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The crystal structures of K2V8O21 and Tl2V8O21 have been determined and refined, using both neutron and X-ray powder diffraction data. K2V8O21 (TI2V8O21) crystallises in the monoclinic space group C2/m (C2/m) with the unit cell parameters a = 14.9402(2) (15.1405(4)) Angstrom, b = 3.61823(4) (3.61309(6)) Angstrom, c = 14.7827(2) (14.9712(2)) Angstro...
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... crystal structures of a number of compounds in the K 2 O-V 2 O 5 and Tl 2 O-V 2 O 5 systems are found in the litera- ture, see Table 1. The most common structural unit in these compounds shifts from VO 4 tetrahedra at the K 2 O/Tl 2 O-rich end to distorted VO 5 square pyramids (trigonal bipyramids) and VO 6 octahedra at the V 2 O 5 -rich end of the phase di- agram, as shown in Fig. 1. ...
Citations
... In this hollandite-type structure, a portion of V 3+ is substituted by Al 3+ to stabilize the tunnel structure. Moreover, the Al doping leads to a large pore volume, high specific surface area and small pore size, which offers reduced Zn 2+ [127]. For example, K + pillared K 2 V 8 O 21 nanobelts were proposed as a cathode for AZIBs in a ZnSO 4 electrolyte [128]. ...
Aqueous zinc-ion batteries (AZIBs) are considered as a promising alternative to the current lithium-ion battery system due to their environmental benignity, high safety, and cost-effectiveness. Recently, significant research progress has been achieved in the development of manganese/vanadium oxides for AZIBs via guest species incorporation, whereby the intrinsic capacity and cycling stability have been enhanced through improving the structural stability and accelerating the Zn²⁺/e⁻ transportation. In this review, we present an overview of the recent advances in the guest species incorporation of manganese/vanadium oxides for AZIBs. The crystal structures and zinc storage mechanisms have been analyzed with considerations of effects of the various types of guest species incorporated into manganese/vanadium oxides. We also summarized the design strategies, structural advantages and future perspectives of the guest species incorporation for the well-established research in AZIBs.
... The crystal structure of K 2 V 8 O 21 (Inset Fig. 1a) exhibits a tunnel framework isomorphic to that of Ag 0.33 V 2 O 5 with a= 14.9402 Å, b= 3.61823 Å, c= 14.7827 Å [48]. This tunnel structure is formed by the vanadate framework, which consists of VO 6 octahedra and VO 5 pyramids forming [V 8 O 21 ] 2units along the b-axis, while K + ions are filled in the tunnel as "pillars" to stabilize the structure [49]. ...
... 16 In this paper, we have attempted to improve the electrochemical property of K 2 V 8 O 21 by doping redox inactive metal ions such as Nb 5+ and Ti 4+ and investigated the mechanism of charge-discharge and capacity fading by measuring ex-situ XRD. 21 was synthesized by the solid reaction method according to the report by Tyutyunnik et al. 17 V 2 O 5 (Wako: 99%) and K 2 CO 3 (Nakarai: 99%) were mixed with the molar ratio of 4:1 and pelletized. Specified substance was obtained by sintering at 450°C for 50 h under air. ...
... In Fig. 1(a), the XRD pattern for sample sintered at 450°C for 50 h was shown. Obtained pattern agreed with that of K 2 V 8 O 21 indexed to monoclinic C2/m reported by Tyutyunnik et al. 17 The patterns for 1-2 mol% Nb-doped K 2 V 8 O 21 were also shown in Fig. 1(a). The pattern for 1 mol% Nb-doped K 2 V 8 O 21 was also agreed with the reported one, while the reflection for impurity was found in 2 mol% Nb-doped sample. ...
Improvement of electrochemical property of K2V8O21, a stable phase of vanadium bronzes, was attempted by redox inactive metal ion doping. From the XRD pattern and lattice parameter change, it was confirmed that Ti and Nb can be exchanged with vanadium until 2mol%. By doping 1mol% Nb5+ to K2V8O21, the discharged capacity was improved to 210mAh/g from 140mAh/g for non-dope system. In ex-situ XRD measurement, non-dope K2V8O21 became amorphous in the first discharge process. For Nb-doped system, main reflection of K2V8O21 observed after both discharge process and first discharge-charge cycle. The lattice parameter of c axis increased while that of a axis decreased after discharge. Both lattice parameters got back to the initial position after charging process. This result suggests that lithium ions are intercalating into the inter layer part along the c axis during the discharge process. Mechanical mixing active materials with acetylene black was attempted for the further improvement in the electrochemical property. The initial capacity of ball milled Nb-doped K2V8O21 was improved to 315mAh/g. This result suggests that the capacity of K2V8O21 is determined by the numbers of lithium ion that can be intercalated into the lattice without the destruction of its crystal structure.
