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An understanding of the effects of doping in lead perovskites may allow for improved solar cell performance or reduction in toxicity of the materials used. Ba2+ doped CH3NH3PbI3 (CH3NH3Pb1−xBaxI3 with x = 1%, 5% and 10%) are successfully synthesized by cooling down a concentrated aqueous solution containing HI, CH3NH2 and metal acetates and their properties are investigated using x-ray diffraction, differential scanning calorimetry, and impedance spectroscopy (IS). No new structures are formed upon doping with Ba2+ ions, however the lattice expands. The IS measurements show a strong increase in the conductivity and dielectric constants of the doped crystals. The conductivity arises mainly from vacancy mediated iodide ion (I−) migration and the increase in ionic conductivity with dopants is ascribed to increased defect formation due to lattice distortion. In addition, the bulk dielectric constant increases with increasing Ba2+ dopant. The increase in the dielectric constant is consistent with ordering of CH3NH3 dipoles resulting from distortions of the Ba sites in the lattice. The temperature dependence of the dielectric constants is attributed to thermal effects on the orientation of CH3NH3 molecules.

We report on the properties of single crystals of Pr0.5Ir4Sb10.2Sn1.8, a new partially-filled rare earth skutterudite which exhibits Kondo alloy and heavy fermion behavior. Using magnetic susceptibility, specific heat, and resistivity measurements we find evidence of Kondo-screening of the f-moments. This material shows a Kadowaki-Woods ratio consistent with heavy fermion behavior. Susceptibility measurements predict a Kondo temperature T K ≈ 4 K , however the minimum found in the low temperature resistivity appears at a higher temperature T ≈ 10 K . A small fraction of the material ( 0.5 % ) becomes superconducting with a critical temperature T c ≈ 4.2 K .

Article history:Received 13 August 2014Accepted 15 September 2014Available online 20 September 2014Keywords:High dielectric constantCopper phthalocyaninePolarization mechanisms Thedielectricpropertiesofcopperphthalocyanine-3,4′,4″,4‴-tetrasulfonicacidtetrasodiumsalt(CuPc_TS)andcopperphthalocyanineoctacarboxylicacid(CuPc*)wereinvestigatedfrom20Hzto1MHzwithrelativehumid-ityfrom0to75%.AdielectricconstantN10 6 wasfoundat1kHzand20%humidityforthemodifiedcopperphtha-locyanines. Humidity increases the dielectric constant, which is attributed to increasing ionization of theperipheral groups as the water enters into the samples.© 2014 Published by Elsevier B.V. 1. IntroductionSince 1948 when Eley discovered the semiconducting property ofphthalocyanines (Pc's) [1], these compounds have become one of themost investigated organic semiconductors [2] due to their high chemi-cal stability and electrical properties. They have found applicationsin fuel cells [3–5], organic photovoltaics [6–8],organicfield effect tran-sistors (as a gate dielectric) [9,10], and humidity and chemical sensors[11,12].Pc'selectronicandopticalpropertiescanbetunedbysubstitut-ing the central metal atom, the peripheral group or by adding dopants.Metal phthalocyanines (MePcs) can have a wide variety of metalatoms at the center of the molecule. One of the most widely studiedMePcsiscopperphthalocyanine(CuPc),showninFig.1a.TheCuPcmol-eculedoesnothaveadipolemomentbecauseofitssymmetry;howeverthe large delocalization of the π-electrons within the phthalocyaninering leads to a high electronic polarizability of 1.2 × 10

The stability of small molecule copper phthalocyanine bilayer organic solar cells (ITO/PEDOT:PSS/CuPc/PTCDI/Ag) was investigated without encapsulation for 70 days. Photovoltaic performance characteristics were measured as a function of the age of solar cells without illumination (except during testing) under vacuum, dry air (0% humidity), and standard air conditions. The solar cells exposed to dry air and standard air atmosphere showed a rapid degradation in their efficiencies during the measured period. It was found that oxygen has a strong negative influence on the efficiency even in the absence of humidity. In vacuum, we observed a small increase in the performances of organic solar cells for the first days, possibly due to removal of oxygen from the cells, followed by a minor degradation over the measurement period. Moving the cell from vacuum into a dry oxygen atmosphere led to rapid degradation in their efficiencies. A film of CuPc layer exposed to air results in a steady increase in the resistivity of the device.

