POWDER DIFFRACTOMETRY OF THE SYSTEM SR3-X CAXAL2O6 AND SINGLE-CRYSTALSTRUCTURAL-ANALYSES FOR THE CASES X = 1,395(8), 1,62(1) AND 2,12(1)

Powder samples of the system Sr3-xCaxAl2O6 (x = 0: 0.3,..., 2.7, 3.0) were prepared by means of solid state reactions at 1723 K. The lattice constants determined exhibit a linear dependence from the molar fract ion x in the range 0.9 less than or equal to x less than or equal to 3 ., For smaller values of x distinct deviations from this linearity are observed. As shown by the results of three single crystal investigati ons which could be carried out on crystals with x = 1.395(8), 1.62(1), and 2.12(1) this is due to a remarkable distribution of the earth alk aline metal atoms, which is far from being only statistical over the s ix crystallographically different sites.