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[en] Polycrystalline samples of R0.8Ca0.2)Ba2Cu3O7-z (R = Lu and Y) were synthesized by a solid-state reaction route, and the phase stabilities were examined by heating at temperatures between 800 degree C and 900 degree C in various atmospheres. A comparative analyses of the x-ray diffraction data of the (Lu0.8Ca0.2)Ba2Cu3O7-z and (Y0.8Ca0.2)Ba2Cu3O7-z compounds showed that the 123 phase of both compounds is stable under heating in air and O2 of 1 atm. However, contrary to the (Y0.8Ca0.2)Ba2Cu3O7-z compound, the Lu0.8Ca0.2)Ba2Cu3Oz compound was found to become unstable when heated in the low oxygen partial pressure below about 8 %O2 in N2 , Considering the instability of parent LuBa2Cu3O2 compound, this result suggests that the phase stability of Lu-based 123 compounds is sensitive to both the composition and the oxygen partial pressure.
[en] Evolution of the vortex lattice, the rhombus-square transition included, for LuNi2B2C in the field along the c crystal axis, is tracked by the decoration technique pushed up to the record high (for this method) field of 1480 Oe. Decoration images are analyzed with the help of the Fourier transform, which indicates disordered structures in small fields of a few Oe. In fields H<200 Oe the coexisting domains of different structures are observed. A technique based on the Fourier transform is employed to see the domains separately. The transition to the square lattice is recorded near 900 Oe. The results are in agreement with predictions of the nonlocal London theory
[en] The lutetium bisphthalocyanine π-radicals are available in two different crystalline structures which are clearly related to different low-dimensional spin diffusions. On the opposite, the conductivity of these molecular semiconductors appears to be isotropic
[en] The results of studies of spectroscopic and scintillation properties of inorganic scintillation crystals of lutetium-yttrium aluminate with perovskite structure (Lu1-xYx)AlO3 (LuYAP) are presented. This type of crystals was developed at the end of 1990 and are considered now as the most perspective ones for use in medical diagnostic tomography systems. This scintillator is characterized by relatively high light yield, mechanical strength and chemical stability. An influence of the lutetium concentration in LuYAP crystals on their light yield, radioluminescence spectrum, scintillation kinetic were experimentally studied. Mass attenuation coefficients of the scintillation materials depending on the lutetium concentration were calculated. (authors)
[en] The step energy transfers from Pr3+ 4f5d state to Ce3+ 5d state followed by energy back transfer from Ce3+ 5d state to Pr3+ 1D2 level are studied. The Ce3+→Pr3+ energy back transfer upon Pr3+ 4f5d excitation is found to be more efficient than the normal Ce3+→Pr3+ energy transfer upon Ce3+ 5d excitation. The efficient energy back transfer is attributed to preferential excitation of the Ce3+ ion with an adjacent Pr3+ surrounding in Pr3+→Ce3+ energy transfer of the first step, whereas Ce3+ is excited randomly in the normal energy transfer. The efficiencies of Ce3+→Pr3+ energy back transfer as a function of Ce3+ and Pr3+ concentration are evaluated, respectively.
[en] The LuAlO3 : Ce3+ system has been shown to be a promising scintillator for medical imaging devices. Recently, efforts were focused on the improvement of its scintillating properties. Several large crystals with various cerium concentrations were grown. Absorption and excitation spectra were measured in a range extending from the visible to the vacuum ultraviolet (VUV). Emission spectra, fluorescence decay times and light yields, both under γ-ray and x-ray excitation, were measured under various experimental conditions. A reabsorption process is shown to take place in this material. This process is responsible for the observed decrease of the light yield when increasing the size of the sample. (author)
[en] Hydrogen-ordering characteristics are investigated in dilute α-LuDx systems (x=0.06 and 0.08) by diffuse-neutron-scattering techniques. The results indicate the presence of a chainlike hydrogen arrangement essentially similar to that found previously at higher concentrations in LuDx and ScDx. The hydrogen-chain length, however, decreases at lower concentrations. An investigation of local hydrogen modes shows that the split vibrational level found in LuD0.19 is not present in LuD0.06
[en] Single crystals of 0.2% Ce doped Li_6Lu(BO_3)_3 have been grown using the Czochralski technique in air ambient. The crystal growth initiated at temperatures close to the melting point showed inclusions and air bubbles entrapped, while the nucleation initiated at the temperatures about 50°C above the melt temperature showed good transparency without any visible inclusions. The grown crystals have been studied for their luminescence properties. (author)
[en] The double phosphate KLuP2O7 doped with Pr3+ ions was prepared by solid-state reaction. The material obtained was characterized by powder X-ray diffraction. The luminescence spectroscopy and the excited state dynamics of this material were studied upon excitation with VUV synchrotron radiation. The 5d-4f emission of Pr3+ upon both direct and band gap excitation was detected and assigned. The decay kinetics of the Pr3+ 5d-4f emission is characterized by a decay time of about 20 ns and is nearly temperature independent within the range 8-300K. Both dynamics and energy transfer peculiarities revealed in the study suggested good potentials for application of KLuP2O7:Pr3+ as a fast scintillator material. (orig.)
[en] The magnetization and principal magnetic susceptibilities of LuCrO3 are measured from ambient temperature down to 4.20K. It is found that LuCrO3 exhibits a weak ferromagnetic moment along the a crystallographic axis below T/subN/ = 1110K. By applying a magnetic field along the antiferromagnetic c axis, the antiferromagnetic vector can be rotated smoothly in the a-c plane until it coincides with a at and above a critical field H/sub cr/. This field increases with decreasing temperature, its value at T = 4.20K being H/sub cr/ = 3.6 +- 0.4 kOe. By comparing the temperature dependence of the spontaneous a-axis magnetization with that of the c-axis magnetization extrapolated to zero field, a quantitative separation between the Dzyaloshinsky-Moriya antisymmetric exchange (D) and single-ion anisotropy (A/subx//subz/) contributions to the canting is made. We find that vertical-bar A/subx//subz//D vertical-bar < 0.05 for the case of LuCrO3. As a consequence, a temperature-independent constant-canting-angle model is adopted. The temperature dependence of the reduced magnetization can then be analyzed using statistical-mechanical models developed for antiferromagnets. For 0.60 < T/T/subN/ < 0.99 the magnetization exhibits power-law behavior with β approx. = 1/3. For T/T/subN/ < 0.5, its behavior is well described by spin-wave models. A comparison of the experimental results with theoretical curves calculated over the entire temperature range using molecular-field and several Green's-function models is also presented