Papers by Author: Reni Iordanova

Abstract: α-Bi2Mo3O12 and β-Bi2Mo2O9 crystal phases have been synthesized by crystallization of a glass for a short time. Amorphous samples with the compositions corresponding to the alpha and beta bismuth molybdates have been obtained at high cooling rates (104-105 K/s). XRD, DTA and SEM studies were performed to examine the phase formation, thermal behavior of the glasses and the microstructure of obtained crystalline products. By scanning electron microscopy it was shown that the obtained bismuth molybdates consist of dense agglomerates, containing uniform distributed crystals with submicron size.

Abstract: Low melting glasses in the MoO3-Nd2O3-Bi2O3 system were obtained at slow (102 K/s) and high cooling rates (104-105 K/s). The amorphous state of the samples was proved by X-ray diffraction. Comparative analysis of the infrared spectra of the obtained glasses and other available molybdate spectral data was carried out. The structure of glasses with a high MoO3 content was found to consist of corner shared MoO6 units. The increasing of Nd2O3 and Bi2O3 lead to partial transformation of MoO6 to MoO4 units, due to breaking of Mo-O-Mo linkage.

Abstract: Selenite glasses are a new class of amorphous materials which are interesting mainly from a scientific point of view and they are not yet fully examined. Selenite glasses containing other non-traditional glass formers (TeO2, V2O5 and MoO3) as well as network modifiers (Ag+, Cu2+, Zn2+, etc.) were obtained. The aim of the present study is to explain the glass formation ability in selenite systems with the participation of modifiers (Ag+ and Cu2+) and MoO3.

Abstract: Novel low melting glasses in the MoO3-La2O3-Nd2O3 system were obtained at different cooling rates (102 K/s and 104-105 K/s). Characterization of the amorphous samples was made by differential thermal analysis (DTA) and X-ray absorption fine structure (XAFS) method. According to DTA data of the glass samples, the glass transition temperatures are at 325-330 0C, the crystallization started above 410 0C and the melting temperatures are at 660-720 0C. A structural model of glasses was suggested on the basis of XAFS and IR investigations. It was shown that the predominant structural units in the amorphous network of glasses containing 90 -80 mol% MoO3 are MoO6 groups. The appearance of MoO4 groups deteriorates the glass formation ability.