Nasicon-type Phosphate Research Articles

An improvement in the ionic conductivity and electrochemical characteristics of LiFePO4 by heterogeneous doping with NASICON-type phosphate

Composite materials based on LiFePO4 with olivine structure and Li1.3Ti1.7Fe0.3(PO4)3 with NASICON structure have been synthesized and characterized by the XRD analysis, scanning electron microscopy and impedance spectroscopy. The investigation of electrochemical behavior of obtained composites additionally coated with a thin carbon layer demonstrated that the LiFePO4-based materials doped by phosphate with the NASICON structure exhibit higher electrochemical capacity in comparison with the initial LiFePO4.

Catalytic oxidation of methanol on Pt/X (X = CaTP, NaTP) electrodes in sulfuric acid solution

In this paper, we report the synthesis and characterization of electrodes based on NASICON type phosphates. The study of the electrochemical oxidation of methanol at ambient temperature on electrodes based on NASICON type Ca0,5Ti2(PO4)3 (CaTP) and Na5Ti(PO4)3 (NaTP) compared to that of the platinum electrode model has been conducted by cyclic voltammetry in acidic medium. The results showed a significant increase of current density on the electro oxidation of methanol on the material developed based NASICON structure CaTP, cons deactivation of the electro oxidation is observed the closed structure type NaTP.

Synthesis of the new framework phosphates and their catalytic activity in ethanol conversion into hydrocarbons

The series of new framework phosphate catalysts was synthesized and their activity in ethanol conversion to hydrocarbons was studied for the first time. The results were summarized for studies of NASICON (NZP) type phosphates formation A1±xZr2−xMx(PO4)3 (where A=H3O+, Li+, Na+, Cu0.5+, M=In, аt x=0, 0.2) with the desired structure and properties controllable by variation of their chemical composition and synthesis parameters. The surface characteristics and catalytic properties of the resulting systems and the yields of the target products formed by ethanol transformations in inert atmosphere were analyzed on the basis of catalysts synthesis conditions. NaZr2(PO4)3 was the most active in hydrocarbons C3+ formation. On benzene yield the catalysts formed the row LiZr2(PO4)3 {II}≈Li1.2Zr1.8In0.2(PO4)3 {II}>LiZr2(PO4)3 {I}>NaZr2(PO4)3 {I}.

Catalytic activity of NASICON-type phosphates for ethanol dehydration and dehydrogenation

A1 ± x Zr2 − x M x (PO4)3 (A = H3O+, Li+; M = In, Nb; x = 0, 0.1, 0.2) NASICON-type materials have been prepared and characterized by X-ray diffraction, specific surface measurements (capillary condensation of nitrogen), and impedance spectroscopy. We have assessed their catalytic performance for ethanol dehydration and dehydrogenation. The results demonstrate that, when prepared with a large specific surface area, these materials are active catalysts for ethanol conversion to hydrocarbons.

FT-IR and FT-Raman study of Nasicon type phosphates, ASnFe(PO 4) 3 [A = Na 2, Ca, Cd

FT-Raman and FT-IR spectra of ASnFe(PO 4) 3 [A = Na 2, Ca, Cd] were recorded and analyzed. The bands were assigned in terms of the vibrational group frequencies of SnO 6 octahedral and PO 4 tetrahedral. The spectral analysis shows that the symmetry of corner shared octahedral (SnO 6) and the tetrahedral (PO 4) are lowered from their free ion symmetry state. The presence of Fe 3+ ions disrupts the S–N–O–S–N chain in the structure. This causes distortion of SnO 6 and PO 4 in the structure of all the compounds. Also it is seen that there are two distinct PO 4 tetrahedra of different P–O bond lengths. One of these tetrahedra is linearly distorted in all the title compounds. The PO 4 frequencies and bond lengths are calculated theoretically and are in agreement with the experimental values. The presence of PO 4 polyanion in the structure can reduce the redox energy and hence reduce the metal oxygen covalency strength in the structure.

