The bond lengths and bond angles of orthorhombic black phosphorus have been determined as a function of hydrostatic pressures to 26.6(5) kbar using time-of-flight neutron powder diffraction. We show that the markedly anisotropic compression reported previously results from a large pressure-induced shortening of the van der Waals bonds separating layers of atoms combined with a shear motion within the layers. Covalently bonded chains of atoms along the a direction remain very rigid. The average effective linear compressibility for van der Waals bonds is 1.48(9) ×10−3 kbar−1 while the average effective linear compressibility for covalent bonds is an order of magnitude smaller, 2.6(8) ×10−4 kbar−1.
We report on the temperature dependence of the far-infrared conductivity of YBa2Cu408 single crystals for E~~c. With decreasing temperature, the conductivity shows a transition from a Drude-like behavior to a pseudogap at 180 cm ' which grows deeper below 180 K without any abrupt changes at the superconducting transition at T, =80 K. In the superconducting state the formation of the superfluid condensate can be seen. We show that in a variety of high-T, . superconductors the value of the London penetration depth for E~~c correlates with the conductivity along the c direction. With respect to this correlation we (liscuss the possibility of Josephson coupling between the Cu02 layers.The electromagnetic response of high-T, superconductors is strongly anisotropic offering a striking contrast between the nearly insulating c direction and the well conducting ab plane. ' Recently, it has been shown that the semi-insulating behavior of the c-axis properties in the underdoped YBa2Cu306 70 is the result of the formation of a pseudogap in the real part of the conductivity tr, (to). The closely related material, YBa2Cu408 is naturally underdoped as well as untwinned and has been reported to show evidence of a gap in NMR measurements' " as well as in the a-axis resistivity. ' In this paper we report on the temperature dependence of the c-axis far infrared (FIR) conductivity which shows the opening of a pseudogap at temperatures well above the superconducting transition at 80 K. We discuss the formation of the superfluid at T~T, , as seen in the c-axis response, in terms of the Josephson coupling between Cu02 layers. Within this model we are able to describe the observed correlation between the c-axis London penetration depth X, and the c-axis conductivity in a variety of high-T, materials.The details of sample preparation and characterization were reported elsewhere. ' The typical size of the crystals was 500X500&60 p, m, and in order to obtain an area of sufficient size for FIR spectroscopy, four samples were mounted together. The reflectance was measured between 70 and 5000 cm '. To account for the finite sample size and surface irregularities the sample was coated in situ with a gold layer and the spectrum of the gold-coated sample was then used as a reference. ' The uncertainty of the absolute reflectivity was estimated to be about 1%.In Fig. 1 we show the reflectivity spectra in the FIR region at several different temperatures. The response is that of a poor metal with additional contributions from IR active phonon modes. In the normal state, the reflectivity decreases as the temperature is lowered, contrary to what is expected 0 1 a0
Reduced conductivity in poly(3,4-ethylenedioxythiophen)-poly(styrene sulfonate) and indium tin oxide nanocomposite for low indium tin oxide content J. Appl. Phys. 105, 054318 (2009); 10.1063/1.3080154 Impedance spectroscopy and optical characterization of polymethyl methacrylate/indium tin oxide nanocomposites with three-dimensional Voronoi microstructuresThe defect structure of bulk and nano-indium-tin oxide was investigated by a combination of experimental techniques, including high-resolution synchrotron x-ray diffraction, extended x-ray absorption fine structure, and time-of-flight neutron diffraction on powder specimens. The structural results include atomic positions, cation distributions, and oxygen interstitial populations for oxidized and reduced materials. These structural parameters were correlated with theoretical calculations and in situ electrical conductivity and thermopower measurements as well as existing defect models, with special reference to the model of Frank and Köstlin [G. Frank and H. Köstlin, Appl. Phys. A 27, 197 (1982)].
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