scholarly journals Crystal Structure of the Intermediate Na2V2(PO4)3 Phase and Electrochemical Reaction Mechanisms in NaxV2(PO4)3 (1 ≤ x ≤ 4) System

2021 ◽  
Author(s):  
Sunkyu Park ◽  
Ziliang Wang ◽  
Zeyu Deng ◽  
Iona Moog ◽  
Pieremanuele Canepa ◽  
...  
Keyword(s):  
Phase Transition ◽  
Density Functional ◽  
Lattice Mismatch ◽  
Density Functional Theory Calculations ◽  
Charge Ordering ◽  
Phase Reaction ◽  
Two Phase ◽  
Space Groups ◽  
Cell Parameters ◽  
Positive Electrode Material

The Na-superionic-conductor (NASICON) Na3V2(PO4)3 is an important positive electrode material for Na-ion batteries. Here, we investigate the mechanisms of phase transition in NaxV2(PO4)3 (1 ≤ x ≤ 4) upon a non-equilibrium battery cycling. Unlike the widely believed two-phase reaction in Na3V2(PO4)3 – Na1V2(PO4)3 system, we determine a new intermediate Na2V2(PO4)3 phase using operando synchrotron X-ray diffraction. Density functional theory calculations further support the existence of the Na2V2(PO4)3 phase. We propose for the first time two possible crystal structures of Na2V2(PO4)3 analyzed by Rietveld refinement. The two structure models with the space groups P21/c or P2/c for the new intermediate Na2V2(PO4)3 phase show similar unit cell parameters but different atomic arrangements, including a vanadium charge ordering. As the appearance of the intermediate Na2V2(PO4)3 phase is accompanied by symmetry reduction, Na(1) and Na(2) sites split into several positions in Na2V2(PO4)3, in which one of the splitting Na(2) position is found to be a vacancy whereas the Na(1) positions are almost fully filled. The intermediate Na2V2(PO4)3 phase reduces the lattice mismatch between Na3V2(PO4)3 and Na1V2(PO4)3 phases facilitating a fast phase transition. This work paves the way for a better understanding of great rate capabilities of Na3V2(PO4)3.

scholarly journals Predicted polymorph manipulation in an exotic double perovskite oxide

2019 ◽  
Vol 7 (39) ◽  
pp. 12306-12311 ◽  
Author(s):  
He-Ping Su ◽  
Shu-Fang Li ◽  
Yifeng Han ◽  
Mei-Xia Wu ◽  
Churen Gui ◽  
...  
Keyword(s):  
Phase Transition ◽  
Density Functional Theory ◽  
First Principles ◽  
Density Functional ◽  
Double Perovskite ◽  
Density Functional Theory Calculations ◽  
Perovskite Oxide ◽  
Functional Theory ◽  
First Time ◽  
Perovskite Type

First-principles density functional theory calculations, for the first time, was used to predict the Mg3TeO6-to-perovskite type phase transition in Mn3TeO6 at around 5 GPa.

Janus monolayer of WSeTe, a new structural phase transition material driven by electrostatic gating

Nanoscale ◽  
2018 ◽  
Vol 10 (46) ◽  
pp. 21629-21633 ◽  
Author(s):  
Yajing Sun ◽  
Zhigang Shuai ◽  
Dong Wang
Keyword(s):  
Phase Transition ◽  
Density Functional Theory ◽  
Structural Phase Transition ◽  
Density Functional ◽  
Structural Phase ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Electrostatic Gating ◽  
Phase Transition Kinetics

By density functional theory calculations, we show that the Janus monolayer of WSeTe has faster semiconductor–semimetal phase transition kinetics than MoTe2.

scholarly journals Synthesis, Characterization, and Crystal Structure Determination of a New Lithium Zinc Iodate Polymorph LiZn(IO3)3

Crystals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 464 ◽  
Author(s):  
Hebboul ◽  
Galez ◽  
Benbertal ◽  
Beauquis ◽  
Mugnier ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Density Functional Theory ◽  
Density Functional ◽  
Second Harmonic ◽  
Infrared Absorption Spectrum ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters

Synthesis and characterization of anhydrous LiZn(IO3)3 powders prepared from an aqueous solution are reported. Morphological and compositional analyses were carried out by using scanning electron microscopy and energy-dispersive X-ray measurements. The synthesized powders exhibited a needle-like morphology after annealing at 400 °C. A crystal structure for the synthesized compound was proposed from powder X-ray diffraction and density-functional theory calculations. Rietveld refinements led to a monoclinic structure, which can be described with space group P21, number 4, and unit-cell parameters a = 21.874(9) Å, b = 5.171(2) Å, c = 5.433(2) Å, and  = 120.93(4)°. Density-functional theory calculations supported the same crystal structure. Infrared spectra were also collected, and the vibrations associated with the different modes were discussed. The non-centrosymmetric space group determined for this new polymorph of LiZn(IO3)3, the characteristics of its infrared absorption spectrum, and the observed second-harmonic generation suggest it is a promising infrared non-linear optical material.

