No abstract

No abstract

No abstract

Low-temperature (LT) X-ray diffraction (XRD) studies of 13 ZrH, samples in the range 1.50 5 x 5 2.00 were made by using a Guinier-Simon (GS) focusing camera and other methods. The ZrH, phase diagram was made more complete for the fcc (&phase) and fct (€-phase) regions from ambient to low temperature (i.e,, to about 110 K). No new low-temperature phases were obbserved by XRD. Careful determinations of the composition and temperature dependences of the following parameters were made: c/a ratio, V (unit-cell volume), and Al/(ZAT). When the XRD results are combined with the solid-state proton NMR parameters that reflect the density of electron states at the Fermi level, mutual support is obtained for the Jahn-Teller splitting of the Zr d bands to produce the tetragonal distortion of the ideal fcc lattice when the stoichiometry exceeds x = 1.66. The lattice constants from XRD confirm that the maximum in the values of the proton NMR parameters that are observed when 1 .80 5 x I 1.85 is due primarily to the Fermi level falling at the maximum of the lower split d band and is not merely a lattice-temperature effect.A systematic study of the influence of chemical structure on the performance of merocyanine dyes as solar energy converters has been made. Key correlations between current-generating capability and chemical properties such as chain length, electronegativity, and acid strength have been established. While these correlations are helpful in leading to systematic improvements in performance, certain chemical group substitutions give rise to disproportionate increases signaling the simultaneous advancement of several underlying mechanisms. While the highest sunlight efficiencies achieved to date have been with binuclear structures, certain trinuclear structures have been developed which exhibit broader spectral width and higher quantum efficiency than their binuclear counterparts. The inherently higher solar efficiency potential of devices made from these structures has not yet been realized, however, because of instability problems. Squarylium dyes also exhibit performance indicative of potential high efficiency. Broad spectral widths occur for certain structures due to aggregate formation, High quantum efficiency and open circuit voltage, however, seem to correlate with narrow solid-state absorption bands rather than with broadened aggregate-induced absorption.

Most of the small particles (50 to 100 micrometers in diameter) of microcrystalline beta-rhombohedral boron that quickly transit an argon plasma maintained within a radio-frequency induction-coupled torch emerge as better crystallized spheroids of the same crystalline form and nearly the same size as the starting material. A few crystals of each of four distinctive, well-faceted habits are formed along with the general product. Three of these types are monocrystals of the beta-rhombohedral polymorph, of the tetragonal-III modification, and of an unreported cubic form of boron. Specimens of the fourth type are polycrystals of another unreported form of boron, apparently consisting of many hexagonal platelets stacked in an imprecise fashion.