The Crystal Structure of alpha-Sr2P2O7.

Abstract

The lattice parameters of the 0c (low temperature) phase of MgzP207 are a= 13.198(10), b=8.295(5), c= 9.072(5)/~, p= 104-9(1) ° and Z= 8. The space group, B21/e, although non-primitive, allows an easy comparison of the e and p phases of this compound. A primitive cell could be chosen with space group P21/e and a=6.981(5), b=8.295(5), c=9.072(5)/~, fl= 113"0(1) ° and Z=2. In contrast with the apparently linear P-O-P group found for the/~ phase, stable above 70°C, this group is bent to an angle of 144 ° in the ~ phase. The P2Ov 4-ion nearly has C2 symmetry with average inner and outer P-O bond distances of 1.59+0.02/~ and 1.52+0.02/~ respectively. The diffuse phase transition which occurs between 60 and 70°C appears to be related to the fact that the cations show five-and six-fold coordination in the ~ phase whereas in the p phase all the cations are equivalent and sixfold coordinated.