Vanadate Phosphate Research Articles

Structure–polaronic conductivity relationship in vanadate–phosphate glasses

AbstractThis work provides new insights into the nature of the polaronic transport in xV2O5–(100−x)P2O5, 41 ≤ x ≤ 89 mol% glasses from analysis of their conductivity over a wide range of frequencies and temperatures, and correlation of the electrical parameters to the structural models of these materials. The results show that the linear increase in direct current (DC) conductivity with the increase in V2O5 could be related to the formation of a vanadate subnetwork, which is characterized by a length distribution of V–O bonds and variations in linkages between different vanadate units. Such a structurally complex network offers multiple conduction pathways which are favorable for polaron hopping. The Summerfield scaling of conductivity spectra reveals a temperature‐invariant mechanism of polaron transport for all glasses and the same local structural environment of polarons at higher V2O5 contents due to the same ratio of vanadate units present in the network. Also, this study highlights the similarities and differences in the nature of the polaronic transport of vanadate–phosphate glasses and other polaronically conducting phosphate glasses containing WO3, MoO3, and Fe2O3, and pins down a pivotal role of the glass structure in electrical processes in these materials.

Effects of coexisting oxoanions on SO<sub>3</sub> decomposition activity of molten-phase potassium metavanadate catalysts

Molten-state potassium metavanadate (KVO3) supported on mesoporous SiO2 materials have emerged as active catalysts for SO3 decomposition over a moderate temperature range (≤650 °C), which is a potential O2 evolution reaction useful for solar thermochemical water splitting. The molten phase formed at ≥520 °C contained tetrahedral VO42−, which plays a vital role in accelerating the SO3 uptake and conversion to SO2/O2. The present study aimed to reveal how the SO3 decomposition activity is affected by adding other oxoanions such as borate (BO33−), carbonate (CO32−), and phosphate (PO43−) into the melt. Although borate showed a deteriorating effect, phosphate tended to improve the catalytic activity when the P/V molar ratio was equal to or less than 0.5. The addition of phosphate produced a mixed phosphate vanadate with a composition of KV2PO8, which consists of infinite tetrahedral PO4 and pyramidal VO5 linked by vertex sharing. Because of the congruent melting at temperature as low as ∼530 °C, KV2PO8 may be expected as another candidate of active molten phase catalyst for SO3 decomposition.

The Synthesis of Nanophosphors YPxV1–xO4 by Spray Pyrolysis and Microwave Methods

За счет редкоземельного допирования фосфаты и ванадаты являются ведущими материалами для синтеза люминофоров благодаря их термостойкости, низкой температуре спекания, химической стабильности. Особый интерес привлекают люминофоры в наноразмерном состоянии. Простой, быстрый и масштабируемый синтез нанолюминофоров высокой химической гомогенности является актуальной задачей. Целью работы являлся синтез порошков смешанных кристаллов ванадат-фосфата иттрия различного состава методами соосаждения под действием микроволнового излучения и спрей-пиролиза, а также сравнительный анализ характеристик полученных образцов.Методами соосаждения под действием микроволнового излучения и спрей-пиролиза в различных режимах синтезированы образцы YVхP1–хO4 разного состава. Данные рентгенофазового анализа в случае синтеза ванадат-фосфата иттрия YVхP1–хO4 методом спрей-пиролиза с последующим отжигом подтверждают образование однофазных нанопорошков. Методами просвечивающей электронной микроскопии и растровой электронной микроскопии выявлены морфологические характеристики образцов. В зависимости от режима отжига образцы представляют собой ограненные либо сферические частицы размером менее 100 нм. Состав образцов YVхP1–хO4, синтезированныхметодом соосаждения под действием микроволнового излучения, сильно зависит от рН раствора прекурсоров.Минимальное содержание примесных фаз достигается при рН, равном 9.Метод спрей-пиролиза позволяет синтезировать нанопорошки ванадат-фосфата иттрия YVхP1–хO4 высокой химической гомогенности с размером частиц менее 100 нм. При синтезе YVхP1–хO4 методом соосаждения под действием микроволнового излучения максимальной химической однородности порошков ванадат-фосфата иттрия удается достигнуть при рН = 9. Однако дисперсия частиц по размеру велика, лежит в интервале 2–60 мкм. ЛИТЕРАТУРА 1. Wu C., Wang Y., Jie W. 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Natural mushroom spores derived hard carbon plates for robust and low-potential sodium ion storage

