Leiming Fang

We present detailed measurements of the longitudinal resistivity ${\ensuremath{\rho}}_{xx}(T,H)$ and the upper critical field ${H}_{c2}$ of ${\text{NdFeAsO}}_{0.7}{\text{F}}_{0.3}$ single crystals in strong dc and pulsed magnetic fields up to 45 and 60 T, respectively. We found that the field scale of ${H}_{c2}$ is comparable to ${H}_{c2}\ensuremath{\sim}100\text{ }\text{T}$ of high-${T}_{c}$ cuprates. ${H}_{c2}(T)$ parallel to the $c$ axis exhibits a pronounced upward curvature similar to what was extracted from earlier measurements on polycrystalline LaFeAs(O,F), NdFeAs(O,F), and SmFeAs(O,F) samples. Thus, this behavior of ${H}_{c2}^{\ensuremath{\perp}}(T)$ is indeed an intrinsic feature of oxypnictides rather than manifestation of vortex lattice melting or granularity. The orientational dependence of ${H}_{c2}(\ensuremath{\theta})$ as a function of the angle $\ensuremath{\theta}$ between $H$ and the $c$ axis shows deviations from the one-band Ginzburg-Landau scaling. The mass anisotropy parameter $\ensuremath{\gamma}(T)={({m}_{c}/{m}_{ab})}^{1/2}={H}_{c2}^{\ensuremath{\parallel}}/{H}_{c2}^{\ensuremath{\perp}}$ obtained from these measurements decreases as temperature decreases from $\ensuremath{\gamma}\ensuremath{\simeq}9.2$ at 44 K to $\ensuremath{\gamma}\ensuremath{\simeq}5$ at 34 K, where $\ensuremath{\parallel}$ and $\ensuremath{\perp}$ correspond to $H$ parallel and perpendicular to the $ab$ planes, respectively. Spin-dependent magnetoresistance and nonlinearities in the Hall coefficient suggest contribution to the conductivity from electron-electron interactions modified by disorder reminiscent of that in diluted magnetic semiconductors. The Ohmic resistivity ${\ensuremath{\rho}}_{xx}(T,H)$ measured below ${T}_{c}$ but above the irreversibility field exhibits a clear Arrhenius thermally-activated behavior $\ensuremath{\rho}={\ensuremath{\rho}}_{0}\text{ }\text{exp}[\ensuremath{-}{E}_{a}(T,H)/T]$ over 4--5 decades of ${\ensuremath{\rho}}_{xx}$. The activation energy ${E}_{a}(T,H)$ has very different field dependencies for $H\ensuremath{\parallel}ab$ and $H\ensuremath{\perp}ab$ varying from $4\ifmmode\times\else\texttimes\fi{}{10}^{3}\text{ }\text{K}$ at $H=0.2\text{ }\text{T}$ to $\ensuremath{\sim}200\text{ }\text{K}$ at $H=35\text{ }\text{T}$. We discuss to what extent different pairing scenarios suggested in the literature can manifest themselves in the observed behavior of ${H}_{c2}$, using the two-band model of superconductivity in oxypnictides. The results indicate the importance of paramagnetic effects on ${H}_{c2}(T)$ in oxypnictides, which may significantly reduce ${H}_{c2}(0)$ as compared to ${H}_{c2}(0)\ensuremath{\sim}200--300\text{ }\text{T}$ based on extrapolations of ${H}_{c2}(T)$ near ${T}_{c}$ down to low temperatures.

Abstract Dye‐sensitized solar cells (DSSCs) are receiving considerable attention as low‐cost alternatives to conventional solar cells. In DSSCs based on liquid electrolytes, a photoelectric efficiency of 11 % has been achieved, but potential problems in sealing the cells and the low long‐term stability of these systems have impeded their practical use. Here, we present a thermoplastic gel electrolyte (TPGE) as an alternative to the liquid electrolytes used in DSSCs. The TPGE exhibits a thermoplastic character, high conductivity, long‐term stability, and can be prepared by a simple and convenient protocol. The viscosity, conductivity, and phase state of the TPGE can be controlled by tuning the composition. Using 40 wt % poly(ethylene glycol) (PEG) as the polymeric host, 60 wt % propylene carbonate (PC) as the solvent, and 0.65 M KI and 0.065 M I 2 as the ionic conductors, a TPGE with a conductivity of 2.61 mS cm –2 is prepared. Based on this TPGE, a DSSC is fabricated with an overall light‐to‐electrical‐energy conversion efficiency of 7.22 % under 100 mW cm –2 irradiation. The present findings should accelerate the widespread use of DSSCs.

The average measured Hv for polycrystalline ReB2 and Ti–B composites under different loads shows that the tendency of Hv to decrease becomes weak for large loads, and the measured hardness of ReB2 is always lower than that of Ti–B composites. For comparison, the results from Chung et al. were inserted into the figure.

Three ZnAl2O4 samples were prepared via a modified polyacrylamide gel method using a citric acid solution with different aluminum salt starting materials, including AlCl3 ∙ 6H2O, Al2(SO4)3 ∙ 18H2O, and Al(NO3)3 ∙ 9H2O under identical conditions. The influence of different aluminum salts on the morphologies, phase purity, and optical and fluorescence properties of the as-prepared ZnAl2O4 nanoparticles were studied. The experimental results demonstrate that the phase purity, particle size, morphology, and optical and fluorescence properties of ZnAl2O4 nanoparticles can be manipulated by the use of different aluminum salts as starting materials. The energy bandgap (Eg) values of ZnAl2O4 nanoparticles increase with a decrease in particle size. The fluorescence spectra show that a major blue emission band around 400 nm and two weaker side bands located at 410 and 445 nm are observed when the excitation wavelength is 325 nm. The ZnAl2O4 nanoparticles prepared from Al(NO3)3 ∙ 9H2O exhibit the largest emission intensity among the three ZnAl2O4 samples, followed in turn by the ZnAl2O4 nanoparticles prepared from Al2(SO4)3 ∙ 18H2O and AlCl3∙6H2O. These differences are attributed to combinational changes in Eg and the defect types of the ZnAl2O4 nanoparticles.