Oxygen vacancy defects in Ta2O5 showing long-range atomic re-arrangements

Guo, Yuzheng; Robertson, John

doi:10.1063/1.4869553

Cited by 44 publications

(38 citation statements)

References 39 publications

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“…1a and b shows the geometry of the k phase from two different angles. The lattice parameters and formation energy from our calculation could be found in our previous work [40]. sX gives similar values to the GGA [31] for these parameters.…”

Section: Resultssupporting

confidence: 51%

Comparison of oxygen vacancy defects in crystalline and amorphous Ta2O5

Guo

Robertson

2015

Microelectronic Engineering

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Section: Resultssupporting

confidence: 51%

Comparison of oxygen vacancy defects in crystalline and amorphous Ta2O5

Guo

Robertson

2015

Microelectronic Engineering

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“…In spite of these efforts, the ground state crystal structure of L-Ta 2 O 5 is still elusive. Recent theoretical works based on the L SR or the λ-phase have shown that, the ground state atomic structures of L-Ta 2 O 5 can be energetically highly degenerated, and the creation of dilute oxygen vacancies can induce long-ranged perturbations on the atomic positions [34][35][36]. The concept of infinitely adaptive crystal structure [37] may account for such uncertainties or varieties of crystal structures, and leaves open the possibility of finding new phases/polymorphs of Ta 2 O 5 .…”

Section: Introductionmentioning

confidence: 99%

Prediction of new ground-state crystal structure of Ta2O5

Yang

Kawazoe

2018

Phys. Rev. Materials

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Tantalum pentoxide (Ta 2 O 5 ) is a wide-gap semiconductor which has important technological applications. Despite the enormous efforts from both experimental and theoretical studies, the ground state crystal structure of Ta 2 O 5 is not yet uniquely determined. Based on first-principles calculations in combination with evolutionary algorithm, we identify a triclinic phase of Ta 2 O 5 , which is energetically much more stable than any phases or structural models reported previously. Characterization of the static and dynamical properties of the new phase reveals the common features shared with previous metastable phases of Ta 2 O 5 . In particular, we show that the d-spacing of ~ 3.8 Å found in the X-ray diffraction (XRD) patterns of many previous experimental works, is actually the radius of the second Ta-Ta coordination shell as defined by radial distribution functions. *Corresponding Author (wateratnanoscale@hotmail.com; yyang@theory.issp.ac.cn) Previous experimental studies have established that, Ta 2 O 5 undergoes a phase transition at T ~ 1593 K (1320 °C), from the low-temperature phase (L-Ta 2 O 5 ) to the high-temperature phase (H-Ta 2 O 5 ) [20]. In the research works that followed, many efforts are devoted to studying the crystallographic structures of both L-Ta 2 O 5 and H-Ta 2 O 5 , which still remain an issue of debate [21, 22]. Our work will focus on the atomic structures of the low-temperature phase of Ta 2 O 5 , L-Ta 2 O 5 , which is more relevant to technological applications. Due to the difficulties of growing high-quality single crystals of Ta 2 O 5 , the structural information provided by powder X-ray diffraction (XRD) is very limited. Indeed, the crystal structures are found to be critically dependent on the conditions (e.g., temperatures, pressures) of synthesis and the method of analysis [23]. A number of phases and/or structural models have been suggested for L-Ta 2 O 5 . Based on the data of powder XRD, Stephenson and Roth proposed the 11-formula-units (Z = 11, 22 Ta and 55 O atoms) orthorhombic model (referred to as L SR ) [24]. Later, the Hummel et al. proposed the T-phase (orthorhombic, space group: Pmm2) which is however nonstoichiometric in chemical components (unit cell contains 24 Ta and 62 O atoms) [21]. Grey, Mumme, and Roth

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“…31 The defect formation energies are calculated for each state using the supercell method. [32][33][34] The relative importance of the processes ((b)-(d)) in Fig. 1 can be estimated from the defect formation energies in their various charge states.…”

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confidence: 99%

“…The 2-fold coordinated intralayer vacancy is the most stable vacancy, and this gives a 0/2þ state at about 2.0 eV above the valence band edge, near midgap. 34 The other vacancies are less stable in their neutral state and give levels nearer the conduction band edge. Crystalline Ta 2 O 5 has an unusual "adaptive" lattice, 40 so its vacancies migrate by shuffling rearrangements with low migration energies.…”

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confidence: 99%