Dielectric Constant Of Glasses Research Articles

An influence of a glass composition on the structure and properties of Bi2O3–B2O3–SiO2–ZnO glass system with addition of BaO, CaO and Fe2O3

The Bi2O3–B2O3–SiO2–ZnO glass system with addition of network modifier (BaO, CaO and Fe2O3) were synthesized using the conventional melt quenching method. The effect of chemical compositions on the glass network structure, thermal properties, crystallization characteristics and electrical properties were systematically investigated. With rising the Bi2O3 content, the number of [BiO3] and [BiO6] units increases and a new bridging of Bi–O–B bond forms. Moreover, either the increase of Bi2O3 content or the decrease of SiO2 content induce a progressive conversion of [BO4] into the [BO3] unit. However, the influence of a network modifier on the conversion of [BO4] to [BO3] unit depends on the composition. An addition of network modifier helps stabilize the glass structure against a crystallization. A high content of Bi2O3 and ZnO promotes the formation of Bi-rich and Zn-rich crystals during heat-treated process, respectively. The Bi content of Bi-rich crystal increases and the Zn-rich crystal decomposes with increasing the heat-treated temperature. Both of the glass network structure and the formation of Bi-rich crystal in glass matrixes during testing process combine to determine the change rule of the CTEs (coefficients of thermal expansion). The variation of the T g (glass transition temperature) only depends on the glass network structure. The dielectric constant of glasses without network modifier decreases with decreasing the Bi2O3 content. Moreover, an addition of network modifier could decrease the dielectric constant. Each glass offers a dielectric loss tangent below 0.005 and an electrical resistivity above 107 Ω cm.

DC creeping discharges over insulating surfaces in different gases and mixtures

This paper deals with the propagation of discharges over insulators of Bakelite and glass, in gases and their mixtures (namely N2, SF6, CO2, SF6 - N2 and SF6 - CO2) under DC voltage in a point - plane electrode arrangement. The shape and stopping length, Lf, of these discharges are investigated versus the type of insulator material and its thickness, the amplitude of applied voltage, the type of gas/mixture and pressure. The obtained results show that the discharges do not always propagate radially; this depends on the type of solid/gas interface. However, as we reported elsewhere for lightning impulse voltage, Lf increases quasi-linearly with the voltage; it decreases when the gas/mixture pressure increases. Lf is shorter in SF6 than in CO2 or N2; and the increase of SF6 content in the investigated mixtures leads to a significant decrease of Lf. Also, for a given gas, Lf is slightly longer with glass than with Bakelite indicating that the higher the dielectric constant, the longer the discharge is; the dielectric constant of glass and Bakelite being εG = 5.0 and εB = 4.8, respectively. Thus the density of the discharge branches and Lf reduce when the thickness of insulators increases and/or their dielectric constant decreases indicating that the capacitive charge effect and electric field influence the development of creeping discharges.

Study of PbO-SrO-TiO2-B2O3 glass and glass ceramics

The glasses with composition (50−X)PbO–XSrO-25TiO2-25B2O3 (where X=0, 5, 10 and 15mol%) were prepared using conventional quenching technique. The Tg, Tc, density and CTE of the glass samples were measured. The Tg observed to increase with increasing concentration of SrO, while the Tc first decreased and then increased. The glass samples were converted to glass ceramics by following two stage heat treatment schedule. The glass ceramic samples were characterized by XRD, SEM and dielectric measurements. The XRD results revealed the formation of ferroelectric lead titanate as a major crystalline phase in glass ceramics. Additional phases observed include Sr2B2O5 and PbB2O4. The room temperature (RT) dielectric constant of glass and glass ceramics are in the range of 100–120 which is promising for capacitor application.

Dielectric Measurements as a Function of Temperature of Sodium‐Lithium Phosphate Glasses Evaluated at 10 MHz and 9 GHz

Dielectric constant measurements can be performed at temperatures greater than room temperature; some techniques are shown in this work. The dielectric constant of phosphate glasses, measured in the X‐band microwave range, was determined using a microwave setup assembled to measure the shift in the standing wave pattern produced by the insertion of the sample inside the waveguide. The glass system 50P2O5 · 25Li2O · 25Na2O was chosen in this work due to its lower melting point and lower transition temperature (Tg) values. The dielectric constant of the glass studied in this work increases in the temperature range 25–330°C, as shown by the results at radio and microwave frequencies. The method of standing wave shift was applied, and it is shown to be a useful tool to estimate the Tg of glasses. This assumption was confirmed by differential thermal analysis technique. Measurements were compared to that at 10 MHz by impedancimetric methods.

Dielectric constant of glasses: evidence for dipole-dipole interactions.

The 1 kHz real part chi(') of the dielectric constant of a structural glass (a-SiO(2+x)C(1+y)H(z)) was measured at low temperature T. Reducing the sample thickness h below 100 nm weakens the slope /delta(chi('))/delta (T) for T less than or approximately equal 0.1 K, for all measuring fields E. This contrasts with the predictions of the two-level system (TLS) model but is in agreement with the recently proposed delocalization of excitations derived from a field-induced TLS-TLS interaction mechanism. For small h this interaction is screened, which explains the h effects on chi('). Hence, interactions must play a key role in standard thick samples as soon as T less than or approximately equal 0.1 K.

Magnetic field effect on the dielectric constant of glasses: Evidence of disorder within tunneling barriers

The magnetic field dependence of the low frequency dielectric constant $e_r$(H) of a structural glass a - SiO2 + xCyHz was studied from 400 mK to 50 mK and for H up to 3T. Measurement of both the real and the imaginary parts of $e_r$ is used to eliminate the difficult question of keeping constant the temperature of the sample while increasing H: a non-zero $e_r$(H) dependence is reported in the same range as that one very recently reported on multicomponent glasses. In addition to the recently proposed explanation based on interactions, the reported $e_r$(H) is interpreted quantitatively as a consequence of the disorder lying within the nanometric barriers of the elementary tunneling systems of the glass.

Raman spectra and dielectric properties of glasses of the Sb-S-I system

The authors present the results of investigations of the Raman spectra and dielectric constant of glasses of the Sb-S-I system. On the basis of the results obtained it may be concluded that the two-mode character of the Raman and IR spectra is evidence of the ''quasieutectic'' structure of the glasses of the Sb-S-I system, since solid solutions do not form in this system.

On the determination of the dielectric constant of glass by aid of very rapid electrical oscillations

On the determination of the dielectric constant of glass by aid of very rapid electrical oscillations