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We present a new method to synthesize bulk indium nitride by means of a simple solid-state chemical reaction carried out under hydrostatic high pressure/high temperature conditions in a multi-anvil apparatus, not involving gases or solvents during the process. The reaction occurs between the binary oxide $In_2O_3$ and the highly reactive $Li_3N$ as nitrogen source, in powder form. The formation of the hexagonal phase of InN, occurring at 350 {\deg}C and P $\geq$ 3 GPa, was successfully confirmed by powder X-ray diffraction, with the presence of $Li_2O$ as unique byproduct. A simple washing process in weak acidic solution followed by centrifugation, allowed to obtain pure InN polycrystalline powders as precipitate. With an analogous procedure it was possible to obtain pure bulk GaN, from $Ga_2O_3$ and $Li_3N$ at T $\geq$ 600{\deg}C and P $\geq$ 2.5 GPa. These results point out, particularly for InN, a clean, and innovative way to produce significant quantities of one of the most promising nitrides in the field of electronics and energy technologies., Comment: Under revision in a peer-review journal

Copper-doped antimony selenide (Cu-doped Sb2Se3) thin films were deposited as absorber layers in photovoltaic solar cells using the low-temperature pulsed electron deposition (LT-PED) technique, starting from Sb2Se3 targets where part of the Sb was replaced with Cu. From a crystalline point of view, the best results were achieved for thin films with about Sb1.75Cu0.25Se3 composition. In order to compare the results with those previously obtained on undoped thin films, Cu-doped Sb2Se3 films were deposited both on Mo- and Fluorine-doped Tin Oxide (FTO) substrates, which have different influences on the film crystallization and grain orientation. From the current-voltage analysis it was determined that the introduction of Cu in the Sb2Se3 absorber enhanced the open circuit voltage (VOC) up to remarkable values higher than 500 mV, while the free carrier density became two orders of magnitude higher than in pure Sb2Se3-based solar cells.

Multiferroics, showing the coexistence of two or more ferroic orderings at room temperature, could harness a revolution in multifunctional devices. However, most of the multiferroic compounds known to date are not magnetically and electrically ordered at ambient conditions, so the discovery of new materials is pivotal to allow the development of the field. In this work, we show that BaFe

A crucial issue in cuprates is the extent and mechanism of the coupling of the lattice to the electrons and the superconductivity. Here we report Cu K edge extended X-ray absorption fine structure measurements elucidating the internal quantum tunneling polaron (iqtp) component of the dynamical structure in two heavily overdoped superconducting cuprate compounds, tetragonal YSr2Cu2.75Mo0.25O7.54 with superconducting critical temperature, Tc = 84 K and hole density p = 0.3 to 0.5 per planar Cu, and the tetragonal phase of Sr2CuO3.3 with Tc = 95 K and p = 0.6. In YSr2Cu2.75Mo0.25O7.54 changes in the Cu-apical O two-site distribution reflect a sequential renormalization of the double-well potential of this site beginning at Tc, with the energy difference between the two minima increasing by ∼6 meV between Tc and 52 K. Sr2CuO3.3 undergoes a radically larger transformation at Tc, >1-A displacements of the apical O atoms. The principal feature of the dynamical structure underlying these transformations is the strongly anharmonic oscillation of the apical O atoms in a double-well potential that results in the observation of two distinct O sites whose Cu–O distances indicate different bonding modes and valence-charge distributions. The coupling of the superconductivity to the iqtp that originates in this nonadiabatic coupling between the electrons and lattice demonstrates an important role for the dynamical structure whereby pairing occurs even in a system where displacements of the atoms that are part of the transition are sufficiently large to alter the Fermi surface. The synchronization and dynamic coherence of the iqtps resulting from the strong interactions within a crystal would be expected to influence this process.

The purpose of this work is to study the influence of the annealing temperature on the structural, morphological, compositional and optical properties of CuSbSe2 thin films electrodeposited in a single step. CuSbSe2 thin films were grown on fluorine-doped tin oxide (FTO)/glass substrates using the aqueous electrodeposition technique, then annealed in a tube furnace under nitrogen at temperatures spanning from 250 to 500 °C. The resulting films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis, Raman spectroscopy and UV-Vis spectrophotometer. The annealing temperature plays a fundamental role on the films structural properties; in the range 250–350 °C the formation of pure CuSbSe2 phase from electrodeposited binary selenides occurs. From 400 to 500 °C, CuSbSe2 undergoes a preferential phase orientation change, as well as the increasing formation of copper-rich phases such as Cu3SbSe3 and Cu3SbSe4 due to the partial decomposition of CuSbSe2 and to the antimony losses.

