High-pressure synchrotron-diffraction study of the superconducting spin-ladder compounds (Sr, M) 14Cu24O41 (M = Ca, Ba, Nd)

The evolution of the cell parameters as a function of pressure of five samp les of the spin-ladder compounds (Sr, M)(14)Co24O41, With M = Ca, Ba, Nd ha s been investigated up to approximate to 10 GPa by high-pressure synchrotro n x-ray diffraction on the ID9 beam line of the ESRF. A large anisotropy of compressibility is observed, with a very strong compression along the b ax is, corresponding to the stacking direction of the ladder and chain layers. A striking lattice anomaly is detected in the 5-8 GPa range, depending on composition. It consists of an abrupt increase of the a parameter value, a measure of the in-plane separation between ladders, with increasing pressur e. This anomaly could play a role in the disappearance of superconductivity above approximate to 6 GPa in this system. [S0163-1829(99)00818-8].