scholarly journals High-Pressure Structural Behavior and Equation of State of Kagome Staircase Compound, Ni3V2O8

Crystals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 910
Author(s):  
Daniel Diaz-Anichtchenko ◽  
Robin Turnbull ◽  
Enrico Bandiello ◽  
Simone Anzellini ◽  
Daniel Errandonea
Keyword(s):  
High Pressure ◽  
Equation Of State ◽  
Density Functional ◽  
Room Temperature ◽  
Ambient Pressure ◽  
Density Functional Theory Calculations ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cell Parameters ◽  
A Chain

We report on high-pressure synchrotron X-ray diffraction measurements on Ni3V2O8 at room-temperature up to 23 GPa. According to this study, the ambient-pressure orthorhombic structure remains stable up to the highest pressure reached in the experiments. We have also obtained the pressure dependence of the unit-cell parameters, which reveals an anisotropic compression behavior. In addition, a room-temperature pressure–volume third-order Birch–Murnaghan equation of state has been obtained with parameters: V0 = 555.7(2) Å3, K0 = 139(3) GPa, and K0′ = 4.4(3). According to this result, Ni3V2O8 is the least compressible kagome-type vanadate. The changes of the crystal structure under compression have been related to the presence of a chain of edge-sharing NiO6 octahedral units forming kagome staircases interconnected by VO4 rigid tetrahedral units. The reported results are discussed in comparison with high-pressure X-ray diffraction results from isostructural Zn3V2O8 and density-functional theory calculations on several isostructural vanadates.

Lithium electrochemical deintercalation from O2-LiCoO2: structural study and first principles calculations

2002 ◽  
Vol 756 ◽  
Author(s):  
D. Carlier ◽  
A. Van der Ven ◽  
G. Ceder ◽  
L. Croguennec ◽  
M. Ménétrier ◽  
...  
Keyword(s):  
Phase Transformations ◽  
Density Functional ◽  
Driving Forces ◽  
Charge Ordering ◽  
Ionic Exchange ◽  
Two Phase ◽  
Entropy Maximization ◽  
Vacancy Ordering ◽  
Voltage Curve ◽  
Ordered Phases

ABSTRACTWe present a detailed study of the O2-LiCoO2 phase used as positive electrode in lithium batteries. This phase is a metastable form of LiCoO2 and is prepared by ionic exchange from P2-Na0.70CoO2. The O2-LiCoO2 system presents interesting fundamental problems as it exhibits several phase transformations upon lithium deintercalation that imply either CoO2 sheet gliding or lithium/vacancy ordering. Two unusual structures are observed: T#2 and O6. The T#2 phase was characterized by X-ray, neutron and electron diffraction, whereas the O6 phase was only characterized by XRD.In order to better understand the structures and the driving forces responsible for the phase transformations involved in lithium deintercalation, we combine our experimental study of this system with a theoretical approach. The voltage-composition curve at room temperature is calculated using Density Functional Theory combined with Monte Carlo simulations, and is qualitatively in good agreement with the experimental voltage curve over the complete lithium composition range. Pseudopotential and thermodynamic calculations both show that two tetrahedral sites have to be considered for Li in the T#2 structure. The calculated voltage curve thus exhibits a two-phase O2/T#2 region that indicates that this phase transformation is driven by the entropy maximization and not by a non-metal to metal transition. We also predict two ordered phases for Li1/4CoO2 (O2) and Li1/3CoO2 (O6) and show that the formation of the O6 phase is not related to Li staging or Co3+/Co4+ charge ordering.

scholarly journals Crossover from metal to insulator in dense lithium-rich compound CLi4

2016 ◽  
Vol 113 (9) ◽  
pp. 2366-2369 ◽  
Author(s):  
Xilian Jin ◽  
Xiao-Jia Chen ◽  
Tian Cui ◽  
Ho-kwang Mao ◽  
Huadi Zhang ◽  
...  
Keyword(s):  
Phase Transition ◽  
Density Functional Theory ◽  
Fermi Surface ◽  
Density Functional ◽  
Alkali Metals ◽  
Alkaline Earth ◽  
Density Functional Theory Calculations ◽  
Alkaline Earth Metals ◽  
Functional Theory ◽  
Surface Filling

At room environment, all materials can be classified as insulators or metals or in-between semiconductors, by judging whether they are capable of conducting the flow of electrons. One can expect an insulator to convert into a metal and to remain in this state upon further compression, i.e., pressure-induced metallization. Some exceptions were reported recently in elementary metals such as all of the alkali metals and heavy alkaline earth metals (Ca, Sr, and Ba). Here we show that a compound of CLi4 becomes progressively less conductive and eventually insulating upon compression based on ab initio density-functional theory calculations. An unusual path with pressure is found for the phase transition from metal to semimetal, to semiconductor, and eventually to insulator. The Fermi surface filling parameter is used to describe such an antimetallization process.

