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

Abstract

Neutron total scattering measurements were conducted on MgTiO3, CaTiO3, SrTiO3, and BaTiO3 to simultaneously investigate the local and average structure of these materials. The local structures of MgTiO3, CaTiO3, and SrTiO3 were well modelled using the refined average structural models: trigonal R3 ¯ , orthorhombic Pbnm, and cubic Pm3 ¯ m respectively. However the local structure for BaTiO3, at both temperatures where the average structure is orthorhombic Amm2 and tetragonal P4mm, was best described by the rhombohedral R3m model. Only the R3m 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 Amm2 and P4mm.