Neutron Total Scattering Studies of Group II Titanates (ATiO3, A2+ = Mg, Ca, Sr, Ba)

Neutron total scattering measurements were conducted on MgTiO 3 , CaTiO 3 , SrTiO 3 , and BaTiO 3 to simultaneously investigate the local and average structure of these materials. The local structures of MgTiO 3 , CaTiO 3 , and SrTiO 3 were well modelled using the refined average structural models: trigonal R 3 ¯ , orthorhombic Pbnm , and cubic Pm 3 ¯ m respectively. However the local structure for BaTiO 3 , at both temperatures where the average structure is orthorhombic Amm 2 and tetragonal P 4 mm , was best described by the rhombohedral R 3 m model. Only the R 3 m model was able to account for the observed displacement of titanium in the [111] direction. Furthermore, box-car type refinements were conducted. These refinements show that the coherence length of the rhombohedral distortion is around 10 Å, at larger r -ranges the local distortions become misaligned and average out to Amm 2 and P 4 mm .