Half-filled electron systems, even with the maximized spin angular moment, have been given little attention because of their zero-orbital angular moment according to Hund's rule. Nevertheless, there are several measurements that show evidence of a nonzero orbital moment as well as spin-orbit coupling. Here we report for the first time the orbital order in a half-filled 4f-electron system GdB_{4}, using the resonant soft x-ray scattering at Gd M_{4,5}-edges. Furthermore, we discovered that the development of this orbital order is strongly coupled with the antiferromagnetic spin order. These results clearly demonstrate that even in half-filled electron systems the orbital angular moment can be an important parameter to describe material properties, and may provide significant opportunities for tailoring new correlated electron systems.

MERIX (Medium Energy Resolution Inelastic X-ray Scattering) is an instrument for Resonant Inelastic X-ray Scattering (RIXS) studies, in the hard X-ray regime, designed to work with photons in the 5–12 keV range, spanning atomic resonances near the K-edges of 3d elements, and the L-edges of 4f and 5d elements. The energy analysis of inelastically scattered photons is performed with segmented spherical crystal analyzers in close to Bragg backscattering geometry. For each resonance (edge) a specially designed analyzer is used, fabricated from Ge, Si, or LiNbO 3 crystals. MERIX uses a position sensitive (micro-strip) detector to take snapshots of IXS spectra which are dispersed in space and over an energy range of a few eV with ≃20–40 meV energy resolution. The spectral resolution of the MERIX spectrometer depends on the analyzer and varies from ≃45 meV to ≃170 meV, while the momentum transfer resolution is ≃1–4 nm −1 . Samples are illuminated by micro-focused beams of size ≃10 μm × 45 μm, allowing for studies at high-pressure and other extreme conditions. Polarization selectivity is ensured by vertical or horizontal momentum transfer scans. MERIX features ≃100 times higher count-rates compared to previously built RIXS instruments.

Unencapsulated small molecular solar cells with a layer of carboxylated copper phthalocyanine (CuPc⁎) introduced between the donor copper phthalocyanine (CuPc) and acceptor 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDI), and using ITO and Ag as the cathode and anode were investigated for 35 days. The performance and stability were compared between traditional ITO/PEDOT:PSS/CuPc/PTCDI/Ag cells and the new ITO/PEDOT:PSS/CuPc/CuPc*/PTCDI/Ag cells. The comparison shows that the modified cell has an enhanced stability compared to traditional cells. The improvement of the lifetime is likely due to the CuPc* layer working as buffer layer to prevent humidity and oxygen from diffusing into the active layer. Different thicknesses of CuPc were investigated to study the effects of CuPc layer thickness on the electrical properties of these devices. It was found that the properties of the cell with 20 nm thickness of CuPc were the best.

The existence of charge-density-wave (CDW) correlations in cuprate superconductors has now been established. However, the nature of the CDW ground state has remained uncertain because disorder and the presence of superconductivity typically limit the CDW correlation lengths to only a dozen unit cells or less. Here we explore the field-induced 3D CDW correlations in extremely pure detwinned crystals of YBa2Cu3O2 (YBCO) ortho-II and ortho-VIII at magnetic fields in excess of the resistive upper critical field ([Formula: see text]) where superconductivity is heavily suppressed. We observe that the 3D CDW is unidirectional and possesses a long in-plane correlation length as well as significant correlations between neighboring CuO2 planes. It is significant that we observe only a single sharply defined transition at a critical field proportional to [Formula: see text], given that the field range used in this investigation overlaps with other high-field experiments including quantum oscillation measurements. The correlation volume is at least two to three orders of magnitude larger than that of the zero-field CDW. This is by far the largest CDW correlation volume observed in any cuprate crystal and so is presumably representative of the high-field ground state of an "ideal" disorder-free cuprate.

