THERMAL-EXPANSION MISMATCH AND INTERGROWTH TYPES IN THE SYSTEM LA2-YNDYCUO4

Stabilization of intergrowth structures of the copper-oxide superconductors requires bond-length matching across the intergrowth interface. The influence of thermal-expansion mismatch on the stabilization of T O vs T′ intergrowths in the La2-yNdyCuO4 system is demonstrated by firing the coprecipitated hydroxides/carbonates at 500-1050°C. A larger thermal expansion for the (LaNd)O bond compared to that for the CuO bond shifts the T OT′ phase boundary to a higher y value in La2-yNdyCuO4 as the synthesis temperature is increased. Above 950°C, an equilibrium phase diagram is obtained with a new line phase T″ appearing at y = 0.5. The T″ phase appears to be an ordered variant of the T′ phase and could be doped neither n-type nor p-type. © 1991.