PO4 Tetrahedra Research Articles

Crystalline and vitreous Na3.89Ca0.67Al0.23Ti0.77(PO4)3 : Synthesis, crystal structure, vibrational and UV–Visible spectra

Na3.89Ca0.67Al0.23Ti0.77(PO4)3 phosphate exists in both crystalline and vitreous forms. It has been synthesized as microcrystalline powder, single crystals and glass. The structure of the crystalline form, belonging to Nasicon family with M(1)M(2)3A2(PO4)3 formula, was solved by single crystal X-ray diffraction (Space group R32, Z = 6, ah = 8.9976(1) Å, ch = 21.8312(3) Å, R1 = 0.03, wR2 = 0.06). A Rietveld refinement was also performed. The structure is formed by a 3D network of PO4 tetrahedra and AO6 (A= Na/Ca and Al/Ti) octahedra sharing corners. One of the two positions of A sites is statistically occupied by Na+ and Ca2+, the other position is statistically occupied by Al3+ and Ti4+. The remaining sodium atoms occupy totally M(1) and partially M(2) interstitial sites. Raman and infrared spectra show for the crystalline powder, broad peaks attributed principally to monophosphate PO4 modes. The structure of the glass contains PO4 and P2O7 groups and short -Ti-O-Ti-O- chains. UV–Visible spectra consist of strong bands at high energy assigned to O-Ti and O-Al electronic charge transfers.

Structure and Characterization of K2Na3B2P3O13, a New Nonlinear Optical Borophosphate with One-Dimensional Chain Structure and Short Ultraviolet Cutoff Edge.

Nonlinear optical (NLO) crystals, being the primary medium for laser wavelength conversion, are crucial in all-solid-state lasers. Borophosphates offer more structural varieties than pure borates and phosphates, and they have become popular as NLO crystal candidates. Through spontaneous crystallization, we acquired a noncentrosymmetric alkali metal borophosphate crystal material, K2Na3B2P3O13 (KNBPO). KNBPO crystallizes in the orthorhombic Cmc21 space group with the following unit cell parameters: a = 13.9238(18) Å, b = 6.7673(8) Å, c = 12.1298(15) Å, and Z = 4, and its structure is characterized by a fundamental building unit 1∞ [B2P3O13] chain structure made up of bridging oxygen linkages between BO4 and PO4 tetrahedra. KNBPO has a short ultraviolet (UV) cut-off edge (<186 nm), a congruent melting characteristic, good thermal stability, and a moderate second harmonic generation response roughly 0.42 times that of KH2PO4. Theoretical calculations reveal that the optical properties of the compound mainly originate from BO4 and PO4 units. Due to the short UV cut-off edge, KNBPO can be used as a potential NLO material in the UV and even deep UV regions, and it enhances the structural variety of borophosphates, which has a reference value for scholars investigating similar materials.

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.

(Na,Li)3(Cl,OH)[Cu3OAl(PO4)3]: a first salt-inclusion aluminophosphate oxocuprate with a new type of crystal structure.

The synthesis and characterization of a first salt-inclusion aluminophosphate oxocuprate, (Na,Li)3(Cl,OH)[Cu3OAl(PO4)3], obtained as single crystals, is reported. A novel phase, with a strongly pseudo-orthorhombic structure, is described as a monoclinic crystal structure established by the study of a pseudomerohedric microtwin. It was investigated using scanning electron microscopy, microprobe analysis and low-temperature X-ray diffraction. The composite crystal structure represents an original framework assembled from Cu-centered polyhedra, AlO6 octahedra and PO4 tetrahedra with channels, which incorporate the Na/Li salt component [(Na,Li)3(Cl,OH)]2+ that ensures electroneutrality of the compound. Layers of strongly corrugated chains of Cu-centered octahedra with shared edges and linked by PO4 tetrahedra are shown to be topologically identical with the layers also built from Cu-centered polyhedra and AsO4/VO4 tetrahedra forming the crystal structure of a fumarolic mineral aleutite, (M0.5Cl)[Cu5O2(AsO4)(VO4)] [Siidra et al. (2019). MinMag, 83, 847-853]. `Sawtooth chains' and pairs of Cu-centered octahedra inherent in the title structure may be of interest in solid-state physics, engaging studies in the field of low-dimensional and frustrated magnetism.

