Crystal-Structure And Critical-Temperature Of Rba2cu4o8 (R = Tm, Er, Ho, Y, Dy And Gd)

Bulk superconductors RBa2Cu4O8 (R = rare earth element; Tm, Er, Ho, Y, Dy and Gd) were synthesized by hot isostatic pressing (HIP) technique. The highest T(c) ( = 84 K) was obtained for the substitution of Er. The T(c) decreases systematically with the increase of the ionic radius of these rare earth ions, and reaches 77 K for the largest ion Gd. The crystal structure of the compounds with R = Tm, Er, Ho and Y has been refined by Rietveld analysis of neutron powder diffraction data at room temperature. Structural changes due to the substitution of these rare earth elements are compared With those of YBa2Cu4O8 under high pressure, and they are discussed in connection with the variation of T(c). The results indicate that l(Cu(2)-O(2)) and l(Cu(2)-O(3)), the bond lengths between Cu and O in the CuO2 plane, are the most important parameters to decide the T(c) of the present Systems.