444 research outputs found
On the diffraction pattern of C60 peapods
We present detailed calculations of the diffraction pattern of a powder of
bundles of C peapods. The influence of all pertinent structural
parameters of the bundles on the diffraction diagram is discussed, which should
lead to a better interpretation of X-ray and neutron diffraction diagrams. We
illustrate our formalism for X-ray scattering experiments performed on peapod
samples synthesized from 2 different technics, which present different
structural parameters. We propose and test different criteria to solve the
difficult problem of the filling rate determination.Comment: Sumitted 19 May 200
Torus-invariant prime ideals in quantum matrices, totally nonnegative cells and symplectic leaves
The algebra of quantum matrices of a given size supports a rational torus
action by automorphisms. It follows from work of Letzter and the first named
author that to understand the prime and primitive spectra of this algebra, the
first step is to understand the prime ideals that are invariant under the torus
action. In this paper, we prove that a family of quantum minors is the set of
all quantum minors that belong to a given torus-invariant prime ideal of a
quantum matrix algebra if and only if the corresponding family of minors
defines a non-empty totally nonnegative cell in the space of totally
nonnegative real matrices of the appropriate size. As a corollary, we obtain
explicit generating sets of quantum minors for the torus-invariant prime ideals
of quantum matrices in the case where the quantisation parameter is
transcendental over .Comment: 16 page
Evidence for distinct polymer chain orientations in KC60 and RbC60
The KC60 and RbC60 polymer phases exhibit contrasting electronic properties
while powder diffraction studies have revealed no definite structural
difference. We have performed single crystal X-ray diffraction and diffuse
scattering studies of these compounds. It is found that KC60 and RbC60 possess
different chain orientations about their axes, which are described by distinct
space groups Pmnn and I2/m, respectively. Such a structural difference will be
of great importance to a complete understanding of the physical properties.Comment: To be published in Phys. Rev. Let
Theory of Distinct Crystal Structures of Polymerized Fullerides AC60, A=K, Rb, Cs: the Specific Role of Alkalis
The polymer phases of AC60 form distinct crystal structures characterized by
the mutual orientations of the (C60-)n chains. We show that the direct electric
quadrupole interaction between chains always favors the orthorhombic structure
Pmnn with alternating chain orientations. However the specific quadrupolar
polarizability of the alkali metal ions leads to an indirect interchain
coupling which favors the monoclinic structure I2/m with equal chain
orientations. The competition between direct and indirect interactions explains
the structural difference between KC60 and RbC60, CsC60.Comment: 4 pages, 2 figures, 1 tabl
Carbon Nanotubes Synthesized in Channels of Alpo4-5 Single Crystals : First X-Ray Scattering Investigations
Following the synthesis of aligned single-wall carbon nanotubes in the
channels of AlPO4-5 zeolite single crystals, we present the first X-ray
diffraction and diffuse scattering results. They can be analysed in terms of a
partial filling of the zeolite channels by nanotubes with diameter around 4A.
The possible selection of only one type of nanotube during the synthesis, due
to the constraints imposed by the zeolite host, is discussed.Comment: to appear in Solid State Com
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