99 research outputs found
Crystal engineering using functionalized adamantane
We performed a first principles investigation on the structural, electronic,
and optical properties of crystals made of chemically functionalized adamantane
molecules. Several molecular building blocks, formed by boron and nitrogen
substitutional functionalizations, were considered to build zincblende and
wurtzite crystals, and the resulting structures presented large bulk moduli and
cohesive energies, wide and direct bandgaps, and low dielectric constants
(low- materials). Those properties provide stability for such
structures up to room temperature, superior to those of typical molecular
crystals. This indicates a possible road map for crystal engineering using
functionalized diamondoids, with potential applications ranging from space
filling between conducting wires in nanodevices to nano-electro-mechanical
systems
Electronic properties and hyperfine fields of nickel-related complexes in diamond
We carried out a first principles investigation on the microscopic properties
of nickel-related defect centers in diamond. Several configurations, involving
substitutional and interstitial nickel impurities, have been considered either
in isolated configurations or forming complexes with other defects, such as
vacancies and boron and nitrogen dopants. The results, in terms of spin,
symmetry, and hyperfine fields, were compared with the available experimental
data on electrically active centers in synthetic diamond. Several microscopic
models, previously proposed to explain those data, have been confirmed by this
investigation, while some models could be discarded. We also provided new
insights on the microscopic structure of several of those centers.Comment: 21 pages, 8 figure
Probing crystal structure at the atomic level: Insights from PAC spectroscopy and ab-initio studies
Perturbed angular correlation spectroscopy combined with
electronic structure calculations is used to unravel the structural phase
transition path from the low-temperature polar structure to the
high-temperature structural phase in , a hybrid improper
ferroelectric. This procedure explores the unique features of a local probe
environment approach by monitoring the evolution of the electric field gradient
tensor at the calcium sites. The local environments, observed above 1057 K,
confirm a structural phase transition from the symmetry to an
orthorhombic symmetry in the crystal lattice, disagreeing
with the frequently reported avalanche structural transition from the polar
phase to the aristotype phase. Moreover, the EFG temperature
dependency, within the temperature stability, is shown to be sensitive
to the recently proposed ferroelectric polarization decrease
within the 500-800~K temperature range
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