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[en] Neutron total scattering data of extruded model ODS alloy samples (with 0.3 vol % Y2O3 doped 1) pure Fe, 2) Fe + 0.2 % Ti, 3) Fe +14% Cr, 0.2 % Ti) was collected at the NOMAD instrument of the SNS, ORNL, Oak Ridge, USA, at ambient and elevated temperatures between 600 to 1200 deg C. The high temperature data allowed identification of the alpha to Gamma phase transition of the Fe in these samples. Good fits were obtained between the experimentally observed and the calculated PDFs of the alpha and gamma structures of Fe with refined values of lattice parameters, scale factor and the thermal parameters. Preliminary results of our study of the temperature evolution of the local arrangements of atoms in these samples will be presented. (author)
[en] The intensities of neutron Bragg diffracted from the front- and back-faces of a 22 mm thick perfect Ge single crystal undergoing on ultrasound excitation has been measured and calculated theoretically. It is shown that at the same time as the acoustic wave amplitude is increased, the main Bragg peaks grow and the back-face peak becomes asymmetric and tends to disappear. Such a back-face scattering was observed for the first time and successfully described within frameworks of the dynamic theory of neutron scattering modified in the presence of ultrasound excitation and Kato's quasiclassical approximation taking into account new ultrasonic extinction length appearance.
[en] In this paper we report the results of an extensive investigation of the La0.7Ca0.3Mn1-xCoxO3 system. Substitution of Mn by Co dilutes the double-exchange (DE) mechanism and changes the long range ferromagnetic order of La0.7Ca0.3MnO3 to a cluster glass-type ferromagnetic (FM) order similar to that observed in La0.7Ca0.3CoO3. This happens even for the lowest Co substitution of x=0.05 and persists over the entire composition range studied (0.05≤x≤0.5). The Co substitution also destroys the metallic state and the resistivity increases by orders of magnitude even with a very small extent of Co substitution. The charge localization due to Co substitution is likely to have its origin in polaronic lattice distortion. The Co substitution also suppresses the colossal magnetoresistance (CMR) of the pure manganate (x=0) over the entire temperature and composition range and it becomes very small for x≥0.2. We conclude that the DE interaction and the resulting metallic state is very open-quotes fragileclose quotes and hence even a small amount of Co substitution can destroy the FM order, the metallic state, and the CMR. copyright 1997 The American Physical Society
[en] The effect of gel polymer electrolytes on the performance of dye-sensitized solar cells have been systematically analyzed using polymer and its composites. Two series of gel electrolytes were synthesized, one based on PEO-copolymers (PEG-block-PPG-block-PEG) with LiI salts and the other one based on nano-porous metal structures (NPoS) with LiI salts as fillers salts and its solar cells performance has been analyzed. The PEO/copolymer was synthesized with variation in the weight percentage of copolymers ranging from 2% to 16% in the incremental order of 2%. Similarly, the Au97.5Pt2.5/C NPoS-copolymer was synthesized with various weight percentages starting from 0.4 to 2.4 in the incremental order of 0.4%. All the synthesized gel polymer electrolytes were subjected to various analyses such as XRD, TGA/DTA, DSC, AFM, HRTEM to confirm their morphology or texture and the photo-conversion efficiency of fabricated device was tested using solar simulator with ‘one sun’ condition under the illumination of 100 mW cm−2. The polymer/copolymer composites with the weight percentage of 14% showed better ionic conductivity of 4.1 × 10−6 S cm−1 at room temperature and exhibits the photo-conversion efficiency (PCE) of 4.1%. Likewise, the NPoS-copolymer composite with weight percentage of 1.6% exhibits PCE of 5.1%. (paper)
[en] An inverted bulk heterojunction organic photovoltaic device based on blend of conjugated polymers and fullerenes derivatives with Cs2CO3/PVDF composites as an electron transporting layer. The entire device structure ((Cs2CO3/PVDF)/P3HT: PCBM/V2O5/Al) has been fabricated using spin coating method and the final metal contact was made using thermal evaporation technique. The mol % of Cs2CO3: PVDF ratio and the spin rate of electron transport and P3HT:PCBM was subjected to be varied and its device performance were evaluated using solar simulator under one sun condition. The physio-chemical characterizations such as UV-Visible, FTIR, PL, XRD, FESEM and AFM were performed for all the materials used in the device fabrications. By varying the spin rate of conjugated polymers/fullerene blends it may helps in scaling up of self-organized molecules of an active layer. Also the variation of spin rate will plays a role in the surface roughness of the film and thereby contributing enhancing the photo-conversion efficiency of fabricated devices. The device fabricated with optimized conditions under ambient atmosphere exhibits efficiency of 1.8 % with JSC of 5.8 mA/cm2 and VOC of 0.57 V. The performance of the device can be enhanced further by controlling exposure of electrode materials. (author)
