The Crystal Structures of the Strontium Gallates Sr_(10)Ga_6O_(19) and Sr_3Ga_2O_6

摘要

The crystal structures of Sr_(10)Ca_6O_(19) and Sr_3Ga_2O_6 have been characterized using X-ray diffraction techniques.In the case of Sr_(10)Ca_6O_(19),the structure was determined from a single crystal diffraction data set collected at room conditions and refined to a final R index of 0.061 for 3471 observed reflections (I > 2 #sigma#(I)).The compound is monoclinic with space group C12/Cl(a=34.973(4)A,b=7.934(1)A,c=15.943(2)A,#beta#=103.55(1) deg,V=4300.7(6)A~3,Z=8,D_(calc)=4.94 g/cm~3,#mu#(MoK#alpha#)=32.04mm~(-1)) and can be classified as an oligogallate.It is the first example of an inorganic compound where six [TO_4]-tetrahedra of only one chemical species occupying the tetra-hedral centres are linked via bridging oxygen atoms to form [T_6O_(19)]groups.The hexamers are not linear,but highly puckered.Eleven symmetrically different Sr cations located in planes parallel (100) crosslink between the oligo-groups.They are coordinated by six to eight oxygen ligands.The structure of Sr_3Ga_2O_6 has been refined from powder diffraction data using the Rietveld method (space group Pa3,a=16.1049(1),V=4177.1(1)A~3,Z=24,D_(calc)=4.75g/cm~3).The compound is isostructural with tricalcium aluminate and contains highly puckered,six-membered [Ga_6O_(18)]~(18-) rings.The rings are linked by strontium cations having six to nine nearest oxygen neighbors.