Structural properties of A2SnO4(A = Ba,Sr). A neutron diffraction study

Abstract

The structural properties of the layered oxides Ba₂SnO₄ and Sr₂SnO₄ have been studied as a function of temperature by high resolution powder neutron diffraction. As a result of excellent size matching between the SnO₂ and Ba₂O₂ layers, Ba₂SnO₄ adopts the tetragonal K₂NiF₄ structure (space group I4/mmm) and undergoes no structural phase transition on cooling. Sr₂SnO₄, on the other hand, is orthorhombically distorted, (b–a)/(b + a)= 7.2(7)× 10^–4 at ambient temperature (space group Bmab) as a result of the co-operative rigid tilt of the corner-sharing SnO₆ octahedra, which relieves the compressive stress of the SnO₂ layers. Upon cooling, it undergoes a phase transition to a primitive tetragonal phase (space group P4₂/ncm) which is characterised by a different rotational mode of disortion.