Topology of anion channel in an apatite structure and position of the X anion therein

Abstract

Total 53 out of 117 structures of apatite-type compounds hitherto published were examined in view of the relationships among position of X anion (0 0 z) and sizes of A(2)₃ (at z = 1/4) and O(3)₃ (at z ≈ 0) triangles which compose an X anion channel along the c axis. In general X anion is most stable at z = 0 as far as the O(3)₃ triangle is large, and moves to the center of A(2)₃ triangle when the O(3)₆ trigonal antiprism is small and repulsive force from those oxide ions is unignorable.