| dc.description.abstract | Structural, Dielectric, and Optical Properties of Lithium Tetraborate and Lithium Borate-Bismuth Tungstate Glass Nanocomposites
Abstract and Synopsis
Introduction
Lithium tetraborate (LBO) glasses were fabricated using the conventional melt-quenching technique. Their structural, dielectric, and optical properties were investigated under various heat-treatment conditions. These glasses exhibited a dielectric anomaly close to the crystallization temperature.
Dielectric and Conductivity Studies
In polycrystalline samples, the dielectric constant increased monotonically with temperature, especially at high temperatures.
In glassy samples, the dielectric constant showed similar behavior in the low-temperature region (300-450 K), attributed to comparable structural units.
Differences near the crystallization temperature were linked to structural changes.
AC conductivity measurements were consistent with dielectric loss data, with comparable activation energies.
The large dielectric constant near
was attributed to increased ionic conductivity/polarization during softening of the amorphous structure prior to crystallization.
Optical Properties
Optical transmission of lithium borate glasses was similar to single crystals.
Refractive indices were slightly lower than single-crystal values.
Second Harmonic Generation (SHG) was observed in heat-treated LBO glasses, and the nonlinear optical coefficient was computed relative to quartz.
Methods to improve SHG efficiency were suggested.
Glass Nanocomposites (Li
2
B
4
O
7
-Bi
2
WO
6
)
Glasses and nanocomposites of composition (100-x) Li
2
B
4
O
7
- x Bi
2
WO
6
(x = 0-35 mol%) were fabricated.
Controlled heat-treatment achieved nanocrystallization of monophasic Bi
2
WO
6
in the LBO matrix.
Structural studies (XRD, TEM) showed nanometric crystallite growth with increasing Bi
2
WO
6
content and heat-treatment temperature.
Density increased with Bi
2
WO
6
content, and nanocomposites were denser than glasses.
Dielectric and Electrical Properties
Dielectric constant increased with Bi
2
WO
6
content, while dielectric loss decreased.
Nanocomposites exhibited dielectric anomalies analogous to crystalline ferroelectrics near the crystallization temperature.
Predicted dielectric constants (Maxwell’s and logarithmic mixture rules) agreed with experimental values.
Impedance spectroscopy revealed both electronic and ionic conduction.
Activation energies: electronic conduction = 0.59 eV (glass), 0.77 eV (nanocomposite); ionic conduction = 0.17 eV (glass), 0.01 eV (nanocomposite).
Ferroelectric and Pyroelectric Behavior
Ferroelectric hysteresis loops were observed at 300 K in glasses containing nanosized Bi
2
WO
6
crystallites.
Pyroelectric coefficients were significantly high.
Optical transmission and refractive indices could be tuned by varying Bi
2
WO
6
content.
Linear and nonlinear (third-order) optical susceptibilities increased with Bi
2
WO
6
concentration.
Nanocomposites exhibited birefringence, with temperature-dependent variation linked to microstructural changes.
Strong SHG confirmed their ferroelectric nature, highlighting potential for device applications.
Conclusions
Lithium tetraborate glasses show dielectric anomalies near crystallization due to ionic polarization.
Nanocomposites with Bi
2
WO
6
exhibit enhanced dielectric, ferroelectric, pyroelectric, and nonlinear optical properties.
These materials are promising for optical and electronic device applications, particularly due to their SHG efficiency and tunable optical characteristics. | |
