Tuesday 9 July 2013, Strathblane & Cromdale Halls, 16:30-18:30
Poster session A - Electronic and nuclear materials
P.021 SANS studies on the Internal nano-morphology in bulk and ordered heterojunction organic photovoltaics
K Char1, J Ko2, W T Choi2, T-H Kim3 and Y-S Han3
1
Seoul National University, Korea, 2The National Creative Research Initiative Center for Intelligent Hybrids, The WCU
Program of Chemical Convergence for Energy & Environment, School of Chemical & Biological Engineering, Seoul
National University, Korea, 3HANARO Center, Korea Atomic Energy Research Institute, Korea
The recent research interest of our group has been focused on the development of functional thin films based on
organic functional materials. In order to satisfy specific requirements for specific applications, materials
components should have unique nanoscale spatial arrangements within thin films to achieve desired functions and
properties. Most notably in the case of organic photovoltaics (OPVs), the nanomorphology is known to critically
influence the performance of the devices. In the present study, we elucidate the correlation between
nanomorphology and performance by using both the bottom up and the top down method which are frequently
used to control the nanostructure in OPVs. We have systematically varied phase separated structures based on new
additives, which could increase the poly[3-hexylthiophene] (P3HT) crystallinity as well as adjust the domain size of
phenyl-C61-butyric acid methyl ester (PCBM) phase, as a bottom up approach. As the results, we obtained the
maximum power conversion efficiency of 3.24%, which shows the 43% enhancement as compared to the reference
without additives. In addition, based on the patterning with AAO templates, we examine the effect of diffusion of
PCBM competing with the recrystallization of P3HT on nanostructure as well as on the device performance. We
performed the small angle neutron scattering (SANS) to characterize the nano-morphology of P3HT:PCBM
nanoblends. Smaller nanodomains of PCBM agglomerates caused by the addition of the new additive as well as the
smeared nano-patterns caused by PCBM diffusion was effectively measured by SANS. These fundamental
characterizations based on SANS would give us new insight on understanding and designing hierarchical structures
for OPVs.
P.022 Understanding the mechanism of low thermal conductivity of CrN with rock salt structure
S Christensen1, C X Quintela2, B Rivas-Murias2, M Jørgensen1, H Mutka3, F Rivadulla2 and M Christensen1
1
Aarhus University, Denmark, 2University of Santiago de Compostela, Spain, 3ILL, France
Abstract unavailable
P.023 Phase morphology in poly(thiophene)- fullerene thin film devices
N Deb1, D Bucknall1, A Karim2, X Gong2, B Sumpter3 and M Skoda4
1
Georgia Institute of Technology, USA, 2University of Akron, USA, 3Oak Ridge National Laboratory, USA, 4Rutherford
Appleton Laboratory - ISIS, UK
Organic photovoltaic devices are promising inexpensive technologies, and source of future energy needs. Thin film
bulk heterojunction (BHJ) systems consisting of fullerenes dispersed in conjugated polymers are popular material
candidates for the same and can also be easily chemically tuned to change the interactions and properties. The
inherent morphology in BHJs is thus dependent on a number of parameters such as polymer-fullerene interaction,
degree of crystallinity, which make them highly versatile, but difficult to study rationally not least because of kinetic
factors associated with processing.
ICNS 2013 International Conference on Neutron Scattering
To understand the underlying morphological and phase behaviour, we have used neutron reflection (NR) and
grazing incidence small angle neutron scattering (GISANS) to study model BHJ films in which processing effects
have been carefully controlled. We have studied a set of model BHJ films in full device configuration, based on
mixtures of different poly(3-alkyl thiophene)s (P3BT, P3HT and P3OT) and fullerenes (C60, PCBM and bis-PCBM) i.e.
with varying side-chains. To study crystallinity effects, we also prepared these devices with an additive (1, 8octanedithiol).
