Structural, electronic and optical properties of monoclinic Na 2 Ti 3 O 7 from density functional theory calculations: A comparison with XRD and optical absorption measurements

Filho

et al. 2018

J Raman Spectroscopy

Self Cite

Sodium trititanate Na2Ti3O7 microcrystals were carefully prepared by sodium carbonate and titanium dioxide solid‐state reaction and characterized by scanning and transmission electron microscopies, selected area electron diffraction, X‐ray powder diffraction, and Raman and Fourier transform infrared spectroscopies. Electron microscopic techniques revealed that the samples were formed by elongated particles several microns long with broad size distributions. The zone axis and crystal growth direction of the elongated particles were determined by selected area electron diffraction. These results were useful for identifying the symmetries of the optical vibrational modes obtained by infrared absorption and polarized Raman scattering of oriented crystals. For a complete assignment of the depicted phonon modes, Fourier transform infrared spectroscopy and Raman data were compared with theoretical data obtained from first‐principles calculations within the framework of the density functional theory. A very nice agreement was established between the characteristic features of measured and calculated vibrational modes. In particular, all optical phonon modes of Na2Ti3O7 could be experimentally observed and assigned to their correct symmetries. These results must be useful for describing the physical behavior of the system and designing new technological applications.

Section: Resultssupporting

confidence: 79%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Polarized Raman, FTIR, and DFT study of Na₂Ti₃O₇ microcrystals

Filho

et al. 2018

J Raman Spectroscopy

Self Cite

“…NTO has a monoclinic crystal structure in space group P 21/ m consisting of layers of edge‐sharing and corner‐sharing [TiO 6 ] octahedra (Figure a), and the Na ions are located between the layers with 9‐(Na1) or 7‐(Na2) coordinated to nearby oxygen atoms . The calculated lattice constants are a =8.42, b =3.81, and c =9.08 Å, which are in very good agreement with experimental studies and other theoretical data . The projected density of states (PDOS) of NTO near the Fermi energy level (Figure b) demonstrates semiconductor characteristics with a band gap of 3.23 Å.…”

Section: Resultssupporting

confidence: 74%

Phosphorus‐Doping‐Induced Surface Vacancies of 3D Na₂Ti₃O₇ Nanowire Arrays Enabling High‐Rate and Long‐Life Sodium Storage

Liu

Jin

Huang

et al. 2019

Chemistry A European J

Sodium‐ion batteries have attracted interest as an alternative to lithium‐ion batteries because of the abundance and cost effectiveness of sodium. However, suitable anode materials with high‐rate and stable cycling performance are still needed to promote their practical application. Herein, three‐dimensional Na2Ti3O7 nanowire arrays with enriched surface vacancies endowed by phosphorus doping are reported. As anodes for sodium‐ion batteries, they deliver a high specific capacity of 290 mA h g−1at 0.2 C, good rate capability (50 mA h g−1at 20 C), and stable cycling capability (98 % capacity retention over 3100 cycles at 20 C). The superior electrochemical performance is attributed to the synergistic effects of the nanowire arrays and phosphorus doping. The rational structure can provide convenient channels to facilitate ion/electron transport and improve the capacitive contributions. Moreover, the phosphorus‐doping‐induced surface vacancies not only provide more active sites but also improve the intrinsic electrical conductivity of Na2Ti3O7, which will enable electrode materials with excellent sodium storage performance. This work may provide an effective strategy for the synthesis of other anode materials with fast electrochemical reaction kinetics and good sodium storage performance.

A New Triclinic Phase Na₂Ti₃O₇ Anode for Sodium‐Ion Battery

Cao

Wang

et al. 2020

Adv Funct Materials

A new phase Na 2 Ti 3 O 7 compound is synthesized by solid-state method for the first time, which is verified to belong to the triclinic structure in P-1 space group. Compared to the conventional monoclinic Na 2 Ti 3 O 7 (m-NTO), in P2 1 /m1 space group, the triclinic Na 2 Ti 3 O 7 (t-NTO) possesses a shorter O-O band in the distorted TiO 6 octahedron, which accounts for more smooth Na + transport channels and a more stable layered structure with smaller fluctuation. The experimental results show that the t-NTO keeps a low charge potential plateau at 0.3 V compared to the m-NTO, but with much promoted structure resilience. It delivers a capacity retention of 94.7%, far exceeding the 25.7% of the m-NTO upon decades of cycles. In situ X-ray diffraction reveals that the conventional m-NTO experiences an irreversible phase transition during insertion/de-insertion of Na + , while the new t-NTO can recover its structure reversibly after discharge and charge, which is consistent with its improved cycling performance. The results demonstrate a new t-NTO anode and provide a new understanding for the phase diversity of sodium-ion battery materials.