Drop In Tc Research Articles

A comparative study of cationic distribution in the systems Li1+5XM1−XO3and Li1+XM1−XM′XO3(M=Nb, M′=Ti; M=Ta, M′=Ti, Zr, Sn)

Abstract A comparative ferroelectric and NMR studies of the systems Li1+5X M1−XO3 and Li1+XM1−XM′ XO3 (M=Nb, M′=Ti M = Ta; M′=Ti, Zr, Sn) have indicated that plot of TC versus composition can be qualitatively explained on the basis of cationic distribution. The strong drop of TC has been found in systems with all cations in octahedral sites, whereas little change of TC was observed along the solid solutions with Li-ions in interstitial tetrahedral sites.

Thickness dependence of the critical solution temperature of hydrogen in Pd films

The isotherms of very thin PdHx films (60 Å<d<600 Å) have been determined below room temperature by equilibrium potential measurements. One finds that the critical temperature Tc is lowered when the film thickness decreases: for the 60-Å film Tc would be near 173 K. This marked drop of Tc is attributed to clamping effects of the sample on the substrate, which decreases the effective H–H interaction and favors short-range coherency effects.

Influence of rf Plasma in Plasma Cleaning Process on Properties of Thin Superconducting Nb3Ge Films

The damage to A15 Nb3Ge films caused by Ar plasma or Ar+SF6 plasma cleaning has been studied by means of Tc and X-ray diffraction measurements. The degradation of the films was found to depend on the voltage, etching period, SF6 content, and film thickness. The drop in Tc was drastic for thinner films. Broadening of the X-ray diffraction peaks and a shift in the diffraction angle were observed after etching. An enlargement of lattice constant was detected for cathode voltages above 200 V for pure Ar plasma and below 100 V for SF6 plasma. The etch rate for Nb3Ge films in SF6 plasma was more than 100 times larger than that in pure Ar plasma.

Synergism of hyperoxia and high helium pressures in the causation of convulsions.

Hyperoxia beyond 1.8 ATA results in a striking reduction of high-pressure neurological syndrome (HPNS) type I convulsion threshold pressures but is without measurable effect on type II convulsions. The synergism is partially or completely reversed by increasing alveolar or tissue CO2 levels. High total pressures (PI) result in striking reductions in the duration of hyperoxic exposure preceding seizure onset (tc). The interaction of hyperoxia and high pressure gives rise to three zones on the PO2-Pt plane. In zone I, Pt less than 30 ATA, the duration of hyperoxia prior to convulsion onset is given by the equation PO2 -- PO2 lim = K/(tc -- tc lim), where PO2 lim and tc lim both decrease with increasing total pressure. Zone II, Pt = 30-50 ATA and PO2 1.8-2.3 ATA, is characterized by a sharp drop in tc, as Pt is increased beyond 30 ATA, to a value near 15 min that is constant within the PO2 limits given. In zone III, Pt greater than 50 ATA and PO2 greater than 0.2 ATA, tc is of the order of 2 min, and the seizures are essentially HPNS seizures only slightly modified by hyperoxia. The data are interpreted as suggesting that zone I represents hyperoxic seizures facilitated by high pressures, whereas zone II represents HPNS type I seizures facilitated by hyperoxia.

The superconductivity and magnetic susceptibility of some zirconium-transition-metal compounds; evidence for an anticorrelation

The properties of the superconducting transition temperatureT cof the CuAl 2 -type compounds of Zr 2 Co, Zr 2 Ni, Zr 2 Rh, Zr 2 Fe, and Zr 2 Ir are discussed with respect to effects due to alloying and heat treatment. Dilute pseudobinary alloys of transition-metal elements with Zr 2 Rh (T c=11.3 K) produced lower transition temperatures suggesting that the valence-electron concentration of 5.67 electrons/atom gives a maximum inT c for this crystal type. Results for Zr 2 Co (T c=5.0 K) and Zr 2 Ir (T c=7.3 K) show that their transition temperatures are raised somewhat when the electron concentration is increased by alloying. A peak is seen near 5.72 electrons/atom. A peak in the room-temperature magnetic susceptibility in the Zr 2 Co-Zr 2 Ni system occurs near the same electron concentration as the peak inT c. Similar susceptibility behavior takes place in the Zr 2 Rh-Zr 2 Ni system, however, with no peak inT c. Results of susceptibility measurements on Zr 2 Ir and its isomorphic alloys indicate correlation betweenT c and susceptibility. An anticorrelation occurs for Zr 2 Co alloys suggesting the presence of Coulomb interactions. A sharp symmetric drop inT c near the stoichiometric composition as well as a marked decrease of the transition temperature with a low-temperature (600 C) anneal indicate that the coulomb interactions are sensitive to crystalline order. The lattice parameters of Zr 2 Ir are reported as a=6.508 A andc=5.721 A. The superconductivity of Zr 3 Co (T c=3.9 K) and Zr 3 Ir (T c=2.13 K) is reported.

The Effect of Pressure on Superconducting State Parameters and Transition Temperature of Simple Metal Superconductors

AbstractA method is presented for the theoretical calculation of the logarithmic volume derivatives of the three superconducting state parameters, the phonon interaction parameter, the coulomb pseudopotential, and the energy renormalization parameter. The two representative cases of lead and aluminium have been studied. The initial linear drop of Tc when plotted against change in volume, which is experimentally observed fact, is theoretically confirmed.

Conductivity anisotropy and hot electron temperature in silicon : W.E.K. Gibbs (Australian Defense Scientific Service, Department of Supply, Defence Standards Laboratories, Maribyrnong, Victoria, Australia)

The superconducting phase diagrams for primitive tetragonal (pt) R(Rh1−xIrx)4B4 and body centered tetragonal (bct) R(Rh1−xRux)4B4 have been measured down to 4 mK revealing the characteristic drop of Tc for x⩾xcr. For pseudoternary R(Rh1−xRux)4B4 high resolution photoemission spectra clearly a shift of EF to lower energies upon alloying Ru for Rh. From a comparison between the experimental data and bandstructure calculations it can be concluded that variations of N(EF) connected with this shift are the underlying mechanism for the observed Tc(x) behavior. Contrary to this, the spectra forR(Rh1−xIrx)4B4 reveal a broadening and an increasing bandwidth of the transition metal d-band originating from the more extended 5d-wavefunctions of Ir. A numerical simulation of this broadening implies that the restriction of a constant number of occupied states leads to a shift of EFto higher energies. This results in a decrease of N(EF) and Tc. In addition to the peculiar superconducting phase diagram inHo(Rh1−xRux)4B4 a change in magnetic order from antiferromagnetism for x<xcr to ferromanetism for x close to 1 is observed by neutron scattering. Whereas in case of x=0.90 and 1.00 the magnetic phase can be described by a superposition of a ferromagnetic and an antiferromagnetic component, the sample with x=0.10 orders magnetically at 1.5 K with a complicated acollinear antiferromagnetic structure.