By means of single-crystal X-ray diffraction, we give direct crystallographic evidence of a centrosymmetry breaking below TS = 200 K, concomitant with the onset of a commensurate structural modulation in the quadruple perovskite YMn3Mn4O12. This result, which explains the anomalously large thermal coefficient of the Y3+ ion in previously reported structural models, is attributed to the small size of the Y3+ ion, which causes its underbonding within the dodecahedral coordination polyhedron. The present data are consistent with a commensurate superstructure described by an I-centered pseudo-orthorhombic cell with polar Ia symmetry and a ? aF?2 = 10.4352(7) Å, b ? 2bF = 14.6049(9) Å, c ? cF?2 = 10.6961(7) Å, and ? = 90.110(3)°, where aF ? cF ? 7.45 Å, bF ? 7.34 Å, and ? ? 91° are the unit cell parameters of the I2/m structure observed at room temperature. Consistent with the above polar structure, at lower temperature, T* = 70 K, we observe in polycrystalline samples an anomaly of the direct current (DC) and alternating current (AC) magnetization, concomitant with the appearance of a net electric polarization, as indicated by pyrocurrent and dielectric constant measurements. These results, complemented by electrical transport measurements, suggest a magnetic ferroelectricity driven by short-range magnetic order in YMn3Mn4O12.

Photovoltaic cells offer a clean and sustainable solution by allowing the reduction of fossil energy. In recent decades, several types of solar cells have been proposed to overcome the limitation of stiffness of common silicon-based solar cells. Due to their flexibility, thin-film solar cell technology is now of great interest to the community. Now, most of the thin-film solar cell market belongs to CdTe or CIGS based, but its implementation involves a high cost due In/Ga and safety problem to the high toxicity of Cd. Thanks to its abundance and non-toxicity [1] Sb 2 Se 3 is one of the main candidates to overcome these limitations. Furthermore, laser scribing technology, the main candidate for guaranteeing a large production volume with a high precision manufacturing, needs to support the growth of new types of absorbent material without damaging others. In this work, Sb 2 Se 3 based solar cells have been grown by the low-temperature pulsed electron deposition (LT-PED) technique [2] and the so-called P3 process has been performed by laser scribing. Photovoltaic devices were fabricated as described in [3] with the following architecture: ZnO: Al/ZnO/CdS/Sb 2 Se 3 /Mo/Glass, shown in Figure 1a . The films were deposited onto 2.5×2.5 cm 2 soda-lime glass substrates, coated with molybdenum (Mo).

BiFe0.5Mn0.5O3 (BFMO) is an intriguing magnetic double perovskite, only obtainable through high pressure-high temperature synthesis. It shows bulk multiferroic properties, namely the coexistence between a spin canted antiferromagnetic structure superimposed to an externally induced electric polarization at least from 77 K. In particular, the system is characterized by a significant weak ferromagnetic hysteresis loop and by a very rare phenomenon: the spontaneous magnetization reversal (MRV) versus temperature in the low field regime. To clarify the BFMO exotic magnetic phase in the low field regime, the Electron Spin Resonance (ESR) and the low field microwave absorption (LFMA) techniques were used, providing the first observation of LFMA in the bulk BFMO as an additional functionality of this material. A striking feature is that the hysteresis in LFMA signals vanishes above 45 K, while the bulk M-H loop hysteresis, measured in the same field range of LFMA, persists till room temperature. The temperature at which LFMA hysteresis vanishes qualitatively matches the position of the magnetic susceptibility’s second derivative peak, corresponding to the temperature at which the local second order mechanism responsible for MRV is maximum. The line shape of LFMA completely changes above 45 K and the ESR linewidth starts decreasing above this temperature, indicating the role of defect/disorder induced inhomogeneity. The temperature evolution of LFMA hysteresis and line shapes as a measure of the competition between Fe- and Mn-rich clusters suggests a sort of local frustration at the microscopic scale, responsible for the peculiar magnetization reversal of this system.

