Introduction of a tolerance factor for the Nd2CuO4 (T′)-type structure

Abstract

A tolerance factor, tf = [3√2ro + 2√6(rA + ro)]/9(rB + rO), has been established for the Nd2CuO4-type structure, where rA, rB, and rO are the radii of the A, B, and O ions, respectively. It is based on the geometrical matching between the A-O, B-O, and O-O bond distances, and it can be used to distinguish between Nd2CuO4 (T′)-, T*-, and K2NiF4 (T)-type phases. Using Shannon's ionic radii, it is found that the T′ phases occur for tf < 1.00 while T phases form for tf > 1.00. As expected, the T* structure exists in a very narrow region between the stability boundaries of these two structure types. The fact that T′ and T separate at tf = 1.00 suggests that the new tolerance factor model is applicable to both structure types. © 1996 Academic Press, Inc.