Depth profile analysis using NR showed the presence of varying amounts of segregated fullerene at both the top (Al)
and bottom (PEDOT:PSS) electrodes, with intermixing at the Al-BHHJ interface. GISANS data also shows that the
phase domain morphology laterally also varies as a function of depth through the film. These results show that the
vertical composition and morphological factors strongly correlate to specific characteristics of the device
performance.
This fundamental study allows us an understanding of the complex interplay between phase morphology, kinetics,
and the effect on electronic properties, and will subsequently let us develop more efficient and viable solar devices
and related technologies of the future.
P.024 Enhanced thermoelectric performance in arc-melted TiNiSn
R Downie1, D MacLaren2, R Smith3 and J-W Bos1
1
Heriot-Watt University, UK, 2University of Glasgow, UK, 3ISIS, UK
Thermoelectric energy generation by harvesting waste heat offers the possibility of increasing the efficiency of any
heat generating process. Intermetallic half-Heusler phases have attracted considerable interest in this field due to
their naturally high Seebeck coefficients (S) and low resistivity (r). Reduction of the thermal conductivity (k) is the
focus of much of the research into these phases so that large thermoelectric figures of merit ZT = (S2/rk)T may be
obtained. The literature, however, contains a large scatter in k-values for nominally identical samples, which may be
linked to differences in experimental composition and structure, but this information is often not provided.
We used arc-melting to prepare TiNiSn based half-Heusler samples, and found that these have an unusually low k
= 4 W m-1 K-1 [1]. This leads to ZT = 0.5 at 700 K for TiNiSn0.95 and ZT = 0.6 at 700 K for TiNiSn. Rietveld analysis of
neutron powder diffraction data revealed that the actual compositions of these samples are TiNi 1.06Sn and TiNi1.03Sn
with the excess Ni located on a vacant interstitial site. The non-stoichiometry is facilitated by kinetic constraints
during the synthesis, and coincides with the presence of TiNi2Sn and Ti5Sn3 impurity phases. The low k-values
suggest that the excess Ni may have phase separated but preliminary HRTEM data show no evidence for
nanostructuring.
[1]
R. A. Downie, D. A. MacLaren, R. I. Smith and J. W. G. Bos, Chem. Comm. (2013)
DOI:10.1039/c2cc37121a
P.025 Irradiated-amorphous state of rapidly quenched alloys R2Fe14B (R=Nd, Er)
A Pirogov1, Y Chukalkin1, S Bogdanov1, N Kudrevatykh2, A Gubkin1 and A Teplykh1
1
Institute of Metal Physics - Ural Branch of the Russian Academy of Sciences, Russia, 2Ural Federal University,
Russia
The permanent magnets based on the Nd2Fe14B phase possess record value of maximal energy product. A possible
way to increase the maximal energy product is to synthesize the composite system where exchange coupled
crystalline and amorphous phases coexist. Along with conventional liquid quenching the amorphous state can be
reached by means of fast neutrons irradiation. We present the results of neutron diffraction study and magnetic
measurements on the amorphous Nd2Fe14B and Er2Fe14B samples irradiated by fast neutrons with the fluence of
1.2×1020 n/cm2. It has been found that both samples irradiated completely loose the long-range structural and
ICNS 2013 International Conference on Neutron Scattering
magnetic order. However, a few narrow Bragg reflections, ascribed to the Fe a-phase, were observed in neutron
powder diffraction patterns. The magnetic measurements revealed that amorphization of the Nd2Fe14B sample leads
to the coercive force falling down to nearly zero, while the saturation magnetization almost keeps its value. Thus, the
magnetization of irradiated Nd2Fe14B particles can be easily aligned by exchange field and increase the total
magnetization of composite material. In case of Er2Fe14B the Curie temperature reduces its value by 200 K and the
saturation magnetization at room temperature becomes two times as less. This work was supported by RFBR project
No. 12-02-12065.
