CHARGE-DENSITY DISTRIBUTIONS OF STRONTIUM-TITANATE OBTAINED BY THE MAXIMUM-ENTROPY METHOD

Strontium titanate (SrTiO3) shows a displacive phase transition at 110 K. In order to study electron level structural changes throughout the phase transition, the charge density distributions of SrTiO3 were obt ained by applying the Maximum Entropy Method (MEM) to X-ray diffractio n data at Room Temperature (R.T.) and 70 K. From the MEM charge densit ies at R.T., it was found that Ti-O shows a rather strong covalent bon d and that no covalency of Sr atoms was detected, which means that the Sr atom exists as an ion. From these results, chemical bonds of SrTiO 3 could be described as the Sr ion Boating electro-statically between three dimensional Ti-O networks. The symmetry of the lattice changes t hrough the 110 K phase transition, which causes the super-lattice refl ection at the R point. The displacement of oxygen atoms throughout the phase transition can be easily seen by taking the difference in charg e density distribution between these two temperatures. The MEM charge densities at 70 K reveal that the structural changes throughout the ph ase transition are rather small, that is, the Ti-O strong covalent bon d is maintained. The nature of the chemical bond of Sr atoms is basica lly unchanged. (C) 1998 Elsevier Science B.V. All rights reserved.