A neutron powder diffraction study of Na1−xSrxTaO3 (x=0.2 and 0.3)

Abstract

Black powder samples of the reduced oxotantalates Na1−x Srx TaO3 x = 0.2 and 0.3 were prepared via solid state reactions from appropriate amounts of NaTaO3 ,S r 5Ta4O15 and Ta (99.99%) in sealed tantalum ampoules at 1500 ◦ C. They crystallize in variants of the perovskite type structure (aper). According to structural refinements from neutron powder diffraction data Na 0.8Sr0.2TaO3 crystallizes orthorhombic in the GdFeO3 type structure with unit cell parameters a ≈ √ 2 × aper ,b ≈ 2 × aper, c ≈ √ 2 × aper and space group Pnma. The structure of the more reduced phase Na0.7Sr0.3TaO3 is tetragonal with unit cell parameters a ≈ √ 2 × aper ,c ≈ 2 × aper and space group