Synthesis and properties of AgTi2(PO4)3-based NASICON-type phosphates doped with Nb5+, Zr4+, and Ga3+

We have synthesized materials based on a silver titanium phosphate with partial substitution of tri-, tetra-, or pentavalent cations for titanium: Ag1±xTi2−xMx(PO4)3 (M = Nb5+, Ga3+) and AgTi2−xZrx(PO4)3. The materials have been characterized by X-ray diffraction and impedance spectroscopy and have been shown to have small thermal expansion coefficients. Their ionic conductivity has been determined. Silver ions in these materials are difficult to replace with protons.

Contributions on Thermal Behaviour and Crystal Chemistry of Anhydrous Phosphates. XXXXI [1]. Refinement of the Superstructure of FeTi4(PO4)6 – An Example of a Highly Ordered Member of the NASICON Structure Family

AbstractSingle crystals of NASICON type phosphates Mn1.65TiIII/IV4(PO4)6 (black), FeTi4(PO4)6 (orange‐red) and CoTi4(PO4)6 (lavender colour) were grown by chemical vapour transport. The crystal structures of Mn1.65Ti4(PO4)6 and FeTi4(PO4)6 were refined from single crystal data. For the first time a superstructure for a NASICON type phosphate of general formula AIIBIV4(PO4)6 is observed and successfully refined (FeTi4(PO4)6 [data for Mn1.65Ti4(PO4)6 in brackets] rhombohedral, R32 [R3], Z = 6 (3), a = 8.5164(8) [8.5575(17)]Å, c = 41.852(6) [20.898(5)]Å, R1 = 0.053 [0.025], wR2 = 0.136 [0.061], 2598 [1261] independent reflections, 109 [59] variables). For FeTi4(PO4)6 a structure with a highly ordered cation distribution among the octahedral voids and crystal chemical reasonable interatomic distances (2.18 ≤ d(FeII‐O) ≤ 2.20) results. SXRD investigations on CoTi4(PO4)6 reveal also the presence of a superstructure along the NASICON c‐axis (c′= 5cNASICON). A new description of the NASICON structure based on group‐subgroup considerations shows its close relationship to the NiAs structure (3 x NiAs ⇒ 3 x AX ⇒ AB2(XO4)3 ⇒ □AB4(XO4)6).

High-Trivalent Rare Earth Ion Conduction in Solids Based on NASICON-Type Phosphate

Abstract Trivalent rare earth ion conductors of the (R0.05Zr0.95)80⁄79Nb(PO4)3 (R: rare earths) series with NASICON-type structures were successfully prepared and the optimum size of ion-conducting pathways for rare earth ions in (R0.05Zr0.95)80⁄79Nb(PO4)3 solids was investigated. The most suitable ion-conducting pathway for rare earth ion conduction in this series was realized for R=Dy and the highest conductivity of 3.2×10−4 S cm−1 at 600 °C was obtained for (Dy0.05Zr0.95)80⁄79Nb(PO4)3 solids. Since R3+ ion conduction was strongly dependent on the ratio of conducting R3+ ion size to crystal lattice size (VR3+⁄Vlattice; we denote this ratio as A ratio in this article), it was clear that the A ratio is a key factor to optimize R3+ ion conduction in NASICON-type structures.

FTIR features of lithium-iron phosphates as electrode materials for rechargeable lithium batteries

The essential structural features of lithium-metal phosphates (LMP) have been studied using FTIR spectroscopy which is a sensitive tool to probe the local environment in the solid materials. Various LMP materials where M is iron have been investigated including phospho-olivine LiFePO 4, diphosphate LiFeP 2O 7, Nasicon-type phosphate Li 3Fe 2(PO 4) 3 and dihydrate FePO 4·2H 2O. Vitreous and amorphous materials are also considered. Analysis of internal and external modes of vibration allows to distinguish between the different phases and the type of cationic environment in the framework. Results corroborate the contribution of the main factors which are responsible for the complexity of the spectra, i.e. departure from ideal symmetry, interactions between polyhedra, bridging atoms and lattice distortion.