The study of electronic excitations by inelastic X-ray scattering (IXS) has a rich history. Very early IXS work, for example, provided seminal demonstrations of the validity of relativistic kinematics and the quantum hypothesis [1] and of Fermi-Dirac statistics [2]. While there have been many important results in the interim [3], it has been the development of the third generation light sources together with continuing innovations in the manufacture and implementation [4–6] of dispersive X-ray optics that has led to the rapid growth of IXS studies of electronic excitations.

The dielectric constant of pressed pellets and thin films of branched copper phthalocyanine (CuPc) was investigated as a function of frequency from 0.1 kHz to 1 MHz and temperature from 20 °C to 100 °C. Surface morphology was studied using a scanning electron microscope. The high-frequency values of the dielectric constant of pellets and thin films are ~3.5 and ~5.8, respectively. The response was only weakly dependent on frequency and temperature. The branched structure of the CuPc molecules helped to cancel out the effects of low-frequency polarization mechanisms. A planar delocalized charge system with two-dimensional localization was found using time-resolved photoluminescence measurements.

In this paper, we present recent progress on polarization optics using the 1-BM beamline at the Advanced Photon Source, Argonne National Laboratory. Beamline 1-BM was recently repurposed for optics and detector testing. SHADOW software, a ray-tracing program for the simulation of optical systems of synchrotron radiation beamlines, is used to model the beamline. In this paper, we present optical ray-tracing studies for test set-ups that take advantage of the polarization variation of the bending magnet radiation above and below the horizontal plane of the beamline.

We report high-resolution inelastic x-ray scattering measurements in the metallic liquid Li(NH3)4, which to a good approximation can be treated as a dilute alkali metal. We see a well-defined excitation out to large momentum transfers. This excitation shows a strong softening at wave vectors near the first peak in the structure factor, which occurs near twice the Fermi momentum.

Gadolinium gallium garnet, Gd3Ga5O12 (GGG) has an extraordinary low-temperature phase diagram. Although the Curie–Weiss temperature of GGG is ∼−2 K, GGG shows no long-range order down to T∼0.4 K. At low temperatures GGG has a spin glass phase at low fields (≲0.1 T), a field-induced long-range ordered antiferromagnetic state at fields of between 0.7 and 1.3 T, and, at intermediate fields, an apparent spin-liquid state without long-range order. We have characterized the intermediate field (IF) state through heat capacity, thermal conductivity, and magnetocaloric measurements. Our results show a sharp high-field phase boundary of the thermal irreversibility of the spin glass phase of GGG implying that the intermediate field phase is distinct from the spin glass. The lower field boundary of the AFM phase is shown to have distinct minimum at T∼0.2 K, in analogy to the minimum in the melting curve of 4He. The existence of such a minimum is confirmed by measurements of the latent heat of the transition below that temperature.

We demonstrate the gradual evolution of the first-order vortex melting transition into a continuous transition with the systematic addition of point disorder induced by proton irradiation. The evolution occurs via the decrease of the upper critical point and the increase of the lower critical point. The collapse of the first-order melting transition occurs when the two critical points merge. We compare these results with the effects of electron irradiation on the first-order transition. (c) 2000 The American Physical Society.

We report inelastic x-ray scattering measurements of the energy, linewidth, and dispersion of the plasmon in metallic lithium ammonia at an electron concentration of $4\ifmmode\times\else\texttimes\fi{}{10}^{21}{e}^{\ensuremath{-}}/{\mathrm{cm}}^{3}$. These are the first measurements of plasmons in this system, which has the lowest electronic density for which a metal plasmon has been studied. We find a plasmon whose dispersion is only slightly reduced from the RPA value, and which is quite broad with an unusual momentum dependence.