Co-substitution design: a new glaserite-type rare-earth phosphate K2RbSc(PO4)2 with high structural tolerance.

An alkali rare-earth phosphate K2RbSc(PO4)2 was successfully obtained as a derivative of glaserite-type K3Na(SO4)2 by co-substitution of K(1)O12 → RbO12, K(2)O10 → KO7, NaO6 → ScO6 and SO4 → PO4, while maintaining the original anionic framework. K2RbSc(PO4)2 exhibits a layered [Sc(PO4)2]∞ framework built from ScO6 octahedra and PO4 tetrahedra, with K and Rb residing in the interlayers. Its isostructural lanthanide analogues K2RbEr(PO4)2 and K2RbLu(PO4)2, inspired by an elemental substitution strategy, were also prepared by a high-temperature solid state reaction. The successful substitution indicates that the skeleton of K2RbSc(PO4)2 is stable with high structural tolerance, which can provide a possibility for substitution of resident ions to obtain diverse structural types and applications.

Tetrahedrally coordinated rigid crystal structure enables partial self-reduction of mixed-valence europium for optical thermometric application.

Mixed-valence europium-activated phosphors are receiving attention in many fields, such as lighting, anti-counterfeiting, optical recording, encryption, and temperature sensing. However, it remains difficult to construct mixed-valence europium-activated compounds due to the reductive and oxidative synthesis conditions required to obtain Eu2+ and Eu3+ ions, respectively. Herein, mixed-valence Eu2+/Eu3+ was realized in the CaBPO5 built by rigidly connected BO4 and PO4 tetrahedrons by partial Eu3+ → Eu2+ self-reduction in the air atmosphere. Commendably, the CaBPO5:Eu2+/Eu3+ phosphor exhibits excellent ratiometric temperature sensing performance with the maximum absolute and relative sensitivity being as high as 0.184 K-1 and 3.444% K-1 with good signal discriminability, due to the high and low, respectively, temperature-dependence of Eu2+ and Eu3+ emissions. The rapid dropping intensity of Eu2+ in CaBPO5 with increasing temperature was due to the small energy gap (∼0.48 eV) between the Eu2+-5d state and the conduction band. Our work not only provides a novel thermometer candidate but also enlightens researchers to a method of effectively designing new mixed-valence metal-ion activated luminescent thermometers via selective tetrahedrally coordinated rigid crystal structure.

Synthesis, crystals structures and theoretical studies of novel alkali copper indium orthophosphates ACuIn(PO4)2 (A = Na, K and Rb)

ACuIn(PO4)2 compounds (A ​= ​K and Rb) have been prepared by the flux method and solid-state reaction. They were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray analysis (EDX), Fourier Transform Infra-Red (FTIR), Raman and optical spectroscopies, as well as a Density Functional Theory (DFT) study has been performed. Single XRD analysis shows that the compounds were isostructural and crystallize in the monoclinic centrosymmetric P21/n space group. There are one A (Na, K or Rb), one Cu, one In, two P and eight O sites in the asymmetric unit of the ACuIn(PO4)2 structure. Its structure is made up from corners-sharing between InO6 octahedra and Cu2O8 units, built up from edge-sharing of two CuO5 polyhedra, to form zigzag chains ranging infinitely along the b axis. The inter-connection between these chains is assured by the PO4 tetrahedra creating a 3D framework with six-sided tunnels parallel to the [101] direction, where the A+ ions are located. XRD diagrams of the powder samples reveal the formation of single purity phases with monoclinic symmetry. FTIR and Raman spectroscopies revealed the presence of two isolated PO4 groups in the analyzed phosphates. The SEM-EDX verifies the morphology and the chemical composition of the synthesized samples. The diffuse reflectance spectroscopy (DRS) has proven an indirect bandgap of 3.34 ​eV, 3.33 and 2.82 ​eV for NaCuIn(PO4)2, KCuIn(PO4)2 and RbCuIn(PO4)2, respectively. The electronic bandgap structure and bonding character analysis of important atom pairs in the ACuIn(PO4)2 structure are also studied in details.