P.026 Study of the aging behavior of materials important in nuclear energy field - Incoloy 800 HT and 304L steelusing neutron scattering techniques
I Ionita1, M M Balasoiu2, G Bokuchava3, A Kuklin3, G Torok4, D Soloviev3, M Fulger1 and P Beran5
1
Institute for Nuclear Research Pitesti, Romania, 2Horia Hulubei National Institute of Physics and Nuclear
Engineering, Romania, 3Joint Institute of Nuclear Research, Dubna, Russia, 4KFKI, Hungary, 5Neutron Physics
Institute Rez, Czech Republic
The 800 HT Incoloy is widely used in power generation for steam generators tubing and high temperature heat
exchangers for gas cooled nuclear reactors and as a candidate material for fuel cladding in GEN IV reactors. The
304L steel has a high ductibility. Low yield stress and high tensile strength and is used widely in nuclear power
plant.
There were manufactured 4 samples of Incoloy 800HTand 4 samples of 304L steel, all of 2x15x25mm dimensions
and standing a heat treatment of 60 days at 450, 500, 550 and 600 degrees respectively.
The samples were investigated by neutron diffraction and small angle neutron scattering at the FSD, HRFD and
MEREDIT diffractometers, YuMO-SANS and KFKI SANS spectrometers (in function at IBR-2 reactor, Dubna,
respectively Budapest). Lattice cell and peak width parameters changes for both sample series (using neutron
diffraction measurements) together with information on heat treatment effects concerning precipitate size and
volume distribution of alloying elements (using SANS measurements) were found.
Structural properties of the above mentioned materials of significant importance in nuclear energy field, revealed
through high temperature heat treatment are described.
P.027 The structural aspects of optical properties forming in Y 3Al5O12:Ce3+ phosphors
S Kichanov1, E Frolova2, G Shevchenko2, D Kozlenko1, A Belushkin1, G Malashkevich3 and B Savenko1
1
Joint Institute for Nuclear Research, Russia, 2Research Institute for Physical Chemical Problems - Belarusian State
University, Belarus, 3B.I.Stepanov Institute of Physics NASB, Belarus
The features of crystal structure of phosphors Y3Al5O12:Ce3+/Lu2O3(Lu2O3:Ce3+) obtained colloid-chemical method
have been studied by means of neutron diffraction at room temperature and those structural and luminescence
properties as function of method Lu2O3 doping studies have been performed. The studies were shown that for
samples obtained in nonequilibrium conditions are characterised by the Stokes shift and high intensity of
luminescence. This fact has been caused by disordering of crystal structure due stable associate-defects forming.
ICNS 2013 International Conference on Neutron Scattering
P.028 Magnetic short-range order in Ho5Pd2 with large magnetocaloric effect
H Kitazawa1, Y Kawamura2, L Keller3, N Terada1, H Mamiya1, H S Suzuki1, A Doenni1, S Toyoizumi4, N Metoki5, K
Kaneko5, N Igawa5 and A Tamaki4
1
National Institute for Materials Science (NIMS), Japan, 2CROSS-Tokai, Japan, 3Paul Scheller Institute,
Switzerland, 4Tokyo Denki University, Japan, 5JAEA, Japan
In recent years, more efficient magnetic refrigerant materials are desired due to potential application in energyefficient environment-friendly refrigeration technology. Samanta et al. discovered that the rare-earth compound
Ho5Pd2 has a large magnetocaloric effect (MCE)[1]. The most interesting point is that the large MCE is originated
from field-induced metamagnetic transition below antiferromagnetic transition temperature TN of 28 K. However, it is
not easy to judge whether Ho5Pd2 is antiferromagnetic or not only from magnetization. In order to determine the
magnetic structure, neutron diffraction is most powerful technique. We have performed neutron powder diffraction
experiments of polycrystalline Ho5Pd2 at JRR-3, Tokai, Japan and at SINQ, PSI, Switzerland. We could not observe
sharp magnetic Bragg peaks, but rather broad peaks below 28 K. We could partly index the magnetic peaks with a
propagation vector k = (δ, δ, δ) (δ = 0.18) which are gradually developing below about 100 K. These results
indicate that Ho5Pd2 showed the short-range magnetic correlation with a propagation vector k = (0.18, 0.18,
0.18). This short-range magnetic correlation must have some relation with the specific crystal structure of Ho5Pd2.
