| Summary: | 碩士 === 國立中山大學 === 物理學系 === 86 ===
We have successfully synthesized high quality Y1-xPrxBa2Cu4O8 (0≦x≦l) polycrystalline samples by nitric pyrolysis method. Powder X-ray diffraction patterns of Y1-xPrxBa2Cu4O [(Y,Pr)124] show a nearly single 1-2-4 phase. Thermogravimetric analysis indicates no oxygen loss until the temperature is higher than 800℃, which reveals that it is more thermally stable than PrBa2Cu3O7-δ (Prl23). The normal-state resistivity of (Y,Pr)124 is almost independent on Pr-content throughout the whole range ofx in contrast to a metal-insulator transition occurring at x~0.55 in (Y,Pr)123. This may be due to the double CuO chains in (Y,Pr)124 instead of a single CuO chain in (Y,Pr)123. It is clear from the thermo-electric power (TEP) data that the metallic behavior in (Y, Pr)124 for x=0.9 and 1.0 even at low temperature is due to the double CuO chains. The value of TN (~17K) in PrBa2Cu4O8 (Prl24) is obtained from specific-heat and ac susceptibility measurements. Both Tn and electronic linear term y decrease with magnetic field up to 8T as in Prl23. The entropy change ΔS=~6.7 J/mol-K in specific-heat measurement is independent of magnetic field. In both (Y,Pr)123 and (Y,Pr)124, (dTc/dP)p=o changes sign from positive to negative with increase of Pr-content. The value of TN for both Prl23 and Prl24 are nearly identical (~17K) and both decreases with pressure at anomalously large rate dTN/dP~-l K/kbar. These results for Tc and TN variations with Pr-doping and pressure effect in (Y,Pr)124 cannot be fully explained by the hybridization theory.
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