By means of magnetic, specific heat, and pyroelectric measurements, we report on magnetic ferroelectricity in the quadruple perovskite $\mathrm{Na}{\mathrm{Mn}}_{7}{\mathrm{O}}_{12}$, characterized by a canted antiferromagnetic (AFM) CE structure. Surprisingly, ferroelectricity is concomitant to a dramatic broadening of the magnetic hysteresis loop, well below the AFM ordering temperature. This unconventional behavior shows that the formation of ferroelectric domains is induced by the symmetric exchange interaction in the local scale, e.g., at magnetic domain boundaries or defects. The value of electric polarization, $P=0.027\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{C}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$, measured in polycrystalline samples is comparatively large as compared to other magnetic multiferroics, suggesting that the above scenario is promising indeed for the rational design of practical multiferroic materials.

The laser scribing is one of the crucial technological steps in the industrial processing of solar cells, while the mechanical scribing is generally used for practical reasons on the laboratory scale. Using a picosecond laser, preliminary results on the scribing of CuInGaSe2 thin film solar cells deposited by the low temperature pulsed electron technique, are reported. The complete comparison between laser- and mechanical-scribing is still in progress, however SEM imaging and EDX analysis confirm the excellent structural and morphological quality of the laser scribed samples.

We report on the high-pressure solid-state synthesis and the detailed structural characterization of the metastable, CuAu-type CuInS

The temperature behavior of the crystal structure as well as dielectric and magnetic properties of the perovskite bismuth chromate ceramics with the 10 mol % Cr

We present a study on the correlation of the superconducting critical temperature (Tc) and structural morphology with a chemically substituted high-temperature superconductor (HTS) (Bi,Pb)-2212 via Powder X-ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), and d c magnetometry. The elements Zn, Y, Ti, and Nd are incorporated within the bismuth cuprate structure at amounts that extend the ranges currently found in literature.

A common characteristic of many “overdoped” cuprates prepared with high-pressure oxygen is T(c) values ≥ 50 K that often exceed that of optimally doped parent compounds, despite O stoichiometries that place the materials at the edge or outside of the conventional boundary between superconducting and normal Fermi liquid states. X-ray absorption fine-structure (XAFS) measurements at 52 K on samples of high-pressure oxygen (HPO) YSr(2)Cu(2.75)Mo(0.25)O(7.54), T(c) = 84 K show that the Mo is in the (VI) valence in an unusually undistorted octahedral geometry with predominantly Mo neighbors that is consistent with its assigned substitution for Cu in the chain sites of the structure. Perturbations of the Cu environments are minimal, although the Cu X-ray absorption near-edge structure (XANES) differs from that in other cuprates. The primary deviation from the crystal structure is therefore nanophase separation into Mo- and Cu-enriched domains. There are, however, indications that the dynamical attributes of the structure are altered relative to YBa(2)Cu(3)O(7), including a shift of the Cu-apical O two-site distribution from the chain to the plane Cu sites. Another effect that would influence T(c) is the possibility of multiple bands at the Fermi surface caused by the presence of the second phase and the lowering of the Fermi level.

International audience; A common characteristic of many "overdoped" cuprates prepared with high-pressure oxygen is T c values ≥ 50 K that often exceed that of optimally doped parent compounds, despite O stoichiome-tries that place the materials at the edge or outside of the conventional boundary between superconducting and normal Fermi liquid states. X-ray absorption fine-structure (XAFS) measurements at 52 K on samples of high-pressure oxygen (HPO) YSr 2 Cu 2.75 Mo 0.25 O 7.54 , T c = 84 K show that the Mo is in the (VI) valence in an unusually undistorted octahedral geometry with predominantly Mo neighbors that is consistent with its assigned substitution for Cu in the chain sites of the structure. Perturbations of the Cu environments are minimal, although the Cu X-ray absorption near-edge structure (XANES) differs from that in other cuprates. The primary deviation from the crystal structure is therefore nanophase separation into Mo-and Cu-enriched domains. There are, however, indications that the dynamical attributes of the structure are altered relative to YBa 2 Cu 3 O 7 , including a shift of the Cu-apical O two-site distribution from the chain to the plane Cu sites. Another effect that would influence T c is the possibility of multiple bands at the Fermi surface caused by the presence of the second phase and the lowering of the Fermi level.

