Multiphase Refinement Study of the PrBa & u 408 Compound By Rietveld Method
Two samples of compound PrBa&u,Os-s were prepared -one sample was obtained by starting with the oxalate coprecipitation technique in making the powder precursor following by the calcined and sintering process under ambient oxygen pressure, the other sample was obtained by using the conventional ceramic techniques. The structures of the two samples in crystalline phases have been refined from X-ray powder diffraction data by the Rietveld method. The major phase of the product was confirmed to be PrBaQrJOs, with several minor impurity phases confirmed. The multiphase refinement process determined weight fractions of all the phases. Refined cell parameters of PrBa2Cu4Os in the orthorhombic space group Annum, are: a = 3.8901(l)& b = 3.9041(2)& and c = 27.3219(1$. All relevant structure parameters were calculated and listed. Characterizations of this compound by electrical resistivity and magnetization are also reported. Experiments and Rietveld Analysis In 1994 Nobuaki and Yamauchi et al [ l][ 111 synthesized the compound PrBa2Cu4Os-6 using hot isostatic pressing (HIP) apparatus. Here we synthesized this compound under ambient oxygen pressure by using the coprecipitation process and ceramic synthesis techniques. The orthorhombic PrBaQrsO7 with a typical high Nee’l temperature(TN) of 17 K, is the only nonsuperconducting member of the RBa.$ZusO7 system (R = rare earth element) [2-71. Furthermore the oxygen deficiency in the tetragonal PrBa2Cu306 causes the TN to decrease to 10 K [6-81. For better interpretation in the aspect of structural functional relation, the PrBa&&O7 orthorhombic Pmmm system can be rewritten as [Cu]Ba2PrCu207, and categorized as Cu1212Csystem. On the other hand the tetragonal P4/mmm system, PrBa2Cu306, can be rewritten as [Cu]Ba2PrCu206 and re-categorized as Cul212-system[9]. The PrBaQr4Os can be denoted as [Cu]2Ba2PrCu2Os and re-categorized as Cu-2212C system, which is in space group Ammm where Copyright (C) JCPDS-International Centre for Diffraction Data 1999
Magnetic and transport properties of PrBa2Cu4O8-δ prepared at 1 atm oxygen pressure
Measurements of physical properties were performed on the PrBa2Cu4O8-δ sample prepared by the sol-gel method and sintered in I atm oxygen pressure. Instead of exhibiting superconductivity as for R Y or Gd in the RBa2Cu4O8-δ compound. This compound is unstable, insulating but metallic-like at low temperatures. No superconductivity was observed down to 2 K. Since PrBa2Cu4O8-δ can be re-written as Cu2Ba2PrCu2O8-δ which is a compound of two CuO2-layers and two CuO-chains, the possibility of anomalous Pr antiferromagnetic ordering around 18 K observed from preliminary magnetic data and the effect of oxygen stoichiotmetry parameter δ on the metal-insulator transition are explored.
SUPERCONDUCTIVITY OF THE Pr-SUBSTITUTED (Nd1−xPrx)Ba2Cu3O7−δ SYSTEM
Electrical, magnetic and crystallographic measurements have been carried out for the pseudoquaternary (Nd1−xPrx) Ba2Cu3O7−δ system. Orthorhombic phase persists from x = 0.0 up to x = 0.7 and transforms into the tetragonal structure only for x ≥ 0.8. Superconducting transition temperature Tc decreases linearly from 92 K for x = 0.0 to below 10 K for x = 0.3 and extrapolated to 0 K around x = 0.35. Magnetic susceptibility data indicates that the valence of the Pr ion is close to 4+. Pr4+ is a very powerful oxidizing agent and may distort or move oxygen away from the Cu-O chain and/or the CuO2 planes and seriously suppress superconductivity.