Loomisite, Ba[Be2P2O8]⋅H2O, the first natural example with the zeolite ABW-type framework, from Keystone, Pennington County, South Dakota, USA

AbstractA new beryllophosphate mineral species, loomisite (IMA2022-003), ideally Ba[Be2P2O8]⋅H2O, was found from the Big Chief mine near Keystone, Pennington County, South Dakota, USA. It occurs as divergent sprays of very thin bladed crystals with a tapered termination. Individual crystals are found up to 0.80 × 0.06 × 0.03 mm. Associated minerals include dondoellite, earlshannonite, mitridatite, rockbridgeite, jahnsite-(CaMnFe) and quartz. No twinning or parting is observed macroscopically. Loomisite is murky white in transmitted light, transparent with white streak and silky to vitreous lustre. It is brittle and has a Mohs hardness of 3½–4, with perfect cleavage on {100} and {$\bar{1}$10}. The measured and calculated densities are 3.46(5) and 3.512 g/cm3, respectively. Optically, loomisite is biaxial (+), with α = 1.579(5), β = 1.591(5), γ = 1.606(5) (white light), 2V (meas.) = 82(2)° and 2V (calc.) = 85°. It is non-pleochroic under polarised light, with a very weak (r &gt; v) dispersion. The mineral is insoluble in water or hydrochloric acid. An electron microprobe analysis, along with the BeO content measured with an ICP-MS, yields an empirical formula (based on 9 O apfu) (Ba0.96Ca0.06)Σ1.02[(Be1.96Fe0.06)Σ2.02P1.99O8]⋅H2O, which can be simplified to (Ba,Ca)[(Be,Fe)2P2O8]⋅H2O.Loomisite is monoclinic, with space group Pn and unit-cell parameters a = 7.6292(18), b = 9.429(2), c = 4.7621(11) Å, β = 91.272(5)°, V= 342.47(14) Å3 and Z = 2. Its crystal structure is characterised by a framework of corner-sharing PO4 and BeO4 tetrahedra. The framework can be considered as built from the stacking of sheets consisting of 4- and 8-membered rings (4.82 nets) along [001] or hexagonal layers (63 nets) along [010]. The extra-framework Ba2+ and H2O are situated in the channels formed by the 8-membered rings. Topologically, loomisite represents the first natural example with the zeolite ABW-type framework, which is adopted by over 100 synthetic compounds with different chemical compositions.

Atomic-Scale Cryo-TEM Studies of the Thermal Runaway Mechanism of Li1.3Al0.3Ti1.7P3O12 Solid Electrolyte

Understanding the thermal runaway mechanism of solid-state electrolytes is critical for the development of all-solid-state Li-metal batteries (ASLMBs). Herein we employ multiscale methods including in situ optical microscopy and cryo-transmission electron microscopy combining with density functional theory to reveal the failure mechanism of Li1.3Al0.3Ti1.7P3O12 (LATP). Li reacts with LATP to form an amorphous phase at elevated temperatures, which then crystallizes into Li3PO4 and LiP with additional Li3P and Li0.5TiO2 at even higher temperatures. The instability of the corner-sharing PO4 tetrahedra and TiO6 octahedra against Li at high temperature is the root cause of thermal runaway for LATP. Li diffusion into LATP causes the collapse of the PO4 tetrahedra and TiO6 octahedra, forming Li–O, Li–P–O, and Li–Ti–O species which release a large amount of heat, triggering thermal runaway of LATP. This work provides atomic-scale understanding of the thermal runaway of LATP, which offers an important clue to mitigate failure of ASLMBs.