We report resonant inelastic x-ray measurements of insulating La$_2$CuO$_4$ and Sr$_2$CuO$_2$Cl$_2$ taken with the incident energy tuned near the Cu K absorption edge. We show that the spectra are well described in a shakeup picture in 3rd order perturbation theory which exhibits both incoming and outgoing resonances, and demonstrate how to extract a spectral function from the raw data. We conclude by showing {\bf q}-dependent measurements of the charge transfer gap., Comment: minor notational changes, discussion of anderson impurity model fixed, references added; accepted by PRL

A large, liquid mirror telescope on the moon could provide invaluable observations of the early universe. However, current liquid telescopes are unsuitable for observations in the infrared (IR), where much interesting science is expected. While there are many significant engineering challenges for such a telescope, the lack of a suitable liquid has been a major factor limiting discussion. Here we argue that liquid lithium ammonia should be a suitable operating liquid. It has a high reflectivity in the IR, a low melting point (89 K), a low density (~0.5 g cc-1), and extrapolation of its measured vapor pressure indicates that it is suitable for lunar vacuum.

Theoretical calculations have shown that an equilibrium supersolid state is possible in a number of systems. The most studied system is solid 4 He, but experimental searches have failed to find evidence for supersolid behavior. However, it is possible to create a non-equilibrium supersolid state through Bose condensation of a non-thermal distribution of vacancies. In this paper, I discuss the relevant properties of solid 4 He to determine the feasibility of creating such a state in this system. While the relevant vacancy parameters are not known with certainty, there is a range of allowed values that would allow the creation of a non-equilibrium supersolid in 4 He.

We report synchrotron x-ray-diffraction measurements on low-density hcp-solid $^{4}$ He at a temperature of \ensuremath{\sim}0.7 K. The root-mean-square deviation of the atoms from their lattice positions 〈${\mathrm{u}}^{2}$ ${\mathrm{〉}}^{1\mathrm{/}2}$ is determined from measurements of the Debye-Waller factor at the (002), (004), and (006) Bragg peaks. We find 〈${\mathrm{u}}^{2}$ ${\mathrm{〉}}^{1\mathrm{/}2}$ =0.96\ifmmode\pm\else\textpm\fi{}0.02 \AA{} along the c axis. Our results are consistent with Green's function--Monte Carlo calculations. Weak reflections at the hcp-forbidden (001) and (003) Bragg peaks were also observed, probably indicating structural defects in the crystals.

Transmission x-ray diffraction experiments have been carried out on solid helium grown in porous Vycor glass. Measurements were made at temperatures near 0.7 K and at pressures up to 162 bars. The crystalline phases of solid helium in Vycor are found to differ significantly from the bulk. At pressures from 70 bars through 98 bars the helium is polycrystalline and displays a single size broadened scattering peak. Above 98 bars the peak splits into three close peaks. No higher order peaks are seen at any pressure, indicating significant reduction in intensity due to disorder. A broad peak is present at all pressures, which may indicate the presence of amorphous solid. We tentatively identify the low-pressure phase as bcc and the high-pressure phase as coexistence between bcc and hcp. Size broadening indicates an average grain size of approximately 5 nm, comparable to the Vycor pore size.

Resonant soft-x-ray scattering measurements have been performed to investigate interface electronic structures of (LaAlO(3)/SrTiO(3)) superlattices. Resonant scattering intensities at superlattice reflections show clear evidence of degeneracy lifting in t(2g) states of interface Ti ions. Polarization dependence of intensities indicates the energy of d(xy) states is lower by ~1 eV than two other t(2g) states. The energy splitting is insensitive to epitaxial strain. The orbital reconstruction is induced by oxygen vacancies and confined to the interface within two unit cells, indicating charge compensation at the polar interfaces.

