The real and imaginary parts of the frequency dependent response of YBaCuO samples doped with scandium are measured over a wide frequency range (5 Hz to 13 MHz) both, in the normal (at 298 K) and in the superconducting (at 77 K) states. An attempt is made to identify the relaxation mechanisms responsible for ac conduction in the samples. It is suggested that 2p hole-polarons associated with the oxygen atoms play an important role in determining the frequency dependent behaviour in the normal state as well as at their superconductivity.Der Real-und Tmaginiiranteil der frequenzabhingigen Kennlinie von mit Scandium dotierten YBaCuO-Proben werden uber einen groRen Frequenzbereich (5 Hz bis 13 MHz) sowohl im Normal-(bei 298 K) als auch im Supraleitungsiustand (bei 77 K) gemessen. Es wird versucht, den fur die Wechselstromleitfiihigkeit verantwortlichen Relaxationsmechanismus zu identifizieren. Es wird angenommen, dalj 2p-Locherpolaronen, die mit den Sauerstoffatomen verknupft sind, einc wesentliche Rolle bei der Bestimmung des frequenzabhangigen Verhaltens im Normalzustand sowie bei ihrer Supraleitfahigkeit spielen.

The ratio of the real (σ1) and imaginary (σ2) parts of the ac conductivity of Y(1−x)PrxBa2Cu3O7−δ (x = 0,0.1,0.3,0.4) in the frequency range 0.5–12 MHz and in the temperature range 78–300 K is measured. The agreement between the experimental and theoretical results suggests that the normal state ac conduction behaviour can be successfully explained using a correlated barrier hopping (CBH) model for polarons as carriers. The CBH process is dominant in the higher frequency range (above 2.5 MHz), and at lower frequencies tunnelling of polarons has to be considered to explain the nature of the variation of with ω. This analysis may be considered as supporting evidence for Mott’s theory of polaronic conduction in high temperature superconducting materials.

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Measurements were carried out to obtain the ratio of the imaginary (σ 2 ) and the real (σ 1 ) part of ac conductivity for pure and Pr-doped YBCO materials at different temperatures (77-300 K) and frequencies (0.1-10 MHz). The large numbers of data thus obtained were scaled using a model-independent scaling technique. The scaling parameters obtained in this process were also successfully used to scale other experimental data on susceptibility, Hall number, thermo-emf, etc, for the same materials. The scaling parameter T S has a range of values that are close to those of the pseudogap (PG) parameter in the corresponding cases. It was also observed that the variations of T S and the PG with Pr concentration are similar.