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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.

In order to examine possible sources of the discrepancies between the proton NMR parameters for ZrH"as reported by R. C. Bowman, Jr. , et ai. [Phys. Rev. B 27, 1474(1983] and C. Korn [Phys. Rev. B 28, 95 (1983)],proton spin-lattice relaxation times (T&), lattice parameters, and magnetic susceptibilities g') have been measured for high-purity ZrH"samples in the composition range 1.5 &x & 1.9 that had been typically annealed at 525'C for 21 d. When these results are compared with the corresponding parameters obtained on the as-prepared ZrH"samples of Bowman et al. it was found that the anneals generally had only minor effects on the proton Tl values, lattice parameters, or g(T) behavior. The most notable exception is a ZrHl 70 sample that was initially composed of a mixture of 5(fcc) and e(fct) phases and converted to just the e phase upon annealing. Although the anneals gave small systematic decreases in the unit-cell volumes, the tetragonal distortions (i.e. , c /a ratios) were not affected within experimental accuracy. Furthermore, both the proton ( Tl T) ' peak and Tl T temperature dependences were also not significantly changed by these anneals. Although the P(T) values in the e phase decrease rapidly with increasing hydrogen content, a 1ocal g(T) maximum that reflects the Pauli component from a peak in the Fermi-level density of states is observed near x =1.80. The dominant p(T) decrease is primarily attributed to reductions in the orbital contribution with the increasing tetragonal distortion. Variations in the concentrations and distributions of oxygen and paramagnetic impurities are believed to be responsible for most of the differences found in the previous studies.