Synthesis, crystal structure, optical, color, thermal, magnetic, and spectroscopic properties of the substituted honeycomb-lattice BaNi2-xCox(PO4)2 (x = 0, 0.5 and 1)

The ceramic phosphate materials BaNi2-xCox(PO4)2 (x = 0, 0.5 and 1) have been elaborated for the first time by the hydrothermal process at T = 180 °C and characterized by various techniques. The structure was determined from X-ray powder diffraction using Fullprof software based on Rietveld refinement. All investigated materials crystallize in trigonal system with R3‾ (no.148) space group. The BaNi2-xCox(PO4)2 (x = 0, 0.5 and 1) structure can be described as a three-dimensional framework, where two layers including edge-sharing XO6 (X = Ni2-xCox) octahedra and PO4 tetrahedra are connected by Ba2+ cations possessing twelve-fold coordination. The octahedral environment of both Ni2+ and Co2+ ions was confirmed through optical analysis. Numerous bands between 400 and 760 nm were assigned to allowed and forbidden d–d transitions of Ni2+ and Co2+ ions. CIE L∗a∗b∗ and RGB parameters were measured in order to analyse the color properties of the prepared materials. DTA/TGA analysis showed excellent thermal stability of the substituted honeycomb-lattices. Magnetic measurements revealed the presence of an antiferromagnetic order in the studied systems; for x = 0, one transition at TN = 24 K was observed. For x = 0.5 and 1, two transitions at TN and Tsr were detected pointing out the spin reorientation caused by the ferromagnetic (FM) and antiferromagnetic (AFM) competition occurred when substituting between Ni2+ and Co2+ ions. FTIR spectroscopy revealed the existence of vibration modes of PO4 tetrahedra.

Supramolecular Organic Nanowires of 2,6‐Naphthalene Dicarboxylic Acid Observed in the Lamellar Space of Zn3(PO4)4and Zn1.6Co1.4(PO4)4Host Lattices

AbstractThe formation of unique nanometer‐sized organic supramolecular assemblies was observed in the lamellar space of metal phosphate host lattices. Two new chiral and achiral organic‐inorganic hybrid materials, zinc phosphate, (H3tren)2[Zn3(PO4)4]⋅2NDA (ZnP‐NDA) and zinc‐cobalt phosphate, (H3tren)2[Zn1.6Co1.4(PO4)4]⋅2NDA (ZnCoP‐NDA) have been synthesized under hydrothermal conditions. The crystalline host framework was built with corner‐sharing MO4(M=Zn or Zn/Co) and PO4tetrahedra. In between these framework layers, aromatic dicarboxylic acid, 2,6‐Naphthalene dicarboxylic acids (NDA) are held together by means of strong hydrogen bonding and π‐π stacking interactions resulting in infinite supramolecular zigzag chains. After incorporating the cobalt into inorganic host lattice, astonishingly, the chiral structure tuns achiral. The crystal structures were elucidated by single crystal X‐ray diffraction and characterized by powder XRD, elemental analysis, thermogravimetry and photoluminescence measurements.

Degradation of a Li1.5Al0.5Ge1.5(PO4)3-Based Solid-State Li-Metal Battery: Corrosion of Li1.5Al0.5Ge1.5(PO4)3 against the Li-Metal Anode

Solid-state Li-metal batteries were widely studied to reach an energy density of 500 mAh kg–1 before 2030. However, the interfacial parasitic reaction between the Li1.5Al0.5Ge1.5(PO4)3 (LAGP) solid-state electrolyte and Li metal generates a mixed conducting interphase (MCI), which grows continuously and leads to the fast degradation of the battery. In previous work, the role of electron transport in the corrosion of LAGP is highlighted. Herein, it has been found that Li-ion transport also plays an important role in the corrosion of LAGP. In the degradation of LAGP, the Li-ion injection through Li1 sites on the (012) plane leads to the fast corrosion of the plane, as detected by grazing incidence X-ray diffraction. The extra Li ion brings electrons to occupy the nearby Ge4+. Simultaneously, the additional interstitial Li ion distorts the local structure and breaks the PO4 tetrahedron. As a result, the corner-shared GeO6 octahedron and PO4 tetrahedron are destructed. The decomposition of LAGP generates a Li-rich MCI, which shows increased electronic conductivity compared with pristine LAGP. The high chemical potential of the Li atom at the MCI results in the continuous corrosion of LAGP. Furthermore, it has been found that ambipolar diffusion at the interface plays an important role in the growth of MCI. The MCI grows faster when ions and electrons are diffused in the same direction motivated by the chemical potential differences of the Li atom. If the cell is cycled at a small current of 0.05 mA cm–2 to separate the diffusion of electrons and ions, the MCI grows at a slower rate. Therefore, the corrosion of LAGP can be ascribed to the chemical diffusion of the Li atom. The ion and electron transport play equally important roles in the electrochemical corrosion of LAGP.