We report on the high-pressure solid-state synthesis and the detailed structural characterization of the metastable, CuAu-type CuInS2 (CA-CIS) phase. Although often present in CIS thin films as unwanted phase, it has been never synthesized in pure form, and its effect on the performance of CIS-based solar cells has been long debated. In this work, pure CA-CIS phase is synthesized in bulk polycrystalline form through a high-pressure-high-temperature solid-state reaction. Single-crystal X-rays diffraction reveals the formation of tetragonal CA-CIS (a = 3.9324(5), c = 5.4980(7) A) either in cation-ordered and disordered phase, pointing out the role of the pressure/temperature increase on the Cu/In ordering. The resistivity measurements performed on CA-CIS show low resistivity and a flat trend vs temperature and, in the case of the ordered phase, highlight a bad-metallic behavior, probably due to a high level of doping. These findings clearly rule out the possibility of a beneficial effect of this phase on the CIS-based thin film solar cells.

We report on the room temperature, simple and cheap preparation by mechano-synthesis of polycrystalline targets of complex sulphide semiconductors, namely CuInS (CIS), to be used for film deposition in physical vacuum techniques such as PLD, sputtering or LT-PED. The sulphur (S)-based targets usually require expensive high pressure equipment to compensate the high S vapour pressure; nevertheless they are indispensable for the deposition of high band-gap semiconductor materials. The comparison of CIS films grown by mechano-synthesis and by commercial targets demonstrates similar material quality, making the mechano-synthesis a viable solution in the fabrication of high band-gap, S-based targets of complex chalcogenides.

The temperature behavior of the crystal structure as well as dielectric and magnetic properties of the perovskite bismuth chromate ceramics with the 10 mol % Cr3+-to-Sc3+ substitution were studied and compared with those of the unmodified compound. Using a high-pressure synthesis, BiCrO3 and BiCr0.9Sc0.1O3 were obtained as metastable perovskite phases which are monoclinic C2/c with the √6ap × √2ap × √6ap superstructure (where ap is the primitive perovskite unit-cell parameter) under ambient conditions. At room temperature, the unit cell volume of BiCr0.9Sc0.1O3 is ∼1.3% larger than that of BiCrO3. Both perovskites undergo a reversible structural transition into a nonpolar GdFeO3-type phase (orthorhombic Pnma, √2ap × 2ap × √2ap) in the temperature ranges of 410-420 K (BiCrO3) and 470-520 K (BiCr0.9Sc0.1O3) with a relative jump of the primitive perovskite unit cell volume of about -1.6 and -2.0%, respectively. Temperature dependences of the complex dielectric permittivity demonstrate anomalies in the phase transition ranges. The Pnma-to-C2/c crossover in BiCrO3 is accompanied by a decrease in the direct current (dc) conductivity, while in BiCr0.9Sc0.1O3 the conductivity increases. The onset of an antiferromagnetic order in BiCr0.9Sc0.1O3 is observed at the Néel temperature (TN) of about 85 K as compared with TN = 110 K in BiCrO3. In contrast to BiCrO3, which exhibits a spin reorientation at Tsr ∼ 72 K, no such a transition occurs in BiCr0.9Sc0.1O3. published

In this paper we report on the single stage deposition of CuInxGa1−xSe2 (CIGS)-based bifacial solar cells on glass coated with Fluorine-doped Tin Oxide (FTO) or Indium Tin Oxide (ITO) by single-stage low-temperature (250 °C) pulsed electron deposition (LTPED). We show that the mechanism of Sodium incorporation during the low-temperature deposition of CIGS on both FTO and ITO leads to the formation of a stable n+/p+ ohmic tunnel junction and photovoltaic efficiencies exceeding 14% can be obtained without any intentional bandgap grading of CIGS. The significant degradation of the cell fill factor with decreasing CIGS thickness is found to be related to the presence of craters left behind by micro-fragments of CIGS target, which are weakly incorporated in the film during the LTPED growth and removed during the subsequent process steps. Evidence is also presented that the low-temperature deposition of CIGS on ITO leads to the formation of a Ga-rich CIGS layer at the interface and to an unintentional compositional grading propagating towards the active region of the solar cells. The defects associated with this grading may be responsible for the loss in FF and Voc with respect to the cells deposited on FTO and Mo back contacts.

