The lattice parameters and ac susceptibility of Y1-xCaxSrBaCu2.9Ga0.1O
6+z (X = 0, 0.05, 0.1, and 0.2) are reported. T(c) decreases as a resu
lt of (0.1) Ga substitution from 83 to 67.5 K but increases to 79.5 an
d 80 K for x = 0.1 and 0.2, respectively. The present data in comparis
on with those on Al and Co which have been shown to occupy chain sites
suggest strongly that Ga also preferentially occupies the chain sites
.