https://doi.org/10.1007/s100510050236
Cesium ordering and electron localization-delocalization phenomena in the quasi-one-dimensional diphosphate tungsten bronzes: Cs1-xP8W8O40
1
Laboratoire de Physique des Solides (CNRS-URA 02) ,
Université de Paris Sud, Bâtiment 510, 91405 Orsay Cedex, France
2
Department of Chemistry,
Rutgers, The State University of New Jersey,
New Brunswick, N.J. 08903, USA
Corresponding author: a foury@lps.u-psud.fr
Received:
10
October
1997
Revised:
11
December
1997
Accepted:
16
December
1997
Published online: 15 March 1998
We present a structural investigation of the
family of quasi-one-dimensional
(quasi-1D) conductors, which exhibit intriguing
charge transport properties where, for x small, the
conductivity exhibits a crossover from
a semiconducting to a metallic like regime when the
temperature decreases. In these materials the
double zig-zag chains, together with the
diphosphate groups, delimit channels
which are partially filled with the
ions. It is found, from
an X-ray diffuse scattering investigation,
that at room temperature the
ions are locally ordered
on a lattice of well-defined sites
in the channel direction and not ordered
between neighboring
channels. These
ions form 1D
incommensurate concentration waves whose periodicity depends
on the
stoichiometry. In
upon cooling, the intrachannel order increases
significantly, and an interchannel order between
the 1D
concentration waves develops. But,
probably because of kinetic effects, no
tridimensional (3D) long range order of the
ions is
achieved at low temperature. The 3D low-temperature
local order has been determined and it is
found that the phase shift between the
concentration waves minimizes their Coulomb
repulsions. This local order is increasingly reduced as the Cs concentration diminishes. We
interpret the intriguing features of the electrical conductivity in relationship with the thermal
evolution of the Cs ordering effects. We suggest that in
, for x small, a
localization-delocalization transition of the Anderson type occurs due to the thermal variation of the Cs
disorder. When x increases, the enhancement of the disorder leads to a localization of the electronic
wave function in the whole temperature range measured. Finally, and probably because of the
disorder, no charge density wave instability is revealed by our X-ray diffuse scattering
investigation.
PACS: 61.50.Ks – Crystallographic aspects of phase transformations; pressure effects / 64.70.Kb – Solid-solid transitions / 71.45.Lr – Charge-density-wave systems
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1998