Physical Review B · 2004 · 86 citations · 35 references
Natural SciencesMaterials SciencePhysicsCondensed Matter PhysicsSolid State PhysicsSpectroscopyAb Initio MethodsDensity Functional TheoryDielectric PropertiesElectronic StructureElectronic Structure Of SolidsTransmission Electron MicroscopyAb Initio CalculationsAb Initio Few-body CalculationsCore Loss AnalysisDielectric LossesElectron Energy LossElectron Energy-loss SpectroscopyEnergy Loss SpectraLow-energy Electron Spectroscopy
LELS from EELS in TEM typically lack structural detail, yet rutile units—M₃O₁₅ clusters of edge‑ and corner‑sharing octahedra—are present in rutile and other phases such as Ramsdellite or high‑pressure TiO₂, all of which exhibit a characteristic spectral feature. The study aims to broaden LELS applicability by examining the 10–15 eV range in MO₂ compounds to identify a characteristic peak associated with a specific structural unit. Experimental EELS spectra were compared with ab initio DFT calculations (WIEN2K) and band‑structure/orbital analyses were used to elucidate the peak’s origin. A universal peak near 14 eV appears in the imaginary part of the dielectric function for all rutile‑containing phases, regardless of M (Ti, V, Cr, Mn, Si, Ge, Sn, Pb), confirming its universality.
Low-energy loss spectra (LELS) from electron energy loss spectroscopy (EELS) in a transmission electron microscope do not yield structural information as readily as do core loss spectra. In order to make LELS a more general technique, we have studied the 10--15 eV energy range in some $M{\mathrm{O}}_{2}$ compounds in great detail and identified a characteristic peak of a specific structural unit. A comparison of experimental EELS spectra and ab initio density-functional theory calculations (WIEN2K code) is presented. A definite peak around 14 eV appears in the imaginary part of the dielectric functions of those structures containing rutile units. These rutile units are ${M}_{3}{\mathrm{O}}_{15}$ clusters made of edge- and corner-sharing octahedra, which when stacked lead to rutile structures, among others. The peak is present in rutile phases with $M=\mathrm{Ti},$ V, Cr, Mn, Si, Ge, Sn, and Pb. Other structures, such as Ramsdellite or high-pressure ${\mathrm{TiO}}_{2}$ phases, also contain the necessary structural unit and indeed present the same feature. The origin of the peak can be elucidated by means of band structure calculations and an analysis of the orbitals involved in the transition. The existence of such a peak, always visible around 14 eV whatever $M,$ shows its remarkable universality.
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