967 research outputs found
Very weak electron-phonon coupling and strong strain coupling in manganites
The coupling of the manganite stripe phase to the lattice and to strain has
been investigated via transmission electron microscopy studies of
polycrystalline and thin film manganites. In polycrystalline \PCMOfiftwo a
lockin to in a sample with has been observed for the first
time. Such a lockin has been predicted as a key part of the Landau CDW theory
of the stripe phase. Thus it is possible to constrain the size of the
electron-phonon coupling in the CDW Landau theory to between 0.04% and 0.05% of
the electron-electron coupling term. In the thin film samples, films of the
same thickness grown on two different substrates exhibited different
wavevectors. The different strains present in the films on the two substrates
can be related to the wavevector observed via Landau theory. It is demonstrated
that the the elastic term which favours an incommensurate modulation has a
similar size to the coupling between the strain and the wavevector, meaning
that the coupling of strain to the superlattice is unexpectedly strong.Comment: 6 pages, 7 figure
High-pressure/high-temperature synthesis of transition metal oxide perovskites
Perovskite and related Ruddlesden-Popper type transition metal oxides synthesised at high pressures and temperatures during the last decade are reviewed. More than 60 such new materials have been reported since 1995. Important developments have included perovskites with complex cation orderings on A and B sites, multiferroic bismuth-based perovskites, and new manganites showing colossal magnetoresistance (CMR) and charge ordering properties
Exploring the importance of reflection in the control room
While currently difficult to measure or explicitly design for, evidence suggests that providing people
with opportunities to reflect on experience must be recognized and valued during safety-critical
work. We provide an insight into reflection as a mechanism that can help to maintain both individual
and team goals. In the control room, reflection can be task-based, critical for the 'smooth' day-to-day
operational performance of a socio-technical system, or can foster learning and organisational change
by enabling new understandings gained from experience. In this position paper we argue that
technology should be designed to support the reflective capacity of people. There are many
interaction designs and artefacts that aim to support problem-solving, but very few that support
self-reflection and group reflection. Traditional paradigms for safety-critical systems have focussed
on ensuring the functional correctness of designs, minimising the time to complete tasks, etc. Work
in the area of user experience design may be of increasing relevance when generating artefacts that
aim to encourage reflection
Charge order in Fe2OBO3: An LSDA+U study
Charge ordering in the low-temperature monoclinic structure of iron oxoborate
(Fe2OBO3) is investigated using the local spin density approximation (LSDA)+U
method. While the difference between t_{2g} minority occupancies of Fe^{2+} and
Fe^{3+} cations is large and gives direct evidence for charge ordering, the
static "screening" is so effective that the total 3d charge separation is
rather small. The occupied Fe^{2+} and Fe^{3+} cations are ordered alternately
within the chain which is infinite along the a-direction. The charge order
obtained by LSDA+U is consistent with observed enlargement of the \beta angle.
An analysis of the exchange interaction parameters demonstrates the
predominance of the interribbon exchange interactions which determine the whole
L-type ferrimagnetic spin structure.Comment: 7 pages, 8 figure
Materials chemistry under high pressures - Some recent aspects
Among the thermodynamic parameters governing the preparation of novel materials, temperature (T) and pressure (p) play an important role. In Materials Chemistry, the synthesis of materials needs energy in order to enhance the diffusion of atoms to the equilibrium positions required by the specific structure and to induce the formation of chemical bonds..
- …