A quadrupole coupling induced 47Ti and 49Ti satellite background which transforms into well-defined satellite lines below T(c) in the ferroelectric phase has been observed in the cubic phase of an ...ultrapure BaTiO3 single crystal. The results demonstrate the coexistence of a displacive and order-disorder component in the phase transition mechanism and tetragonal breaking of the cubic symmetry due to biased Ti motion between off-center sites in the paraelectric phase above T(c).
Climate changes, biofuels and the sustainable future Zidanšek, Aleksander; Blinc, Robert; Jeglič, Anton ...
International journal of hydrogen energy,
08/2009, Letnik:
34, Številka:
16
Journal Article, Conference Proceeding
Recenzirano
Climate change is one of the most dangerous problems of the contemporary world. We can either adapt to the corresponding changes or try to reduce their impact by significantly reducing fossil fuel ...burning. A hydrogen-based economy using energy from biomass, solar, wind and other renewable sources and/or nuclear energy seems to be a viable alternative. Here we analyse the possibilities of the biofuels to replace fossil fuels and their potential to contribute to hydrogen economy.
This book presents the basic physics of ferroelectric and antiferroelectric liquid crystals in a simple and transparent way. It treats both the basic and the applied aspects of ferroelectric and ...antiferroelectric liquid crystal research, starting from the discovery of ferroelectricity in liquid crystals in 1975 and ending with the resonant X-ray experiment in ferrielectric and antiferrielectric phases in 1998. Particular attention is paid to the optical properties, electrooptic effects, phase transitions and experimental methods used in liquid crystal research. Special chapters are devoted to dielectric spectroscopy, light scattering, NMR, STM and AFM in complex fluids. The more than 300 illustrations help to present the basic physics of liquid crystalline ferroelectrics and antiferroelectrics in a way that can be easily followed by students, engineers and scientists dealing with liquid crystal research.
The oxygen isotope exchange of
16
O by
18
O in SrTiO
3
causes a drastic change from paraelectric to ferroelectric, due to the suppression of quantum fluctuation. The phase transition and origin of ...the huge domain wall response were evaluated by dielectric, magnetic (NMR), and optical measurements (SHG, light scattering). The results obtained corroborate (1) smeared ferroelectric transition at T
c
due to quenched random field, (2) a quite large dielectric contribution from domain walls, (3) incomplete softening of the transverse optic mode, and (4) a large contribution from the relaxational mode to the phase transition. Quantitative explanations, given to individual results, may give hints to grasp the mechanism for the evolution of ferroelectricity, in which quantum fluctuation and random fields are dominant perturbations. Finally, some of the news studies on the SrTiO
3
were also introduced.
Electron paramagnetic resonance (EPR) measurements have been carried out over the frequency range of 1–370 GHz on single crystals of potassium peroxychromate (K3CrO8) with the view of examining the ...current models of exchange narrowing of EPR signals in solids. K3CrO8has a simple (tetragonal) lattice structure, can be grown as single crystals pure or diluted with an isostructural diamagnetic host K3NbO8, and its paramagnetism can be described by a very simple (S=12,I= 0) spin Hamiltonian. The measurements were made at various orientations of single crystals in the Zeeman field, with emphasis on the principal directions of theg-tensor. For essentially all orientations, the linewidth decreases monotonically for measurements at resonance frequencies, ω0, from 1 to about 100 GHz, and then starts to increase at higher ω0. In order to delineate the spin exchange effects from other sources of line broadening, the measurements were repeated with a diluted spin system, K3NbO8containing ≅0.5 mole % of K3CrO8, representing the broadening effect of all the magnetic field dependent terms, such as the broadening due to theg-strain and sample holder/waveguide magnetization at the high field utilized, up to 14 T. Using these data, the K3CrO8linewidths were analyzed in terms of the current models of spin exchange narrowing in three-dimensional systems. A reasonably good agreement was found with the Anderson–Weiss model, when modified for various line broadening effects. The accuracy of the analysis procedure was confirmed by the comparison of the presently determined values of the exchange constant,J,and the dipolar field,Hp,with their values obtained by dc magnetic susceptibility measurements and theoretical analysis, respectively; the agreement was within 5% forJ(=1.35 K) and about 25% forHp(160 G). However, some deviations and unusual splittings were noted in measurements at 370 GHz, whose origin remains unclear.
Solar orbital power: Sustainability analysis Zidanšek, Aleksander; Ambrožič, Milan; Milfelner, Maja ...
Energy (Oxford),
04/2011, Letnik:
36, Številka:
4
Journal Article, Conference Proceeding
Recenzirano
Solar power plants positioned in space for terrestrial electricity use have been proposed due to the ever-rising world energy consumption and its environmental impacts. This idea is analysed here in ...the context of sustainability of such power generation. To that end we have performed some new economic, environmental and social effects analysis of electricity generation by solar space power plants of both photovoltaic and solar thermal types power using the best currently available technology. The plants in the analysis were assumed to be in different Earth orbits, or on the Moon built by a robotised factory. One of our results is that both economically and environmentally the best scenario may be to launch a thermal solar power plant to the geostationary orbit from the Moon. Electricity produced in this way could be economically competitive to that generated by fossil fuels on Earth already for as few as 100 space power plants of about 5–10 GW each. This option is also deemed socially responsible with its capacity to reduce poverty with large amounts of cheap clean energy, and environmentally friendly, because it produces more than a hundred times less emissions than the same amount of electricity produced from fossil fuels on Earth.
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