Biomass derived hard carbon has been considered a sustainable solution for sodium ion storage to improve the energy density of sodium ion batteries for low cost and large-scale energy storage. However, developing this kind of carbon materials with high specific capacity at low-potential platform is a critical issue. Herein, a new structure of hard carbon plate was developed via pyrolysis of mushroom spore (Ganoderma lucidum). The spore is mainly composed of chitin, distinguished from the lignin and cellulose in widely investigated biomass. The carbon plates obtained at 1400 °C have a suitable d002-spacing (0.371 nm) and ultra-low surface area down to 14.7 m2 g−1, resulting in a high reversible total discharge capacity of 305.8 mA h g−1 with an exceptional discharge capacity of 188.0 mA h g−1 at low-potential platform (0–0.1 V vs. Na+/Na) and excellent cycle stability as anode for SIBs. Meanwhile, the proportion of low-potential capacity in total capacity is 61.5%, which is significantly superior to previously reported carbon materials prepared using biomass from advanced plants. Furthermore, a full-cell constructed using the carbon plates as anode and sodium vanadate phosphate as cathode further validates the outstanding Na+ storage performance at low-potential, in which the battery delivers a high working voltage of 3.25 V, approaching the discharge potential of 3.3 V of sodium vanadate phosphate and a considerable energy density of 199.2 W h kg−1 (based on the total mass of cathode and anode). And it is also revealed that this high capacity for Na+ storage in the low potential range is attributed to the intercalation mechanism of NaC6 as the most possible intercalation compound. The hard carbon derived from natural spores in the work presents a new route to design low cost and efficient carbon materials as advanced anode for SIBs.

High specific capacity lithium ion battery cathode material prepared by synthesizing vanadate–phosphate glass in reducing atmosphere

Although vanadium-based materials are potential electrode materials for Li-ion batteries, the development of commonly known vanadium-based crystalline phases is hindered by their inferior cyclic performance. Unlike crystalline phases, the amorphous vanadium-based materials do not exhibit undesirable phase transformations during the charge/discharge process leading to poor cyclic performance. Herein, we demonstrate the influence of a reducing atmosphere on the structure of vanadate–phosphate (V2O5-P2O5) glass and its electrochemical properties as a lithium-ion battery cathode. By employing various characterization techniques, we unveil the influence of reducing atmosphere on valence state of vanadium ions and structure of V2O5-P2O5 glass. The V2O5-P2O5 glass, synthesized in a reducing atmosphere, exhibits an ultra-high specific capacity of 270 mAh g−1 with excellent capacity retention of ∼90% after 100 cycles. Moreover, a stable specific capacity of 220 mAh g−1 is delivered at a high current density of 85 mA g−1 after 300 cycles, corresponding to 80% capacity retention. Overall, the V2O5-P2O5 glass, synthesized in a reducing atmosphere, renders higher capacity, excellent rate performance and stable cyclic performance than the V2O5-P2O5 glass, synthesized in the air atmosphere. The current work provides a novel route to develop multi-valence transition metal oxide electrodes for Li-ion batteries.

Nanocrystallisation in vanadate phosphate and lithium iron vanadate phosphate glasses

Nanocrystallisation in vanadate phosphate and lithium iron vanadate phosphate glasses

AC/DC conductivity studies of composites of glassy electronic and ionic conductors

A series of all-glass composites has been prepared from the ionically conducting silver–phosphate glass 30AgI·35Ag2O·35P2O5 (denoted as I) and the electronically conducting vanadate–phosphate glass 90V2O5·10P2O5 (denoted as E). Component glasses were ground, mixed in five volume ratios (E:I=3:1, 2:1, 1:1, 1:2, 1:3) and pelletized under pressure. X-ray diffractometry and DSC analyses confirmed an amorphous structure of both component glasses and all final composites. Electrical properties were investigated using DC (Hebb–Wagner polarization method) and AC (impedance spectroscopy) methods. The analysis of the impedance spectra (measured down to μHz) evolution with the proportions of the electronic-to-ionic component was done. Mixed character of the conductivity was confirmed and a synergy effect (charge storage capacity) arising from the interface interactions between glasses was observed.

