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This study addresses a perennial problem in the synthesis of copper vanadates, namely, that of phase purity. A time-efficient solution combustion synthesis (SCS) was employed for obtaining α-CuV2O6in a polycrystalline powder form in a matter of minutes. Admixture of the final product with α-Cu2V2O7or V2O5was avoided by a combination of careful pH control of the SCS precursor mixture and by a postsynthesis NaOH wash. The phase purity of the resultant product was demonstrated by Rietveld refinement of the X-ray diffraction data, energy-dispersive X-ray analyses, and laser Raman spectroscopy. Photoelectrochemical (PEC) measurements showed the material to be an n-type semiconductor. Possible applicability of α-CuV2O6in PEC devices designed for solar water splitting hinges on a comprehensive study of its structural, optical, magnetic, and optoelectronic attributes; this was done by a combination of theory and experiment. Intensity-modulated photocurrent spectroscopy on thin film samples permitted an assessment of the balance between charge transfer and surface recombination, underlining that the charge separation efficiency determined the photocurrent magnitude. Finally, experiments on the PEC stability of this material on prolonged (∼4 h) irradiation revealed self-healing behavior induced by incipient photocorrosion product layer formation on the oxide semiconductor surface.

This study focuses on a solid solution series, Ca(La1–xCex)2S4(0 ≤ x≤ 1), where the f electron density is absent in CaLa2S4and is progressively increased until it is maximized in CaCe2S4. Correspondingly, these samples, synthesized by a sealed ampule method, showed progressive variations in color ranging from gray for CaLa2S4to orange-red for CaCe2S4. The crystal structural nuances of both the end members and three solid solutions with x= 0.25, 0.50, and 0.75 were established with the complementary use of synchrotron X-ray diffraction and neutron scattering. Interestingly, these data were consistent with a two-phase composition centered around each nominal solid solution stoichiometry. Optical characterization via diffuse reflectance spectroscopy and Tauc analyses showed a shrinking of the energy band gap (from the UV to vis range) when Ce was progressively introduced into the host CaLa2S4structure. These data were in concert with electronic band structure calculations, using density functional theory, which showed the progressive formation of an intermediate f band when Ce was introduced intro the structure. Photoelectrochemical measurements in an aqueous redox electrolyte, as well as surface photovoltage and Kelvin probe measurements, revealed all samples to be n-type semiconductors. The valence and conduction band edge positions of the end members and the three solid solutions could be mapped, on both the redox and vacuum reference energy scales, by combining these measurements with the optical data.

The Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae), devastates wheat and barley production on all continents except Australia. Although D. noxia–resistant cultivars exist, virulent D. noxia populations exist in Asia, North America, and South America that have the ability to overcome resistance. In this study, synthetic hexaploid wheat genotypes created at the International Maize and Wheat Improvement Center (CIMMYT) were evaluated and characterized for resistance to North American biotype 2 (RWA2). Fewer RWA2 were produced on several genotypes, and D. noxia–induced leaf rolling and chlorosis were reduced on these genotypes as well. Aphid numbers were positively correlated with chlorosis and with leaf rolling. However, some genotypes were highly resistant to leaf rolling and chlorosis while supporting large RWA2 populations. There were negative correlations between leaf chlorosis and leaf dry weight (r = −0.267, df = 106, P = 0.006) and between aphid numbers and leaf dry weight (r = −0.297, df = 105, P = 0.002). These results indicate that chlorosis and aphid number individually explain at least 27% of the changes observed in leaf dry weights. Interestingly, there was no correlation between leaf rolling and leaf dry weight. The RWA2-resistant lines identified, which are also resistant to D. noxia populations in Mexico and to greenbug (Schizaphis graminum Rondani) biotype G, are strong candidates for use in improving the genetic diversity in bread wheat for resistance to different biotypes of both S. graminum and D. noxia.