Manifestation of incommensurate structural modulations in the Ti- L 2,3 electron energy-loss near-edge structure of Sr2TiSi2O8

Abstract

Structural modulations hosted by complex oxides are–beyond relative orientation changes of ‘rigid units’–accompanied by characteristic distortions of coordination polyhedra. Electronic structure calculations in the local density approximation, performed at model clusters derived from positionally modulated structures, proved that the molecular–orbital structure also sensitively reflects such distortions. The latter crystal-field splitting of unoccupied states is accessible by high-resolution electron energy-loss near-edge structure (ELNES) spectroscopy. However, since ELNES spectra average over many different individual target-ion environments, the resulting ELNES possesses significantly broadened spectral features. In this contribution, such broadening is shown to dramatically influence the spectral shape of the Ti-L 2,3 ELNES acquired at the strongly modulated fresnoite framework compound Sr2TiSi2O8.