24,010 research outputs found
First-principles calculations of a high-pressure synthesized compound PtC
First-principles density-functional method is used to study the recently
high-pressure synthesized compound PtC. It is confirmed by our calculations
that the platinum carbide has a zinc-blende ground-state phase at zero pressure
and the rock-salt structure is a high-pressure phase. The theoretical
transition pressure from zinc-blende to rock-salt is determined to be 52GPa.
Furthermore, our calculation shows the possibility that the experimentally
synthesized PtC by Ono et al. under high pressure condition might undergo a
transition from rock-salt structure to zinc-blende after the pressure quench to
ambient condition.Comment: A revised versio
Out of plane effect on the superconductivity of Sr2-xBaxCuO3+y with Tc up to 98K
A series of new Sr2-xBaxCuO3+y (0 x 0.6) superconductors were prepared using
high-pressure and high-temperature synthesis. A Rietveld refinement based on
powder x-ray diffraction confirms that the superconductors crystallize in the
K2NiF4-type structure of a space group I4/mmm similar to that of La2CuO4 but
with partially occupied apical oxygen sites. It is found that the
superconducting transition temperature Tc of this Ba substituted Sr2CuO3+y
superconductor with constant carrier doping level, i.e., constant d, is
controlled not only by order/disorder of apical-O atoms but also by Ba content.
Tcmax =98 K is achieved in the material with x=0.6 that reaches the record
value of Tc among the single-layer copper oxide superconductors, and is higher
than Tc=95K of Sr2CuO3+y with optimally ordered apical-O atoms. There is
Sr-site disorder in Sr2-xBaxCuO3+y which might lead to a reduction of Tc. The
result indicates that another effect surpasses the disorder effect that is
related either to the increased in-plane Cu-O bond length or to elongated
apical-O distance due to Ba substitution with larger cation size. The present
experiment demonstrates that the optimization of local geometry out of the Cu-O
plane can dramatically enhance Tc in the cuprate superconductors.Comment: 23 Pages, 1 Table, 5 Figure
Observation of Andreev Surface Bound States in the 3-K phase Region of Sr_2RuO_4
The tunneling spectrum of the superconducting phase with T_c ~ 3.0 K has been
measured in the Ru-embedded region of Sr_2RuO_4 using cleaved junctions. A
sharp zero-bias conductance peak (ZBCP) has been observed below 3 K. All
characteristics of this ZBCP suggest that it originates from Andreev surface
bound states, indicating that the pairing in the 3-K phase is also non-s-wave.
Below the bulk T_c of Sr_2RuO_4 (~1.5 K), a bell-shaped ZBCP was found. This
supports that there is a phase transition in the 3-K phase region near the bulk
T_c.Comment: 4 pages, to appear in Phys. Rev. Lett. 87 (2001
Optical properties of in the normal state
We present the optical reflectance and conductivity spectra for non-oxide
antiperovskite superconductor at different temperatures. The
reflectance drops gradually over a large energy scale up to 33,000 cm,
with the presence of several wiggles. The reflectance has slight temperature
dependence at low frequency but becomes temperature independent at high
frequency. The optical conductivity shows a Drude response at low frequencies
and four broad absorption features in the frequency range from 600 to
33,000 . We illustrate that those features can be well understood from
the intra- and interband transitions between different components of Ni 3d
bands which are hybridized with C 2p bands. There is a good agreement between
our experimental data and the first-principle band structure calculations.Comment: 4 pages, to be published in Phys. Rev.
Feasibility Study of Tractor-Test Vehicle Technique for Practical Structural Condition Assessment of Beam-Like Bridge Deck
The tractor-test vehicle technique of non-destructive testing for indirect measurement of the modal properties of a bridge deck is revisited in this paper with several improvements for possible practical application to the structural condition assessment of a beam-like bridge deck. The effect of damping of the vehicle-bridge system is considered and the modal properties from only the first vibration mode of the structure will be used for a quick and simple assessment. The two test vehicles are designed to have the same modal frequency and damping ratio but with parameters in the follower No.2 test vehicle proportional to those in the follower No.1 test vehicle. This effectively removes the effect of road surface roughness in the response of an equivalent vehicle such that the error in the subsequent condition assessment is reduced. Through data collected on-site transmitted to the remote computer platform, a simple technique based on the moment-curvature relationship acceptable to practical engineers is adopted for the condition assessment with improvements in the estimation of the element bending stiffness of the deck. Scenarios with different damping, vehicle speed, road surface roughness, and local damages in the bridge structure are studied with or without temperature effect in the measurement. Through numerical simulations and field tests, the tractor-test vehicle technique of non-destructive testing with the proposed modifications and improvements has been demonstrated to give consistently accurate estimates of the element bending stiffness of the bridge deck but with a small error close to the end of the deck
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