Physics

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The stability of organic photovoltaic (OPV) devices in ambient conditions has been a serious issue which needs to be addressed and resolved timely. In order to probe the degradation mechanism in a donor-acceptor polymer PDPP-TNT: PC71BM bulk heterojunction basedOPVdevices, we have studied current density-voltage ( J-V ) behavior and impedance spectroscopy of fresh and aged devices. The current-voltage characteristic of optimized fresh devices exhibit a short circuit current density ( Jsc) of 8.9 mA cm2, open circuit voltage (Voc) of 0.79 V, fill factor (FF) of 54.6\%, and power conversion efficiency (PCE) of 3.8\%. For aged devices, Jsc,Voc, FF, and PCE were reduced to 57.3\%, 89.8\%, 44.3\% and 23.7\% of its initial value, respectively. The impedance spectra measured under illumination for these devices were successfully fitted using a CPE-based circuit model. For aged devices, the low-frequency response in impedance spectra suggests an accumulation of the photogenerated charge carriers at the interfaces which leads to a significant lowering in fill factor. Such degradation in device performance is attributed to the incorporation of oxygen and water molecules in devices. An increase in the recombination resistance indicates a deterioration of free charge carrier generation and conduction in devices. © 2016 IOP Publishing Ltd.

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Materials Research Express

Analysis of degradation mechanisms in donor-acceptor copolymer based organic photovoltaic devices using impedance spectroscopy

Metals (Zr, Zn and Cu) containing oil swollen surfactant gels have been utilized as precursors for the preparation of metal oxides (ZrO2, ZnO and CuO) nanoparticles. No metal alkoxide, external gelating agent or any other intricate molecule have been utilized to reinforce gelation; gel stage has been achieved simply through judicial adjustment of water to surfactant ratio and salinity of the reaction mixture. Unlike, several previously published reports, in this approach surfactant has been added not to just increase the viscosity of solution but it has also formed rod shaped gelatinous micelles in response to the variation in water to surfactant ratio, which endowed mechanical strength to the gel. The effect of nature of metal salt on mechanical properties of gel has also been investigated. Zn and Cu containing cetyltrimethylammonium bromide (CTAB) gels have been found to be strongest and weakest, respectively. Metal containing CTAB gels were heat treated at various temperatures (600, 700 and 800 °C) in order to obtain metal oxides nanoparticles. The effect of calcination temperature on crystallinity, particle size and morphology of the metal oxides nanoparticles has also been investigated. A comparison between ZrO2 nanoparticles prepared using conventional sol gel and oil swollen surfactant gel method has also been carried out in terms of crystallinity, particle size and optical property. © 2016 Elsevier Ltd and Techna Group S.r.l.

Ceramics International

Oil swollen surfactant gel based synthesis of metal oxides nanoparticles: An attractive alternative for the conventional sol gel synthesis

We carry out a systematic qualitative analysis of the two quadratic schemes of generalized oscillators recently proposed by Quesne [J. Math. Phys. 56, 012903 (2015)]. By performing a local analysis of the governing potentials, we demonstrate that while the first potential admits a pair of equilibrium points one of which is typically a center for both signs of the coupling strength λ, the other points to a centre for λ < 0 but a saddle λ > 0. On the other hand, the second potential reveals only a center for both the signs of λ from a linear stability analysis. We carry out our study by extending Quesne's scheme to include the effects of a linear dissipative term. An important outcome is that we run into a remarkable transition to chaos in the presence of a periodic force term f cos ωt. © 2016 AIP Publishing LLC.

Journal of Mathematical Physics

Qualitative analysis of certain generalized classes of quadratic oscillator systems

Based on the results of the classification by T.-h. Abe, Nucl. Phys. B894, 374 (2015)., we exhaustively investigate Yukawa sector of U(8) model on magnetized orbifolds T2/Z2, T2/Z3, T2/Z4 and T2/Z6 by evaluating ratios of the mass eigenvalues of the three states in all the possible configurations with one and two Higgs pairs where three generations are realized in fermions. Because of the smearing effect via kinetic mixing, one can realize a hierarchy such as 10-2-10-3, but it is very difficult to achieve the mass ratio between the up and top quarks (mup/mtop∼10-5) on the complicated magnetized orbifolds T2/ZN(N=3,4,6). © 2016 American Physical Society.

Physical Review D

Comprehensive analysis of Yukawa hierarchies on T2 /ZN with magnetic fluxes

The improvement of the plasma illumination (PI) properties of a microplasma device due to the application of nanocrystalline diamond-decorated graphene nanoflakes (NCD-GNFs) as a cathode is investigated. The improved plasma illumination (PI) behavior is closely related to the enhanced field electron emission (FEE) properties of the NCD-GNFs. The NCD-GNFs possess better FEE characteristics with a low turn-on field of 9.36 V μm-1to induce the field emission, a high FEE current density of 2.57 mA cm-2and a large field enhancement factor of 2380. The plasma can be triggered at a low voltage of 380 V, attaining a large plasma current density of 3.8 mA cm-2at an applied voltage of 570 V. In addition, the NCD-GNF cathode shows enhanced lifetime stability of more than 21 min at an applied voltage of 430 V without showing any sign of degradation, whereas the bare GNFs can last only 4 min. The superior FEE and PI properties of the NCD-GNFs are ascribed to the unique combination of diamond and graphene. Transmission electron microscopic studies reveal that the NCD-GNFs contain nano-sized diamond films evenly decorated on the GNFs. Nanographitic phases in the grain boundaries of the diamond grains form electron transport networks that lead to improvement in the FEE characteristics of the NCD-GNFs. © 2016 The Royal Society of Chemistry.