Dondoellite, Ca2Fe(PO4)2·2H2O, a New Mineral Species Polymorphic with Messelite, from Rapid Creek, Yukon, Canada

ABSTRACT A new mineral species, dondoellite, ideally Ca2Fe(PO4)2·2H2O, was found in the Grizzly Bear Creek, Dawson mining district, Yukon, Canada. It is polymorphic with messelite, a member of the fairfieldite group. Dondoellite occurs as spherical aggregates (diameters up to 2 cm) of radiating bladed crystals. Associated minerals include hydroxylapatite, siderite, and quartz. No twinning or parting is observed. The mineral is colorless to pale yellow in transmitted light, is transparent with white streak, and has vitreous luster. It is brittle and has a Mohs hardness of 3½–4, with perfect cleavage on {001}. The measured and calculated densities are 3.14(5) and 3.15 g/cm3, respectively. Optically, dondoellite is biaxial (+), with α = 1.649(5), β = 1.654(5), γ = 1.672(5) (white light), 2V (meas.) = 55(2)°, 2V (calc.) = 58°. An electron probe microanalysis yields an empirical formula (based on 10 O apfu) Ca1.99(Fe0.89Mg0.13Mn0.01)Σ1.03(P1.00O4)2·2H2O, which can be simplified to Ca2(Fe2+,Mg,Mn2+)(PO4)2·2H2O. Dondoellite is triclinic, space group P, a = 5.4830(2), b = 5.7431(2), c = 13.0107(5) Å, α = 98.772(2), β = 96.209(2), γ = 108.452(2)°, V = 378.71(2) Å3, and Z = 2. The crystal structure of dondoellite is characterized by isolated FeO4(H2O)2 octahedra that are linked by corner-sharing with PO4 tetrahedra to form so-called kröhnkite-type [Fe(PO4)2(H2O)2]2– chains along [100], similar to that observed in messelite. These chains are connected to one another by large Ca2+ cations and H bonds to form layers parallel to (001). The layers are further linked together by Ca–O and H bonds. However, unlike messelite, the crystal structure of dondoellite contains two symmetrically independent PO4 tetrahedra (P1O4 and P2O4) and two distinct CaO7(H2O) polyhedra (Ca1 and Ca2). The kröhnkite-type chains in dondoellite are constructed with P1O4 tetrahedra on one side and P2O4 tetrahedra on the other. Topologically, the dondoellite structure can be considered a combination of the collinsite and messelite structures alternating along [001], thus representing a new structure type for minerals with kröhnkite-type chains. The discovery of dondoellite raises the question as to whether polymorphs of fairfieldite, Ca2Mn2+(PO4)2·2H2O, or collinsite, Ca2Mg(PO4)2·2H2O, might also be found in nature.

Hydrothermal synthesis, crystal structure and photoluminescent properties of 2D layered zinc phosphate intercalated with 4,4ˈbiphenyl dicarboxylic acid (ZnPO-BDA)

Herein, we report a new inorganic-organic hybrid, (H3tren)2⸱[Zn3(PO4)4(BDA)]⸱xH2O (ZnPO-BDA) prepared under hydrothermal conditions. This hybrid structure of zinc phosphate layers pillared with 4,4′-biphenyl-dicarboxylic acid (BDA) was characterized by single-crystal X-ray diffraction. The compound, ZnPO-BDA, crystallizes in the monoclinic crystal system (space group C2) with a = 14.9348(3) Å, b = 8.7058(2) Å, c = 17.6455(5) Å, β = 111.6760(10), V = 2132.02(9) Å3, Z = 2. The crystalline host of the 2D zinc phosphate framework was built with vertex linked ZnO4 and PO4 tetrahedra and anchored with tris(2-aminoethyl)amine (H3tren). Biphenyl dicarboxylic acid (BDA) molecules stack between the phosphate framework layers by means of strong hydrogen bonding, resulting in an interlayer distance of 16.4 Å. ZnPO-BDA displayed blue photoluminescence with an emission maximum at 404 nm on photoexcitation at 340 nm.