Thermal expansion of MZr2(AsO4)3 and MZr2(TO4) x (PO4)3–x (M = Li, Na, K, Rb, Cs; T = As, V)

The thermal expansion parameters of the MZr2(AsO4)3 (M = Li, Na, K, Rb, Cs) arsenates and MZr2(TO4)x(PO4)3–x (T = As, V) arsenate phosphate and vanadate phosphate solid solutions with the NaZr2(PO4)3 (NZP) structure have been determined by high-temperature X-ray diffraction. The effects of the size of the alkali metal cation and arsenic or vanadium substitution for phosphorus on the thermal expansion of the arsenates and solid solutions have been studied systematically. The potassium-, rubidium-, and cesium-containing arsenates, arsenate phosphates, and vanadate phosphates are low-expansion materials (αav < 2 × 10–6 °C–1); sodium zirconium arsenate and sodium zirconium and lithium zirconium arsenate phosphates and vanadate phosphates have intermediate thermal expansion (3 × 10–6 °C–1 < αav < 7 × 10–6 °C–1); and lithium zirconium arsenate is a high-expansion material (αav = 9.9 × 10–6 °C–1). The present results demonstrate that, increasing the size of the alkali metal cation in the arsenates and varying the composition of the solid solutions, one can produce NZP materials with controlled linear thermal expansion coefficients and extremely low thermal expansion anisotropy.

The role of vanadium in biology.

Vanadium is special in at least two respects: on the one hand, the tetrahedral anion vanadate(v) is similar to the phosphate anion; vanadate can thus interact with various physiological substrates that are otherwise functionalized by phosphate. On the other hand, the transition metal vanadium can easily expand its sphere beyond tetrahedral coordination, and switch between the oxidation states +v, +iv and +iii in a physiological environment. The similarity between vanadate and phosphate may account for the antidiabetic potential of vanadium compounds with carrier ligands such as maltolate and picolinate, and also for vanadium's mediation in cardiovascular and neuronal defects. Other potential medicinal applications of more complex vanadium coordination compounds, for example in the treatment of parasitic tropical diseases, may also be rooted in the specific properties of the ligand sphere. The ease of the change in the oxidation state of vanadium is employed by prokarya (bacteria and cyanobacteria) as well as by eukarya (algae and fungi) in respiratory and enzymatic functions. Macroalgae (seaweeds), fungi, lichens and Streptomyces bacteria have available haloperoxidases, and hence enzymes that enable the 2-electron oxidation of halide X(-) with peroxide, catalyzed by a Lewis-acidic V(V) center. The X(+) species thus formed can be employed to oxidatively halogenate organic substrates, a fact with implications also for the chemical processes in the atmosphere. Vanadium-dependent nitrogenases in bacteria (Azotobacter) and cyanobacteria (Anabaena) convert N2 + H(+) to NH4(+) + H2, but are also receptive for alternative substrates such as CO and C2H2. Among the enigmas to be solved with respect to the utilization of vanadium in nature is the accumulation of V(III) by some sea squirts and fan worms, as well as the purport of the nonoxido V(IV) compound amavadin in the fly agaric.

Synthesis and structure of alkali metal zirconium vanadate phosphates

Mixed vanadate phosphates in the systems MZr2(VO4)x(PO4)3 − x, where M is an alkali metal, were synthesized and studied by X-ray diffraction, electron probe microanalysis, and IR spectroscopy. Substitutional solid solutions with the structure of the mineral kosnarite (NZP) are formed at the compositions 0 ≤ x ≤ 0.2 for M = Li; 0 ≤ x ≤ 0.4 for M = Na; 0 ≤ x ≤ 0.5 for M = K; 0 ≤ x ≤ 0.3 for M = Rb; and 0 ≤ x ≤ 0.2 for M = Cs. Apart from the high-temperature NZP modification, lithium vanadate phosphates LiZr2(VO4)x(PO4)3 − x with 0 ≤ x ≤ 0.8 synthesized at temperatures not exceeding 840°C crystallize in the scandium tungstate type structure. The crystal structures of LiZr2(VO4)0.8(PO4)2.2 (space group P21/n, a = 8.8447(6) A, b = 8.9876(7) A, c = 12.3976(7) A, β = 90.821(4)○, V = 985.4(1) A3, Z = 4) and NaZr2(VO4)0.4(PO4)2.6 (space group \(R\bar 3c\) = 8.8182(3) A, c = 22.7814(6) A, V = 1534.14(1) A3, Z = 6) were refined by the Rietvield method. The framework of the vanadate phosphate structure is composed of tetrahedra (that are statistically occupied by vanadium and phosphorus atoms) and ZrO6 octahedra. The alkali metal atoms occupy extra-framework sites.

