E. Kaldis, P. Fischer, A.W. Hewat, E.A. Hewat, J. Karpinski, S. Rusiecki, "Low temperature anomalies and pressure: effects on the structure and Tc of the superconductor YBa2Cu4O8 (Tc = 80 K)," Physica C, 159, 668-80, 15 July 1989.

Emanuel Kaldis (Laboratory of Solid State Physics ETH, Zurich, Switzerland): "With this experiment it became evident that the contraction of the apical bond (Cu2--O1) is correlated with the substantial increase of Tc under hydrostatic pressure, which we had found earlier at Zurich. This demonstrated clearly that minute structural changes of the Y-Ba-Cu-O phases may have a very important influence on the physical properties. These findings also directly supported the ideas of K. Alex Müller (IBM, Zurich)20about the importance of the apical bond. Our experiment is a particularly clean one, because in contrast to the 123 phase, which shows a similar effect under the influence of oxygen nonstoichiometery, here no chemical parameters affecting...

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