Na@C composite anode for a stable Na|NZSP interface in solid-state Na–CO2 battery

Na–CO2 battery is one of the most promising energy storage devices for the exploration of Mar. To fix the evaporation problem of liquid electrolytes in an open system, solid-state electrolyte Na3Zr2Si2PO12 (NZSP) is used to fabricate a solid-state Na–CO2 battery. In the battery, the interface between the Na-metal anode and NZSP plays a vital role in improving electrochemical performance. The interfacial parasitic reaction between NZSP and Na-metal results in a Na-rich kinetically stable interphase. (200) and (−111) planes are the preferentially etched crystal planes of NZSP, as SiO4 and PO4 tetrahedrons on the planes are easily broken by extra Na-ion injection. Aside from the interfacial reaction, the poor contact between Na-metal and NZSP is a more serious problem, which leads to large interfacial resistance and poor cycling stability. To fix this problem, carbon black is mixed with melted Na-metal to prepare a composite anode (Na@C). The Na@C composite anode easily wets NZSP, thus decreasing the interfacial resistance from 918 to 98 Ω cm2. Symmetrical cells stably cycled 1100 h at 0.1 mA cm−2, when using Na@C as the electrode. Furthermore, Na–CO2 battery with Na@C composite anode also shows a prolonged cycling life.

Thorasphite, Th2H(AsO4)2(PO4)·6H2O, a New Mineral from Elsmore, New South Wales, Australia

ABSTRACT The new mineral species thorasphite, Th2H(AsO4)2(PO4)·6H2O, has been discovered at the abandoned tin deposit at Elsmore, New South Wales, Australia. It occurs as brownish pink to salmon pink, prismatic to acicular crystals up to 0.08 mm in length and 0.002 mm across, associated with jarosite in cavities in a quartz-muscovite matrix. Thorasphite has a white streak and a vitreous luster. The calculated density is 4.185 g/cm3. The mineral is orthorhombic, space group Pbcn, a = 13.673(3), b = 9.925(2), c = 10.222(2) Å, V = 1387.2(5) Å3, and Z = 4. The eight strongest lines in the X-ray powder diffraction pattern are [dobs Å (I) (hkl)]: 8.007 (100) (110), 5.127 (57) (002), 4.934 (71) (020, 211), 4.320 (24) (112), 4.251 (38) (121), 3.225 (22) (130, 312), 3.189 (27) (321), 2.926 (27) (213). Electron microprobe analysis gave (average of n = 9): ThO2 51.35, Na2O 0.17, K2O 0.20, Al2O3 0.35, FeO 0.90, Ce2O3 0.27, As2O5 19.65, P2O5 12.27, SiO2 0.08, Cl 0.20, H2O(calc) 13.58, O=Cl –0.05, Total 98.97 wt.%. On the basis of 18 anions per formula unit, the empirical formula is Th1.72Fe2+0.11Al0.06Na0.05K0.04Ce0.01As1.51P1.53Si0.01O17.95Cl0.05H13.31. The crystal structure has been solved from synchrotron single-crystal data and refined to R1 = 7.48% on the basis of 1432 reflections with Fo &amp;gt; 4σ(Fo). The structure consists of Th2[O12(H2O)4] dimers which link in the c direction by edge-sharing PO4 tetrahedra and corner-sharing AsO4 tetrahedra to form chains along [001]. Chains link by corner-sharing Th[O7(H2O)2] polyhedra and AsO4 tetrahedra, giving rise to a framework hosting channels along [001] which are occupied by H2O molecules.

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

Single crystals of β-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.

