The in-plane resistivity, in-plane absolute thermopower, and upper critical field measurements are reported for single-crystal samples of YNi 2 B 2 C and LuNi 2 B 2 C superconductors. The in-plane resistivity shows metallic behavior and varies approximately linearly with temperature near room temperature ͑RT͒ but shows nearly quadratic behavior in temperature at low temperatures. The YNi 2 B 2 C and LuNi 2 B 2 C single-crystal samples exhibit large transverse magnetoresistance ͑Ϸ6-8 % at 45 kOe͒ in the ab plane. The absolute thermopower S(T) is negative from RT to the superconducting transition temperature T c. Its magnitude at RT is a few times of the value for a typical good metal. S(T) is approximately linear in temperature between Ϸ150 K and RT. Extrapolation to Tϭ0 gives large intercepts ͑few V/K͒ for both samples suggesting the presence of a much larger ''knee'' than would be expected from electron-phonon interaction renormalization effects. The upper critical fields for H parallel and perpendicular to the c axis and the superconducting parameters derived from it do not show any anisotropy for the YNi 2 B 2 C single-crystal samples in agreement with magnetization and torque magnetometry measurements, but a small anisotropy is observed for the LuNi 2 B 2 C single crystals. The analysis shows that these are moderately strong-coupling type-II superconductors ͑similar to the A-15 com-pounds͒ with a value of the electron-phonon coupling parameter ͑0͒ approximately equal to 1.2 for YNi 2 B 2 C and 1.0 for LuNi 2 B 2 C, the Ginzburg-Landau coherence length ͑0͒ approximately equal to 70 Å, and H c2 (0)ϳ60-70 kOe. The temperature dependence of the upper critical field shows a positive curvature near T c in disagreement with the Werthamer, Helfand, Hohenberg, and Maki ͑WHHM͒ theory but in agreement with a recent solution of the Gor'kov equation using a basis formed by Landau levels ͑Bahcall͒; however, the data show a severe disagreement between the observed low-temperature behavior of H c2 (T) and that predicted either by WHHM or Bahcall's expressions. ͓S0163-1829͑97͒06413-8͔

Se1-xTex semiconducting glasses have been prepared and characterized by optical, electrical and X-ray measurements. It is found that homogeneous Se1-xTex glasses can only be prepared, without any trace of detectable crystallinity, up to x approximately=0.30 by the usual conventional quenching technique. Due to the high absorbance of Se1-xTex glasses in the visible region, photoacoustic absorption spectroscopy has been used for the first time to study their optical energy gap variation as a function of x. The optical energy gap Eg of amorphous Se is found to be about 0.12 eV higher than that of c-Se. It is observed that initial small substitution of Te into a-Se rapidly decreases Eg. For x>0.10, the variation in Eg becomes smaller and linear with x. Temperature dependence of the conductivity suggests that the electronic conduction in these glasses takes place via extended states. The activation energy and conductivity prefactor both decrease with x and show sudden changes at x approximately=0.1. An attempt is made to explain these results based on the charge defect model and the tailing of energy bands in the gap region.