HRTEM, SAED and XRD investigations of RE4O4[AsO4]Cl (RE = La, Pr, Nd, Sm, Eu, Gd)

The new compounds RE4O4[AsO4]Cl (RE = La, Pr, Nd, Sm, Eu, Gd) were synthesised by solid state reaction via a salt flux route and investigated by HRTEM, SAED, and single crystal X-ray diffraction. The samples crystallise with a tetragonal cell, space group P42/mnm and Z = 2. Their crystal structure consists of an alternation of [RE4O4]4+ and [ClAsO4]4– layers. The [RE4O4]4+ layer contains ORE4/4 tetrahedra which share common edges. The anions AsO43– and Cl– are located between these layers in disordered manner. SAED and HRTEM experiments confirmed this structural model and enabled us to propose an ordered model for the [ClAsO4]4– layers.