[en] The magnetic ordering in ErFe0.3Ge2 and ErNi0.65Ge2 compounds crystallizing in the orthorhombic structure of the CeNiSi2-type has been investigated by neutron diffraction and magnetic measurements. The Er magnetic moments have been found to order antiferromagnetically below 2.5 K in ErFe0.3Ge2 and 2.3 K in ErNi0.65Ge2. The magnetic structure of the former compound can be described by the propagation vector k = (0.044(1); 0; 0.384(1)). The Er magnetic moments are aligned along the a-axis and alternate with the sequence ++-- in the unit cell. At 1.5 K they are equal to 5.9(1) μB. In contrast, the magnetic unit cell of ErNi0.65Ge2 has been established to be equal to the chemical one. The magnetic moments in this compound are arranged in a collinear manner pointing along the a-axis with the sequence +-+-. The Er moment value measured at 1.5 K is 2.90(8) μB. (author)
[en] A reentrant transition from an incipient charge-ordered (CO) state to a charge-delocalized ferromagnetic (CDFM) state has been established in the manganate Nd0.25La0.25Ca0.5MnO3, in which the average A-site ionic radius is 1.19 Angstrom. The reentrant CDFM phase is associated with a first-order phase transition that reduces the orthorhombic distortion of the lattice, in contrast to the CO transition in other manganates where the orthorhombically distorted CO state is stabilized at low temperatures. At the CO-CDFM transition, there is a collapse of the charge-ordering gap as measured by vacuum tunneling spectroscopy. copyright 1998 The American Physical Society
[en] Polycrystalline samples of Ln1/2Sr1/2MnO3 (Ln = La, Pr, La0.33Nd0.67, Nd, Nd0.5Sm0.5, Sm, and Gd) and Ln1/2Ca1/2MnO3 (Ln = La, Pr, La0.5Nd0.5, Nd, Sm, and Y0.5Sm0.5) have been prepared, and structure determinations have been carried out at room temperature using high-resolution synchrotron X-ray powder diffraction data. The octahedral tilting distortion increases as the average ionic radius of the Ln/.A cations, (rA), decreases. The two crystallographically distinct Mn-O-Mn bonds are almost identical for Ln0.5Ca0.5MnO3 compounds, with the exception of La0.5Ca0.5MnO3. All of the Ln0.5Ca0.5MnO3 compounds have Pnma symmetry, whereas across the Ln0.5Sr0.5MnO3 series with increasing (rA), an evolution from Pnma over Imma to I4/mcm symmetry is observed. Changes in the octahedral tilt system at room temperature are linked to changes in the low-temperature magnetic structure. In particular, the simultaneous onset of charge ordering and CE-type antiferromagnetism in the Ln0.5Sr0.5MnO3 series appears to be closely associated with the Imma structure. The average Mn-O bond distance is relatively constant across the entire series, but individual Mn-O bond distances show the presence of a cooperative Jahn-Teller effect (orbital ordering) at room temperature in Sm0.5Ca0.5MnO3 and Sm0.25Y0.25Ca0.5MnO3
[en] Highlights: ► The series Gd1−xCaxBaCo2O5.5 was synthesised by solid state reaction. ► Magnetisation studies were carried out in the 4–300 K temperature range in magnetic fields upto 16 Tesla. ► Results were used to formulate the T versus Ca fraction, phase diagram. ► Evidence for Magnet–electronic phase separation is shown for the first time in the compound. -- Abstract: Magnetic properties of hole doped, oxygen deficient double perovskite compounds, Gd1−xCaxBaCo2O5.5, have been investigated. Ferromagnetic transition temperatures increase and the anti-ferromagnetic transition temperatures decrease with Ca substitution leading to stabilisation of ferromagnetisim for x ≥ 0.05. A detailed study of the ferromagnetic phase indicates the presence of double hysterisis loops for Ca fractions, 0.05 ≤ x ≤ 0.2 in the 50–200 K temperature range, suggestive of the co-existence of two ferromagnetic phases with different co-ercivities. Based on the magnetisation and transport measurements a phase diagram is proposed for Ca doped GdBaCo2O5.5.
[en] Magnetic properties, including magnetic structure, of some RTIn compounds (R = Tb-Er; T = Cu, Ni, Pd, Pt, Au) with the hexagonal ZrNiAl-type crystal structure are reported. Distribution of the rare earth atoms in the basal plane is similar to the kagome-lattice. Magnetic moments are localized exclusively on the rare earth atoms and form different types of magnetic ordering. Experimental results are analyzed within the Ruderman-Kittel-Kasuya-Yosida and crystal electric field frames. Monte Carlo simulations, including the J1 and J2 exchange integrals between nearest and next nearest spins and Dzialoshinsky-Moriya interaction, were performed resulting in a number of magnetic phases, some of which are in good agreement with the magnetic ordering determined in the neutron diffraction experiments. (authors)