Insights into structure, morphology and conductivity of the earth-abundant NASICON phosphate, Na4MnFe(PO4)3.

Phosphate-based NASICON materials are an excellent candidate for both electrode and solid electrolyte materials in sodium-ion batteries (SIBs). The development of new NASICON materials with higher ionic and electronic conductivities based on low cost and abundant elements is necessary for advancement of SIBs. In this study, we report the structure, morphology and conductivity of the earth-abundant Mn/Fe-based NASICON phosphate Na4MnFe(PO4)3. Pure phase powders were synthesized by solution-assisted solid-state reaction, sol-gel and Pechini methods. From refined X-ray diffraction data, the prepared phosphate was found to crystallize in trigonal symmetry with space group R3̄c. The effect of synthesis method on microstructure and conductivity was investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM) and impedance measurements. Smaller particle size and regular distribution of the powder was designed using a Pechini route. Impedance measurement showed a notable enhancement in conductivity, from 0.543 × 10-7 to 1.52 × 10-7 S cm-1 at 30 °C, when the powder synthesis method was altered from a solution-assisted solid-state reaction to the Pechini route, highlighting the remarkable effect of the synthesis method on conductivity.

A novel phosphate with CoII square planar coordination, BaCo0.5Fe(PO4)2: structural and magnetic features.

A novel phosphate containing barium, cobalt, and iron was synthesized in single-crystal and polycrystalline forms. Single crystal-based X-ray measurements revealed that it crystallizes in the monoclinic system with the P21/c space group. The structure is made up of linkages between FeO6 octahedra, CoO4 square planar units, CoO5 square pyramidal units, and PO4 tetrahedra through edges and/or vertices. The interconnection of these polyhedra leads to a three-dimensional framework with tunnels along the a-axis where the Ba2+ cations are located. The polycrystalline form was prepared via the sol-gel method and its XRD pattern was refined by the Le Bail method. Morphological and elemental mapping analyses of this phosphate were performed by scanning electron microscopy. In addition, infrared and Raman spectroscopy provided more insights into chemical bonding. The magnetic behavior was antiferromagnetic below TN ∼ 20 K. Optical measurements revealed a direct bandgap with an energy Eg of 2.83 eV.

Crystal structure of barium dinickel(II) iron(III) tris-[orthophosphate(V)], BaNi2Fe(PO4)3.

The orthophosphate BaNi2Fe(PO4)3 has been synthesized by a solid-state reaction route and characterized by single-crystal X-ray diffraction and energy-dispersive X-ray spectroscopy. The crystal structure comprises (100) sheets made up of [Ni2O10] dimers that are linked to two PO4 tetra-hedra via common edges and vertices and of linear infinite [010] chains of corner-sharing [FeO6] octa-hedra and [PO4] tetra-hedra. The linkage of the sheets and chains into a framework is accomplished through common vertices of PO4 tetra-hedra and [FeO6] octa-hedra. The framework is perforated by channels in which positionally disordered Ba2+ cations are located.

Crystal structure reinvestigation and spectroscopic analysis of tricadmium orthophosphate.

Single crystals of tricadmium orthophosphate, Cd3(PO4)2, have been synthesized successfully by the hydro-thermal route, while its powder form was obtained by a solid-solid process. The corresponding crystal structure was determined using X-ray diffraction data in the monoclinic space group P21/n. The crystal structure consists of Cd2O8 or Cd2O10 dimers linked together by PO4 tetra-hedra through sharing vertices or edges. Scanning electron microscopy (SEM) was used to investigate the morphology and to confirm the chemical composition of the synthesized powder. Infrared analysis corroborates the presence of isolated phosphate tetra-hedrons in the structure. UV-Visible studies showed an absorbance peak at 289 nm and a band gap energy of 3.85 eV, as determined by the Kubelka-Munk model.

Crystal growth, structure elucidation and CHARDI/BVS investigations of ß-KCoFe(PO4)2.

