Thermodynamics of oxygen defective Magnéli phases in rutile: A first-principles study

Abstract

Ab initio thermodynamics has been used to calculate the formation energies, in different environmental conditions, for a number of oxygen-defective structures in rutile. In addition to the Ti n O 2n−1 ͑3 ഛ n ഛ 5͒ Magnéli phases, the two fundamental points defects, Ti interstitials and neutral oxygen vacancies, were also considered. The predicted phase stability is compared to available experimental data and there is reasonable agreement between the calculated phase boundaries and those observed. These results are used to discuss a mechanism that has been proposed as an explanation for the formation of the crystallographic shear planes in rutile.

Polaronic interactions between oxygen vacancies in rutile TiO2

“…Due to the metallic conductivity, they have been widely considered as possible electrode materials in batteries and fuel cells [23][24][25]. The desirable chemical stability and abundant low-temperature behaviors of Magnéli phases also generated substantial research interests lately [26][27][28][29][30]. For example, various bipolaron models have been proposed to explain the two-step metal-insulator transitions of Ti 4 O 7 between 125K and 150K [28][29][30].…”

“…The desirable chemical stability and abundant low-temperature behaviors of Magnéli phases also generated substantial research interests lately [26][27][28][29][30]. For example, various bipolaron models have been proposed to explain the two-step metal-insulator transitions of Ti 4 O 7 between 125K and 150K [28][29][30]. In previous studies, the isolated and clustered oxygen vacancies in titanium oxide have been investigated separately and it is still unclear how a pair of oxygen vacancies will interact when they come close to each other.…”

Atomic structure of the (001) surface of CuGaSe2

“…It is for this reason that the unreconstructed Se-terminated surface is stable for most environmental conditions. Except from the Se-poor environmental conditions described by region 5-1in figure 3, it is the Cu and Ga coordination to Se which dominates the surface energy, and this helps explain the low surface energies of reconstructions It is well known that in chalcopyrites such as CuAlS 2 [45], CuGaS 2 [46], CuInSe 2 and CuGaSe 2 [47] Cu vacancies have the lowest formation energies under most environmental conditions. When chalcopyrites are doped with Na, AES evidence shows that Na tends to accumulate at the surfaces and grain boundaries [48].…”

“…This results in the quenching of the In Cu and V Cu defects, which results in a decrease of the concentration of the (2V −1 Cu +In +2 Cu ) complex defect. The presence of small quantities of Na then contributes to the synthesis of Cu-poor chalcopyrites, avoiding the formation of the so called ordered defective compounds [45], increasing the p-type layer conductivity [50], and reducing the dependence on the compositional ratio of Cu/In [51].…”

Overview of emerging memristor families from resistive memristor to spintronic memristor

“…Although the secret behind EPIR is still uncovered, the consensus is that the EPIR effect will cause the formation and rupture of a conductive filament (CF) inside the resistive materials [33]. Thermochemical effect has been regarded as one of the most plausible explanations for the CF hypothesis [34][35][36]. The thermochemical mechanism assumes a large number of O 2-ions accumulated around the electrode, thus leading to a formation of oxygen vacancies.…”