... For examples of the two typical thallium environments, crystals with both a low and a high Tl 2 O content need to be considered. Fig. 6(a) shows the thallium site which occurs in the crystal V 8 Tl 2 O 21 [45]. This crystal contains 11.1 mol% Tl 2 O, and typifies the symmetric environment and long Tl-O bonds which are formed when the thallium content is low and the thallium behaves as a modifier. ...
... There have been several neutron diffraction studies of alkali germanate glasses, in which the alkali acts as a modifier for all compositions. In particular, an extensive neutron diffraction study of caesium germanate glasses has been reported [29] and, although the Cs-O bond lengths were not determined, the Cs-O distances in caesium germanate crystals Cs 10 Ge 2 O 9 and Cs 6 Ge 3 O 9 [47] are between 2.8 and 3.2 Å, and similar in length to the Tl-O bonds for thallium atoms acting as a modifier [45]. Therefore, the correlation functions of the thallium and caesium glasses, particularly at distances shorter that 3 Å, should be very similar if thallium behaves purely as a modifier. ...
... Fig. 8 compares n Ge-O for these two systems, showing that n Ge-O declines rapidly as the amount of Cs 2 O is increased above 18 mol%, whereas the sample with 30 mol% Tl 2 O has a germanium coordination number which remains high. The second peak for the thallium-containing glass is much broader than for the caesium [45] and b) Tl 8 Ge 5 O 14 [46]. germanate glass, and the increased area at about 2.5 Å is evidence for [TlO 3 ] units in the structure. ...
Neutron diffraction data, measured for two thallium germanate glass compositions, are presented and compared with previously published data for caesium germanate glasses. The measured coordination number, nGe–O, for the 10 mol% Tl2O thallium germanate glass is in good agreement with the average coordination number measured for the equivalent caesium germanate. However, while nGe–O declines for caesium germanate glasses as the amount of modifier increases above 18 mol% Cs2O, nGe–O for the 30 mol% Tl2O thallium germanate glass remains high with, on average, 4.40 ± 0.03 oxygen neighbours per germanium. The difference in behaviour of the germanium coordination, compared to caesium germanate glasses, arises from a change in the average thallium environment, as the role of the thallium changes from that of a modifier (similar to an alkali), to a role where some of the thallium atoms act as network formers. This is supported by 205Tl NMR measurements which indicate the presence of two thallium environments.
... In view of the similarity of X-ray diffraction patterns of Tl 2 V 8 O 23 [6] and K 2 V 8 O 21 [3, 7], we may suggest that the compound synthesized in [6] was actually thallium(I) octavanadate. X-ray crystallography shows that potassium and thallium(I) octavanadates are isostructural compounds [8]. This suggests the possibility of existence of K 2x Tl x V 8 O 21 solid solutions. ...
... The solid solutions exist in air at temperatures within 450°ë . As temperature increases to 500°ë , the homogeneity range slightly decreases as a result of the formation of a phase of suggested composition 8 . The octavanadate structure is conserved under these conditions for compositions with x ≥ 0.025. ...
... Their pleochroism is as in Tl 2 V 8 O 21 (Ng is black, Nm dark grayish brown and Np yellow); extinction relative to prismatic elongation is direct. As judged by X-ray diffraction, the M 2 V 8 O 21 compounds crystallize in monoclinic space group C2/m, Z = 2, with the following unit cell parameters [8]: for the potassium compound, a = 14.9402 (2) (1) Å, β = 93.8 ° , ρ obs = 3.213 g/cm 3 [2]. ...
Formation parameters and properties of M2V8O21 octavanadates where M = K and Tl were studied using X-ray powder diffraction, microscopy, thermogravimetry, vibrational spectroscopy, EPR, and voltammetry. Original synthesis processes for these compounds were developed; their thermal stability parameters were determined. Potassium and thallium(I) octavanadates were shown to form complete solid solutions with each other. Potassium octavanadate in air is stable to 450°C; above this temperature, it transforms, on account of partial reduction of vanadium, to vanadium bronze by the reaction K2V8O21 ↔ K2V8O20.8 + 0.1O2. The K2V8O20.8 percentage in the sample increases with rising temperature. The substitution of small thallium amounts for potassium (x ≥ 0.025) enhances the stability of the phase until it melts at ∼525°C.