Resonant Inelastic X-ray Scattering (RIXS) is a powerful probe for studying electronic excitations in materials. Standard high energy RIXS measurements do not measure the polarization of the scattered x-rays, which is unfortunate since it carries information about the nature and symmetry of the excitations involved in the scattering process. Here we report the fabrication of thin Si-based polarization analyzers with a double-concave toroidal surface, useful for L-edge RIXS studies in heavier atoms such as the 5-d transition metals.

We compare the properties of vacancies in4He implied by X-ray, NMR, and acoustic measurements with specific heat, pressure, and melting curve data. Taken together, these different measurements indicate that the model of vacancies as occupying a narrow band of states cannot be correct. Better agreement can be obtained by assuming that vacancies occupy a wide band but inconsistencies remain. An unambiguous determination of the properties of vacancies requires additional experimental and theoretical work.

Resonant inelastic x-ray scattering (RIXS) is a powerful technique for studying electronic excitations in correlated electron systems. Current RIXS spectrometers measure the changes in energy and momentum of the photons scattered by the sample. A powerful extension of the RIXS technique is the measurement of the polarization state of the scattered photons which contains information about the symmetry of the excitations. This long-desired addition has been elusive because of significant technical challenges. This paper reports the development of a new diffraction-based polarization analyzer which discriminates between linear polarization components of the scattered photons. The double concave surface of the polarization analyzer was designed as a good compromise between energy resolution and throughput. Such a device was fabricated using highly oriented pyrolytic graphite for measurements at the Cu K-edge incident energy. Preliminary measurements on a CuGeO(3) sample are presented.

We have carried out inelastic X-ray scattering measurements of the plasmon in liquid lithium ammonia solutions with the composition Li(NH 3 ) 4 . We find a well-defined plasmon at an energy loss of approximately 2 eV, which displays a positive dispersion in momentum transfer q . The dispersion is reduced from that predicted by the random phase approximation (RPA), but is still larger than is predicted by some local field correction models.

Gadolinium gallium garnet, Gd3Ga5O12 (GGG) has an extraordinary low temperature phase diagram. Although the Curie–Weiss temperature of GGG is about −2 K, GGG shows no long-range order down to T∼0.4 K. At low temperatures GGG has a spin glass phase at low fields (⩽0.1 T) and a field-induced long-range order antiferromagnetic state at fields of between 0.7 and 1.3 T [P. Schiffer et al., Phys. Rev. Lett. 73, 2500 (1994), S. Hov, H. Bratsberg, and A. T. Skjeltorp, J. Magn. Magn. Mater. 15–18, 455 (1980); S. Hov, Ph.D. thesis, University of Oslo, 1979 (unpublished), A. P. Ramirez and R. N. Kleiman, J. Appl. Phys. 69, 5252 (1991)]. However, the nature of the ground state at intermediate fields is still unknown, and has been hypothesized to be a three-dimensional spin liquid. We have measured the thermal conductivity (κ) and heat capacity (C) of a high-quality single crystal of GGG in the low temperature regime in order to study the nature of this state. The field dependence of κ shows that phonons are the predo...

X-ray diffraction experiments show that solid $^{4}\mathrm{He}$ grown in aerogel is highly polycrystalline, with an hcp crystal structure (as in bulk) and a crystallite size of approximately 100 nm. In contrast to the expectation that the highly disordered solid will have a large supersolid fraction, torsional oscillator measurements show a behavior that is strikingly similar to high purity crystals grown from the superfluid phase. The low temperature supersolid fraction is only $\ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$, and the onset temperature is $\ensuremath{\sim}100\text{ }\text{ }\mathrm{mK}$.

We report resonant inelastic x-ray scattering (RIXS) measurements on polycrystalline and single crystal samples of the organic semiconductor {beta}-copper phthalocyanine (CuPc) as well as time dependent density functional theory calculations of the electronic properties of the CuPc molecule. Resonant and nonresonant excitations were measured along the three crystal axes with 120 meV resolution. We observe molecular excitations as well as charge-transfer excitons along certain crystal directions and compare our data with the calculations. Our results demonstrate that RIXS is a powerful tool for studying excitons and other electronic excitations in organic semiconductors.