Because Ho5Pd2 has three crystallographic sites in a unit cell. Ho1 at 48f is fully occupied. However Ho2, Ho3 and
Pd at 32e are partially occupied.
[1]
T. Samanta, I. Das, S. Banerjee, Appl. Phys. Lett. 91, 082511 (2007)
P.029 SANS studies on the effect of additives on morphological changes in bulk heterojunction organic solar cells
J Ko1, W T Choi1, T-H Kim2, Y-S Han2 and K Char1
1
The National Creative Research Initiative Center for Intelligent Hybrids, The WCU Program of Chemical Convergence
for Energy & Environment, School of Chemical & Biological Engineering, Seoul National University, Korea, 2HANARO
Center, Korea Atomic Energy Research Institute, Korea
Despite recent rapid developments in OPVs, the OPVs still struggle with low device performance compared with the
inorganic counterparts due to their short exciton diffusion length as well as low charge mobility. As a result, the
morphology of BHJ films critically influences on the performance of devices. In order to obtain favorable
(nano)morphology of BHJ films, there have been reports on using self-organized poly[3-hexylthiophene]s (P3HT),
called as P3HT nanowires, to create continuous and percolated pathways as well as to enhance the crystallinity of
P3HT. However, there is a lack of studies on the control of the domain size of phenyl-C61-butyric acid methyl ester
(PCBM) surrounding the P3HT nanowires. In the present study, we report the effect of crystallinity, domain size and
interface structure on the performance of OPV devices based on a new additive, which could increase the P3HT
crystallinity and, at the same time, adjust the domain size of PCBM phase. We performed the small angle neutron
scattering (SANS), which has the spatial resolution ranging from a few to thousands of nanometers to characterize
the nano-morphologies of P3HT:PCBM blends. The SANS results showed that by keeping the P3HT solubility low in
the blend solution, higher P3HT crystallinity was achieved. At the same time, the increase in PCBM solubility led to
smaller nanodomains of PCBM agglomerates. Based on the morphological variations by the new additive,
P3HT:PCBM BHJ solar cell devices were fabricated and the maximum power conversion efficiency of 3.24% was
achieved with the addition of the new additive, which shows the 43% enhancement in power conversion efficiency
when compared with the reference sample without additives.
ICNS 2013 International Conference on Neutron Scattering
P.030 Diffuse scattering from disordered multi-vacancy clusters in sodium cobaltate
D Porter1, D J P Morris2, M Roger3, M J Gutmann4, S Uthayakumar1, M S Pandiyan1, D F Bowman1, D Prabhakaran5,
D A Tennant2 and J P Goff1
1
Royal Holloway University of London, UK, 2Helmholtz-Zentrum Berlin fur Materialien und Energie, Germany, 3Service
de Physique de l'Etat Condensé, CEA Saclay, France, 4ISIS Facility, Rutherford Appleton Laboratory,
UK, 5Department of Physics, University of Oxford, UK
Sodium cobaltate (NaxCoO2) has emerged as a material of exceptional scientific interest due to the potential for
thermoelectric applications, and for use in rechargeable batteries in portable electronics. Single-crystal neutron
Laue diffraction measurements on SXD at ISIS revealed a kaleidoscope of superlattice patterns as a function of
sodium concentration,x, due to the stabilization of multi-vacancy clusters that order long range at simple fractional
fillings. As the temperature is raised there is a sodium reordering transition from the fully-ordered superstructures to
a partially ordered stripe phase close to room temperature. The superlattice patterns disappear at elevated
temperature, and we observe diffuse neutron scattering in this disordered phase. Our Monte Carlo simulations show
that the diffuse scattering arises from short-range ordering of the multi-vacancy clusters. The sodium vacancy
ordering plays a decisive role in both the thermoelectric properties and the diffusion, and we show that the multivacancy clusters continue to be important at the elevated temperatures relevant to power recovery applications.
