A superconducting oxide Y0.4Ba0.6CuO2.22 with T
c higher than 88 K was synthesized. The crystal structure was found to be a derivative of the perovskite structure with orthorhombic unit cell dimensions of a=3.818 (1) Å, b=3.888 (1) Å, c=11.667 (4) Å, and V=173.19 (8) Å3. Basic unit cell of the cubic perovskite structure was tripled along the c axis, probably due to the ordering of Y3+ and Ba2+ ions and/or of oxygen vacancy. Apparent short bond length for Cu-O may partly be explained by oxygen vacancy amounting to a quarter, but the observed high T
c suggests actual contraction of Cu-O bonds.
We have performed an x-ray photoemission (XPS) experiment using tunable x rays in the photon-energy range between 1500 and 3000 eV. The deep metal 3p core-level spectra of the tetravalent oxides MO2, M=Ce, Pr, Tb, and Hf have been measured. The results show that the configuration interaction between localized 4f and 4f "+'L configuration in the initial state gives final-state peaks 3p4f", 3p4f"+'L, and 3p4f"+ L . The final states of Ce 3p core levels of Ce02 have been calculated by the many-body theory in the frame of the filled-band Anderson model.
Continuum x rays induced by bombardments of a Be target with 20.14-MeV/amu protons and He2+ ions have been measured with a Si(Li) detector in the direction of 90' with respect to the incident beam. Differences in the x-ray -production cross sections multiplied by the x-ray energy 8'ay Pro [o-I, (tao)/4 -oz(leo) jJ and ratio of the cross sections R (A'au) f= -o&(Aced) j4az(has)] for the proton and He +-ion impact, where (7&(fo)) and o. z(A'e) are the x-ray -production cross sections for proton and He2+-ion impact, respectively, were obtained as a function of the x-ray energy. Both the difference and the ratio show peaks in the region where the x-ray energy is equal to the relative kinetic energy between the projectile and the inner-shell electron to be scattered by the projectile. From the comparison with a theory of quasi-free-electron bremsstrahlung based on the impulse approximation, it is found that this peak corresponds to the maximum of the velocity-distribution function of the inner-shell electron. Furthermore, the contribution of the radiative electron-capture process in the case of proton and 3He2+ impact is clearly found.Recently, ' we have bombarded targets of Be, C, and Al with 6 -40-MeV protons and have found a new component of continuum x rays. These continuum x rays are predominant in the region where the x-ray energy tao is smaller than the energy T, = --,m, V»', where m, is the electron mass and V~is the projectile velocity, and the Doppler effect is definitely observed in the angular distributions of these x rays. From these experimental results, the x rays have been well understood in terms of the bremsstrahlung produced by the orbital electrons scattered by the projectile Coulomb field; we call this process the quasi-free-electron bremsstrahlung (QFEB). The lllIX r '1/2 projectile-energy dependence and the angular dependence of QFEB have been well explained by a simple theory assuming that the orbital electrons are free.Further, a calculation taking into account the velocity distribution of orbital electrons has been developed, ' and it was found that the spectrum of QFEB in the vicinity of the high-energy limit of Ace = T, is sensitively dependent on the velocity distribution of orbital electrons.On the basis of the impulse approximation which Jakubassa and Kleber have developed for the bremsstrahlung in heavy-ion reaction, 3 a more accurate formula for the cross section of QFEB can be given by with v, '"= -, '
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