Coloring of Bi4Ge3O12 – Mn crystals induced by electric field

The effect of the direct electric field on the optical transmittance of Bi4Ge3O12 single crystals doped with Mn is studied in the mode of using asymmetric contacts when only one electrode (Ag or In-Ga) is injected. It is found that changes in the optical transmittance spectra under the action of unipolar injection of electrons and holes are different. They also differ from the case of using symmetrical electrodes (double injection mode). The optimal temperature and field conditions for electrochromic coloring are determined from the correspondence between the manifestations of the electrochromic effect in Bi4Ge3O12 ─ Mn crystals and the current-voltage characteristics. It is shown that the maximum effect is achieved by injecting holes into a Bi4Ge3O12 ─ Mn sample annealed in a reducing atmosphere.

I─V characteristics of Bi4Ge3O12─Mn crystals in the unipolar injection mode

Current-voltage relations in Bi4Ge3O12 ─ Mn crystals were measured under the conditions of unipolar injection of charge carriers. The characteristics obtained for electrons and holes are different. I-V curves in the case of electron injection contain ohmic, quadratic regions and regions of a sharp increase in current. This indicates the formation of a space charge enriched in electrons. The values of conductivity, effective drift mobility, and electron concentration calculated at different temperatures are close to the values obtained for pure crystals. In the case of hole injection I-V curves are characterized by the presence of sublinear regions. It is assumed that injection of the holes causes the formation of a space charge layer depleted in electrons due to the recombination. It is shown that doping with manganese does not change the nature of conductivity in bismuth germanate crystals and strongly affects the recombination processes.

Electro-thermo-convection in dielectric liquid subjected to partial unipolar injection between two eccentric cylinders

Purpose The purpose of this work is to highlight the effects of partial unipolar injection on electro-thermo-convection (ETC) in dielectric liquid contained between two eccentric cylinders. Design/methodology/approach A finite volume method was used to solve governing equations. The study is performed for different parameters, such as radius ratio (0.2 ≤ Γ ≤ 0.6), dimensionless electric Rayleigh number (0 ≤ T ≤ 900), eccentricity (−0.4 ≤ e ≤ 0.4) and thermal Rayleigh number (10 ≤ Ra ≤ 5.105). Findings It is found that heat transfer increases with increase in dimensionless electric Rayleigh number and eccentricity ratio. Originality/value The originality of this work is to analyze the ETC in dielectric liquid subjected to partial unipolar injection between two eccentric cylinders