Selectivity of alkali metal ion and lithium isotopes on ion exchangers prepared from MTi0.5Zr1.5(PO4)3(M = Li, Na)

Inorganic ion exchangers, H-TZP(Li) and H-TZP(Na), in the hydrogen form have been prepared by ion exchange from the precursors, LiTi_0.5Zr_1.5(PO₄)₃ and NaTi_0.5Zr_1.5(PO₄)₃, respectively. The degrees of leaching of lithium and sodium ions were 99.7% and 68%, respectively. No substantial difference in ion exchange property was observed between the two ion exchangers. Both showed high selectivity toward lithium and sodium ions, while rubidium and cesium ions showed low affinity among alkali metal ions. Isotopically, they were ⁶Li-specific like other inorganic ion exchangers so far examined. The ⁷Li-to-⁶Li isotopic separation factor, S, was found of 1.023 to 1.025 in acidic conditions at 25°C and nearly unity in highly basic conditions (pH 12 or higher). The latter S value was consistent with the formation of new ion exchange sites with low isotope selectivity of lithium.     

Immobilization of cesium by crystalline zirconium phosphate

HZr₂(PO₄)₃ was prepared by the thermal decomposition of NH₄Zr₂(PO₄)₃ which was synthesized in advance by a hydrothermal reaction from a mixed solution of ZrOCl₂, H₃PO₄ and H₂C₂O₄. Mixtures of HZr₂(PO₄)₃ with various amounts of CsNO₃ were treated at 700–1200°C, in order to investigate the immobilization of Cs ion. When a mixture of CsNO₃/HZr₂(PO₄)₃ in a molar ratio of 0.36 was treated at 700°C, the main product was suggested to be CsZr₂(PO₄)₃ from XRD measurements. The leaching rate of Cs ion from this product was less than 10^–10 g · cm^–2 · day^–1 in 0.1 mol · 1^–1 HCl solution at 100°C, indicating that HZr₂(PO₄)₃ reacts with CsNO₃ to give a stable Cs-immobilized product.     

Preparation of (NH4)Zr2(PO4)3 and HZr2(PO4)3

(NH₄)Zr₂(PO₄)₃ has been prepared, hydrothermally, from α-zirconium phosphate in three different ways; (1) from amine intercalates at 300°C, (2) from mixtures of ZrOCl₂·8H₂O in excess (NH₄)H₂PO₄ and (3) reaction of NH₄Cl with Zr(NaPO₄)₂. Ammonium dizirconium triphosphate is rhombohedral with a = 8.676(1) and $\text{c}\text{= 24.288(5)}\text{A}\text{?}$. It decomposed on heating to HZr₂(PO₄)₃. Below 600°C a complex, as yet unindexed, X-ray pattern was obtained. A very similar X-ray pattern was obtained by washing LiTi_0.1Zr_1.9(PO₄)₃ with 0.3N HCl. Heating this phase or NH₄Zr₂(PO₄)₃, above 600°C resulted in the appearance of a rhombohedral phase of HZr₂(PO₄)₃ with cell dimensions a = 8.803(5) and $\text{c}\text{= 23.23(1)}\text{A}\text{?}$. The protons were not completely removed until about 1150°C. Decomposition of (NH₄)Zr₂(PO₄)₃ at 450°C yielded an acidic gas whereas at 700°C NH₃ was evolved. A possible explanation for this behavior is presented.     

Phase transitions and ionic mobility in hydrogen zirconium phosphates with the NASICON structure, H1±XZr2−XMX(PO4)3·H2O, M = Nb, Y

Phase transitions and the mobility of proton-containing groups in hydrogen zirconium phosphate HZr₂(PO₄)₃·nH₂O with the NASICON structure were studied by X-ray powder diffraction, ¹H, ³¹P NMR, IR spectroscopy and TG analysis. Heating HZr₂(PO₄)₃·H₂O above 420 K results in dehydration and in a rhombohedral-triclinic phase transition. Continued heating to about 490 K results in the thermal activation of cation disordering and phase transition of HZr₂(PO₄)₃ from triclinic to rhombohedral phase. Parameter “a” of HZr₂(PO₄)₃ lattice decreases during the heating. It is shown that oxonium ions in HZr₂(PO₄)₃·H₂O are characterized by high rotation and translation mobility. Rotation mobility of oxonium ions can be increased by the substitution of zirconium by yttrium or niobium.     

On the proton conductor (H3O)Zr2(PO4)3

The compound HZr₂(PO₄)₃ was converted to (H₃O)Zr₂(PO₄)₃ by refluxing in water for 12 or more hours. The water is lost above 150°C to regenerate the original triphosphate. The hydronium ion phase is rhombohedral with hexagonal axes of a = 8.760(1) and $\text{c}\text{= 23.774(4)}\text{A}\text{?}$. Proton conduction in these compounds was investigated by an ac impedance method over the frequency range 5Hz – 10MHz. The activation energy for (H₃O)Zr₂(PO₄)₃ in the temperature range of 25 to 150°C was 0.56eV while the corresponding value for HZr₂(PO₄)₃ (125 – 300°C) was 0.44eV.     

