Un nouveau type de deformation orthorhombique dans les perovskites metalliques

Abstract In order to study the structural phase transitions of the metallic perovskites, the system As 1−y Sb y Mn 3 N has been investigated. SbMn 3 N and AsMn 3 N crystallise respectively in the pseudocubic T1 and T4 structures, this latter related with an alternate rotation of the Mn 6 N octahedra. In this system, a new orthorhombic phase - called 08 - has been found and solved on the basis of the Fmmm space group. The opposite variations of the T1 and T4 distorsions with the composition and their orthogonal directions in the 08 form where they coexist show they are due to different mechanisms.