P.031 Cation partitioning and thermoelectric properties of shandites
A Powell1, J Corps2 and P Vaqueiro2
1
University of Reading, UK, 2Heriot-Watt University, UK
Materials of general formula Co3M2S2 (M = Sn, In), which adopt the shandite structure, exhibit promising
thermoelectric properties at modest temperatures, suggesting they may be candidates for energy recovery from lowgrade waste heat. The structure consists of sheets of metal atoms with the Kagome-type topology stacked in an ABC
fashion. Triangular arrays of cobalt atoms in adjacent layers generate trigonal anti-prismatic inter-layer sites. Each
of the Co3 triangles is capped above and below the Kagome sheets by a sulphur atom. M atoms are distributed over
M(2) sites in the Kagome layers and M(1) inter-layer sites.
The tin- and indium-containing ternary phases exhibit metallic behaviour: the former having been identified as a
half-metallic ferromagnet (TC = 177 K). Progressive substitution in the series, Co3Sn2-xInxS2 (0 ≤ x ≤2) provides a
means of controlling the electron count, thereby tuning the electrical transport properties and hence thermoelectric
power factor. The series shows a double metal-semiconductor-metal transition with increasing levels of indium
incorporation, with the optimum thermoelectric properties occurring at compositions just prior to the onset of
semiconductivity. DFT calculations suggest that semiconductivity in the quaternary phase, Co 3SnInS2, requires
complete ordering of main-group metals over M(1) and M(2) sites. We have exploited the contrast between tin and
indium afforded by neutron methods to establish the metal-atom distribution as a function of indium substitution in
this series. The results demonstrate that whilst complete partitioning is not observed, indium atoms preferentially
occupy M(1); the extent of this preference varying with composition.
ICNS 2013 International Conference on Neutron Scattering
P.032 Synthesis of mixed-metal garnets and their study by neutron diffraction
R Skaudzius1, A Akelis1, A Katelnikovas1, I Bogdanoviciene1, T Juestel2, C Rueegg3, D Sheptyakov3 and A Kareiva1
1
Vilnius University, Lithuania, 2University of Applied Science Muenster, Germany, 3Paul Scherrer Institut, Switzerland
The Ln3+ doped garnet materials are important components in light-emitting diodes (LEDs), fluorescence lamps (FL),
cathode ray tubes (CRTs), field emission displays (FEDs), electroluminescence displays (ELDs) and plasma display
panels (PDPs). It is known that the chemical composition and structure of the host materials influence the optical
properties of such materials considerably. Yttrium aluminium garnet (YAG) is widely used as the core host material
in luminescence. Therefore, in the present work the matrices of garnet structure compounds are modified by
replacing different molar parts of aluminium by chromium or indium in YAG. The sinterability and microstructural
evolution of mixed-metal Y3Al5-xMxO12 (M= Cr or In) garnets are investigated. Moreover, Y3Al5-x(In,Cr)xO12 samples are
employed as host materials for luminescence by doping with Ce3+, Eu3+, Er3+ or Tb3+ ions and new series of garnets,
phosphates and silicates are synthesized to investigate Eu3+ emission in more detail. X-ray and neutron diffraction
techniques are used for phase identification and refinement of the crystal structures. The luminescence properties of
the synthesized samples are characterized by VUV and UV/Vis spectroscopy. Investigation of the optical properties
of mixed-metal garnets in combination with the diffraction results demonstrates that the Ln3+ emission is slightly
dependent on the Y3Al5-xInxO12 matrix, while in the Y3Al5-xCrxO12 matrix chromium emission is obtained and
Ln3+emission is quenched.
P.033 Local and average structures of hydrogen loaded Pu-Ga alloys
A I Smith, K L Page, S Richmond, J Siewenie, T A Saleh, F Hampel, M Ramos, A Llobet-Megias, J N Mitchell and D S
Schwartz
Los Alamos National Laboratory, USA
Plutonium phase stability and phase transformations are critical for applications, but despite many years of
extensive research, the stabilizing mechanisms induced by additions (Ga, Al, Ce, Am, In) are still not well
understood. Of particular interest for these applications is the face-centered cubic δ-phase, with unusual properties
(negative thermal expansion coefficient, volume expansion, large low-temperature electronic specific heat, volume
expansion).
