Phase Transitions in V2O5 Intercalation Compounds
About: This article is published in Advanced Materials Research.The article was published on 1994-09-01. It has received 5 citations till now. The article focuses on the topics: Intercalation (chemistry) & Phase transition.
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TL;DR: In this article, an important contribution to the modulation results from repulsive Li+-Li+ forces, which impose an incommensurate ordering of the Li+ ions along b∗ in strings of cuboctahedral cavities between adjacent V2O5 layers.
Abstract: Electron diffraction was used to study the lithium-intercalated V2O5 bronzes Li x V2O5. In the course of these investigations a new incommensurately modulated structure was detected at room temperature. The space group of the basic structure is Pmmn; the superspace group characterizing the one-dimensionally modulated structure is found to be Pmmn (0 γ ½). The incommensurate component γ of the modulation vector q is a function of the lithium stoichiometry and varies between γ = 0.531(4) and γ = 0.550(4) for ∊′-Li x V2O5 with 0.605(3) ≤ x ≤ 0.620(3). In the present paper we propose that an important contribution to the modulation results from repulsive Li+-Li+ forces, which impose an incommensurate ordering of the Li+ ions along b∗ in strings of cuboctahedral cavities between adjacent V2O5 layers.
15 citations
TL;DR: In this paper, a line of thermally induced structural phase transitions was detected in the x-T field and the reversible continuous phase transitions can be described in terms of a classical Landau-type theory.
Abstract: With high-resolution Guinier diffractometry the low-temperature stability of the intercalated lithium vanadium oxide bronzes e - Li x V2O5, with 0.32 ≤ x ≤ 0.80, was studied. In the course of these investigations a line of thermally induced structural phase transitions was detected in the x-T field. The reversible continuous phase transitions can be described in terms of a classical Landau-type theory. They are proper (potentially) ferroelastic with an one-dimensional order parameter transforming as the Γ+ 3 irreducible representation of space group Pmmn. The symmetry is orthorhombic P21/m21/m2/n above Tc , but monoclinic P21 /m11 below Tc . The transition temperatures depend strongly on the stoichiometry of the intercalated lithium ions. The critical exponent β, and, hence, the character of the phase transition do not change significantly with the lithium concentration. However, for x ≤ 0.52 corresponding phase transitions could not be detected, supporting the idea that the accepted stability fi...
12 citations
TL;DR: In this article, an extended Frenkel - Kontorova model was proposed to describe the variation of the modulation wave vector on the lithium stoichiometry in one-dimensional structures.
Abstract: Electron diffraction was used to study the stoichiometric dependence of the modulation wave vector in the incommensurately modulated structures of - and . For and the space group of the basic structure is Pmmn, and the superspace group characterizing the one-dimensionally modulated structure is found to be . The stoichiometry dependence of the modulation wave vector q can be described by a staircase function, with being constant at for . A second plateau has been observed in the stability field of for with . For the stoichiometry range varies continuously between and . In the present paper we will show that the system can be described by an extended Frenkel - Kontorova model. Despite its extreme simplicity in the one-dimensional case, the model exhibits most of the features necessary for understanding the variation of the dependence of the modulation wave vector on the lithium stoichiometry.
8 citations
TL;DR: In this article, a structural analysis for the highly disordered monoclinic structure of the ferroelastic low-temperature phase of ∈'-Li 0.620(3) V 2 O 5 was performed by fitting a calculated intensity curve to the observed X-ray powder diffraction pattern.
Abstract: A structural analysis is performed for the highly disordered monoclinic structure of the ferroelastic low-temperature phase of ∈'-Li 0.620(3) V 2 O 5 by fitting a calculated intensity curve to the observed X-ray powder diffraction pattern. The one-dimensional disorder can be described in terms of a 3-layers disorder model of Reichweite s = 1, in which a random disorder of monoclinic and orthorhombic layers stacked along [001] is assumed. The monoclinic layers are characterized by a unit layer thickness and translations of +Δy and -Δy parallel to [010], respectively, while the orthorhombic layer is characterized by a layer thickness 1 + Δd and no translation parallel to [010]. The diffraction intensity is calculated after Kakinoki and Komura, taking into account a probability matrix for the occurrence of the different layer types. The best fit to the observed synchrotron X-ray powder pattern is obtained assuming a coexistence of monoclinic and orthorhombic domains within one crystal in a volume ratio of 90:10.
2 citations
TL;DR: In this paper, the paraelastic-to-ferroelastic phase transition in the lithium vanadium oxide bronze epsilon (1)-Li 0.527V2O5 was studied by low-temperature, high-resolution Guinier diffractometry.
Abstract: The paraelastic-to-ferroelastic phase transition in the lithium vanadium oxide bronze epsilon (1)-Li0.527V2O5 was studied by low-temperature, high-resolution Guinier diffractometry. At the transition the symmetry changes from orthorhombic Pmmn to monoclinic P2(1)/m11 at T-c = 285(5) K. At all temperatures anisotropic broadening of the reflections occurs, indicating the presence of stacking faults in this laver structure. X-ray intensity calculations in terms of a one-dimensional model of stacking disorder were carried out in order to elucidate the structural changes induced by the phase transition, and to determine the critical behaviour of the order parameter Q. The symmetry relations between the Pmmn and P2(1)/m11 phases allow the development of the spontaneous strain which is, in this system, proportional to the change in cos alpha. A bilinear coupling between e(s) and Q was found.
Cites methods from "Phase Transitions in V2O5 Intercala..."
...A thermally induced structural phase transition in the V2O5-subsystem has been observed for E-LixV2O5 using low-temperature Guinier diffractometry [3, 9]....
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