Properties of BaTiO3 confined in nanoporous Vycor and artificial opal silica

Abstract

Using the sol-gel technique, BaTiO3 was embedded into nanoporous Vycor and artificial vitreous opal silica for the first time. About 50 vol% of the pores was filled. In case of the Vycor glass (pore diameter 4-6 nm) only amorphous phase was revealed by XRD, IR reflectivity and Raman spectra. After additional gradual annealing, no crystallization was achieved. Chemical reaction with the SiO2 skeleton started at ~1000 K. The room-temperature IR and Raman spectra clearly show characteristic vibrational modes of the ferroelectrically distorted TiO6 octahedra without any long-range order. In case of the opal matrix (densely packed silica spheres, pore diameter up to ~50 nm), crystallization of the ferroelectric BaTiO3 appeared in coexistence with the amorphous phase, but the penetration depth of the crystalline BaTiO3 was limited. From the apparent temperature independence of the effective wide-frequency dielectric response due to the essentially temperature independent effective soft mode stiffened to ~100 cm-1, we can deduce that no macroscopic percolation of the crystalline BaTiO3 has appeared in our opal matrix. Nevertheless, Raman spectra bring evidence of a diffuse ferroelectric phase transition in the opal-BaTiO3 composite.

Addition of BaTiO₃ and carbon nanoparticles to silica aerogel and its dielectric properties

“…As a conclusion, it was thought that the relative permittivity of 1.3 and dielectric loss of 1 © 10 ¹3 were in accordance with literature values, e.g., relative permittivity of 1.1 at 1 MHz for an aerogel with porosity of 95% prepared by Kawakami and Uehara, 4) and the relative permittivity of 1.25 and dielectric loss of 5 © 10 ¹4 at 1 kHz for an aerogel with porosity of 92% prepared by Brüesh et al 5) As shown in Fig. 9, the relative permittivity of the BaTiO 3 -silica aerogel nanocomposites increased slowly with increasing BaTiO 3 loading, reach about 2.1 for the BT/S = 20/100 sample, However, these dielectric properties were considered to be proper in comparison with a report by Nuzhnyy et al 10) They confined BaTiO 3 in a nanoporous artificial opal silica with 35 to 40 vol % porosity, where the BaTiO 3 content was 45 wt % and filled about 50 vol % of the pores. The relative permittivity and dielectric loss in this case decreased with increasing frequency to become almost constant, where the relative permittivity was 5 to 10 in the range of 10 MHz to 1 GHz.…”

“…10) In addition, there have been some reports on the enhancement of permittivity by constructing a BaTiO 3 core-silica shell nanostructure, where silica was coated on the surface of BaTiO 3 particles, and used for Malti-Layer Ceramic Capacitor, high-frequency dielectric applications, 14) and supercapacitors. 15) However, these were not porous materials.…”

High-Frequency Dielectric Properties of Nanocomposite and Ceramic Titanates

“…The quasi-optical THz measurements were completed with complex permittivity calculations based on the Maxwell's equations. More details and references on the used method are in [7], [18], [26], [27].…”

“…The artificial opal periodical matrices prepared by sedimentation of amorphous silica nanoballs of 200-400 nm diameter [17] have 35-40 vol% porosity with percolated pores of complex topology and sizes from zero up to ∼50 nm. The opal-based composites are prepared by impregnation of the pores with magnetic ferrites [17] or ferroelectric BaTiO 3 [18]. Owing to periodicity of the matrix and embedded nanoparticles, opal-based composites have a number of specific features.…”

Modeling of metal-dielectric nanocomposite coatings with ferromagnetic inclusions for electromagnetic protection of electronic devices

“…Dielectric and ac conductivity spectra were measured using impedance methods by the techniques described in [7,8]. Standard LF dielectric measurements were performed with the dielectric analyzer Novocontrol Alpha AN, HF measurements -with the Novocontrol BDS 2100 coaxial sample cell and Agilent 4291B impedance analyzer, MW measurements - 1-4799-4580-1/14/$31.00 ©2014 IEEE with the open-end coaxial probe and Agilent E8364B vector network analyzer.…”