Crystal structures and crystal chemistry of compounds M5−p T4+p O14*

Abstract A structural family of the summarizing formula M 5− p T 4+ p O 14 with p = 0 or p = 1 is described. It comprises three structure types I, II and III and a large number of compounds. The structure types of I ( P 321) and II ( I 2/ a ) are known. For the unknown monoclinic structure of III a partial structure proposal is developed. The basic unit of all structures is a strongly folded tetrahedral vierer single chain with Ge or Ga as predominant tetrahedral ions T. An unusually large variety of cations M is observed with eightfold positions occupied by mono- to trivalent ions (e.g. Na + , Sr 2+ , Nd 3+ ) and octahedral sites occupied by bi- to pentavalent ions (e.g. Mg 2+ , Ga 3+ , Ge 4+ , Sb 5+ ). 25 new compounds were synthesized, enlarging the total number of known representatives to 80. 72 of them belong to structure type I, seven to type II and one to type III. Several solid solution series were investigated.