Effect of the lattice volume on the Al3+ ion conduction in NASICON type solid electrolyte

New trivalent Al3+ ion conductors with NASICON type structure, [Al0.2(Zr1–xTix)0.8]20/19Nb(PO4)3 and (Al1–xLax)4/19(1–x)Zr(16–19x)/19(1–x)Nb(PO4)3, were developed and their ion conducting properties were investigated. The lattice size of the NASICON type (AlxZr1–x)4/(4-x)Nb(PO4)3 series was successfully controlled by intentionally doping Ti4+ ion or La3+ ion in the crystal lattice, and the most suitable lattice size for the Al3+ ion conduction was identified from the relationship between the Al3+ ion conductivity and the lattice volume. The highest ion conductivity of 6.1×10−4 S·cm−1 at 600 °C was obtained for [Al0.2(Zr0.8Ti0.2)0.8]20/19Nb(PO4)3 among the NASICON type phosphate series prepared. Since the Al3+ ion conduction was dependent upon the crystal lattice size, it was demonstrated that the crystal lattice volume can be one of the key factors to optimize the ion conduction in the NASICON type structure.

Tetravalent Zr4+ ion conduction in NASICON-type phosphate solids

The ionic conduction of mono-, di-, and trivalent ions in solids is popular in solid state science and the next target ion species to migrate in solids are tetravalent ions. Here, a tetravalent cation conductor which shows high conductivity, comparable to the conductivity range of the representative divalent oxide anion conductors, was artificially designed by strictly selecting the constituent elements and the structure. The tetravalent ion conducting solid electrolyte proposed here shows considerable high ion conductivity and promising applications, such as in rechargeable batteries and chemical sensors for global environmental monitoring, are greatly expected.

Physical and optical properties of NASICON-type phosphate glasses

NASICON (A m B n P 3O 12)-type phosphate glasses are examined for the physical and optical properties. A novel technique, frequency domain interferometry, has been employed to measure refractive indices over the transparency region for these glasses. From the refractive index variation, we estimated various linear and nonlinear parameters. Overall studies suggest that the replacement of constituent metal ion in the structure of NASICON, from Al 3+ to Ti 4+, invariably led to a significant change in the optical properties.

Rare earth ion conduction in tungstate and phosphate solids

The quasi two-dimensional Sc 2(WO 4) 3 type structure and the three-dimensional NASICON type R 1/3Zr 2(PO 4) 3 (R=Al 3+, rare earths) series were prepared and their trivalent ion conducting characteristics were compared. Among the Sc 2(WO 4) 3 type and the NASICON type series, the solid electrolytes with Sc 3+ as a migrating species show the highest ion conductivity. Especially, the NASICON type phosphate series holds such advantages of having a considerable high relative density and also more than seven times as high hardness compared with the Sc 2(WO 4) 3 type series, promising applications for various types of devices are greatly expected.

Absorption spectral studies of rare earth ions (Pr 3+, Nd 3+, Sm 3+, Dy 3+, Ho 3+ and Er 3+) doped in NASICON type phosphate glass, Na 4AlZnP 3O 12

The absorption spectral studies have been performed for rare earth (Pr 3+, Nd 3+, Sm 3+, Dy 3+, Ho 3+ and Er 3+) doped NASICON type phosphate glass, Na 4AlZnP 3O 12 (NAZP) to derive the phenomenological Judd–Ofelt parameters Ω λ ( λ=2, 4, 6). The variation of Ω 2 values with f electrons shows a pronounced rise in the middle of the series arises due to the differences in the distribution of sites occupied by the rare earth ions in the present phosphate glass. The hypersensitive nature of absorption transitions of Nd 3+, Er 3+ and Ho 3+ are explained in the light of covalency and site asymmetry effects. Emission studies of Eu 3+ and Dy 3+ indicate that these rare earths are situated in highly distorted sites compared to other fluoride, phosphate and oxyfluoride glasses.