RSC Advances

Growth, structural and plasma illumination properties of nanocrystalline diamond-decorated graphene nanoflakes

Microwave processing of SrBi2Nb2O9 ferroelectric ceramics was targeted in the current work. In particular, Curie temperature, dielectric constant, dielectric loss and dc conductivity were studied for microwave sintered SrBi2Nb2O9 ferroelectric ceramics in the range 1050-1200 °C. The space charge dielectric relaxation was found noticeable in all sintered samples and electrical properties like dielectric constant, loss and dc conductivity were significantly affected due to this dielectric relaxation. An optimum processing condition was targeted by investigating frequency and temperature dependent dielectric responses along with dc conductivity. © 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Microwave processed SrBi2Nb2O9 ferroelectric ceramics with controlled dielectric relaxation and metallic conduction

The variation of electron density in TiO2-x nanochannels, exhibiting resistive switching phenomenon, produced by Ar+ ion-irradiation at the threshold fluence of 5 × 1016 ions/cm2 is demonstrated by X-ray reflectivity (XRR). The transmission electron microscopy reveals the formation of nanochannels, while the energy dispersive X-ray spectroscopy confirms Ti enrichment near the surface due to ion-irradiation, in consistent with the increase in electron density by XRR measurements. Such a variation in Ti concentration indicates the evolution of oxygen vacancies (OVs) along the TiO2-x nanochannels, and thus paves the way to explain the operation and performance of the Pt/TiO2-x/Pt-based memory devices via OV migration. © 2016 Author(s).

Applied Physics Letters

Probing electron density across Ar+ irradiation-induced self-organized TiO2- x nanochannels for memory application

The crystal structure of a ternary sulfide with the approximate composition LiCuS, which is a promising candidate for environment-friendly battery and solar cell materials is reported. The crystal structure was solved by a combination of neutron and X-ray powder diffraction data and 7 Li solid-state NMR analysis. A yellow powder, Li1.1Cu0.9S, was obtained by the reaction of CuS with a slight excess of Li metal. The compound crystallizes in the Na3AgO2 structure type in the space group Ibam. An idealized crystal structure of Li1.1Cu0.9S can be derived from the cubic Li2S structure by moving a part of the Li along the c axis so that these Li atoms become linearly coordinated by S. All the metal sites are occupied by randomly mixed Li and Cu atoms; however, there is a strong preference for linear coordination by Cu. The density functional theory calculations show that Li1.1Cu0.9S is a direct band-gap semiconductor with an energy gap of 1.95 eV in agreement with experimental data.

Solid State Sciences

LiCuS, an intermediate phase in the electrochemical conversion reaction of CuS with Li: A potential environment-friendly battery and solar cell material

Ga71 NQR, magnetization and specific-heat measurements have been performed on polycrystalline Ge-doped FeGa3 samples. A crossover from an insulator to a correlated local moment metal in the low-doping regime and the evolution of itinerant ferromagnet upon further doping is found. For the nearly critical concentration at the threshold of ferromagnetic order, xC=0.15, (1/T1T)71 exhibits a pronounced T-4/3 power law over two orders of magnitude in temperature, which indicates three-dimensional quantum critical ferromagnetic fluctuations. Furthermore, for the ordered x=0.2 sample (TC≈6 K), (1/T1T)71 could be fitted well in the frame of Moriya's self-consistent renormalization theory for weakly ferromagnetic systems with 1/T1T∼$\chi$. In contrast to this, the low-doping regime nicely displays local moment behavior where 1/T1T∼$\chi$2 is valid. For T→0, the Sommerfeld ratio $\gamma$=(C/T) is enhanced (70mJ/moleK2 for x=0.1), which indicates the formation of heavy 3d electrons.

Physical Review B

Towards ferromagnetic quantum criticality in FeGa3-xGex: Ga 71 NQR as a zero-field microscopic probe

The microscopic magnetism in the helical, conical and ferromagnetically polarized phases in an itinerant helical magnet, MnSi, has been studied by an extended 29Si NMR at zero field and under external magnetic fields. The temperature dependence of the staggered moment, MQ (T), determined by the 29Si NMR frequency, $\nu$(T) and the nuclear relaxation rate, 1=T1 (T), at zero field is in general accord with the SCR theory for weak itinerant ferromagnetic metals and its extension to helical magnets. The external field dependence of resonance frequency, $\nu$(H), follows a vector sum of the contributions from the atomic hyperfine and macroscopic fields with a field induced moment characteristic to itinerant magnets. A discontinuous jump of the resonance frequency at the critical field, Hc , between the conical and the polarized phases has also been found, which suggests a first order like change of the electronic states at Hc.