The Effect of Lanthanide (Ln) Elements on the Tc of LnBa2Cu4O8

The effect of Ln elements on the Tc of LnBa2Cu4O8 were studied through a comparison of the pressure coefficient of Tc between Y1-xCaxBa2Cu4O8 and LnBa2Cu4O8, and an x-ray diffraction study. The pressure derivative, dTc/dP, of Y1-xCaxBa2Cu4O8 shows decreasing positive values with increasing Tc, whereas the dTc/dP of LnBa2Cu4O8 has no dependency on the Ln element in spite of the variation of Tc. On the other hand, the x-ray diffraction results on LnBa2Cu4O8 indicate that the stacking sequence along the c-axis and the orthorhombicity degrade with decreasing Ln ion radii. A possible explanation on the Tc dependency on the Ln elements will be discussed from these results.