietveld refinement of the data for the reagent grade of the BaTiO₃ revealed that the structure is a tetragonal phase (space group P4mm). The energy dispersive X-Ray (EDX) spectra and scanning electron microscopic (SEM) micrographs exhibit the two phases (BaTiO₃ nanopatricles/clusters phase and residual glass phase) of the GNCs samples. The BaTiO₃ nanoparticles/clusters in the glass matrix were confirmed by transmission electron microscopic (TEM) and Fourier transform infrared (FTIR) studies. The deconvolution of the FTIR spectra of the GNCs samples reveals the presence of BO₃, BO₄, NbO₄ and NbO₆ units. The dielectric results exhibit the ferroelectric of BaTiO₃ nanoparticles/clusters in the GNCs samples at x = 10, 12.5 and 15 mol%. The dielectric constant, dielectric loss and ac conductivity for the GNCs samples as a function of temperature at various frequencies in 120Hz−100 k Hz range have been studied.

Introduction

In recent years, BaTiO₃ nanoparticles/clusters embedded in the glass matrix (the so called GNCs) have attracted much attention due to their promising technological properties and relatively easy preparation method [[1], [2], [3]]. These GNCs exhibit mixed properties for the two components, BaTiO₃ nanoparticles and host glass matrix, such as ferroelectric and high dielectric which are used to develop modern electronics [1,2,4]. BaTiO₃ nanoparticles/clusters in the GNCs samples can be prepared by conventional melt quenching method in many reports [[4], [5], [6]]. Moreover, these samples undergo structural phase transitions as a function of temperature; therefore the GNCs can be used in capacitors, piezoelectric transducers, etc [1,7]. BaTiO₃ in polycrystalline has three phase transitions with the decrease in the temperature from a cubic phase (space group Pm3 m) to a tetragonal phase (space group P4mm), then to an orthorhombic phase (space group Amm2) and to a rhombohedral phase (space group R3m) at 403, 278 and 183 K, respectively [8,9]. The glass forming ability of BaTiO₃ is weak and its melting temperature is high (1898 K) so to obtain GNCs containing BaTiO₃ nanoparticles/clusters, it is required to add a host glass matrix such as lithium tetraborate (Li₂B₄O₇) [2,5,10]. Abdel-Khalek et al. [2,3] studied the structural and dielectric properties of high concentration of BaTiO₃ embedded in Li₂B₄O₇ glass matrix [(100-x) Li₂B₄O₇- xBaTiO₃] with x = 0, 20 and 60 mol%. They found that the GNCs containing BaTiO₃ nanoparticles exhibited dielectric anomalies (ferroelectric nature). The addition of Nb₂O₅ oxide into the glass composition led to the change in the structure and physical properties such as electrical and dielectric constant. The change in the structure due to Nb₂O₅ which acts as an intermediate, one as a glass former with NbO₄ in Nb⁴⁺ (glass is blue) and other as a glass modifier with NbO₆ in Nb⁵⁺ (glass is yellow) [11,12]. The change in the electrical and dielectric constant is due to Nb₂O₅ ions which have high polarizability and the change in the glass network (NbO₄ and NbO₆) [13]. Moreover, the volume of nonbridging oxygens (NBOs) sites formed by the addition of Nb₂O₅ into the glass network is larger than that formed by alkaline earth [11]. Wang et al. [14] studied the structure of niobium alkali borate glass. They found that the glass structural units are NbO₆, BO₃ and BO₄. Sanghi et al. [11] studied the influence of Nb₂O₅ on the structural, optical and electrical properties of alkaline earth borate glasses [xNb₂O₅- (30-x) MO- 70B₂O₃] where M = Ca, Sr and Ba with 0 ≤ x ≤ 12 mol%. They found that from the IR spectra the presence of NbO₄ and NbO₆ units for Ca and Sr and NbO₆ units for Ba glasses. The conductivity results show that the conductivity is varying with the concentration of Nb₂O₅ (up to 8 and for Nb₂O₅ ≥ 8 mol %) and depend on the presence of NbO₄ and NbO₆ units in these glasses which support by the IR analysis. In view of the aforementioned aspects, we reported the ferroelectricity of tetragonal BaTiO₃ nanoparticles/clusters in GNCs at a low concentration of BaTiO₃ in the presence of Nb₂O₅ compared to previous studies [2,3]. In the present work, we study the influence of BaTiO₃ nanopatricles/clusters on the structural and dielectric properties of [(90-x) Li₂B₄O₇- x BaTiO₃-10 Nb₂O₅] (where x = 5, 7.5, 10, 12.5 and 15 (in mol %)) GNCs samples.