  Solid solutions of the magnetic insulators Ba3Cr2O8 and Sr3Cr2O8
(Ba3-xSrxCr2O8) have been prepared in polycrystalline form for the first time.
Single crys- talline material was obtained using a mirror image floating zone
technique. X-ray diffraction data taken at room temperature indicate that the
space group of Ba3-xSrxCr2O8 remains unchanged for all values of x, while the
cell parameters depend on the chemical composition, as expected. Magnetization
data, measured from 300 K down to 2 K, suggests that the interaction constant
Jd within the Cr5+ dimers varies in a peculiar way as a function of x, starting
at Jd = 25K for x = 0, then first slightly dropping to Jd = 18K for x = 0.75,
before reaching Jd = 62K for x = 3.