We report measurements of the atomic form factor of lithium, beryllium, and aluminum single crystals at low-momentum transfers $(Q=1.6--50\phantom{\rule{0.3em}{0ex}}{\mathrm{nm}}^{\ensuremath{-}1})$ from the intensity of phonons observed by inelastic x-ray scattering. Comparing to Hartree-Fock calculations, the form factor deviates significantly in the case of lithium and beryllium around ${k}_{F}$. These deviations can be mostly understood on the basis of electron redistribution by a pseudopotential. The influence of multiple scattering due to coherent phonon scattering and possible deviations from the adiabatic approximation are also discussed.

We report inelastic x-ray scattering measurements of the atomic collective excitations of an early transition metal, namely liquid titanium at T=2020 K. The data show well-defined sound excitations with a low damping constant comparable to the damping observed in liquid alkali metals. Calculations of the spectrum of density fluctuations as a function of the excitation wave number based on a self-consistent mode-coupling approach were carried out. The calculations use only the number density and measured structure factors for the titanium and have no adjustable parameters. A remarkable agreement between the prediction of mode-coupling theory and experimental results was observed.

We report measurements of the ionic collective excitations of a metal-ammonia system [lithium-ammonia with 20, 16, 13 mole % metal (MPM) at T=240 K and sodium-ammonia with 18. 14, 10 MPM at T = 222 K]. These data were analyzed to determine the acoustic collective excitation dispersion relation and the linewidth. Deviations from the Bohm-Staver model for electron-ion coupling are discussed for the low electronic densities found in these systems.

Inelastic x-ray scattering was used to measure the plasmon as a function of electron density in liquid lithium ammonia as well as the low temperature solid phase. As the electronic density is lowered, electronic correlation effects cause the random-phase approximation (RPA) to break down, requiring more advanced theoretical treatments. The deviation from RPA becomes greatest at the lowest electronic densities. We also see evidence for decreased electronic screening as shown by an increase in the strength of the pseudopotential at lower concentrations. Plasmon behavior in the solid is similar to that of the heavier alkali metals, but surprisingly different than in the liquid.

We report a resonant inelastic x-ray scattering study of the dispersion relations of charge-transfer excitations in insulating La(2)CuO(4).. These data reveal two peaks, both of which show two-dimensional characteristics. The lowest energy excitation has a gap energy of approximately 2.2 eV at the zone enter, and a dispersion of approximately 1 eV. The spectral weight of this mode becomes dramatically smaller around (pi, pi). The second peak shows a smaller dispersion ( approximately 0.5 eV) with a zone-center energy of approximately 3.9 eV. We argue that these are both highly dispersive exciton modes damped by the presence of the electron-hole continuum.

Using magnetic x-ray and neutron diffraction in UP${\mathrm{t}}_{3}$, we find that a suppression of the antiferromagnetic scattering intensity in the superconducting phase is due to a reduction in the magnitude of the staggered moment with no change in symmetry. The existence of the suppression as well as the magnetic correlation lengths are not affected by the presence or absence of a visible splitting in the superconducting transition. The simplest models wherein antiferromagnetic order provides the symmetry-breaking field for the splitting do not provide a compete explanation of our results.

We have carried out high-resolution inelastic x-ray scattering measurements of the excitations of lithium dissolved in ammonia. The incident x-ray energy was 21.6 keV and the resolution was about 2 meV. Several different excitations are observed in the energy range of 0-60 meV (0-500 cm(-1)). In addition to acoustic phonons at low energies, we see excitations that are associated with vibrations of Li(NH3)4+ complexes. We examined these excitations as a function of momentum transfer, lithium concentration, temperature, and state of the system (solid versus liquid). Data are compared with Hartree-Fock and density-functional theory calculations of the excitations of this complex, which agree well with the measured excitation energies.