Phase transitions of the NASICON-type mixed phosphates LiM<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> (M = Ti,Zr) and LiInNb(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

The structural phase transitions of LiTi₂(PO₄)₃, LiInNb(PO₄)₃, and LiZr₂(PO₄)₃ have been studied by X-ray diffraction, impedance spectroscopy, ⁷Li NMR spectroscopy, and calorimetry. The results indicate that, as the temperature is raised, the lithium ions in the structure of LiTi₂(PO₄)₃ and LiInNb(PO₄)₃ redistribute between the M1 and M2 sites. The thermal expansion coefficients along the crystallographic axes of LiTi₂(PO₄)₃ and LiInNb(PO₄)₃ are estimated.     

Luminescence properties of long-lasting phosphor SrMg2(PO4)2:Eu2+, Ho3+, Zr4+

Novel long lasting phosphors SrMg₂(PO₄)₂:Eu²⁺, SrMg₂(PO₄)₂:Eu²⁺, Zr⁴⁺, SrMg₂(PO₄)₂:Eu²⁺, Ho³⁺ and SrMg₂(PO₄)₂:Eu²⁺, Ho³⁺, Zr⁴⁺ were synthesized by conventional solid-state reaction method. The luminescent properties were systematically characterized by X-ray diffraction, photoluminescent excitation and emission spectra, as well as thermoluminescence spectrum and decay curves. The XRD patterns indicated that the samples belonged to monoclinic phase and co-doping Eu²⁺, Ho³⁺ and Zr⁴⁺ ions had no effect on the basic crystal structure. These phosphors emitting purplish blue light is related to the characteristic emission of Eu²⁺. The afterglow time of Eu²⁺ activated SrMg₂(PO₄)₂ can be greatly enhanced by the co-doping of Ho³⁺, Zr⁴⁺. After the 365 nm UV light excitation source switching off, the Sr_0.92Mg_1.95(PO₄)₂:Eu²⁺_0.01, Zr⁴⁺_0.05, Ho³⁺_0.07 phosphorescence can be observed for more than 1013 s in the limit of light perception of dark-adapted human eyes (0.32 mcd/m²). Different kinds of TL peaks at 423, 448 and 473 K have appeared, and traps densities have increased compared with the Eu²⁺ single doped SrMg₂(PO₄)₂ phosphor. By analyzing the TL curve the depths of traps were calculated to be 0.846, 0.896 and 0.946 eV, respectively, which suggested that the co-doping of Ho³⁺, Zr⁴⁺ improved the electron storage ability of material. Besides, the mechanism was discussed in this report.     

Low thermal expansion and low thermal expansion anisotropy ceramic of Sr0.5Zr2(PO4)3 system

A low thermal expansion ceramic with a very low thermal expansion anisotropy was synthesized from the Sr_0.5Zr₂(PO₄)₃ system. The sintering was promoted by addition of MgO, and the solgel technique also improved the sinterability. The thermal expansion of the crystal was lowered by substituting Nb⁵⁺ for Zr⁴⁺ and 1/2Sr²⁺ pairs, becoming near-zero for Sr_0.25Nb_0.5Zr_1.5(PO₄)₃. All dense ceramics in this system had a strength of about 80 MPa, and did not suffer microcracking even in the coarse-grained polycrystalline ceramics, owing to the very low thermal expansion anisotropy of the crystals.     

Dispersed materials for rechargeable lithium batteries: Reactive and non-reactive grinding

Reactive and non-reactive grinding has been used to prepare high dispersed lithium-transition metal cathode materials (LiMn₂O₄, LiCoO₂, LiV₃O₈, Li₃Fe₂(PO₄)₃, LiTi₂(PO₄)₃) and inorganic solid state Li-ion electrolytes (Li_1.3Al_0.3Ti_1.7(PO₄)₃) for rechargeable lithium batteries. Submicron particle size and the presence of cationic vacancies and cationic disordering positively influence electrochemical properties of as prepared cathodes, leading to larger practical capacity and stability upon intercalation-deintercalation of lithium ions. However, the advantages are observed only when the first electrochemical step is an insertion of Li⁺ ions (Li battery discharge). The conductivity of the Li_1.3Al_0.3Ti_1.7(PO₄)₃ lithium ion electrolyte prepared by using MA was of 2-3 order of magnitude higher than that for nonactivated sample owing to the absence of non-conductive impurities and lower grain boundary resistance.     

