489 research outputs found
Unusual Compression Behavior of Columbite TiO2 via First-Principles Calculations
The physical mechanisms behind the reduction of the bulk modulus of a
high-pressure cubic TiO2 phase are confirmed by first-principles calculations.
An unusual and abrupt change occurs in the dependence of energy on pressure at
43 GPa, indicating a pressure-induced phase transition from columbite TiO2 to a
newly-identified modified fluorite TiO2 with a Pca21 symmetry. Oxygen atom
displacement in Pca21 TiO2 unexpectedly reduces the bulk modulus by 34%
relative to fluorite TiO2. This discovering provides a direct evidence for
understanding the compressive properties of such groups of homologous materialsComment: [email protected] or [email protected]
Ab initio study of the formation of transparent carbon under pressure
A body-centered tetragonal carbon (bct-Carbon) allotrope has been predicted
to be a transparent carbon polymorph obtained under pressure. The structural
transition pathways from graphite to diamond, M-Carbon, and bct-Carbon are
simulated and the lowest activation barrier is found for the graphite-bct
transition. Furthermore, bct-Carbon has higher shear strength than diamond due
to its perpendicular graphene-like structure. Our results provide a possible
explanation for the formation of a transparent carbon allotrope via the cold
compression of graphite. We also verify that this allotrope is hard enough to
crack diamond.Comment: [email protected] or [email protected]
Device modeling of superconductor transition edge sensors based on the two-fluid theory
In order to support the design and study of sophisticated large scale
transition edge sensor (TES) circuits, we use basic SPICE elements to develop
device models for TESs based on the superfluid-normal fluid theory. In contrast
to previous studies, our device model is not limited to small signal
simulation, and it relies only on device parameters that have clear physical
meaning and can be easily measured. We integrate the device models in design
kits based on powerful EDA tools such as CADENCE and OrCAD, and use them for
versatile simulations of TES circuits. Comparing our simulation results with
published experimental data, we find good agreement which suggests that device
models based on the two-fluid theory can be used to predict the behavior of TES
circuits reliably and hence they are valuable for assisting the design of
sophisticated TES circuits.Comment: 10pages,11figures. Accepted to IEEE Trans. Appl. Supercon
Effects of Vanadium doping on BaFe2As2
We report an investigation of the structural, magnetic and electronic
properties of Ba(Fe(1-x)V(x))2As2 using x-ray, transport, magnetic
susceptibility and neutron scattering measurements. The vanadium substitutions
in Fe sites are possible up to 40\%. Hall effect measurements indicate strong
hole-doping effect through V doping, while no superconductivity is observed in
all samples down to 2K. The antiferromagnetic and structural transition
temperature of BaFe2As2 is gradually suppressed to finite temperature then
vanishes at x=0.245 with the emergence of spin glass behavior, suggesting an
avoided quantum critical point (QCP). Our results demonstrate that the avoided
QCP and spin glass state which were previously reported in the superconducting
phase of Co/Ni-doped BaFe2As2 can also be realized in non-superconducting
Ba(Fe(1-x)V(x))2As2.Comment: 5 pages, 6 figure
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