Metal-insulator transitions in VO₂, Ti₂O₃and Ti_2-xV_xO₃

Atomic-scale electrochemistry on the surface of a manganite by scanning tunneling microscopy

“…The same calculation for event (1) in Fig. 3(c) yields $104 pm also, and $79 pm for event (2). However, we note that the spike in the current trace or the onset of hysteresis if observed, always appears to occur at $2.1 6 0.17 V (95% confidence).…”

“…2 One of the most widely explored classes of these materials are the mixed-valence manganites, 3 in which the strong electronic correlations are coupled with additional degrees of lattice and charge freedom 4 and results in phenomena such as coexistence of metallic and insulating phases, 5,6 colossal magnetoresistance, and charge ordering producing rich phase diagrams that have attracted attention for the best part of the last two decades. Owing to its high conductivity and low thermal mismatch with Zr-based solid electrolytes, the manganite series La x Sr 1Àx MnO 3 has been used as the cathode material in solid oxide fuel cells, 7 where oxygen vacancies and molecular oxygen react and reduce to oxygen ions.…”

Atomic Origins of Monoclinic-Tetragonal (Rutile) Phase Transition in Doped VO2 Nanowires

“…A characteristic behavior of Mott insulators is that below a critical carrier density, added electrons remain localized at dopant sites. 70,71 The origin of this electron localization continues to be debated 72,73 but it is thought to be due to formation of small polarons and is facilitated by local lattice distortion around the dopant sites. Such distortion is indeed verified by our atomically resolved measurements presented here.…”

Calculation of bandgaps in nanomaterials using Harbola-Sahni and van Leeuwen-Baerends potentials

“…Furthermore, in an insulator or a semiconductor, it is expected that adding an extra electron at the bottom of the conduction band would hardly change the density of the bulk system and therefore all the eigenvalues of the KS spectrum will remain essentially unchanged. It is therefore anticipated that the difference in the KS eigenenergies corresponding to the lowest orbital of the unoccupied band (negative of the electron affinity ÀA) and the highest orbital of the occupied band (negative of the ionization energy ÀI) should give the correct fundamental gap (I À A) of semiconductors and insulators (Mott and Friedman, 1974;Mott, 1974). However, the results obtained by applying the traditional exchange-correlation functionals such as the local density approximation (LDA) (Von Barth and Hedin, 1972) are contrary to this expectation and grossly underestimate the bandgap with respect to experiments.…”