CuSbSe2 belongs to the Copper antimony chalcogenides CuSbCh 2 (Ch=S,Se). An emerging family of absorbers studied for thin-film solar cells. CuSbSe2 thin films have been prepared by electrodeposition in one-step followed by the annealing process in tubular furnace at 300°C for 5min under N2 atmosphere. The reduction potentials region was determined by cyclic voltammetry and linear sweep voltammetry. Then the samples have been deposited by chronoamperometry at different potentials during 1h. The structural, morphological and optical properties of CuSbSe2 thin films were studied by X-ray diffraction, SEM and spectrophotometer respectively.

By means of single-crystal X-ray diffraction, we give direct crystallographic evidence of a centrosymmetry breaking below

This chapter reports the progress on the fabrication of thin film CIGS-based solar cells by means of the low temperature pulsed electron deposition technique. The innovative and multidisciplinary approach aims to solve the main issues preventing a possible industrial scale up of the process, i.e. the need of a fast, reliable and automated process, suitable for both static and dynamic deposition of CIGS solar cells on flexible substrates. The final goal is to open new opportunities, particularly in the emerging field of the building-integrated photovoltaic.

In the last few decades, the persisting scientific interest in high temperature superconductor (HTS) cuprates has been accompanied by the search for new families of superconducting compounds (SPCs) [...]

CdZnTe is nowadays a reference semiconductor for detection of X and γ-radiation. The electrical properties of CdZnTe-based (CZT) detectors are strongly affected by the surface and subsurface defects, which can cause an excessive surface leakage current (SLC). This issue strongly degrades the sensor performance and becomes critical for multi-stripes detectors, where the stripes are kept at different voltage potentials in order to shape the electric field inside the semiconductor material.In this work, we propose a passivation method based on the deposition of a thin Al 2 O 3 film on the non-metallized CZT surface. To demonstrate the effectiveness of the method, we fabricated several 19.4x19.4x5 mm3 CZT multi-stripes detectors with 48 parallel Au stripes on the anode face (12 collecting anodes and 36 drift stripes) and subsequently deposited a Al 2 O 3 polycrystalline thin film on the CZT surface between the stripes. Al 2 O 3 deposition was achieved by sputtering technique. Electrical characterization of surface leakage current before and after Al 2 O 3 is presented.Al 2 O 3 coating treatment allowed us to obtain exceptionally low surface leakage current values, 10 to 100 times lower than those measured after our best wet passivation method for CZT surface chemical oxidation. Since Al 2 O 3 passivation significantly reduces surface leakage current and thus improves the signal-to-noise ratio, our finding is very promising for a substantial advancement of multi-stripe detectors performance.

We present the discovery and refinement by neutron powder diffraction of a new magnetic phase in the Na_{1-x}Ca_{x}Mn_{7}O_{12} quadruple perovskite phase diagram, which is the incommensurate analogue of the well-known pseudo-CE phase of the simple perovskite manganites. We demonstrate that incommensurate magnetic order arises in quadruple perovskites due to the exchange interactions between A and B sites. Furthermore, by constructing a simple mean field Heisenberg exchange model that generically describes both simple and quadruple perovskite systems, we show that this new magnetic phase unifies a picture of the interplay between charge, magnetic, and orbital ordering across a wide range of compounds.

We report a detailed study on the magnetic properties of the pyroxene series M2M1Si