Single crystals of ß-KCoFe(PO4)2, potassium cobalt(II) iron(III) bis-(ortho-phosphate), were grown from the melt under atmospheric conditions. This phosphate crystallizes isotypically with KZnFe(PO4)2 in space group C2/c, adopting a zeolite-ABW type of structure. The structure of the present phosphate is distinguished by an occupational disorder of the two transition-metal sites with ratios Fe:Co of 0.5725:0.4275 for the first and 0.4275:0.5725 for the second site. In the crystal structure, PO4 and (Co,Fe)O4 tetra-hedra are linked through vertices to form elliptical rings with the sequence DDDDUUUU of up (U) and down (D) pointing vertices. Each eight-membered ring is surrounded by four other rings of the same type, delimiting inter-stices with rectangular shape. This arrangement leads to the formation of [(Co/Fe)(PO4)]- ∞ sheets parallel to (001). Stacking of the sheets into a three-dimensional framework results in the formation of two types of channels. The first one is occupied by potassium cations, whereas the second one remains vacant. Calculations of bond-valence sums and charge distribution were used to confirm the structure model.

Synthesis, crystal structure determination of a novel phosphate Ag1.64Zn1.64Fe1.36(PO4)3 with an alluaudite-like structure.

Single crystals of Ag1.64Zn1.64Fe1.36(PO4)3 [silver zinc iron phosphate (1.64/1.64/1.36/3)] have been synthesized by a conventional solid-state reaction and structurally characterized by single-crystal X-ray diffraction. The title compound crystallizes with an alluaudite-like structure. All atoms of the structure are in general positions except for four, which reside on special positions of the space group, C2/c. The Ag+ cations reside at full occupancy on inversion centre sites and at partial occupancy (64%) on a twofold rotation axis. In this structure, the unique Fe3+ ion with one of the two Zn2+ cations are substitutionally disordered on the same general position (Wyckoff site 8f), with a respective ratio of 0.68/0.32 (occupancies were fixed so as to ensure electrical neutrality for the whole structure). The remaining O and P atoms are located in general positions. The three-dimensional framework of this structure consists of kinked chains of edge-sharing octa-hedra stacked parallel to [10]. These chains are built up by a succession of [MO6] (M = Zn/Fe or Zn) units. Adjacent chains are connected by the PO4 anions, forming sheets oriented perpendicular to [010]. These inter-connected sheets generate two types of channels parallel to the c axis, in which the Ag+ cations are located. The validity and adequacy of the proposed structural model of Ag1.64Zn1.64Fe1.36(PO4)3 was established by means of bond-valence-sum (BVS) and charge-distribution (CHARDI) analysis tools.

Crystal structure of SrCo4(OH)(PO4)3, a new hy-droxy-phosphate.

Single crystals of strontium tetra-cobalt tris-(orthophosphate) hydroxide, SrCo4(OH)(PO4)3, were grown serendipitously under hydro-thermal conditions at 473 K. The crystal structure consists of undulating chains of edge-sharing [CoO6] octa-hedra that are linked into (010) layers by common vertices between chains. Adjacent layers are linked along [010] into a framework structure by tetra-hedral [CoO4] units and by PO4 tetra-hedra. The framework delimits channels extending along [100] in which the eleven-coordinate strontium cations are situated. Bifurcated O-H⋯O hydrogen bonds of weak strengths consolidate the crystal packing. The title compound was also characterized by infrared spectroscopy.

Synthesis and crystal structure of NaCuIn(PO4)2.

Single crystals of sodium copper(II) indium bis-[phosphate(V)], NaCuIn(PO4)2, were grown from the melt under atmospheric conditions. The title phosphate crystallizes in the space group P21/n and is isotypic with KCuFe(PO4)2. In the crystal, two [CuO5] trigonal bipyramids share an edge to form a dimer [Cu2O8] that is connected to two PO4 tetra-hedra. The obtained [Cu2P2O12] units are inter-connected through vertices to form sheets that are sandwiched between undulating layers resulting from the junction of PO4 tetra-hedra and [InO6] octa-hedra. The two types of layers are alternately stacked along [101] and are joined into a three-dimensional framework through vertex- and edge-sharing, leaving channels parallel to the stacking direction. The channels host the sodium cations that are surrounded by four oxygen atoms in form of a distorted disphenoid.

