A glass melt with the composition 24Bi2O3/40TiO2/10SiO2/10Nd2O3/16 Al2O3 was prepared and rapidly quenched between two copper blocks (sample A). A part of this glass was subsequently crystallised at 800 °C for 8 h (sample B). For the preparation of another two samples, the melt was slowly cooled on a cooper plate (sample C) or cast into a graphite mould and subsequently thermally treated at 300 °C for 3 h (sample D). As shown by X-ray diffraction (XRD) and scanning electron microscopy (SEM) including energy dispersive X-ray spectroscopy (EDXS) and electron backscatter diffraction (EBSD) measurements, the rapidly cooled samples contained notable amounts of uncrystallised glassy phase next to the Aurivillius phase Bi4Ti3O12. The latter occurred in higher concentrations in all other samples and formed oriented layers. Minor concentrations of Bi2Al4O9 and Al2O3 were also detected in the microstructure.
The city of Sofia is exposed to a high seismic risk. Macroseismic intensities in the range of VIII – X (MSK) can be expected in the city. The earthquakes that can influence the hazard in Sofia originate either beneath the city or are caused by seismic sources located within a radius of 40 km. The city of Sofia is also prone to the remote Vrancea seismic zone in Romania, and particularly vulnerable are the long-period elements of the built environment. The high seismic risk and the lack of instrumental recordings of the regional seismicity make the use of appropriate credible earthquake scenarios and ground-motion modelling approaches for defining the seismic input for the city of Sofia necessary. Complete synthetic seismic signals, due to several earthquake scenarios, were computed along chosen geological profiles crossing the city, applying a hybrid technique, which combines the modal summation technique and finite differences. The modelling takes into account simultaneously the geotechnical properties of the site, the position and geometry of the seismic source and the mechanical properties of the propagation medium. Acceleration, velocity and displacement time histories and related quantities of earthquake engineering interest (e.g., response spectra, ground-motion amplification along the profiles) have been supplied. The approach applied in this study allows us to obtain the definition of the seismic input at low cost, exploiting large quantities of existing data (e.g. geotechnical, geological, seismological). It may be efficiently used to estimate the ground motion for the purposes of microzonation, urban planning, retrofitting or insurance of the built environment, etc.
Four glasses in the Bi2O3/TiO2/SiO2 and Bi2O3/TiO2/SiO2/Nd2O3 systems are melted and poured into graphite moulds where they show spontaneous crystallization during cooling. The crystal phases α-Bi2Ti4O11, Bi4−xNdxTi3O12, Bi2Si1−yTiyO5, TiO2 and probably Bi2Ti2O7 are shown to crystallize using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDXS) and electron backscatter diffraction (EBSD). A previously unknown miscibility of Bi2SiO5 and Bi2TiO5 is indicated. Oriented layers of monoclinic α-Bi2Ti4O11, Bi4−xNdxTi3O12 and Bi2Si1−yTiyO5 are observed. A perfectly epitaxial relationship between Bi4−xNdxTi3O12 and Bi2Si1−yTiyO5 is proven by EBSD. Crystals with the composition Bi2Si1−yTiyO5 with y = 0.33, 0.5 and 0.66 are detected.