CuSb(S,Se)2 is emerging as an alternative absorber for thin film photovoltaics, for its intrinsic p-type conductivity, tunable energy bandgap (1.0÷1.6 eV), high absorption coefficient > 104 cm-1 and very low cost of the constituent elements. In this work, we studied the structural, compositional and electro-optical properties of CuSbSe2 (CASe) films grown by Low Temperature Pulsed Electron Deposition (LTPED), a developing technology in thin film photovoltaics. We proved that stoichiometric or Cu-poor CASe films can be obtained at low temperature (< 200 °C) from a stoichiometric target with no need for post-deposition treatments to adjust the stoichiometry. Solar cells based on Cu-poor and stoichiometric CASe absorbers exhibit a similar open circuit voltage (~290÷310 mV), while the JSC increases from ~3 mA/cm2 up to ~20 mA/cm2 as the Cu/Sb ratio increases from 0.55 to 0.95. A low FF ~40% still limits the performance of all the cells indicating that the standard architecture of thin film solar cells, currently used for CIGS and CdTe devices, need to be significantly reviewed. The results of the structural and optoelectrical characterization presented in this paper show that JSC, VOC and FF can all be improved as a result of the optimization of the device architecture. The best of the LTPED-grown CASe cells obtained so far, reached an efficiency of 3.8%, very close to the state of the art reported so far in literature.

Pyroelectric current and magnetoelectric coupling measurements on polycrystalline samples of the quadruple perovskite (LaMn$_{3}$)Mn$_{4}$O$_{12}$ give evidence of ferroelectricity driven by the antiferromagnetic ordering of the $B$-site Mn$^{3+}$ ions at $T_{N,B}$=78 K with record values of remnant electric polarization up to $P$=0.56 $\mu$C cm$^{-2}$. X-ray diffraction measurements indicates an anomalous behavior of the monoclinic $\beta$ angle at $T_{N,B}$, which suggests that $P$ lies in the $ac$-plane, where the moments are collinear, so we conclude that exchange striction is the mechanism of spin-driven ferroelectricity. Polarization values $\sim$3 $\mu$C cm$^{-2}$ are expected in single crystals, which would open the avenue towards practical multiferroic applications., Comment: 5 pages, 5 figures

Low-temperature experiments of Raman scattering and heat capacity have been performed in a B2O3 glass, pressure quenched from 1200 degrees C in order to obtain the density as largest as possible (rho=2373kg/m(3)). When compared to those of compacted B2O3 glasses having smaller density, the Raman spectrum of this glass exhibits a strong decrease of the intensities of the Boson peak and the band at 808cm(-1), both the features being determined by the decrease of the boroxol ring population. Moreover, the Boson peak exhibits a large shift to 68cm(-1) (from 26cm(-1) observed in normal vitreous B2O3). The high atomic packing of the glassy network also leads to a marked decrease of the excess heat capacity over the Debye T-3-behaviour characterizing the crystal. The density g(nu) of low-frequency vibrational states has been assessed by using the low-frequency Raman intensity to determine the temperature dependence of the low-temperature heat capacity. The observations performed over a wide range of glass densities are compared to the predictions of theoretical models and computer simulations explaining the nature of the Boson peak. Consistency with the results of a simulation study concerning the vibrations of jammed particles leads to evaluate a nanometre length scale which suggests the existence of poorly packed domains formed from several connected boroxols. These soft regions are believed to be the main source of low-frequency optic-like vibrations giving rise to the Boson peak.

In this study, a comparison between Al-doped ZnO (AZO) as Transparent Conductive Oxide for Cu(In,Ga)Se-2-based solar cells grown by Pulsed Electron Deposition (PED) and Radio Frequency Magnetron Sputtering (RFMS) was performed. PED yielded polycrystalline [002] mono-oriented thin films with low electrical resistivity and high optical transparency with heater temperatures ranging from room temperature (RT) to 250 degrees C. The electrical resistivity of these films can be tuned by varying the heater temperature, reaching a minimum value of 3.5 x 10(-4) Omega cm at 150 degrees C and an average transmittance over 90% in the visible range. An AZO film grown at RT was deposited by PED on an actual Cu(In,Ga)Se-2-based solar cell, resulting to an efficiency value of 15.2% on the best device. This result clearly shows that PED is a suitable technique for growing ZnO-based thin films for devices/applications where low deposition temperature is required. On the other hand, an optimized AZO thin film front contact for thin film solar cells was studied and fabricated via RFMS. The parameters of this technique were tweaked to obtain highly conductive and transparent AZO thin films. The lowest resistivity value of 3.7 x 10(-4) Omega cm and an average transmittance of 86% in the 400-1100 nm wavelength range was obtained with a heater temperature of 250 degrees C. A thick sputtered AZO film was deposited at RT onto an identical cell used for PED-grown AZO, reaching the highest conversion efficiency value of 14.7%. In both cases, neither antireflection coatings nor pure ZnO layer was used. (C) 2014 Elsevier B.V. All rights reserved.