Metal-hydrogen alloys, at high temperature and high hydrogen pressures, form metal vacancies, called
superabundant vacancies (SAV) [1, 2]. SAVs play a role in the stability of the M-H system, enhance the M-atom
diffusion and creep, and have influence on mechanical, physical and chemical properties. Hydrogen solubility
studies of the Pu-H system showed that conditions for SAVs formation are favorable, and below 525°C hydrogen
atoms form Pu-Vac-H clusters [3,4].
We present results of an experimental study of the local structure/short- and medium-range order around the
plutonium and gallium atoms in δ-PuGa alloys, hydrogen-charged and uncharged, by total scattering technique, for
a better understanding of the SAVs formation mechanism. Diffraction patterns and pair distribution function data
were collected on the Neutron Powder Diffractometer (NPDF) at the Los Alamos Neutron Scattering Center, Los
Alamos National Laboratory.
[1]
[2]
[3]
[4]
Y. Fukai J. Alloys and Compounds 356-357 (2003) 263-269
Y. Fukai and N. Nobuyuki, Phys. Rev. Letters, 37 (1994), 12, 1640
J. Ward and JM Hashke Handbook on the Physics and Chemistry of Rare Earth vol 18
S. Richmond et al, 2010 IOP Conf. Ser.: Mat. Sci. Eng. 9 (2010) 012036
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P.034 Analysis of SANS measurements on highly irradiated15H2MFA steel
G Torok1, A Ulbricht1,2, G Török1, F Gillemot3, F Bergner2 and A Wagner2
1
Wigner Research Centre for Physics of Hungarian Academy of Sciences, Hungary, 2Helmholtz-Zentrum DresdenRossendorf, Germany, 3Centre for Energy Research -Hungarian Academy of Sciences, Hungary
A 15H2MFA type VVER440 rpv forging material in the unirradiated reference condition (code: ZAI) and three
different irradiation conditions up toneutron fluences of 2.94x1020, 9.52x1020 and 14.5x1020 cm-2 (E> 0.5 MeV),
respectively, were investigated by SANS at the Budapest Research Reactor
The size distributions of the clusters were calculated using the indirect Fourier transform method, using the Glatter
method. The absolute value of volume fraction of clusters is estimated under the assumption that the clusters are
non-magnetic scatterers, This nuclear scattering contrast can vary for different irradiation levels. Differences in
scaling of both magnetic and nuclear size distributions give a hint of different cluster composition. Information about
the cluster composition is included in the A-ratio. Primary, the A-ratio was defined by the ratio of the SANS
intensities perpendicular and parallel to the magnetic field direction. In practice, we observe a Q-dependence of the
A-ratio.
We observed a difference in the scaling of the magnetic and nuclear size distributions. The reason of this difference
is discussed.
P.035 In-situ Electrochemical Neutron Reflectometry Study of
M Vezvaie1, J Noël2, Z Tun1 and C Wren2
1
Canadian Neutron Beam Centre, Canada, 2University Of Western Ontario, Canada
The understanding of the reaction mechanism of silver/silver oxides (Ag/Ag2O) with halide (I-, Cl-, etc.) is important
for a range of industrial applications such as the immobilization/release of radioiodine isotopes in cancer therapy ,
radioiodine containment following a severe accident at a nuclear reactor, and nuclear safety analysis.
Here we employed in-situ electrochemical neutron reflectometry (EC-NR) to a) investigate whether the Ag2O/AgI
conversion mechanism follows a distinct layer-by-layer mechanism and b) determine the relative locations of Ag2O
and AgI films at the Ag/Ag2O/AgI interfaces. The anodic oxidation of a Ag film at 0.25 and 0.6 VSCE in 0.2 M KOH
solution resulted in the growth of a rough Ag2O, film followed by significant dissolution of the Ag film. After
anodization, the roughness of the Ag2O/electrolyte interface was much more than the roughness of the Ag/Ag2O
interface. The data did not support the distinct formation of Ag2O and AgI layers on the electrode surface during the
conversion reaction but revealed that the Ag2O porosity allows diffusion of I- through the oxide layer to the Ag
surface. With such diffusion occurring, before the completion of the conversion reaction, the coupling
electrochemical mechanism was observed. After a timely period, when the Ag 2O was replaced by AgI, the electrode
potential became defined by the Ag/AgI/ I- equilibrium.
