Electrical Relaxation in Mixed Alkali Bi_2O_3-K_2O-Li_2O-Fe_2O_3 Glasses

A new glass system （Bi2O3）50（Fe2O3）10（Li2O）x（K2O）40-x, where x changes in steps of 5 mole fraction between 0 and 40, was selected to study the electrical relaxation and the mixed alkali effect （MAE） phenomena. Measurements of ac conductivity σac, dielectric permittivity ε′ and loss factor tanδ in the frequency range of 0.12～10^2 kHz and in the temperature range of 300～650 K were carried out. The temperature dependence of the ac conductivity shows a slow increasing rate at low temperature and high frequency and a rapid increase at high temperature and low frequency. At constant temperature, the ac conductivity is found to be proportional to ω^8, where s is the frequency exponent, which is less than 1. Analysis of the conductivity data and the frequency exponent shows that the overlapping large polaron tunnelling （OLPT） model of ions is the most favorable mechanism for the ac conduction in the present glass system. The ac response, the dc conductivity and dielectric relaxation have the same activation energy and they originate from the same basic transport mechanism. The results of the dielectric permittivity show no maximum peak in the temperature and frequency range studied. This absence of maximum peak is an indication of non-ferroelectric behavior of all the studied samples. The MAE has been detected in the ac conductivity, which is the same as the classical MAE in the dc conductivity. The electrical parameters such as dielectric permittivity ε′ and real dielectric modulus M′ show a typical minimum deviation from linearity by about two orders of magnitude. The loss factor tanδ and the imaginary dielectric modulus M″ are insignificantly dependent on composition even at the same transition temperature Tg.

Effect of lithium-potassium mixed alkali on spectroscopic properties of Er^3＋-doped aluminophosphate glasses

Er^3＋-doped lithium-potassium mixed alkali aluminophosphate glasses belonging to the oxide system xK2O-（15-x）Li2O-4B2O3-11Al2O3-5BaO-65P2O5 are obtained in a semi-continuous melting quenching process. Spectroscopic properties of Er^3＋-doped glass matrix have been analysed by fitting the experimental data with the standard Judd-Ofelt theory. It is observed that Judd-Ofelt intensity parameters Ωt（t = 2, 4 and 6） of Er^3＋ change when the second alkali is introduced into glass matrix. The variation of line strength Sed[^4I13/2,^4I15/2] follows the same trend as that of the/26 parameter. The effect of mixed alkali on the spectroscopic properties of the aluminophosphate glasses, such as absorption cross-section, stimulated emission cross-section, spontaneous emission probability, branching ratio and the radiative lifetime, has also been investigated in this paper.

Influence of alkali mixed effect on the mixing enthalpy in 0.75B_2O_3-0.25[xNa_2O-(1-x)K_2O]glass system

The mixed alkali effect was investigated in the glass system 0.75B2O3-0.25[xNa2O-（1 -x）K20] through thermodynamic properties. The calorimetric measurements were performed in HF solution calorimetry at 298 K. The mixing enthalpy values show non-linear behaviour upon substitution of one alkali ion by another. This thermodynamic non-ideality is caused by the slight variations of distance between metallic cations, the macromolecular structure being unchanged. It can be explained, at least qualitatively, using electrolyte theory based on the Coulombic interactions of charged species originally developed by Debye and Hückel.

Thermoluminescence Response and Its Deconvolution on Crystalline Higher Order Mixtures of Alkali Halides Exposed to Gamma-Rays for Dosimetric Use

Alkali halides crystals have been the subject of intense research. High order crystalline one phase mixtures （high order： more that binary） studied by TL （thermoluminiscence technique） proved having persistent peaks along the time after the radiation to which they are exposed. In general in alkali halide crystals the traps associated with highest recorded temperature peaks in the TL due to radiation damage have greater permanence in time too. These features are useful for dosimetric applications. In this work, temperature thermoluminescence glow peaks of ternary and quaternary mixed alkali halide crystals have been studied. The study has been focused on their high temperature glow peaks after being subjected to thermal treatments at 373, 573, and 673 K. The glow peaks of high temperature were isolated and studied 24 h and 48 h after irradiation. The parameters of the recombination processes associated to these peaks were obtained using a glow peak shape method. Orders of kinetics were higher than 1.0 and the activation energy greater than 1.2 eV. The results suggest that such materials have a high potential as dosimeter and energy storage materials.

Thermoluminiscence Response of an Alloy Quaternary Ionic Crystal Exposed to High Energy Radiation

The alkali halide crystals exhibit significant TL （thermoluminescence） properties when exposed to ionizing radiation. The defects in crystals can be produced in high concentration by means of chemical impurities, radiation, mechanical work and others processes. This study is concerned with the TL properties of quaternary mixtures of alkali halide crystals when they are irradiated with beta and gamma-rays. The samples were made mixing KCI, KBr, RbCI, RbBr salts doped with divalent europium （Eu2＋）, by the Czochralski method sintering at 400 ~C during 6 hours in a N2 atmosphere. The samples were exposed to beta and gamma rays. We present the TL glow curves, demonstrating that the nature of the defects in the crystals can be produced by trapping states and recombination mechanisms. The highest temperature TL curves are the most interesting due to possible applications in dosimetry and optical energy storage.