Carbon-coated monoclinic NbOPO4 with polyanionic framework for rechargeable aqueous lithium-ion batteries beyond 2 V

The choice of anode materials for high-voltage aqueous batteries beyond 1.5 V is still far from satisfactory, due to the narrow electrochemical stability window of aqueous electrolytes. With the inherent advantages of low working voltage and fast ionic diffusion, niobium phosphates with polyanionic framework groups built of NbO6 octahedra and PO4 tetrahedra are very promising anode materials for high-voltage aqueous batteries. Herein, carbon-coated NbOPO4 (NPO/C) materials with monoclinic structure has been prepared by the solid-state reaction & chemical vapor deposition method. Between -1.34 V and 0.6 V vs. standard hydrogen electrode, it could deliver a specific capacity of 116 mAh/g with a high coulombic efficiency of 92.0% at a low current rate of 0.33C in aqueous electrolytes based on methylsulfonylmethane, LiClO4 and H2O (DES). The diffusion-controlled process dominates the electrochemical reaction of NPO/C. Upon the reversible insertion/extraction of lithium ion into/from NPO/C, it maintains the monoclinic structure with a small lattice expansion, which is a characteristic of zero-strain effect. Finally, the full cell based on NPO/C anode, LiMn2O4 cathode and DES electrolytes with a high specific energy 101.6 Wh/kg and a high voltage output beyond 2 V has been validated. It also shows excellent cycling performance with the capacity retention of 94.3% after 1000 times at 2C rate, which suggests that monoclinic β-NbOPO4 can be used as a promising electrode material for aqueous lithium-ion batteries with high voltage output for energy storage in the future.

Investigation of structural and optical properties of Pr3+ doped and Pr3+/Dy3+ co-doped multicomponent bismuth phosphate glasses for visible light applications

Pr3+ doped 59.5P2O5+15Bi2O3+10BaF2+10xF+05TeO2+0.5Pr6O11 glasses and Pr3+/Dy3+ co-doped 59P2O5+15Bi2O3+ 10BaF2+ 10xF + 05TeO2+0.5Dy2O3+0.5Pr6O11 glasses (where xF = LiF, NaF, MgF2, KF, CaF2 and SrF2) were synthesized using melt quenching route. Structural properties were researched for different modifier fluorides. With the dopant constant concentration the absorption and luminescence intensity variance influenced by this multicomponent incorporation has been observed. The energy transfer between resonance levels of Pr3+ and Dy3+ through fluorescence studies also examined for Mg and Sr glasses. Long-range nature of prepared glasses, morphological studies with elemental probe, various functional groups pertaining to glass matrices and the non-bridging oxygen bonds with PO4 tetrahedron or depolymarization of oxygen bonds in the presence of the modifier cations with phosphates were thoroughly understood with PXRD, FTIR and 31P NMR characterizations. Judd-Ofelt (J-O) theory has been adopted to estimate important optical parameters. From the fluorescence studies laser characteristic parameters such as optical band gains (σe × τR) and gain bandwidths (σe × Δλeff) were calculated and compared in the present fabricated glasses influenced by various modifiers.

Synthesis and magnetic properties of two fluorophosphates A3Fe4(PO4)2F9 (A = K+ and NH4+) with a tetrahedral spin-cluster chain structure

The fluorophosphate compounds A3Fe4(PO4)2F9 (A ​= ​K+ and NH4+) were found to exhibit a channel framework constructed from {Fe4O8F10} tetrahedral clusters and PO4 tetrahedra, featuring a tetramer chain structure along the a-axis. Here these two compounds were synthesized by a fluorine-rich hydrothermal method. The purity of the samples was characterized by single crystal and powder XRD, EDS, and FT-IR measurements. The results of magnetic and heat capacity measurements confirmed that both compounds possess an antiferromagnetic ordering at ∼10 ​K and ∼6 ​K with Weiss temperatures of −341.5(8) K and −334.3(5) K, respectively, indicating strong spin frustration in the systems due to large frustration factors of ∼34 and ∼56. The presence of spin frustration is suggested to arise from the competition of very close magnetic interactions within the tetrahedral Fe4 clusters.