P.036 Quasi-one-dimensional phonon anomaly in the narrow-gap semiconductor FeSb2
I Zaliznyak1, C Petrovic1, R Hu2, A Savici3, O Garlea3 and B Winn3
1
Brookhaven National Laboratory, USA, 2Boston College, USA, 3Oak Ridge National Laboratory, USA
The narrow-gap semiconductor FeSb2 reveals a variety of unusual properties, ranging from the temperature-induced
electronic paramagnetism to one-dimensional (1D) metallic conductivity at temperatures below 300 K and down
to 30 K, and to giant thermoelectric power factor [1-3]. While it is generally acknowledged that these properties
result from the tight balance between strong covalent hybridization, electronic correlation and the tendency to band
ICNS 2013 International Conference on Neutron Scattering
delocalization, what exactly are the mechanisms leading to these unusual behaviors remain unclear. In particular, it
is a matter of current debate, whether the giant thermoelectric figure of merit observed in FeSb 2 obtained under
specific synthesis conditions can be explained by a purely correlated-electronic mechanism, or it results from
peculiar interaction of electrons with the lattice vibrations - such as the phonon drag effect. Here we present the
inelastic neutron scattering survey of the phonon spectra in FeSb2 using the newly built HYSPEC spectrometer at the
SNS. It reveals phonon dispersions of one-dimensional character, which mirror the 1D metallicity along the b-axis.
Moreover, these dispersions undergo dramatic changes in the temperature range where electronic paramagnetism
emerges. Our observations indicate giant electron-phonon coupling, which is hidden at low temperature, but
emerges upon heating, when the conduction bands become thermally populated.
[1]
[2]
[3]
C. Petrovic, et al., Phys. Rev. B 67, 155205 (2003)
Qing Jie, et al., Phys. Rev. B 86, 115121 (2012)
I. A. Zaliznyak, et al., Phys. Rev. B 83, 184414 (2011)
P.037 Structure of nuclear graphite characterized by neutrons: from atomic to macroscopic scales
Z Zhou1, Wim Bouwman1, Henk Schut1, Catherine Pappas1, Florence Porcher2, Sylvain Desert2, Jacques Jestin2,
Maureen Haverty3, Paul Mummery3 and Stefan Hartmann4
1
Delft University of Technology, The Netherlands, 2Laboratoire Léon Brillouin, France, 3University of Manchester,
UK, 4Paul Scherrer Institute, Switzerland
Nuclear graphite is an important material used as moderator in nuclear reactors. It has a complicated structure and
there is lacking interpretation for the structural information of bulk material. By combining neutron diffraction, small
angle neutron scattering and neutron imaging we obtain unique understanding on the structure from atomic to
macroscopic length scales. First results obtained on non-irradiated specimens show the importance of structural inhomogeneities and stacking faults. Neutron diffraction spectra are best fit by a model, which includes the
probabilities of random and registered translations parallel to adjacent carbon layers. A high concentration of
stacking faults is present. By combining several small angle neutron scattering techniques (SANS, VSANS and
SESANS) the pore structure, which plays an important role in properties changing during neutron irradiation, is seen
over 4 orders of magnitude in length: typically from 1 nanometer to 10 micrometers. The results indicate that
nuclear graphite has a surface fractal structure with fractal dimension around 2.5. Neutron tomography
complements these results and provides structural information at length scales up to millimeters. We discuss these
experimental results, which quantify the disorder on the atomic and macroscopic structure and will eventually lead
to a better understanding of the interplay between structure and irradiation damage.
ICNS 2013 International Conference on Neutron Scattering