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.