Rare earth fluorescence in NASICON type phosphate glass, Na3TiZnP3O12

The emission spectra of Pr3+, Eu3+ and Dy3+ doped in NASICON type phosphate glass, Na3TiZnP3O12 (NTZP) are studied. The dopant rare earth ions occupy sites with 8–9 coordination in a highly covalent environment. For Pr3+ ion, calculated and observed branching ratios for lasing transitions3 P 0→3 H 4,6 agree well and found to be 0·64 and 0·24, respectively. The emissions of Pr3+ show strong temperature dependence on account of Boltzmann population of the higher excited states at room temperature. The excitation spectrum of Eu3+ gives rise to phonon assisted side band for5 D 2←7 F 0 transition at higher energy side with a phonon energy maximum of 1022 cm−1 and an electron phonon coupling strength (g) of 0·018. The value of phonon energy maximum agrees with infrared spectral data. The results show that observation of high energy emissions in phosphate glasses require much higherg values. The red/orange and yellow/blue transitions of Eu3+ and Dy3+, respectively show that the Eu3+ occupy more distorted site than Dy3+.

Location of Cu2+ ions in some protoned Nasicon-type phosphates

Nasicon-type phosphates Cu1−xHxZr2(PO4)3 (0 < x <1) and Cu1−xH2x−1Zr2(PO4)3 (0.5 < x <1) have been investigated by magnetic susceptibility and electron paramagnetic resonance (EPR). Room-temperature EPR spectra at X-band (9.5 GHz) exhibit relatively different local information about paramagnetic environments in the two sets. Analysis by computer simulations of Cu1−xHxZr2(PO4)3 spectra reveals that Cu2+ ion is located in an axially distorted octahedron, which can be assigned to the M(1) site. However, in the case of Cu1−xH2x−1Zr2(PO4)3, EPR parameters suggest that Cu2+ ions are distributed in two types of sites with axial and lower than axial symmetries; these latter can be attributed to M(1) and M(2) sites respectively. g and A components are related to structural properties using molecular orbital method. Data are obtained on variations of the bond covalence with the composition.

Preparation of a new family of NASICON type phosphates Ca0.5NbMP3O12 (M = Fe, Al, Ga and In) and characterization of the iron systems by Mossbauer spectroscopy

Preparation of a new family of NASICON type phosphates Ca0.5NbMP3O12 (M = Fe, Al, Ga and In) and characterization of the iron systems by Mossbauer spectroscopy

Luminescence of, and energy transfer between Dy3+ and Tb3+ in NASICON-type phosphate glasses

Abstract Fluorescence of Dy 3+ and Tb 3+ and the energy transfer between them in Na 5 TiP 3 O 12 and Na 4 NbP 3 O 12 glasses have been studied. Concentration quenching of fluorescence occurs in the case of Dy 3+ at concentrations above 3 weight %, whereas in the case of Tb 3+ , it does not occur up to 5 weight %. The energy transfer from Dy 3+ to Tb 3+ is nonradiative and takes place through dipole-dipole interaction.

31P MAS NMR Investigations of Crystalline and Glassy NASICON-Type Phosphates

31P MAS NMR investigations of crystalline and glassy NASICON-type phosphates have been carried out. The origin for the two signals in the case of the crystalline compounds is discussed. The spectra show the presence of pyrophosphate units in all glasses studied along with various other phosphate species resulting from structural disproportionation.

An EXAFS Investigation on Copper(I-II) Related Nasicon-Type Phosphates

An extended X-ray absorption fine structure study at the copper K-edge of Nasicon-type phosphates with formulas Cu1M2(PO4)3 (M = Ti, Zr), A1-xCuIxZr2(PO4)3 (0 < x ≤ 1, A = Na; x = 0.5, A = H) and CuII0.5M2(PO4)3 (M = Ti, Zr) is reported. For Cu1Zr2(PO4)3, H0.5CuI0.5Zr2(PO4)3, and Na1-xCuIxZr2(PO4)3 (0 <: x ≤ 1) copper pairs have been evidenced (Cu1-Cu1 = 2.40 Å) in the M1 site of the Nasicon structure. In contrast, for the copper(II) phosphates, the Cu2+ ions are surrounded by four oxygen atoms at about 1.95 Å. Copper distribution in these various materials is discussed in relation to structural parameters.