Crystal structure of silver strontium copper orthophosphate, AgSr4Cu4.5(PO4)6.

Crystals of the new compound, AgSr4Cu4.5(PO4)6, were grown successfully by the hydro-thermal process. The asymmetric unit of the crystal structure of the title compound contains 40 independent atoms (4 Sr, 4.5 Cu, 1 Ag, 6 P and 24 O), which are all in general positions except for one Cu atom, which is located on an inversion centre. The Cu atoms are arranged in CuO n (n = 4 or 5) polyhedra, linked through common oxygen corners to build a rigid three-dimensional motif. The connection of these copper units is assured by PO4 tetra-hedra. This arrangement allows the construction of layers extending parallel to the (100) plane and hosts suitable cavities in which Ag+ and Sr2+ cations are located. The crystal-structure cohesion is ensured by ionic bonds between the silver and strontium cations and the oxygen anions belonging to two adjacent sheets. Charge-distribution analysis and bond-valence-sum calculations were used to validate the structural model.

Two new glaserite-type orthovanadates: Rb2KDy(VO4)2 and Cs1.52K1.48Gd(VO4)2.

The crystal structures of dirubidium potassium dysprosium bis-(vanadate), Rb2KDy(VO4)2, and caesium potassium gadolinium bis-(vanadate), Cs1.52K1.48Gd(VO4)2, were solved from single-crystal X-ray diffraction data. Both compounds, synthesized by the reactive flux method, crystallize in the space group P m1 with the glaserite structure type. VO4 tetra-hedra are linked to DyO6 or GdO6 octa-hedra by common vertices to form sheets stacking along the c axis. The large twelve-coordinate Cs+ or Rb+ cations are sandwiched between these layers in tunnels along the a and b axes, while the K+ cations, surrounded by ten oxygen atoms, are localized in cavities.

Magnetic properties of a new cobalt hydrogen vanadate with a dumortierite-like structure: Co13.5(OH)6(H0.5VO3.5)2(VO4)6.

The magnetic properties of a novel cobalt-based hydrogen vanadate, Co13.5(OH)6(H0.5VO3.5)2(VO4)6, are reported. This new magnetic material was synthesized in single-crystal form using a conventional hydrothermal method. Its crystal structure was determined from single-crystal X-ray diffraction data and was also characterized by scanning electron microscopy. Its crystal framework has a dumortierite-like structure consisting of large hexagonal and trigonal channels; the large hexagonal channels contain one-dimensional chains of face-sharing CoO6 octahedra linked to the framework by rings of VO4 tetrahedra, while the trigonal channels are occupied by chains of disordered V2O4 pyramidal groups. The magnetic properties of this material were investigated by DC magnetic measurements, which indicate the occurrence of antiferromagnetic interactions.

Crystal structure of a new tripotassium hexa-nickel iron hexa-phosphate.

A new potassium-nickel iron phosphate, K3Ni6Fe(PO4)6, has been synthesized by solid-state reaction and structurally characterized by single-crystal X-ray diffraction and qualitative energy dispersive X-ray spectroscopy (EDS) analysis. The structure is built up by [FeO6], [PO4], and [NiO6] coordination polyhedra, which are linked to each other by edge and corner sharing to form zigzag layers parallel to the ab plane. These layers are inter-connected by [PO4] tetra-hedra and [NiO6] octa-hedra via common corners, leading to a three-dimensional framework delimiting large channels running along the [100] direction in which the K+ cations are localized.

Na1.85Mg1.85In1.15(PO4)3 and Ag1.69Mg1.69In1.31(PO4)3 with alluaudite-type structures.

Single crystals of two new phosphates, sodium magnesium indium(III) tris-(orthophosphate) and silver magnesium indium(III) tris-(orthophosphate), were obtained from solid-state reactions. The two phosphates are isotypic and exhibit alluaudite-type structures. They are characterized by a cationic disorder of the Mg and In sites and a partial occupation of the Na and Ag sites, respectively. The structure of both phosphates is made up of chains of edge-sharing [(Mg,In)O6] octa-hedra extending parallel to [10]. Adjacent chains are linked by PO4 tetra-hedra to form a three-dimensional framework delimiting two types of channels parallel to [001] in which the monovalent cations are situated. The coordination numbers of the Na+ cations are 6 and 8, and for both Ag+ cations 6. The corresponding coordination spheres are considerably distorted.