We report on the fabrication and characterization of Cu(In,Ga)Se2 (CIGS)-based thin film bifacial solar cells using Al-doped ZnO (AZO) as cost-effective and non-toxic transparent back contact. We show that, by depositing both CIGS and AZO by Low Temperature Pulsed Electron Deposition at a maximum temperature of 250 °C, a good ohmic contact is formed between the two layers and good quality solar cells can be fabricated as a result. Photovoltaic efficiencies as high as 9.3% (front illumination), 5.1% (backside illumination) and 11.6% (bifacial illumination) have been obtained so far. These values are remarkably higher than those previously reported in the literature. We demonstrate that this improvement is ascribed to the low-temperature deposition process that avoids the formation of Ga2O3 at the CIGS/AZO interface and favours the formation of a low-resistivity contact in agreement with device simulations.

This work aims at understanding the large reduction of superconducting critical temperature Tc observed in YSr 2 Cu 3 0 6+x as compared to its YBa 2 Cu 3 O 6+x counterpart (ΔTc = -30 K ). We report on a combined study of structural and electronic properties of RESr 2 Cu 3 O 6+x(RE = Y, Yb) polycrystalline samples. Neutron diffraction data and Cu NQR spectra show that, contrary to REBa 2 Cu 3 O 6+x RESr 2 Cu 3 O 6+x is locally tetragonal and no CuO chains are formed. This arises from the random occupancy of oxygen along the a- or b- direction in the basal planes. Ab-initio calculations of the electronic structure using the full-potential linearized-augmented-plane-wave method (FLAPW) in the local density approximation (LDA) suggest that the CuO chains are not formed because of the large elastic strain associated with the orthorhombic distortion produced by the chain formation. In addition, by using a [Formula: see text] supercell simulating the absence of chains, we find that oxygen disorder greatly alters the band structure near the Fermi level. Our analysis indicates that this alteration leads to a reduction of hole transfer from the CuO chains to the CuO 2 planes, which accounts for the reduction of Tc experimentally observed.

The structural refinement of YSr2Cu3O6.84 allows us to analyze why the chemical pressure applied to YBa2Cu3O6.84, by substituting Sr for Ba, results in a decrease of Tc (88 to 63 K). Even though the chemical pressure induces a volume decrease of 5.7%, the thickness along the c axis of the superconducting block increases by 3.0%. This behavior seems to be due to the incompressibility of the Y coordination polyhedron. The SrO layer becomes negatively strained since the Sr polyhedron does not reduce along with the Sr cation substitution. The calculated bond valence sum for the latter cation is 1.63 v.u. instead of the expected 2. The apical distance of the pyramid around Cu2 decreases drastically from 2.30 to 2.09 Å. All these features induce an instability within YSr2Cu3O6.84, which makes it difficult for the extra oxygen to go in and out of the structure as it does in its Ba counterpart. This instability would also reduce the hole transfer from the CuO chains to the superconducting CuO2 planes. © 2000 Elsevier Science B.V All rights reserved.

The physical properties of disordered systems are in the focus of a large research effort. In particular, one of the open problems related to glasses is their excess of modes in the THz frequency range over the vibrational contribution predicted by the Debye model. In fact, one could expect the continuum approximation underlying the Debye model to hold in glasses at long wavelengths at least as well as in crystalline solids. Experiments, instead, seem to indicate that the specific heat at low temperature (a few Kelvin) and the density of vibrational states at low frequency (a few terahertz) are very different from the Debye prediction. We present here a detailed analysis of specific heat measurements of vitreous GeO2, a prototype of strong glasses, and of permanently densified vitreous GeO2. Our data give experimental evidence that glasses do not show any excess of vibrational modes when compared to their crystalline counterparts of similar mass density.

