In this work the time resolved thermal lens spectrometry was applied to measure the absolute values of the thermo-optical properties of low silica calcium aluminosilicate and soda lime glasses at low temperatures, in the range between 20 and 300 K. The thermal relaxation calorimetry was used as a complementary technique to determine the specific heat. The results showed a marked decrease of the thermal diffusivity with the temperature rise, with a dependence similar to that of the mean free path ͑ϳT −1 ͒ in the interval between 20 and 70 K, while in the range between 70 and 300 K the dependence was T −͑0.33±0.02͒. The marked variation of the temperature coefficient of the optical path length change with the temperature rise was attributed to the increase in the coefficient of the electronic polarizability. The results also showed that for the aluminosilicate glass the excess in the specific heat correlated to the so-called boson peak occurred at about 17 K, higher than that of soda lime, which occurs at about 12 K. In conclusion, our results showed the ability of the time resolved thermal lens to determine the thermo-optical properties of glasses at low temperatures, bringing possibilities for experiments in a wide range of optical materials.
It is reported superconductivity in Nb5Ge3C0.3, an interstitial carbide compound. The temperature dependence of the electrical resistivity, ac-susceptibility, and heat capacity (HC) indicate that a bulk type-II superconductivity appears at TC = 15.3 K. Magneto-resistance measurements suggest an upper critical field of BC2 ∼ 10.6 T and a coherence length of ξ ∼ 55 Å at zero temperature. Neutron diffraction analyzes locate the carbon atoms at the interstitial 2b site of the Mn5Si3 type-structure. Heat capacity data below TC are well described by BCS theory. The size of the jump at TC is in good agreement with the superconducting volume fraction observed in susceptibility measurements. A Debye temperature and Sommerfeld constant were also extracted from heat capacity data as 343 K and 34 mJ/mol K2, respectively.
We have measured the electrical resistivity and ac magnetic susceptibility (T) of (La 1Ϫx Ce x) 3 Al, for 0 рxр1, and the electrical resistivity of (Ce 1Ϫz Y z) 3 Al, for 0рzр0.1. The system was characterized using x-ray diffraction and metallography. From x-ray data we were able to determine the structure for all samples to be hexagonal and that the unit-cell volume decreases linearly in going from the La-rich side to the Ce-rich side. The results show that La 3 Al is a superconductor below 6.2 K and that T c decreases rapidly with the increase of the Ce concentration. For xϾ0.04 we observed a minimum in the resistivity and a reduction of the effective magnetic moment of Ce due to a strong compensation promoted by the Kondo effect. Our results show that the Kondo temperature increases with Ce and Y concentration, according to the reduction of the unit-cell volume. We also show that the antiferromagnetic transition temperature goes through a maximum at zϭ0.025, indicating that there is an interplay between superconductivity, antiferromagnetic ordering, and the Kondo effect. A diagram illustrating the evolution of the T K and T N is presented. The electronic specific heat ͑␥͒ increases with the Ce concentration showing a maximum around xϷ0.4. It was also possible to determine values for the J product and the relative variation of the exchange parameter. ͓S0163-1829͑98͒00609-2͔
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