Crystal structure of disilver(I) dizinc(II) iron(III) tris-(orthovanadate) with an alluaudite-type structure.

The title compound, Ag2Zn2Fe(VO4)3, has been synthesized by solid-state reactions and belongs to the alluaudite structure family. In the crystal structure, four sites are positioned at special positions. One silver site is located on an inversion centre (Wyckoff position 4b), and an additional silver site, as well as one zinc and one vanadium site, on twofold rotation axes (4e). One site on a general position is statistically occupied by FeIII and ZnII cations that are octa-hedrally surrounded by O atoms. The three-dimensional framework structure of the title vanadate results from [(Zn,Fe)2O10] units of edge-sharing [(Zn,Fe)O6] octa-hedra that alternate with [ZnO6] octa-hedra so as to form infinite chains parallel to [10]. These chains are linked through VO4 tetra-hedra by sharing vertices, giving rise to layers extending parallel to (010). Such layers are shared by common vanadate tetra-hedra. The resulting three-dimensional framework delimits two types of channels parallel to [001] in which the silver sites are located with four- and sixfold coordination by oxygen.

Crystal structure of calcium dinickel(II) iron(III) tris-(orthophosphate): CaNi2Fe(PO4)3.

The title compound, CaNi2Fe(PO4)3, was synthesized by solid-state reactions. Its structure is closely related to that of α-CrPO4 in the space group Imma. Except for two O atoms in general positions, all atoms are located in special positions. The three-dimensional framework is built up from two types of sheets extending parallel to (100). The first sheet is made up from two edge-sharing [NiO6] octa-hedra, leading to the formation of [Ni2O10] double octa-hedra that are connected to two PO4 tetra-hedra through a common edge and corners. The second sheet results from rows of corner-sharing [FeO6] octa-hedra and PO4 tetra-hedra forming an infinite linear chain. These layers are linked together through common corners of PO4 tetra-hedra and [FeO6] octa-hedra, resulting in an open three-dimensional framework that delimits two types of channels parallel to [100] and [010] in which the eightfold-coordinated CaII cations are located.

Crystal structure of a silver-, cobalt- and iron-based phosphate with an alluaudite-like structure: Ag1.655Co1.64Fe1.36(PO4)3.

The new silver-, cobalt- and iron-based phosphate, silver cobalt iron tris(ortho-phosphate), Ag1.655Co1.64Fe1.36(PO4)3, was synthesized by solid-state reactions. Its structure is isotypic to that of Na2Co2Fe(PO4)3, and belongs to the alluaudite family, with a partial cationic disorder, the AgI atoms being located on an inversion centre and twofold rotation axis sites (Wyckoff positions 4a and 4e), with partial occupancies of 0.885 (2) and 0.7688 (19), respectively. One of the two P atoms in the asymmetric unit completely fills one 4e site while the Co and Fe atoms fill another 4e site, with partial occupancies of 0.86 (5) and 0.14 (5), respectively. The remaining Co2+ and Fe3+ cations are distributed on a general position, 8f, in a 0.39 (4):0.61 (4) ratio. All O atoms and the other P atoms are in general positions. The structure is built up from zigzag chains of edge-sharing [MO6] (M = Fe/Co) octa-hedra stacked parallel to [101]. These chains are linked together through PO4 tetra-hedra, forming polyhedral sheets perpendicular to [010]. The resulting framework displays two types of channels running along [001], in which the AgI atoms (coordination number eight) are located.

Crystal structures of two alkaline earth (M = Ba and Sr) dimanganese(II) iron(III) tris-(orthophosphates).

