We have measured the specific heat, the electrical resistance and the magnetic susceptibility of YBa2Cu3O7–x in a superconducting (sc) and in a non-superconducting (nsc) version. The latter was obtained by inducing a small loss of oxygen. In the sc sample we find a jump of the specific heat with C=3.6 J mole–1 K–1. Below the maximum nearTc the specific heat of the sc version drops too fast for an electronic effect alone: there is a cross-over from excess to deficiency already at 0.9Tc. The specific heat of the nsc version shows a change of slope in the temperature range between 70 and 80 K, which indicates the existence of a second specific heat anomaly, which apparently exists independently of that due to the onset of superconductivity and explains at least partially the premature crossover.Alexander von Humboldt fellow. On leave in absence from Centro Atomico Bariloche—CNEA Argentina 相似文献
The P-type delayed fluorescence (DF) Si→So of aromatic compounds results from the population of excited singlet states Si by triplet—triplet annihillation (TTA) of molecules in their lowest and metastable triplet state T1 : T1 + T1 Si + So; Si may be any excited singlet state whose excitation energy E(Si ? 2 E(T1). TTA of unlike molecules A and B (hetero-TTA) may lead to excited singlet states either of A or of B. In particular, if E(TA1) < E(T1B), hetero-TTA may lead to excited singlet states SkA which are not accessible by TTA of 2 T1A. In the present paper we report the first example of the detection of the DF from a very short-lived upper excited singlet state SkA which has been populated by hetero-TTA. The systems investigated are liquid solutions of A = anthracene-h10 or anthracene-d10 or 9,10-dimethylanthracene and B = xanthone in 1,1,2-trichlorotrifluoroethane at 243 K. SkA is the lowest 1B3U+ state (Bb state) of anthracene. 相似文献
Oxidative addition reactions of Cl2CPR (R = 2,4,6-tris(trifluoromethyl)phenyl (Ar) or 2,6-bis(trifluoromethyl)phenyl (Ar′) with Pt(PPh3)4 yield the cis and trans (at platinum) complexes [PtCl(ClCPAr)(PPh3)2] and [PtCl(ClCPAr′)(PPh3)2]. All starting materials and intermediates have been characterised by NMR spectroscopy. The crystal and molecular structures of the trans-platinum complexes have been determined by single-crystal X-ray diffraction at low temperature. 相似文献
Results of the superconducting transition temperatureTc of amorphous and microcrystalline films of lead doped with manganese as magnetic impurity are reported in this work. The amorphous films show an Abrikosov-Gor'kov behaviour, whereas for the crystalline films there is a much smaller depression and a peak for higher Mn concentrations, which indicates a region of coexistence of superconductivity and magnetic ordering as a spinglass.Supported by the Deutsche Forschungsgemeinschaft in the Sonderforschungsbereich 125, Fehlordnung in Metallen — Aachen, Jülich, Köln 相似文献