Seung Koo Cho

Electrical conductivity of the solid solutions xCeO2 + (1-x)Dy2O3; 0.01 ⩽ x ⩽ 0.10

Abstract CeO 2 -doped Dy 2 O 3 systems containing 1, 4, 7 and 10 mol.% CeO 2 were found to be solid solutions by X-ray diffraction techniques. The lattice parameter a was obtained by the Nelson-Riley method, and its value increased with increasing dopant content. The average residual factors ( R ) obtained from X-ray intensity analysis based on oxygen interstitial and vacancy models were found to be 0.0631 and 0.1085, respectively, suggesting the oxygen interstitial model. The ratios of measured to calculated densities were found to be greater than 0.96, justifying the oxygen interstitial model. The results of thermal analysis showed that no phase transition occurred in the temperature range 500–1100 °C. The electrical conductivity was measured as a function of temperature from 500 to 1100 °C and of oxygen partial pressure from 5 × 10 −5 to 2 × 10 −1 atm. The exponential dependence of the electrical conductivity (σ) on the oxygen partial pressure ( P O 2 ) gives σαP O 2 1/ n with n = 6, the main defect and charge carriers being the oxygen interstitial and the electron hole, respectively.

Improvement of the high Tc phase and bond ordering in Bi–Sr–Ca–Cu–O superconductors by Pb doping

Abstract High-Tc superconducting materials, (Bi1−xPbx)SrCaCuO with variable amount of lead (x = 0.01–0.12) were synthesized with various processing parameters and characterized by electron microprobe analysis (EPMA), X-ray diffraction, resistivity measurement and micro-Raman spectroscopy. The Pb doping facilitates the formation of the Bi 2223 phase. The best high-Tc superconductivity is found with effective Pb amount around 12 percent, and ten days sintering. Beyond 10% Pb, the doping was found to induce a Cu-O bond ordering in the direction parallel to the c axis.

Structure of lead doped Bi-Sr-Ca-Cu-O superconductor as studied by micro-Raman spectroscopy

Abstract High-Tc superconducting materials, (Bi 1−x Pb x )SrCaCuO with variable amounts of lead ( x = 0.01–0.12) were synthesized with various processing parameters and characterized by several physical methods, in particular by micro-Raman spectroscopy. This technique is revealed to be an easy tool to follow the Pb doping effect facilitating the formation of the Bi 2223 phase. The best high-T c superconductivity was obtained with effective Pb amount around 12 percent and ten days sintering. Beyond 10 % Pb only one narrow and single Cu-O vibrational band is observed, confirming a homogenizing of the Cu-O bonds distribution in the direction parallel to the c axis by Pb doping.

Characterization of YBa2Cu3O7−xFy superconducting materials by Raman spectroscopy

Abstract A series of high-T c superconducting materials, YBa 2 Cu 3 O 7− x F y , x ⩽ 0.33 and 0.10 ⩽ y ⩽ 0.20, were prepared and their Raman spectra recorded and analyzed. Under given conditions, reproducible Raman spectra can be obtained and coherent assignments can be suggested for the YBa 2 Cu 3 O 7− x and YBa 2 Cu 3 O 7− x F y spectra. Several distinct spectra were obtained which corresponded to different scattering configurations of the micro-crystals. The fluorine atoms introduced were found to be localized in pyramidal CuO units rather than in CuO chains. This result helps us in the assignment of the vibrational modes in these materials.

Electrical conductivity and defect structure of the ThxLu2−2xO3−x solid solutions

Abstract ThxLu2−2xO3−x solid solutions containing 1, 3, 5 and 7 mol %ThO2 were synthesized with spectroscopically pure Lu2O3 and ThO2 into polycrystallinc powders. X-Ray spectroscopy revealed that all the synthesized specimens have the rare earth-type cubic structure, and that the lattice parameter of Lu2O3 increases with increasing doping level. Electrical conductivities were measured as a function of temperature from 600 to 1100°C and of po2, from 10−6 to 2 × 10−1 atm. The defect structure and the electrical conduction mechanisms were deduced from the results. The 1/n values in σ ∞ P 1 n o 2 are 1 n = 1 6 and 1 n = 0 at Po2s higher and lower than 10−4 atm, respectively. From the variation of the 1 n values from 1 n − 0 to 1 n = 1 6 , ionic and electronic conduction mechanisms are suggested in the low- and high-oxygen partial pressure regions, respectively, with two possible defect models.