We present a comprehensive study of the electrical properties of bulk polycrystalline BiFe0.5Mn0.5O3, a double perovskite synthesized in high-pressure and high-temperature conditions. BiFe0.5Mn0.5O3 shows an antiferromagnetic character with T-N = 288 K overlapped with an intrinsic antiferroelectricity due to the Be3+ stereochemical effect. Beyond this, the observation of a semiconductor insulator transition at T-p approximate to 140 K allows one to define three distinct temperature ranges with completely different electrical properties. For T > T-N, electric transport follows an ordinary thermally activated Arrhenius behavior; the system behaves as a paramagnetic semiconductor. At intermediate temperatures (T-p < T < T-N), electric transport is best described by Mott's variable range hopping model with lowered dimensionality D = 1, stabilized by the magnetic ordering process and driven by the inhomogeneity of the sample on the B site of the perovskite. Finally, for T < T-p, the material becomes a dielectric insulator, showing very unusual poling-induced soft ferroelectricity with high saturation polarization, similar to the parent compound BiFeO3. Under external electric poling, the system irreversibly evolves from antiferroelectric to polar arrangement.

Zinc Sulphide films were grown by pulsed electron deposition (PED) from room temperature to 350 °C to investigate the possibility of its application in solar cells, in particular as an alternative buffer layer deposited at low temperature. The films were characterized by X-ray diffraction, TEM, AFM, optical absorption and electrical measurements. ZnS films display crystalline structure and columnar growth at room temperature on amorphous substrate; the crystallization improves with the substrate temperature and is predominantly related to the cubic (111) orientation, while the thicker films show coexistence of hexagonal and cubic structures. All the samples have transparencies exceeding 70% in the range 400-1000 nm, energy band gap between 3.25 and 3.65 eV increasing with temperature and resistivity in the range of 104-106 Ωcm. The optimization of the growth rate as a function of the growth parameters (substrate temperature and electron gun voltage) is also discussed. The reported results indicate that ZnS might be a suitable material for photovoltaic applications, specifically in process requiring low deposition temperature. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on the successful implementation of a supersonic molecular oxygen (O 2) beam for the in situ oxidation of superconducting YBCO films. The beam is produced by a specially designed array of conical nozzles that were laser machined in a platinum foil. The array was mounted in proximity of the deposition area of a thermal co-evaporation system for YBCO film deposition. After a brief description of the basic concepts underlying the physics of supersonic beams, we describe the design of the nozzle implemented in our system. Then, we illustrate and discuss the preliminary results obtained by varying a number of key parameters of the supersonic beam. Most Important parameters turn out to be the input O 2 pressure and the nozzle-film distance. We show that excellent electrical properties with zero-resistance superconducting critical temperatures, T c, in excess of 90 K are reproducibly obtained over the entire 20 cm × 20 cm deposition area. These results were obtained using various types of substrates relevant to coated conductor fabrication, including Zr-doped CeO 2 buffered cube-textured Ni-W and MgO buffered hastelloy substrates.

We report a comprehensive study of the spontaneous magnetization reversal (MRV) performed on the disordered polycrystalline perovskite BiFe(0.5)Mn(0.5)O(3), an intriguing compound synthesized in high pressure-high temperature conditions. In disordered systems, the origin of MRV is not completely clarified, yet. In BiFe(0.5)Mn(0.5)O(3), compositional disorder involves the ions on the B-site of the perovskite determining the presence of mesoscopic clusters, characterized by high concentrations of iron or manganese and thus by different resultant magnetization. This leads to the observation of two singular fields H(1) and H(2) dependent on the degree of inhomogeneity, unpredictably changing from sample to sample due to synthesis effects. These fields separate different magnetic responses of the system; for applied fields H H(1), the Fe and Mn clusters weakly interact in a competitive way, giving rise to MRV, while for an intermediate field regime the energy of this weak interaction becomes comparable to the energy of the system under field application. As a consequence, the zero field cooled magnetization thermal evolution depends on the sample degree of inhomogeneity. In this field regime, applied field Mössbauer spectroscopy indicates that the iron rich clusters are highly polarized by the field, while the largest part of the material, consisting of AFM clusters characterized by axial anisotropy and uncompensated moments, shows soft or hard magnetism depending on T. Above the higher singular field, the M(T) curves show the trend expected for a classical antiferromagnetic material and the competitive character is suppressed. The MRV phenomenon results to be highly sensitive on both the thermal and magnetic measurement conditions; for this reason the present work proposes a characterization strategy that in principle has a large applicability in the study of disordered perovskites showing similar phenomenology.