Pressure Induced Structural Transition in the Solid-Solution La2−xNdxCuO4forx= 0.6, 0.7, 1.2, and 1.5

A pressure induced transition from the T′ to the T/O structure has been observed in the La2−xNdxCuO4solid-solution forx= 0.6, 0.7, 1.2, and 1.5 with energy dispersive X-ray diffraction. Indications have been found that such a transition may even occur in thex= 2.0 composition at pressure higher than 18 GPa. In all cases the observed transitions were reversible. The transition pressure has been related to the compressive stress in the Ln–OIIlinkages in the fluorite-likeLnO2layers of the T′ structure. The pressure dependence of the tolerance factortis deduced and discussed. A strong electrostatic repulsion between oxygen ions in the 4dsite is probably responsible for the increase of the T′ structure's bulk modulus with Nd contentx.