... In view of the similarity of X-ray diffraction patterns of Tl 2 V 8 O 23 [6] and K 2 V 8 O 21 [3, 7], we may suggest that the compound synthesized in [6] was actually thallium(I) octavanadate. X-ray crystallography shows that potassium and thallium(I) octavanadates are isostructural compounds [8]. This suggests the possibility of existence of K 2x Tl x V 8 O 21 solid solutions. ...
... The solid solutions exist in air at temperatures within 450°ë . As temperature increases to 500°ë , the homogeneity range slightly decreases as a result of the formation of a phase of suggested composition 8 . The octavanadate structure is conserved under these conditions for compositions with x ≥ 0.025. ...
... Their pleochroism is as in Tl 2 V 8 O 21 (Ng is black, Nm dark grayish brown and Np yellow); extinction relative to prismatic elongation is direct. As judged by X-ray diffraction, the M 2 V 8 O 21 compounds crystallize in monoclinic space group C2/m, Z = 2, with the following unit cell parameters [8]: for the potassium compound, a = 14.9402 (2) (1) Å, β = 93.8 ° , ρ obs = 3.213 g/cm 3 [2]. ...
The crystal structures of K2V8O21 and Tl2V8O21 have been determined and refined, using both neutron and X-ray powder diffraction data. K2V8O21 (Tl2V8O21) crystallises in the monoclinic space group with the unit cell parameters (15.1405(4)) Å, (3.61309(6)) Å, (14.9712(2)) Å and (89.967(2)°). The structures consist of VO6 octahedra and VO5 pyramids forming [V8O21]²⁻ units running along the b axis. These units can then be divided into three columns: (i) two edge-sharing VO5 pyramids, (ii) columns of rock-salt type structure and (iii) single chains of VO5 pyramids. The K/Tl ions are found in tunnels formed by the [V8O21]²⁻ units.
Aqueous zinc‐ion batteries (AZIBs) have attracted considerable attention as promising next‐generation power sources because of the abundance, low cost, eco‐friendliness, and high security of Zn resources. Recently, vanadium‐based materials as cathodes in AZIBs have gained interest owing to their rich electrochemical interaction with Zn²⁺ and high theoretical capacity. However, existing AZIBs are still far from meeting commercial requirements. This article summarizes recent advances in the rational design of vanadium‐based materials toward AZIBs. In particular, it highlights various tactics that have been reported to increase the intercalation space, structural stability, and the diffusion ability of the guest Zn²⁺, as well as explores the structure‐dependent electrochemical performance and the corresponding energy storage mechanism. Furthermore, this article summarizes recent achievements in the optimization of aqueous electrolytes and Zn anodes to resolve the issues that remain with Zn anodes, including dendrite formation, passivation, corrosion, and the low coulombic efficiency of plating/stripping. The rationalization of these research findings can guide further investigations in the design of cathode/anode materials and electrolytes for next‐generation AZIBs.
A facile and scalable strategy, based on a hydrothermal route, has been applied to fabricate potassium vanadate (KVO) nanowires on Ti fabric. The morphology, crystal structure, chemical composition of the prepared sample are tested and presented in detail. When tested as cathode materials for lithium-ion batteries, the flexible KVO electrode has a high reversible capacity of 270 mAh g⁻¹ at a current density of 100 mA g⁻¹ after 300 cycles. Furthermore, the KVO delivers outstanding rate behavior, even at 960 mA g⁻¹, a reversible capacity as high as 214.1 mAh g⁻¹ can be retained. The superior electrochemical performance suggests that the KVO nanowires on Ti fabric can be as a potential cathode candidate for flexible rechargeable lithium-ion batteries.
A solid state reaction method was used for synthesis of potassium vanadium bronzes with ratio K:V=1:5 and K:V=1:4 aimed at obtaining KV 5O 13 and K 2V 8O 21 phases respectively. The obtained products are mainly mixtures of both phases with predominant amount of KV 5O 13-x in the first example and K 2V 8O 21-y in the latter. Both products were treated in a reactor with water using an original procedure developed by our group. The product with 1:5 ratio possesses specific capacity of 220 mAh g -1 in a C/3 current rate and an excellent cycling stability within 100 cycles.
The subsolidus phase relations of a ZnO-V2O5-K2O system are investigated by X-ray powder diffraction. There is 1 ternary compound, 11 binary compounds and 14 three-phase regions in this system. The phase diagrams of V2O5-K2O with the K2O content ranging from 0 to 71 mol% and pseudo-binary system of ZnO-K2ZnV2O7 are also studied by X-ray powder diffraction and differential thermal analysis methods.
