Localization of charge carriers by Pr in theTl2Ba2Ca1

Abstract

We have measured the resistivity and thermoelectric power of Tl 2 Ba 2 Ca 1Ϫx Pr x Cu 2 O y samples with xр0.6 in the temperature range 10-300 K. T c decreases with an increase in the Pr concentration and a crossover from a metallic to insulator state is observed in samples with xӍ0.4. In the highly resistive samples (xϾ0.4) conduction is governed by the in-plane variable range hopping of the carriers while in others, localization of bosons appears to be dominating. A ''spin gap'' is observed in the resistivity of these samples. The resistivity and thermoelectric power show the localization of the carriers to increase with an increase in Pr concentration. These data, examined in the light of existing models of conduction by localized carriers, show a preference for the model proposed by Nagaosa and Lee wherein the fermion contribution decreases and that of the bosons increases with the increase in the Pr concentration. The Pr L 3 -edge absorption data show Pr to be present in the mixed (3 ϩ and 4 ϩ ) valent state. Correlating the hole density ''p'' determined from T c and thermoelectric power with the valence of Pr estimated from x-ray-absorption edge measurements, we find hole filling along with hybridization to be the dominant mechanism for destablization and eventual suppression of superconductivity in these materials.

Transport, magnetic and thermal properties of Pr doped LaSr2Mn2O7: a Kondo-type behaviour of resistivity

“…Thus it appears that the primary effect of Pr substitution is to increase the resistivity and the change in the chemical pressure accompanying this substitution produces the sharp drop in its value at x ∼ 0.6. In other oxides also, Pr substitution increases the resistivity [20]. From the analysis of the XRD data, we find the in-plane Mn-O bond length, d in , to decrease with x for 0…”

Effect of copper on the magnetism of half doped bilayer manganite

“…Resistivity usually contains a sizeable contribution from grain boundaries and may be the reason for the increase of Eρ as the grain size reduces with increasing copper concentration. Thermopower on the other hand is much less sensitive to the presence of such defects [41,42] and therefore yields results closer to those from single crystals. Though the agreement of the data with the model is good but the analysis is not satisfactory as it does not explain the concentration dependence of ρ(T).…”

A Search for a Low Anisotropic Superconductor

“…The critical temperature, however, decreases in TlHg-2223 to 118K but in TlHg-2212 the T c (0) has been raised to 5K higher than pure thallium based superconductor [23]. In Tl-2212 superconductors the doping of tetravalent Pr at Ca site was found to suppress the superconductivity [31]. Two reasons are proposed for the suppression of superconductivity with Pr substitution.…”

“…Hg, Pb, Sr, Y, Pr, Co etc. ) in charge reservoir block and superconducting block [23,[27][28][29][30][31][32][33][34][35][36][37]. Parkin et al have been succeeded to prepare Tl 2 Ba 2 Ca 2 Cu 3 O x superconductor with critical temperature, which varies from 118 to 127K depending upon the synthesis conditions [8].…”