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

Nasicon-type phosphates Cu_1–xH_xZr₂(PO₄)₃ (0 < x <1) and Cu_1–xH_2x–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 Cu_1–xH_xZr₂(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 Cu_1–xH_2x–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.     

Abnormal blue-shift of Eu2+-activated calcium zirconium phosphates CaZr4(PO4)6

The electronic structure of CaZr₄(PO₄)₆ was calculated using the CASTEP code and the band gap for CaZr₄(PO₄)₆ can reach up to 4.30 eV. Ca_1−xEu_xZr₄(PO₄)₆ (0.01 ⩽ x ⩽ 1) samples were prepared by a high temperature solid-state reaction method. XRD analysis shows that Eu²⁺ ion can be totally incorporated into CaZr₄(PO₄)₆ forming complete solid solutions with trigonal lattice. Ca_1−xEu_xZr₄(PO₄)₆ (0.01 ⩽ x ⩽ 1) shows typical broad band emission in wavelength range from 400 to 650 nm for both under ultraviolet (UV) light and X-ray excitation, originating from the 4f⁶5d¹ → 4f⁷5d⁰ transition of Eu²⁺ ions. With increasing Eu²⁺ concentration, there is abnormal blue-shift of the emission peaks for Ca_1−xEu_xZr₄(PO₄)₆ due to the decreasing crystal field strength and Stokes shift. With increasing temperature in CaZr₄(PO₄)₆: Eu²⁺, its emission bands show the anomalous blue-shift with decreasing intensity. The overall scintillation efficiency of Ca_0.9Eu_0.1Zr₄(PO₄)₆ is 1.7 times of that of Bi₄Ge₃O₁₂ (BGO) powder under the same conditions. In addition, its predominant decay time is about 50 ns at room temperature. The potential application of Eu²⁺-doped CaZr₄(PO₄)₆ has been pointed out.     

Synthesis and properties of AgTi<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>-based NASICON-type phosphates doped with Nb<Superscript>5+</Superscript>, Zr<Superscript>4+</Superscript>, and Ga<Superscript>3+</Superscript>

We have synthesized materials based on a silver titanium phosphate with partial substitution of tri-, tetra-, or pentavalent cations for titanium: Ag_1±x Ti_2−x M _x (PO₄)₃ (M = Nb⁵⁺, Ga³⁺) and AgTi_2−x Zr _x (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.     

A study of copper stoichiometry and phase relationships in the copper-zirconium phosphate system: CuZr2(PO4)3 – Cu0.5Zr2(PO4)3

CuZr₂(PO₄)₃ crystallises with the Nasicon-type structure and is a copper(I) ion conductor. The possibility of a solid solution between CuZr₂(PO₄)₃ and Cu_0.5Zr₂(PO₄)₃ has been a controversial issue for many years. As part of a continued study, CuZr₂(PO₄)₃ and Cu_0.5Zr₂(PO₄)₃ were prepared by solid state methods and used to investigate the copper stoichiometry and phase relationships between these two materials as a function of copper content, temperature and oxygen fugacity. The following reversible reaction: Cu_0.5Zr₂(PO₄)₃ (s) + CuO (s) ↔ CuZr₂(PO₄)₃ (s) + O₂(g) was studied by thermogravimetry in an atmosphere of PO₂ = 0.22 atm and was found to occur at 475 ± 10°C. Thus, CuZr₂(PO₄)₃ is a thermodynamically stable phase in air above ∼475°C, which places a lower temperature limit on its use as an electrolyte in air. The results of X-ray powder diffractometry on materials with various copper contents that had been annealed in argon at 750°C indicate that there is no evidence for a significant solid solution between CuZr₂(PO₄)₃ and Cu_0.5Zr₂(PO₄)₃ nor, a reductive decomposition of Cu_0.5Zr₂(PO₄)₃. The coexistence of CuZr₂(PO₄)₃ and Cu_0.5Zr₂(PO₄)₃ as discrete phases is also supported by evidence from electron spin resonance spectroscopy on these materials, which indicate the presence of copper(II) ions in CuZr₂(PO₄)₃ at a dopant and dispersed level of concentration. The results from energy dispersive X-ray analysis, as well as, the novel use of the fluorescent behaviour of CuZr₂(PO₄)₃ in ultra-violet light as an analytical tool, support the above conclusions.     

