Anisotropy of the superconducting critical magnetic field HC2 of LaMCuO system(M = Sr and Ba)

Preliminary measurement of the superconducting critical magnetic field H_c2 of LaMCuO system (M = Sr and Ba) with layered perovskite structure has been carried out. The results show a quite large anisotropy of H_c2 indicating that the present system has a two dimensional character of the electron transport. The measured conductivities seem to be consistent with the values estimated from the observed H_c2 by use of an ideal two dimensional band with free electron mass.     

Zero resistance above 90K in superconducting oxides ErBaCuO and YbBaCuO

Superconductivity transition has been observed by electrical resistance and a.c. magnetic susceptibility measurements in ErBaCuO and YbBaCuO systems. The highest T_c(ϱ=0) is 90.3K for ErBaCuO and 91K for YbBaCuO.     

High Tc superconductivity of a TlBaCaCuO compound

A TlBaCaCuO_4.5+x compound has been investigated from the point of view of superconductivity. Depending on the heat treatment, one part of the samples exhibits superconductivity with an onset of 121 K and a zero resistivity of 106 K, while the other part of them shows only a sharp drop in resistivity at 130 K which hints at the existence of superconducting domains. This picture was confirmed by magnetic and ESR measurements giving possibility for estimation of the critical magnetic fields.     

Pd addition in high Tc YBaCuO oxide

A small amount of Pd addition increases T_c for the YBa₂Cu₃O_7−y oxide. The maximum offset, midpoint and onset temperatures of the YBa₂(Cu_0.999Pd_0.001)₃O_7−y oxide are 92.1, 95.0 and 105 K, respectively. Excess addition of Pd decreases T_c. The T_c change is consistent with the results of the lattice constants.     

Mössbauer resonance investigations on the SnF2SnF4 system

The Mössbauer resonance spectra of the compounds isolated in the SnF₂SnF₄ system have been studied. The isomer shifts allowed the authors to locate the tin atoms in different chemical environments. The results have been correlated with the electronic structures of both oxidation states of tin and an estimate of the ionicities of the bonding orbitals has been given. For tin(IV) the quadrupole splitting can be explained by means of unequivalent neighboring fluorine atoms. For tin(II) it can be interpreted in terms of p-character and hybrid nature of bonding and non-bonding orbitals. A Goldanskii-Karyagin effect is observed for αSnF₂, Sn₃F₈ and Sn₇F₁₆.     

The superconductivity,structure and microstructure of BaYScCu oxides

We added small amount of Sc (0.05–0.35at.%) to BaYCu oxide and found that the superconductivity deteriorated drastically when the Sc content reached 0.325at.%. X-ray and electron diffraction showed that the orthorhombic perovskite structure changed to multi-phase structure with unidentified phases. The microstructures observed by TEM are of needle like morphology. Their phases are not yet identified.     

Zero resistance at 148.5K in fluorine implanted YBaCuO compound

Fluorine ions with an energy of 180keV at a dose of 1×10¹⁵ ions/cm² have been implanted into YBa₂Cu₃O_x. After annealed at 800°C, the resistance of the new Y-Ba-Cu-F-O compound drops to zero at 148.5K.     

Electron diffraction and electron microscopic study of BaYCuO superconducting materials

Electron microscopy and electron diffraction have been applied to show that the orthorhombic phase in the compound Ba₂YCu₃O_7−δ is responsible for the high superconducting transition temperature. A positive correlation is found between the volume fration of the orthorhombic phase and the superconducting transition temperature. By means of an “in-situ” heating experiment it is found that the orthorhombic phase is formed on cooling from a high temperature tetragonal phase with disordered vacancies. It is suggested that the low temperature tetragonal phase that occurs in the same specimens as the orthorhombic phase also contains an ordered arrangement of vacancies different from that present in the orthorhombic phase. The order-disorder transition associated with the structural vacancies is shown to be reversible, provided there has been no oxygen loss.     

Electrical properties of LiBSe ternary system

Amorphous products were obtained in the LiBSe ternary system by quenching melts of Li₂Se, B and Se mixture prepared at 100°C in sealed silica tubes. The vitreous region was slightly lower selenium composition than that of the Li₂SeB₂Se₃ tie-line. The amorphous products were lithium ionic conductors and most of them showed contributions to their total conductivity. The amorphous product of composition Li₂₅B₃₆Se₃₉ has the least electronic contribution to its total conductivity of 6.0 × 10⁻⁶ S/cm at room temperature. A new crystalline compound and crystalline LiBH₄ were also obtained in LiBSe ternary. Both of them were lithium ionic conductors having conductivities of about 1 × 10⁻⁶ S/cm at room temperature.     

Ionic conductivity of ZrF4BaF2MX (M = Li,Na;X = F,Cl) glasses

Glasses were prepared in a wide range of compositions for the two systems oof mixed-cation, ZrF₄BaF₂LiFNaF, and mixed-anion, ZrF₄BaF₂LiFLiCl. Ionic conductivities were measured for these glasses and it was found that these glasses were not only cationic but also anionic conductors depending on the total alkali halide content. Four types of mixed-cation and mixed-anion effects on ionic conductivity were demonstrated for the cation-conducting and anion-conducting glasses. In cation conduction, the cation mixing caused the conductivity decline, whereas the anion mixing led to the conductivity enhancement. In anion conduction, on the other hand, the cation mixing led to the conductivity enhancement, whereas the anion mixing caused the conductivity decline.     

Superconductivity of TiZrNi alloys containing quasicrystals

Superconductivity of rapidly quenched ribbons Ti₅₃Zr₂₇Ni₂₀ at 1.94 K and the beginning of the transition to the superconductivity in ribbons Ti₄₅Zr₃₈Ni₁₇ below 1.5 K were found. X-rays diffractometry measurements showed that the icosahedral quasicrystal phase is dominant in all samples.     

Blue photoluminescence from SiGeSiO2 co-sputtered films

A blue photoluminescence band centered at 440 nm was observed from SiGeSiO₂ co-sputtered films at room temperature. This band gains intensity after the film was annealed at a temperature around 900°C in N₂ atmosphere. From analysis of photoluminescence excitation, Raman and X-ray photoelectron spectra, it turns out that the luminescence is probably from some interfacial state between Si_1−xGe_x nanoparticles and the SiO₂ matrix.     

Lattice dynamics and debye temperature of AlCu,AlSi and AlGe alloy systems

The lattice dynamics and specific heat at constant volume for AlCu alloy system is studied using our previous treatment based on the microscopic electronic theory. Considering the volume and electron density effect on the dynamical matrix of the pure constituent, we obtain the band and local mode frequencies at the temperature-dependent specific heat in the Al_1−x Cu_x solid solution. Then, using the data about the mean elastic wave and the specific heat extrapolated to the absolute zero temperature, the Debye temperature is presented for the Al_1−xCu_x, Al_1−xSi_x and Al_1−xGe_x alloy systems. The Debye temperature decreases as a function of the Cu atomic fraction x for Al_1−xCu_x alloy, and remarkably for Al_1−xSi_x and Al_1−xGe_x solid solutions.     

Mössbauer studies of the charge-density-wave state of 57FeK0.30MoO3

Mössbauer studies have been performed between 6 K and 300 K on single crystals of ⁵⁷Fe-doped K_0.30MoO₃, which show a Peierls transition at 180 K towards on incommensurate charge density wave state. The spectra show three doublets. A strong line broadening below 120 K indicates that the Fe impurities are strong pinning centers for the charge density wave above ∼ 120 K and become progressively weak pinning ones below, in agreement with theoretical models.