Transition phenomenon inTi2O3using the discrete variationalX

Abstract

The electronic structure of the metallic Ti 2 O 3 and insulating phases has been investigated using a combination of the three-dimensional periodic shell model and the discrete-variational (DV)-X␣ cluster method. Besides the effects of intersite repulsive nearest-neighbor electron-electron (d-d) Coulombic interaction and the spin-spin interaction by means of a generalized Hubbard Hamiltonian, the Hamiltonian in the insulating phase includes Anderson's attractive potential due to the electron-phonon interaction. The shell model estimates the electron-phonon coupling constants, and provides direct theoretical evidence that the electronphonon interaction stabilizes the three dimensional periodic distribution of Ti 3ϩ ϪTi 3ϩ pairs along the c axis of the corundum structure. The DV-X␣ cluster method calculates the electron energies in the ͓Ti 2 O 9 ͔ Ϫ12 cluster, the values for the intersite repulsive nearest-neighbor d-d interaction, and the spin-spin interaction. The electron correlation effect and the spin correlation effect are found to be mainly responsible for the broad crossover between a metallic and an insulating state in Ti 2 O 3 , although there is some contribution from the electron-phonon interaction. The present calculation describes the characteristic transition phenomenon in this material. ͓S0163-1829͑97͒07744-8͔

Room and high-temperature scanning tunnelling microscopy and spectroscopy (HT-STM/STS) investigations of surface nanomodifications created on the TiO2(110) surface

“…The appearance of these states constitute pseudo-gap typical for Ti 2 O 3 . It is worth to mention that according to the theoretical calculations based upon the Mott-Hubbard regime, Ti 2 O 3 is an insulator with very small energy gap equals of E g = 0.098 eV for 300 K [21]. However, at temperature 573 K (Fig.…”

“…It may indicate insulator-metal transition, which takes place on the surface. This is because that at about T c = 450 K, Ti 2 O 3 exhibits a smooth insulator-metal transition with increasing temperature [21][22][23][24][25][26]. The disappearance of the pseudo-gap was reversible and it appeared when the temperature was lowered to room temperature.…”

“…As was established the change in the conductivity of Ti 2 O 3 above T c is caused by broad crossover between a 1g and e p g þ e p à g bands [21][22][23][24][25][26]. It should be stressed that at this temperature range the disappearance of very pronounced two surface states at energy about 0.4 eV below the Fermi level and at about 0.4 eV above the Fermi level (i.e.…”

High-Temperature Scanning Tunnelling Spectroscopy of Transition Metal Oxides

“…As wa s observed the di sapp eara nce of the energeti c gap wa s com pl etel y reversi bl e and i t app eared when the tem perature was l owered. As was shown i n [13,14] the I{ M tra nsiti on in Ti 2 O 3 can b e expl ai ned by the com p eti ti on b etween electro n{ electro n correl a ti on energy and el ectro n-band entro py at el evated tem p eratures. As a result the a 1 g and e ¤ + ¤ ba nds overl ap pro duci ng smooth tra nsiti on wi th no chang e in crysta l sym m etry .…”

Influence of strong electric fields on the growth, modification, and destruction of thin oxide films at the titanium surface

“…1. This oxide is formed at the heavily reduced TiO 2 surfaces 12,13 and is characterized by a narrow band gap of 0.1 eV, 14 which is difficult to detect by the STM experiments. It is seen that, if the oxygen adsorption occurs at the tip potential relative to the sample equal to −7.5 V, the dJ / dV curve show a band gap approximately 1 eV ͑curve c͒.…”