Electrical conductance of crystalline Ti<sub>n</sub>O<sub>2n-1</sub>for n=4-9

Inglis, A.D.; Page, Y. Le; Strobel, Pierre; Hurd, C. M.

doi:10.1088/0022-3719/16/2/015

Cited by 62 publications

(49 citation statements)

References 24 publications

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“…Despite the existence of many studies about defects in rutile TiO 2 , both experimental [20][21][22][23][24][25][26][27][28] and theoretical [21,25], there are few works on the intrinsically defective Magnéli phases [29][30][31][32][33][34][35]. Electronic structure calculations have been used to understand mainly the Ti 2 O 3 [32] and Ti 4 O 7 [29][30][31].…”

Section: Introductionmentioning

confidence: 99%

“…Electronic structure calculations have been used to understand mainly the Ti 2 O 3 [32] and Ti 4 O 7 [29][30][31]. Experimental reports [33][34][35] of some of these structures are not conclusive about the origin of the increase of electrical conductivity with respect to the rutile phase, nor about the switching mechanism. The question that arises is how the presence of extended-defect structures is related to the increase of electrical conductivity in this case.…”

Section: Introductionmentioning

confidence: 99%

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TinO2n−1Magnéli phases studied using density functional theory

et al. 2014

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Defects in the rutile TiO 2 structures have been extensively studied, but the intrinsic defects of the oxygendeficient Ti n O 2n−1 phases have not been given the same amount of consideration. Those structures, known as Magnéli phases, are characterized by the presence of ordered planes of oxygen vacancies, also known as shear planes, and it has been shown that they form conducting channels inside TiO-based memristor devices. Memristors are excellent candidates for a new generation of memory devices in the electronics industry. In this paper we present density-functional-theory-based electronic structure calculations for Ti n O 2n−1 Magnéli structures using PBESol+U (0 U 5 eV) and Heyd-Scuseria-Ernzerhof functionals, showing that intrinsic defects present in these structures are responsible for the appearance of states inside the band gap, which can act as intrinsic dopants for the enhanced conductivity of TiO 2 memristive devices.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

TinO2n−1Magnéli phases studied using density functional theory

et al. 2014

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“…Bartholomew and Frankl 3 measured the electrical conductivity of Ti n O 2n−1 with 3 Յ n Յ 6 within the temperature range 78-298 K. Inglis et al 4 studied the temperature dependence of the electrical conductance of Ti n O 2n−1 with 4 Յ n Յ 9 in the 4-320 K temperature range. In these studies no single conduction mechanism was found to dominate across the series.…”

Section: Introductionmentioning

confidence: 99%

“…In these studies no single conduction mechanism was found to dominate across the series. In particular, for Ti 4 O 7 , both works reported discontinuities in the conductivity as the temperature was changed: a semiconductor-semiconductor transition in the 125-140 K temperature range and a semiconductor-metal transition at about 150 K. It is in this Magnéli phase, Ti 4 O 7 , where the bulk of the analysis, regarding the study of the metal-semiconductor and semiconductor-semiconductor transition, has been focused.…”

Section: Introductionmentioning

confidence: 99%

Electronic structure of theTi4O7Magnéli phase

2009

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We have performed density-functional calculations on the Ti 4 O 7 Magnéli phase. Our results provided a consistent description of the high-temperature ͑T Ն 298 K͒ phase, the intermediate-temperature ͑120 K Յ T Յ 140 K͒ phase, and the low-temperature ͑T Յ 120 K͒ phase. The established model for the electronic structure of the low-and intermediate-temperature phases of Ti 4 O 7 states that Ti 3+ -Ti 3+ pairs, bonded through nonmagnetic metal-metal bonds, form ordered bipolarons in the low-temperature phase, and that these bipolarons exist but are disordered in the intermediate-temperature phase. In this work we propose a different picture for the Ti 4 O 7 low-and intermediate-temperature electronic structure. We argue that, in the lowtemperature phase, a combination of a strong on-site Coulomb repulsion and electron-phonon coupling results in the localization of unpaired electrons in the Ti 3+ ions forming the pairs. The electrons are accommodated in specific t 2g -like orbitals for two reasons: to minimize the direct Coulomb repulsion, and to minimize the indirect interaction that results from lattice distortion. The localized electrons are antiferromagnetically coupled, producing bipolarons with zero spin. This orbital ordering results in the widening of the gap between the fully occupied and unoccupied levels. This is a bipolaronic state, but there is no bond in between the Ti 3+ forming the pairs. In the intermediate phase, a subset of the bipolarons dissociate but the electrons remain strongly localized: this state consists of a mixture of polarons and bipolarons placed in a superstructure with long-range order. This model provides a consistent explanation of the observed electric and magnetic properties of Ti 4 O 7 .

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“…21 The defective nature of the oxide has profound consequences for the structure and electronic structure that are revealed, in part, by electronic measurements. Bartholomew and Frankl 22 measured the electrical conductivity of Ti n O 2n−1 with 3 ഛ n ഛ 6 within the temperature range 78-298 K. Inglis et al 23 studied the temperature dependence of the electrical conductance of Ti n O 2n−1 with 4 ഛ n ഛ 9 in the 4 -320 K temperature range. In these studies no single conduction mechanism was found to dominate across the series.…”

Section: Introductionmentioning

confidence: 99%

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

2008

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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.

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Electrical conductance of crystalline Ti_nO_2n-1for n=4-9

Cited by 62 publications

References 24 publications

TinO2n−1Magnéli phases studied using density functional theory

TinO2n−1Magnéli phases studied using density functional theory

Electronic structure of theTi4O7Magnéli phase

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

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Electrical conductance of crystalline TinO2n-1for n=4-9

Cited by 62 publications

References 24 publications

TinO2n−1Magnéli phases studied using density functional theory

TinO2n−1Magnéli phases studied using density functional theory

Electronic structure of theTi4O7Magnéli phase

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

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Electrical conductance of crystalline Ti_nO_2n-1for n=4-9