Synthesis, Structure, and Theoretical Investigations of an Alkaline Earth Vanadate Oxide Compound (Ca4V4O14): Electronic, Optical, and Chemical Bond Properties
Abstract:One novel purely inorganic d 0 polyoxovanadate compound Ca 4 V 4 O 14 (1) was obtained and characterized structurally. The chain-like [V 4 O 14 ] 8À anion, built up from distorted VO 5 trigonal bipyramids and VO 4 tetrahedras is rarely observed. The reason for structural distortions is ascribed to the second-order Jahn-Teller effect. The band structure, the density of states, linear optical response functions, the dielectric constants of the static case e(0), and refractive indexes were calculated by the densi… Show more
“…Therefore, we think that the optical absorption can be assigned to the O-2p → V-3d charge transfer within VO 4 groups. This feature is in accordance with many other reported vanadate compounds, such as Ag 2 Sr(VO 3 ) 4 , Ca 4 V 4 O 14 , and so on.…”
A modulated structure with symmetrical characteristic higher than three-dimensional is a fascinating crystallographic type, and it is randomly encountered by researchers. Herein, we prepared 0.1 mm level single crystals of Na 3 La(VO 4 ) 2 and determined its structure to be a (3 + 1)-dimensional modulated structure using the X-ray diffraction analysis method for single crystals. Its super space group was determined to be Pca2 1 (0β0)-000. On the other hand, we introduced Tb 3+ into the Na 3 La(VO 4 ) 2 host lattice to fabricate phosphors Na 3 La 1-x (VO 4 ) 2 :xTb 3+ and studied their photoluminescence properties. Interestingly, for the strong absorption of the Na 3 La(VO 4 ) 2 host lattice in the range of 200−400 nm, the traditional 330−385 nm light is unable to efficiently excite Tb 3+ ions in the Na 3 La(VO 4 ) 2 host to generate luminescence of Tb 3+ . Instead, Na 3 La 1−x (VO 4 ) 2 :xTb 3+ is suitable to be excited by 487 nm to generate emitting light at 543, 584, and 622 nm, due to Tb 3+ characteristic 4f → 4f transitions of 5 D 4 → 7 F J (J = 5, 4, 3). Hence, the Tb 3+ -doped Na 3 La(VO 4 ) 2 phosphors have potential applications for white-light-emitting diodes.
“…Therefore, we think that the optical absorption can be assigned to the O-2p → V-3d charge transfer within VO 4 groups. This feature is in accordance with many other reported vanadate compounds, such as Ag 2 Sr(VO 3 ) 4 , Ca 4 V 4 O 14 , and so on.…”
A modulated structure with symmetrical characteristic higher than three-dimensional is a fascinating crystallographic type, and it is randomly encountered by researchers. Herein, we prepared 0.1 mm level single crystals of Na 3 La(VO 4 ) 2 and determined its structure to be a (3 + 1)-dimensional modulated structure using the X-ray diffraction analysis method for single crystals. Its super space group was determined to be Pca2 1 (0β0)-000. On the other hand, we introduced Tb 3+ into the Na 3 La(VO 4 ) 2 host lattice to fabricate phosphors Na 3 La 1-x (VO 4 ) 2 :xTb 3+ and studied their photoluminescence properties. Interestingly, for the strong absorption of the Na 3 La(VO 4 ) 2 host lattice in the range of 200−400 nm, the traditional 330−385 nm light is unable to efficiently excite Tb 3+ ions in the Na 3 La(VO 4 ) 2 host to generate luminescence of Tb 3+ . Instead, Na 3 La 1−x (VO 4 ) 2 :xTb 3+ is suitable to be excited by 487 nm to generate emitting light at 543, 584, and 622 nm, due to Tb 3+ characteristic 4f → 4f transitions of 5 D 4 → 7 F J (J = 5, 4, 3). Hence, the Tb 3+ -doped Na 3 La(VO 4 ) 2 phosphors have potential applications for white-light-emitting diodes.
“…(V 4 O 14 ) 8– anions were previously reported in only three known vanadates crystallizing in the triclinic P 1̅ space group. In these compounds, all (V 4 O 14 ) 8– anions were made of a pair of edge-sharing VO 5 (square pyramid or trigonal bipyramid , ). The reported (V 4 O 14 ) 8– unit differs from what was already known.…”
The structure of a novel compound, LiFeV 2 O 7 , has been determined from single-crystal X-ray diffraction data. The phase crystallizes in the noncentrosymmetric monoclinic Cc space group. The structure can be described as a layered type compound alternating (Li,Fe)−O sheets and V−O chains that are perpendicular to the [101] direction. Within the (Li,Fe)−O sheets, "hexagonal" holes are formed and assembled into tunnels running parallel to the [201] direction and hosting the vanadium atoms. Original (V 4 O 14 ) 8− strings are observed within the structure in association with well-known (V 2 O 7 ) 4− pyrovanadate units. Both units alternate parallel to the [−101] direction. LiFeV 2 O 7 displays a reversible insertion− deinsertion mechanism for Li + ions. The theoretical capacity for the insertion of one Li + into LiFeV 2 O 7 reaches 97 mAh/g. When the compound is cycled between 3.50 and 2.35 V versus Li + /Li, the electrochemical curve displays an initial capacity of 100 mAh/g, with 85% of this capacity retained after 60 cycles. No evidence of the formation of Fe 4+ upon oxidation to a high voltage was observed. LiFeV 2 O 7 represents the first reported phase in the Li 2 O−Fe 2 O 3 −V 2 O 5 ternary diagram with electrochemical activities.
“…In this case, according to Tong et al . (2011) it must be described by the formula Ca 3 Cd(V 4 O 14 ) (Figure 3). Figure 3.(Color online) Schematic drawing: (a) a view of the Ca 1.5 Cd 0.5 V 2 O 7 structure along c -axis and (b) the chain-like [V 4 O 14 ] 8− anion.…”
The crystal structures of Ca1.5Mn0.5V2O7 (I) and Ca1.5Cd0.5V2O7 (II) synthesized by the citrate method and by a conventional solid-state reaction, respectively, were determined using X-ray powder diffraction data. It was found that the compound I has a monoclinic crystal structure a = 4.88563(9) Å, b = 11.21279(22) Å, c = 5.69643(11 Å), β = 96.376(7)°, V = 310.132(10) Å3 (space group P21/c), Z = 2). Compound I has a narrow homogeneity region Ca1.5±0.1Mn0.5±0.1V2O7. The vanadate Ca1.5Cd0.5V2O7 crystallizes in the triclinic system with the parameters a = 6.66139(6) Å, b = 6.93019(7) Å, c = 7.02211(6) Å, α = 85.4404(9)°, β = 63.7505(7)°, γ = 82.5515(10)° и V = 288.201(5) Å3 (space group P$\bar 1$, Z = 2). It is one of the formulations of the primary solid solution, formed as a result of the substitution of part of the calcium cations for cadmium cations in Ca2V2O7.
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