162 research outputs found
Hysteresis in the electronic transport of V2O3 thin films: non-exponential kinetics and range scale of phase coexistence
The thermal hysteresis of the electronic transport properties were studied
for V2O3 thin films. The temporal evolution of the resistance shows the
out-of-equilibrium nature of this hysteresis with a very slow relaxation.
Partial cycles reveal not only a behavior consistent with phase coexistence,
but also the presence of spinodal temperatures which are largely separated. The
temperature spreading of phase coexistence is consistent with the bulk phase
diagram in the pressure-temperature plane, confirming that the film is
effectively under an effective pressure induced by the substrate.Comment: Accepted for publication in Europhysics Letter
Structure determination of a brownmillerite Ca2Co2O5 thin film by Precession Electron Diffraction
Calcium cobaltite thin films with a ratio Ca/Co=1 were grown on (101)-NdGaO3
substrate by the pulsed laser deposition technique. The structure of the
deposited metastable phase is solved using a precession electron diffraction 3D
dataset recorded from a cross-sectional sample. It is shown that an ordered
oxygen-deficient Ca2Co2O5+d perovskite of the brownmillerite-type with lattice
parameters a= 0.546nm, b=1.488nm and c=0.546nm (SG: Ibm2) has been stabilized
using the substrate induced strain. The structure and microstructure of this
metastable cobaltite is further discussed and compared to related bulk
materials based on our transmission electron microscopy investigationsComment: 13 pages, 10 figures, 2 tables, accepted in Phys. Rev.
SPORT: A new sub-nanosecond time-resolved instrument to study swift heavy ion-beam induced luminescence - Application to luminescence degradation of a fast plastic scintillator
We developed a new sub-nanosecond time-resolved instrument to study the
dynamics of UV-visible luminescence under high stopping power heavy ion
irradiation. We applied our instrument, called SPORT, on a fast plastic
scintillator (BC-400) irradiated with 27-MeV Ar ions having high mean
electronic stopping power of 2.6 MeV/\mu m. As a consequence of increasing
permanent radiation damages with increasing ion fluence, our investigations
reveal a degradation of scintillation intensity together with, thanks to the
time-resolved measurement, a decrease in the decay constant of the
scintillator. This combination indicates that luminescence degradation
processes by both dynamic and static quenching, the latter mechanism being
predominant. Under such high density excitation, the scintillation
deterioration of BC-400 is significantly enhanced compared to that observed in
previous investigations, mainly performed using light ions. The observed
non-linear behaviour implies that the dose at which luminescence starts
deteriorating is not independent on particles' stopping power, thus
illustrating that the radiation hardness of plastic scintillators can be
strongly weakened under high excitation density in heavy ion environments.Comment: 5 figures, accepted in Nucl. Instrum. Methods
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Stakeholder involvement in redefining Hanford`s Double-Shell Tank waste disposal program
Hanford`s Double-Shell Tank (DST) waste disposal program was redefined following serious challenges to the viability of the previous strategy due to increased regulatory requirements and operating expectations. Redefinition of the DST waste disposal program involved a far-reaching set of decisions and actions. A formal stakeholder involvement process was used to bring the concerns of outside groups into the definition and evaluation of alternative tank waste disposal strategies, broadening the participation and ownership of the revised program
Thickness-dependence of the electronic properties in V2O3 thin films
High quality vanadium sesquioxide V2O3 films (170-1100 {\AA}) were grown
using the pulsed laser deposition technique on (0001)-oriented sapphire
substrates, and the effects of film thickness on the lattice strain and
electronic properties were examined. X-ray diffraction indicates that there is
an in-plane compressive lattice parameter (a), close to -3.5% with respect to
the substrate and an out-of-plane tensile lattice parameter (c) . The thin film
samples display metallic character between 2-300 K, and no metal-to-insulator
transition is observed. At low temperature, the V2O3 films behave as a strongly
correlated metal, and the resistivity (\rho) follows the equation \rho =\rho_0
+ A T^2, where A is the transport coefficient in a Fermi liquid. Typical values
of A have been calculated to be 0.14 \mu\Omega cm K^{-2}, which is in agreement
with the coefficient reported for V2O3 single crystals under high pressure.