Isothermal nanocrystallization of vanadate–phosphate glasses

Abstract Glasses of the nominal composition of 90V2O5 · 10P2O5 were prepared by a standard melt-quenching technique. Their thermal and electrical properties during isothermal annealing have been studied by DSC and impedance spectroscopy. Time dependences of crystallization observed in isothermal DSC experiments at a set of temperatures were satisfactorily fitted with the Avrami formula. The progress in crystallization during the annealing resulted in a monotonic increase in the electronic conductivity. The conductivity changes were adequately represented by a proposed theoretical model of conductivity changes caused by isothermal nanocrystallization.

Tailoring the radiation tolerance of vanadate–phosphate fluorapatites by chemical composition control

The apatite-type structure of AI4AII6(BO4)6(OH, F, Cl)2 (AI, AII = Ca, Na, rare earths, fission product elements such as I and Tc, and/or actinides; B = Si, P, V, or Cr) offers unique structural advantages as an advanced nuclear waste form because a wide variety of actinides and fission products can be incorporated into the structure through coupled cation and anion substitutions. However, apatite undergoes a radiation-induced crystalline-to-amorphous transition, and previously, the effect of composition on the radiation-induced transformation has not been well understood. In this study, we demonstrate that vanadate–phosphate fluorapatite's radiation tolerance can be controlled by varying the composition. Enhanced radiation tolerance is achieved by replacing vanadium with phosphorus at the B-site or by replacing Pb with Ca at the A-site. Correlations among chemical composition, radiation performance and electronic to nuclear stopping power ratio were demonstrated and suggest that the ionization process resulting from electronic energy loss may enhance annealing of defects upon radiation damage.

On vanadate phosphate and arsenate framework structures based on the NbO-net

The recently described framework structure of composition [As(6)V(4+)(12)V(5+)(3) O(51)](-9) is analogous to previously known vanadate phosphate frameworks.

Synergetics of formation of anodic spark coatings

Mechanisms of the formation of an anodic coating under the action of electric discharges based on an aluminum alloy in a vanadate phosphate electrolyte are considered. A process model is constructed for the cases of different current densities and studied; its adequacy is estimated in terms of distributions observed in experiments.

X-ray photoelectron spectroscopy (XPS) and magnetic susceptibility studies of vanadium phosphate glasses

Vanadium phosphate glasses with the nominal chemical composition [(V 2O 5) x (P 2O 5) 1− x ], where x = 0.30, 0.40, 0.50, and 0.60, have been prepared and investigated by X-ray photoelectron spectroscopy (XPS) and magnetization measurements. Asymmetries found in the O 1s, P 2p, and V 2p core level spectra indicate the presence of primarily P–O–P, P–O–V, and V–O–V structural bonds, a spin–orbit splitting of the P 2p core level, and more than one valence state of V ions being present. The magnetic susceptibility data for these glasses follow a Curie–Weiss behavior which also indicates the presence of some V ions existing in a magnetic state, i.e., a valence state other than that of the non-magnetic V 5+. From qualitative comparisons of the abundance of the bridging oxygen or P–O–P sites as determined from the areas under the various O 1s peaks with the abundances of differing phosphate structural groups associated with the presence of different valence states of the vanadium ions, a glass structure model consisting of a mixture of vanadate phosphate phases is proposed for these glass samples. These include V 2O 5, VOPO 4, (VO) 2P 2O 7, VO(PO 3), and V(PO 3) 3 with the abundance of orthophosphate (PO 4) 3− units increasing with increasing vanadium content.

Acid Phosphatases from the Liver of Labeo rohita: Purification and Characterization