Two new orthophosphates, BaMn2Fe(PO4)3 [barium dimanganese(II) iron(III) tris-(orthophosphate)] and SrMn2Fe(PO4)3 [strontium dimanganese(II) iron(III) tris-(orthophosphate)], were synthesized by solid-state reactions. They are isotypic and crystallize in the ortho-rhom-bic system with space group type Pbcn. Their crystal structures comprise infinite zigzag chains of edge-sharing FeO6 octa-hedra (point group symmetry .2.) and Mn2O10 double octa-hedra running parallel to [001], linked by two types of PO4 tetra-hedra. The so-formed three-dimensional framework delineates channels running along [001], in which the alkaline earth cations (site symmetry .2.) are located within a neighbourhood of eight O atoms.

Synthesis and crystal structure of calcium dizinc iron(III) tris-(orthophosphate), CaZn2Fe(PO4)3.

Single crystals of the title compound, CaZn2Fe(PO4)3, were synthesized by conventional solid-state reaction. In the asymmetric unit, all atoms are located in fully occupied general positions of the P21/c space group. The zinc atoms are located on two crystallographically independent sites with tetra-hedral and distorted triangular-based bipyramidal geometries. Two edge-sharing triangular bipyramidal ZnO5 units form a dimer, which is linked to slightly deformed FeO6 octa-hedra via a common edge. The resulting chains are inter-connected through PO4 tetra-hedra to form a layer perpendicular to the b axis. Moreover, the remaining PO4 and ZnO4 tetra-hedra are linked together through common vertices to form tapes parallel to the c axis and surrounding a chain of Ca2+ cations to build a sheet, also perpendicular to the b axis. The stacking of the two layers along the b axis leads to the resulting three-dimensional framework, which defines channels in which the Ca2+ cations are located, each cation being coordinated by seven oxygen atoms.

The alluaudite-type crystal structures of Na2(Fe/Co)2Co(VO4)3 and Ag2(Fe/Co)2Co(VO4)3.

Single crystals of the title compounds, disodium di(cobalt/iron) cobalt tris-(orthovanadate), Na2(Fe/Co)2Co(VO4)3, and disilver di(cobalt/iron) cobalt tris-(orthovanadate), Ag2(Fe/Co)2Co(VO4)3, were grown from a melt consisting of stoichiometric mixtures of three metallic cation precursors and vanadium pentoxide. The difficulty to distinguish between cobalt and iron by using X-ray diffraction alone forced us to explore several models, assuming an oxidation state of +II for Co and +III for Fe and a partial cationic disorder in the Wyckoff site 8f containing a mixture of Co and Fe with a statistical distribution for the Na compound and an occupancy ratio of 0.4875:0.5125 (Co:Fe) for the Ag compound. The alluaudite-type structure is made up from [10-1] chains of [(Co,Fe)2O10] double octa-hedra linked by highly distorted [CoO6] octa-hedra via a common edge. The chains are linked through VO4 tetra-hedra, forming polyhedral sheets perpendicular to [010]. The stacking of the sheets defines two types of channels parallel to [001] where the Na(+) cations (both with full occupancy) or Ag(+) cations (one with occupancy 0.97) are located.

Crystal structure of strontium dicobalt iron(III) tris-(orthophosphate): SrCo2Fe(PO4)3.

The title compound, SrCo2Fe(PO4)3, has been synthesized by a solid-state reaction. It crystallizes with the α-CrPO4 type structure. In this structure, all atoms are on special positions of the Imma space group, except for two O atoms which are located on general positions. The three-dimensional network in the crystal structure is made up of two types of layers stacked normal to (100). The first layer is built from two edge-sharing CoO6 octa-hedra, leading to the formation of Co2O10 dimers that are connected to two PO4 tetra-hedra by a common edge and corners. The second layer results from apex-sharing FeO6 octa-hedra and PO4 tetra-hedra, which form linear chains alternating with a zigzag chain of Sr(II) cations. These layers are linked together by common vertices of PO4 tetra-hedra and FeO6 octa-hedra to form an open three-dimensional framework that delimits two types of channels parallel to [100] and [010] where the Sr(II) cations are located. Each Sr(II) cation is surrounded by eight O atoms.