Determination of the Space Group of Ceramic BaO.Pr2O3.4TiO2 by Electron Diffraction

1995 ◽  
Vol 28 (5) ◽  
pp. 577-581 ◽  
Author(s):  
F. Azough ◽  
P. E. Champness ◽  
R. Freer
Keyword(s):  
Phase Transition ◽  
Electron Diffraction ◽  
Mixed Oxide ◽  
Displacement Vector ◽  
Orthorhombic Symmetry ◽  
Space Group ◽  
Space Groups ◽  
Cell Parameters ◽  
Antiphase Domains

Ceramic specimens of BaO.Pr203 .4TiO2 (Ba4.5Pr9Ti18O54) were prepared by the mixed-oxide route. Electron diffraction indicated that the compound has orthorhombic symmetry with cell parameters a ≃ 22.2, b ≃ 12.2 and c ≃ 7.6 Å. The space group was identified as Pnam, one of the two possible space groups previously identified for Ba3.75Ln9.5Ti18O54, where Ln = Nd, La or Sm. The fact that Pnam is a subgroup of the 2c superlattice of Pbam and the existence of antiphase domains with a displacement vector c/2 in BaO.Pr2O3 .4TiO2 suggests that it underwent a phase transition during cooling from Pbam to Pnam in which the c axis doubled.

scholarly journals Spin-Filtering Effects in Würtzite and Graphite-Like AlN Nanowires with Mn Impurities

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
G. A. Nemnes
Keyword(s):  
Phase Transition ◽  
Density Functional ◽  
Surface States ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Group Iii ◽  
Magnetic Nanowire ◽  
Group Iii Nitride ◽  
Basic Prerequisite ◽  
Spin Filtering

Spin transport properties of magnetic nanowire systems—atomic-sized AlN nanowires with additional Mn impurities—are investigated employingab initioconstrained spin density functional theory calculations and nonequilibrium Green’s functions formalism. The analyzed nanowire structures exhibit a stress-induced phase transition, between würtzite and graphite-like configurations. In these quasi-one dimensional systems, the surface states ensure the basic prerequisite in establishing spin and charge transfer, by reducing the relatively large bandgap of the group III nitride semiconductor. The results show in how far this phase transition affects the surface states, focusing on the consequences which appear in the spin-filtering processes.

scholarly journals Investigation of the structural and electronic properties of CdS under high pressure: an ab initio study

2018 ◽  
Vol 96 (2) ◽  
pp. 216-224 ◽  
Author(s):  
C. Yamcicier ◽  
Z. Merdan ◽  
C. Kurkcu
Keyword(s):  
Phase Transition ◽  
Ab Initio ◽  
Density Functional ◽  
Structural Phase ◽  
Type Structure ◽  
Ambient Conditions ◽  
Space Group ◽  
Space Groups ◽  
Intermediate States ◽  
Calculation Results

An ab initio constant pressure study is carried out to explore the behaviour of cadmium sulfide (CdS) under high hydrostatic pressure. We have studied the structural properties of CdS using density functional theory (DFT) under pressure up to 200 GPa. CdS crystallizes in a wurtzite (WZ)-type structure under ambient conditions. CdS undergoes a structural phase transition from the hexagonal WZ-type structure with space group P63mc to cubic NaCl-type structure with space group [Formula: see text]. Another phase transition is obtained from NaCl-type structure to the orthorhombic CdS-III-type structure with space group Pmmn. The first transformation proceeds via seven intermediate states with space group Cmc21, P21, Pmn21, P21/m, Pmmn, I4/mmm, and Cmcm. The latter transformation is based on two intermediate states with space groups Immm and P21/m. These phase transitions are also studied by total energy and enthalpy calculations. According to these calculations, the phase transformations occur at about 3 and 51 GPa, respectively. Calculation results on the other basic properties, such as lattice constant, volume, and bulk modulus are also compared with those of other recent theoretical and experimental data, and generally, good agreement with the available data are obtained.

THEORETICAL EVIDENCE FOR UNUSUAL BONDING GEOMETRY AND PHASE TRANSITIONS OF Na ON Al(001)

1994 ◽  
Vol 01 (02n03) ◽  
pp. 213-219 ◽  
Author(s):  
C. STAMPFL ◽  
J. NEUGEBAUER ◽  
M. SCHEFFLER
Keyword(s):  
Phase Transition ◽  
Density Functional Theory ◽  
Phase Transitions ◽  
Density Functional ◽  
Alkali Metals ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Island Formation ◽  
Low Concentration ◽  
Theoretical Evidence

We performed density-functional theory calculations for Na on Al(001) for various coverages from a very low concentration up to a monolayer. From the results we predict that for low coverages the Na atoms occupy on-surface hollow sites which is the stable geometry, but for higher coverages this is only metastable; the stable geometry is reached through a phase transition to a condensed c(2×2) structure where the Na atoms are in surface substitutional sites (contrary to previously suggested models). The mechanism which actuates the island formation with a substitutional geometry is described and the differences to the substitutional adsorption of alkali metals on Al(111) are discussed.

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