Low molecular weight acid phosphatase (LM-ACP) peak 2 (the isoenzyme corresponding to isoform 2, IF-2) from the liver of fish Rahu (Labeo rohita) was purified to homogeneity. 900 times purification resulted with specific activity of 35 U/mg of protein and recovery of 0.2%. The enzyme was found homogeneous on sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Molecular weight of 18 killo Daltons (kDa) was obtained. The peak 1 isoenzyme corresponding to isoform1 (IF-1) was partially purified about 160 times with specific activity of 7 U/mg of protein. Major protein band corresponding to 18 kDa was seen along with other protein faint bands. High molecular weight acid phosphatase (HM-ACP) was also partially purified. The molecular weight was estimated to be a 100 kDa by gel filtration on Sephadex G-100. LM-ACP isoenzymes and HM-ACP enzyme were studied for their substrate specificity, sensitivity to inhibitors or activators and other kinetic parameters. LM-ACP isoenzymes were not inhibited by tartrate and fluoride but were inhibited by sulfhydryl reagent whereas high molecular weight enzyme was strongly inhibited by fluoride and tartrate. Phosphate vanadate and molybdate inhibited both types of enzymes competitively, but their action was more pronounced in HM-ACP enzyme. LM-ACP was effectively activated by purine compounds whereas HM-ACP was not. LM-ACP showed strict substrate specificity while HM-ACP showed broad substrate specificity. The two types of acid phosphatases also differed in their rate of hydrolysis of alpha-naphthyl phosphate and beta-glyerophosphate.

Effect of nanocrystallization on the electronic conductivity of vanadate–phosphate glasses

Electronically conducting glasses of the composition xV 2O 5·(100 − x)P 2O 5 for 60 < x < 90 were prepared. The glasses of the composition corresponding to x = 90 exhibited the highest electrical conductivity and they were studied in more detail. The effects of the annealing of the samples on their electrical conductivity, structure and other characteristics were studied by impedance spectroscopy, X-ray diffractometry, DSC and SEM microscopy. It was shown that, at temperatures close to the crystallization temperature T c (determined from DSC), these glasses turned into nanomaterials consisting of crystalline grains of V 2O 5 (average size 25–35 nm) embedded in the glassy matrix. Their electrical conductivity was higher and the temperature stability was better than those of the starting glasses. It is postulated that the major role in this conductivity enhancement is played by the interfacial regions between crystalline and amorphous phases. The annealing at temperatures exceeding T c led to massive crystallization and to a conductivity drop. The XRD and SEM observations have shown that the material under study undergoes structural changes: from amorphous at the beginning, to partly crystalline after the annealing at 340 °C and to polycrystalline after the annealing at 530 °C. The obtained results are in agreement with those of our earlier studies on mixed electronic–ionic conducting glasses of the ternary Li 2O–V 2O 5–P 2O 5 system.

A XANES study of the valence state of vanadium in lithium vanadate phosphate glasses

Valence states of vanadium in Li2O-V2O5-P2O5 electronic-ionic conducting glasses have been studied by X-ray absorption spectroscopy. The composition dependence of the XANES range of the spectra has been used to estimate relative abundance of the vanadium atoms in V4+ or V5+ charge states. This information is important for analysis of electronic transport in these glasses, which occurs via electronic hopping between aliovalent vanadium centers. It was found that in samples with the lowest V2O5 contents (10 mole% of V2O5) a vast majority of vanadium ions are in V4+ charge state. At higher V2O5 contents the proportion of V4+ ions decreases at the expense of V5+ ones, but remains substantial even in glasses with the highest contents of V2O5.

Cyclic voltammetry and impedance spectroscopy studies of silver vanadate phosphate glasses

Electrical and electrochemical properties of the glasses of the AgI–Ag 2O–V 2O 5–P 2O 5 system were characterized by impedance spectroscopy and cyclic voltammetry. The observed correlation between the results obtained by these two methods was analyzed. It was found that for compositions with high content of V 2O 5 and low of Ag 2O and AgI, samples are electronic conductors. For these compositions, voltammograms are linear. At higher contents of AgI, when glasses become electronic–ionic conductors, impedance spectra contain Warburg-like diffusional part and voltammograms reveal some hysteresis. Finally at high contents of AgI and Ag 2O impedance spectra indicate blocking effects at the electrodes. Voltammograms of these glasses contain anodic and cathodic peaks.

Electrical properties of AgI–Ag 2O–V 2O 5–P 2O 5 glasses

Mixed conductive silver vanadate–phosphate glasses were prepared and their electrical properties were studied. Compositions of the glasses were characterized by parameters: x (AgI content) and r=[Ag 2O]/[V 2O 5+P 2O 5]. Total conductivity σ t ( x, r=constant) of a series of samples with fixed r values exhibited minima when plotted vs. x. The conductivity minima were accompanied by maxima of apparent activation energy E t ( x, r=constant). The observed dependencies were attributed to the ion–polaron effect (IPE), i.e. to electrostatic attraction between mobile species: electrons (polarons) and Ag + ions.