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A new silicon clathrate compound containing barium, (Na, Ba),Si46, becomes a type-II superconductor with a critical temperature (T,) of about 4 K. In the compound, the silicon atoms are bonded tetrahedrally with about the same bond distances as in ordinary cubic diamond Si, but form 12and 14-hedral cages which are linked by shared faces. The metal atoms are located in the center of the polyhedra. This is the erst superconductor consisting of a Si sp' covalent network.PACS numbers: 74. 10.+v, 61.66.Fn, 74.70.Ad Silicon and carbon are often discussed in comparison with each other in terms of the same group-IV elements.As for elemental carbon, there are two allotropes, diamond and graphite, and recently fullerene has been added as a new member [1]; only the diamond type structure is known for elemental silicon. The recent discovery

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The ferroelectric BaTiO(3) is a band-gap insulator. Itinerant electrons can be introduced in this material by doping, for example, with oxygen vacancies. Above a critical electron concentration of n(c) approximately 1 x 10(20) cm(-3), BaTiO(3-delta) becomes metallic. This immediately raises a question: Does metallic BaTiO(3-delta) still retain ferroelectricity? One may expect itinerant electrons to destroy ferroelectricity as they screen the long-range Coulomb interactions. We followed the phase transitions in BaTiO(3-delta) as a function of n far into metallic phase. Although their stability range decreases with n, the low-symmetry phases in metallic BaTiO(3-delta) are still retained up to an estimated concentration of n* approximately 1.9 x 10(21) cm(-3). Moreover, it appears that the itinerant electrons partially stabilize the ferroelectric phases in metallic BaTiO(3-delta) by screening strong crystal field perturbations caused by oxygen vacancies.

Communications cut-off filters (RG 610 nm for PtOEP, OG 590 nm for [Ru(4,,]CI2) were placed in front of a liquid-nitrogen cooled CCD detector (Model LN/CCD, Princeton Instruments, Inc.), with 578 x 384 pixels in a cell size of 13.25 x 8.83 mm'. Luminescent light from the sample surface was collected with a camera lens (Nikon, 55 mm, 1:1.2) and an imaged formed on the CCD camera. The pressure of the sample chamber was measured using a pressure gauge (Model FA 233, Wallace & Tiernan) with an accuracy of 5 0.1 psi.Trichloroethane was used as the solvent to dissolve the dyes and the polymer 3. The dye concentration in the polymer matrixes ranged from 10 to 1000 ppm. Solutions containing the dye and polymer were spray coated onto the surface of interest. Some of the surfaces were precoated with an epoxy primer of a two-part system based on Super One-Coatm White D3400 and Glass Activator D3498 supplied by Pratt & Lambert. The dye film itself was very thin (between 5 and 15 pm) except for the measurements shown in [*] Prof.

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The state with a giant permittivity ͑Ј ϳ 10 4 ͒ and ferromagnetism have been observed above 185 K ͑including room temperature͒ in single crystals of diluted semiconductor manganite-multiferroic Eu 0.8 Ce 0.2 Mn 2 O 5 in the investigations of x-ray diffraction, heat capacity, dielectric and magnetic properties, conductivity, and Raman light-scattering spectra of this material. X-ray diffraction study has revealed a layered superstructure along the c axis at room temperature. A model of the state with a giant Ј including as-grown two-dimensional layers with doping impurities, charge carriers, and double-exchange-coupled Mn 3+-Mn 4+ ion pairs is suggested. At low temperatures these layers form isolated electrically neutral small-size one-dimensional superlattices, in which de Haas-van Alphen oscillations were observed. As temperature grows and hopping conductivity increases, the charge carrier self-organization in the crystal causes formation of a layered superstructure consisting of charged layers ͑with an excess Mn 3+ concentration͒ alternating with dielectric layers of the initial crystal-the ferroelectricity due to charge-ordering state. Ferromagnetism results from double exchange between Mn 3+ and Mn 4+ ions by means of charge carriers in the charged layers. Temperature evolution of frequency shifts of A g modes and quasielastic scattering in Raman-scattering spectra agree with the pattern of phase transitions in ECMO suggested.

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