Frequency Dependednt Losses in YBaCuO Superconductors

Abstract

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.

Electrical Study of 123 HTSC (77 to 400 K) with Varying Fraction of Y. Explanation of the Normal State Behaviour

“…For T = 100 K, R = 7.7 nm and W = 0.052eV. This value of W compares well with results obtained in our earlier work [7].…”

“…In our earlier work on frequency dependent losses at room temperature in YBa,Cu,O, [7] we found strong evidence that ac conduction and relaxation in these systems were due to tunnelling and hopping of hole polarons. So we wanted to find out whether the so-called "anomalous metal-like but apparently linear temperature variation of resistivity" was related to hopping of polarons and the degree of localisation.…”

“…Two types of measurements are reported here: a) Electrical resistance measurements by the four-probe method, and b) frequency dependent susceptibility measurements by our contactless method [7].…”

“…So we wanted to find out whether the so-called "anomalous metal-like but apparently linear temperature variation of resistivity" was related to hopping of polarons and the degree of localisation. The contactless method we have developed [7] is eminently suitable for estimating in a sample the volume fraction which becomes superconducting on transition to the superconducting phase. By systematically decreasing the volume fraction of the superconducting phase in a sample we expected to increase systematically the disorder in the system and consequently alter (enhance) the localisation of the carriers.…”

Reflectivity Spectra of YBa2Cu3O7−x in the 0.6 to 6.1 eV Range Evidence for Excitonic Absorption

“…YBa,Cu,O,-, samples fundoped and doped with various amounts of Sc) were prepared in the usual solid state reaction method as described in a previous paper [23]. The manner in which Sc enters YBa,Cu,O, is still undecided though evidences have been put forward against Sc replacing Y [24].…”