Search

© 2001 The American Physical Society. The work performed at the Naval Research Laboratory was supported by ONR. We thank J. Ullrich for help in the dielectric measurements and J. Santamaría and C. T. Moynihan for helpful discussions., Electrical relaxation data of crystalline yttria-stabilized zirconia are used to analyze the permittivity change observed in the spectra of the real part of the permittivity in ionic conducting materials. It is found that this permittivity change is independent of both temperature and mobile-ion concentration, and it is determined solely by the degree of interaction among ions in the relaxation process. This finding is at odds with an expression for the permittivity change in the framework of a proposed universal ac conductivity scaling law for glassy ionic conductors. On the other hand, not only the total permitivity change, but also the particular frequency dependence of the permittivity spectra is found to be consistent with the analysis of electrical relaxation in terms of the electric modulus. The results of this work give further support to the use of the electric modulus in describing electrical relaxation in ionic conductors., ONR, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2001 The American Physical Society. Financial support from CICYT Grant Nos. MAT94-0604, MAT97-0675, and MAT99-1706E is acknowledged. Z.S. thanks AECI for financial support., Epitaxial YBa_(2)Cu_(3)O_(7) thin films, grown by high-pressure dc sputtering, are irradiated with He^(+) ions at 80 keV with doses between 10^(14) and 10^(15) cm^(-2). Irradiation reduces the critical temperature but it does not modify the carrier concentration. Angle-dependent resistivity is used to show that the mass anisotropy does not change upon irradiation. The melting transition in magnetic fields applied parallel to the c axis is analyzed by I-V critical scaling, and all irradiated and nonirradiated samples show a three-dimensional vortex glass transition with the same critical exponents. The dissipation in the liquid state is analyzed in terms of the activation energy of the magnetoresistance in a perpendicular magnetic field. While as-grown samples show an activation energy depending as 1/H on the applied magnetic field, irradiated samples show a dependence as 1/H^(0.5), characteristic of plastic deformation of vortices. This is discussed in terms of the point disorder introduced by ion irradiation., CICYT, AECI, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 1998 The American Physical Society., We present complex admittance measurements on single-crystal yttria-stabilized zirconia and polycrystalline Li_(0.5)La_(0.5)TiO_(3) over the frequency range 5 Hz to 30 MHz and at temperatures ranging between 150 and 650 K. Electric-field relaxation in both fast ionic conductors can be described using Kohlrausch-Williams-Watts decay functions, but departures are observed at high frequencies and low temperatures. Electric modulus data obey the Dixon Nagel scaling that has been proposed to be universal in describing the relaxation processes in supercooled liquids. Our data provide broader universality to the Dixon-Nagel scaling, and are interpreted in terms of the influence of mobile ions positional disorder on the relaxation dynamics., Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub