Diffraction effect of x-rays on the accuracy of quantitative analysis of crystals

In order to understand an apparent discrepancy of concentration of constituent elements in the quantitative analysis of thin KCl crystals with an energy dispersive X-ray analyzer, which has been partly explained by fluorescent X-ray excitation, more detailed experiments were carried out on binary alkali halides and tricomponent amorphous material by changing the azimuthal angle. Intensity ratios of X-rays from the constituent elements in KCl and KBr single crystals varied considerably according to the rotation of the specimens. The observed differences between maximum and minimum intensity ratios were 15% for a thin KCl crystal about 100 nm thick and 20% for a bulk KCl crystal, which corresponded to 4.1% and 4.5% differences in atomic concentration, respectively. It was ascertained that for amorphous materials such as Co₈₇Zr₅Nb₈, such a variation of the intensity ratio of X-rays was not observed. It is thus proved that the variations of the intensity ratios of X-rays from the constituent elements with azimuthal angle for KCl and KBr are attributed to the diffraction effect of characteristic X-rays generated in crystalline specimens. This effect, which is the same as that in the production of Kossel patterns, is one of the essential factors limiting the accuracy of the analysis.     

Anomaly of the thickness dependence of photodarkening in amorphous chalcogenide films

The reversible photodarkening phenomenon in evaporated films of amorphous As-S and As-Se was investigated as a function of film thickness. For stoichiometric films irradiated by band gap illumination at room temperature, the photodarkening disappears when the films are thinner than 50 nm. This anomaly implies that the structure of the films is dependent on the film thickness and /or that the photodarkening exhibits a surface behaviour that is different from bulk bahaviour.     

Dehydration ofn-butanol over highly dispersed heteropolyacid intercalation compounds

Heteropolyacid is introduced in an intercalation compound of zinc aluminum carbonate hydroxide by an anion-exchanging technique. The acid is probably present as H_2.1PW_9.2O^4.2– _33.3 and is shown to be highly dispersed. The compound catalyzes dehydration ofn-butanol with noticeably higher activity and selectivity to 1-butene than free Keggin type 12-heteropolyacid.     

A retarding-grid electron spectrometer for Mössbauer spectroscopy

A new retarding-grid electron spectrometer for conversion electron Mössbauer spectroscopy has been constructed. The structure and performance of the spectrometer are described in detail. The response functions for various settings of energy resolution have been determined using the energy spectrum of a very thin ⁵⁷Co source. The best energy resolution obtained is 0.3% at 7.3 keV with a detection efficiency of $\text{1.2\%}\text{4π}$.     

Electronic structure of Nd2CuO4 and its physical properties

In order to clarify the electronic structure of the electron-doped superconducting material Nd_2?xM_xCuO₄, we have performed a first-principle band structure calculation for the matrix material Nd₂CuO₄. We find that doped electrons can be accommodated in both the Cu 4s and 4p _z conduction bands provided that the Cu 3dx²?y ² band splits into two bands, i.e., the upper and lower Hubbard bands by the strong correlation. Based on this electronic structure, we have calculated the Hall coefficient of the Nd system and have shown for the first time that the sign of the Hall coefficient is negative, coinciding with the experimental result in the low-concentration case. In the overdoped region above x=0.18, the dopant electrons occupy not only 4s and 4p _z bands but also the upper Hubbarddx ²?y ² so that the Hall coefficient changes its sign from negative to positive.     

Wavelength discrimination with a chromatically alternating stimulus

Wavelength-discrimination functions were measured with monochromatic stimuli of 410–660 nm at equal luminance of 220 td, presented as temporally alternating fields at the frequencies of 0.5–12.0 Hz. When the alternation frequency was less than 1.0 Hz, wavelength discrimination was the same at all test wavelengths as that obtained by the classical bipartite-field method. As the frequency was raised, the discrimination thresholds increased more near 450–470 nm than at other wavelengths, and tritanopic-like wavelength-discrimination functions were obtained at frequencies higher than 4.0 Hz. Our results may be explained by the notion that the blue-cone mechanism has poorer temporal resolution than the red-and green-cone mechanisms.     

Electrical conductivity measurement and thermogravimetric study of pure and niobium-doped uranium dioxide

The electrical conductivity and nonstoichiometric composition of UO_2+x and (U_1?yNb_y)O_2+x (y = 0.01, 0.05 and 0.10) were measured in the range $\text{1282 ≦ T ≦ 1373}$ K and Pa by tie four inserted wires method and thermogravimetry, respectively. The electrical conductivity of (U_1?yNb_y)O_2+x plotted against the oxygen partial pressure indicated a minimum corresponding to the transition between $\text{n}$- and $\text{p-}\text{type}$ cone uction. The band-gap energy of (U_1?yNb_y)O_2+x was calculated to be $\text{(248 ± 12)}$ kJmol.^?1, independent of niobium content, which is nearly the same as that of UO_2+x. From the oxygen partial pressure dependences of both the electrical conductivity and the deviation $\text{x}$ of UO_2+x and (U_1?yNb_y)O_2+x, the defect structures in these oxides were discussed with the complex defect model consisting of oxygen vacancies and two kinds of interstitial oxygens.