Moreover, a strong temperature-dependence of the Hall resistance confirms the
electronic correlations of these V2O3 thin films samples.Comment: 4 pages, 4 figure
Absence of long-range Ni/Mn ordering in ferromagnetic La2NiMnO6 thin films
Epitaxial La2NiMnO6 thin films have been grown on (001)-oriented SrTiO3 using
the PLD technique. The thin films are semiconducting and FM with a TC close to
270K, a coercive field of 920Oe, and a saturation magnetization of 5muB per
f.u. TEM, conducted at RT, reveals a majority phase having "I-centered"
structure with a=c=1.4asub and b=2asub along with a minority phase-domains
having "P-type" structure (asub being the lattice parameter of the perovskite
structure). A discusion on the presence of Ni/Mn long-range ordering, in light
of recent literature on double perovskites La2NiMnO6 is presented.Comment: To be published in Applied Physics Letter
Energy deposition by heavy ions: Additivity of kinetic and potential energy contributions in hillock formation on CaF2
The formation of nano-hillocks on CaF2 crystal surfaces by individual ion
impact has been studied using medium energy (3 and 5 MeV) highly charged ions
(Xe19+ to Xe30+) as well as swift (kinetic energies between 12 and 58 MeV)
heavy ions. For very slow highly charged ions the appearance of hillocks is
known to be linked to a threshold in potential energy while for swift heavy
ions a minimum electronic energy loss is necessary. With our results we bridge
the gap between these two extreme cases and demonstrate, that with increasing
energy deposition via electronic energy loss the potential energy threshold for
hillock production can be substantially lowered. Surprisingly, both mechanisms
of energy deposition in the target surface seem to contribute in an additive
way, as demonstrated when plotting the results in a phase diagram. We show that
the inelastic thermal spike model, originally developed to describe such
material modifications for swift heavy ions, can be extended to case where
kinetic and potential energies are deposited into the surface.Comment: 12 pages, 4 figure
Swift heavy ion-irradiated multi-phase calcium borosilicates: implications to molybdenum incorporation, microstructure, and network topology
Abstract: A series of calcium borosilicate glasses with varying [B2O3], [MoO3], and [CaO] were prepared and subjected to 92 MeV Xe ions used to simulate the damage from long-term α-decay in nuclear waste glasses. Modifications to the solubility of molybdenum, the microstructure of separated phases, and the SiâOâB network topology were investigated following five irradiation experiments that achieved doses between 5 Ă 1012 and 1.8 Ă 1014 Xe ions/cm2 in order to test the hypotheses of whether irradiation would induce, propagate, or anneal phase separation. Using electron microscopy, EDS analysis, Raman spectroscopy, and XRD, irradiation was observed to increase the integration of MoO42â by increasing the structural disorder within and between heterogeneous amorphous phases. This occurred through Si/B-O-Si/B bond breakage and reformation of boroxyl and 3/4-membered SiO4 rings. De-mixing of the SiâOâB network concurrently enabled cross directional Ca and Mo diffusion along defect created pathways, which were prevalent along the interface between phases. The initiation and extent of these changes was dependent primarily on the [SiO2]/[B2O3] ratio, with [MoO3] having a secondary effect on influencing the defect population with increasing dose. Microstructurally, these changes to bonding caused a reduction in heterogeneities between amorphous phases by reducing the size and increasing the spatial distribution of immiscible droplets. This general increase in structural disorder prevented crystallization in most cases, but where precipitation was initiated by radiation, it was re-amorphized with increasing dose. These outcomes suggest that internal radiation can alter phase separation tie lines, and can therefore be used as a tool to design certain structural environments for long-term encapsulation of radioisotopes
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