PREPARATION AND STRUCTURE OF AL(SR,CA)(2)HOCU2O7 AND ALSR2(HO,CA)CU2O7 CUPRATES

Chemical composition, lattice parameter's and superstructure of the Al -1212 cuprates are studied for samples with nominal compositions AlSr2 R1-xCaxCu2O7 (R=Y or Ho) by energy dispersive X-ray analysis, powder X -ray diffraction and electron microscopy. It is found that the replace ment of Ho by Ca occurs predominantly at 2 GPa, whereas the substituti on of Sr by Ca occurs at ambient pressure. All the Ca-containing Al-12 12 cuprates examined show a superstructure similar to that of AlSr2YCu 2O7. The fundamental framework structure does not depend on x.