696 research outputs found
Understanding complex magnetic order in disordered cobalt hydroxides through analysis of the local structure
In many ostensibly crystalline materials, unit-cell-based descriptions do not
always capture the complete physics of the system due to disruption in
long-range order. In the series of cobalt hydroxides studied here,
Co(OH)(Cl)(HO), magnetic Bragg diffraction reveals a
fully compensated N\'eel state, yet the materials show significant and open
magnetization loops. A detailed analysis of the local structure defines the
aperiodic arrangement of cobalt coordination polyhedra. Representation of the
structure as a combination of distinct polyhedral motifs explains the existence
of locally uncompensated moments and provides a quantitative agreement with
bulk magnetic measurements and magnetic Bragg diffraction
Practical Application of Outcomes Based Pricing Models in Scotland
Based on consultation with the expert advisory group, the objective of this report is to make recommendations on the next steps necessary to understand the practical application of an Outcomes Based Pricing (OBP) scheme in Scotland
Bulk and film synthesis pathways to ternary magnesium tungsten nitrides
Bulk solid state synthesis of nitride materials usually leads to
thermodynamically stable, cation-ordered crystal structures, whereas thin film
synthesis tends to favor disordered, metastable phases. This dichotomy is
inconvenient both for basic materials discovery, where non-equilibrium thin
film synthesis methods can be useful to overcome reaction kinetic barriers, and
for practical technology applications where stable ground state structures are
sometimes required. Here, we explore the uncharted Mg-W-N chemical phase space,
using rapid thermal annealing to reconcile the differences between thin film
and bulk powder syntheses. Combinatorial co-sputtering synthesis from Mg and W
targets in a N environment yielded cation-disordered Mg-W-N phases in the
rocksalt (0.1< Mg/(Mg+W) <0.9), and hexagonal boron nitride (0.7< Mg/(Mg+W)
<0.9) structure types. In contrast, bulk synthesis produced a cation-ordered
polymorph of MgWN that consists of alternating layers of rocksalt-like
[MgN] octahedra and nickeline-like [WN] trigonal prisms (denoted
"rocksaline"). Thermodynamic calculations corroborate these observations,
showing rocksaline MgWN is stable while other polymorphs are metastable. We
also show that rapid thermal annealing can convert disordered rocksalt films to
this cation-ordered polymorph near the MgWN stoichiometry. Electronic
structure calculations suggest that this rocksalt-to-rocksaline structural
transformation should also drive a metallic-to-semiconductor transformation. In
addition to revealing three new phases (rocksalt MgWN and MgWN,
hexagonal boron nitride MgWN, and rocksaline MgWN), these findings
highlight how rapid thermal annealing can control polymorphic transformations,
adding a new strategy for exploration of thermodynamic stability in uncharted
phase spaces
Feasibility of comparing medical management and surgery (with neurosurgery or stereotactic radiosurgery) with medical management alone in people with symptomatic brain cavernoma - protocol for the Cavernomas:A Randomised Effectiveness (CARE) pilot trial
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