Structural characterization of zinc-substituted hydroxyapatite prepared by hydrothermal method

Zinc-substituted hydroxyapatite (Zn-HA) powders were prepared by hydrothermal method using Ca(NO₃)₂, (NH₄)₃PO₄ and Zn(NO₃)₂ as reagents. X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) were used to characterize the crystalline phase, microstructure, chemical composition, morphology and thermal stability of Zn-HA. The results show that the substitution content of zinc (Zn) in Zn-HA powders prepared in NaOH solution is higher than that prepared in NH₃ solution, and is lower than that of the corresponding amount of starting materials. The substitution of the Zn ion for calcium ion causes a lower crystallinity of Zn-HA and changes the lattice parameters of Zn-HA, since the ionic radius is smaller in Zn²⁺ (0.074 nm) than in Ca²⁺ (0.099 nm). Furthermore, the substitution of the Zn ions restrains the growth of Zn-HA crystal and decreases the thermal stability of Zn-HA. Zn-HA powder prepared in NH₃ solution starts to decompose at 800 °C when the Zn fraction increases to 15 mol%, while that prepared in NaOH solution start to decompose at 5 mol% Zn. The substitution content of Zn significantly influences the thermal stability, microstructure and morphology of Zn-HA.     

Preparation of new zirconium phosphates by solvothermal reaction

Two types of new zirconium phosphates, [enH₂]Zr(OH)(PO₄)(HPO₄) (en; ethylene diamine) and (NH₄)₅[Zr₃(OH)₉(PO₄)₂(HPO₄)] were prepared under solvothermal condition using diethylene glycol as a solvent and their crystal structures were determined by using single crystal X-ray diffraction data. The former compound has the layer structure similar to that of γ-Zr(PO₄)(H₂PO₄) · 2H₂O, and protonated ethylene diamines were located in the interlayer space. At elevated temperatures, this compound decomposed by releasing protonated ethylene diamines and finally changed to ZrP₂O₇. The interlayer space was soft-chemically inactive unlike α-Zr(HPO₄)₂ · H₂O and γ-Zr(PO₄)(H₂PO₄) · 2H₂O. The later compound has the tunnel structure built up by corner-sharing ZrO₆ octahedra and PO₄ tetrahedra, and NH₄ ⁺ ion was located in the tunnel.     

Synthesis of high-surface-area complex zirconium phosphates via mechanochemical activation route

 High-power ball mill activation of the mixture of hydrated zirconium and lanthanum salts (oxonitrates, oxochlorides) with ammonium phosphate followed by hydrothermal treatment at temperatures not exceeding 200°C and a nearly neutral pH was found to yield crystalline dispersed phase of a cubic NH₄Zr₂(PO₄)₃ type along with admixtures of disordered orthorhombic compounds of a zirconium orthophosphate type. In the same conditions and at the same Zr/P ratio, hydrothermal treatment of gels obtained by reacting mixed zirconium and lanthanum nitrates solutions with ammonium phosphates yields no crystalline products, and only treatment in acid media generates a phase of the α-ZrPO₄(OH) type coexisting with the NH₄Zr₂(PO₄)₃ phase if polyethylene oxide is present. X-ray powder diffraction, transmission electron microscopy, ³¹MAS-NMR, FTIRS and thermal analysis were applied to elucidate factors affecting crystallization of complex zirconium phosphates in the hydrothermal conditions. The most essential factor appears to be generation of some nuclei of zirconium phosphates under high pressures developed in the course of mixed solids mechanical activation. These nuclei are embedded into matrix of such well-crystallized solid products as ammonium nitrate or chloride. Hence, metastable cubic or orthorhombic structure of the phases obtained via mechanical activation route can be assigned to the nuclei-matrix orientation relationship. Due to easily scaled-up synthesis procedure, these results appear to be very promising for manufacturing of dispersed framework zirconium phosphates as acid catalysts or fast proton conductors. Received: 18 November 1998 / Reviewed and accepted: 2 December 1998     

KTi2(PO4)3 Electrode with a Long Cycling Stability for Potassium‐Ion Batteries

In this work, rhombohedral KTi₂(PO₄)₃ is introduced to investigate the related theoretical, structural, and electrochemical properties in K cells. The suggested KTi₂(PO₄)₃ modified by electro‐conducting carbon brings about a flat voltage profile at ≈1.6 V, providing a large capacity of 126 mAh (g‐phosphate)^?1, corresponding to 98.5% of the theoretical capacity, with 89% capacity retention for 500 cycles. Structural analyses using electrochemical performance measurements, first‐principles calculations, ex situ X‐ray absorption spectroscopy, and operando X‐ray diffraction provide new insights into the reaction mechanism controlling the (de)intercalation of potassium ions into the host KTi₂(PO₄)₃ structure. It is observed that a biphasic redox process by Ti^4+/3+ occurs upon discharge, whereas a single‐phase reaction followed by a biphasic process occurs upon charge. Along with the structural refinement of the electrochemically reduced K₃Ti₂(PO₄)₃ phase, these new findings provide insight into the reaction mechanism in Na superionic conductor (NASICON)‐type KTi₂(PO₄)₃. The present approach can also be extended to the investigation of other NASICON‐type materials for potassium‐ion batteries.     

Synthesis, luminescence, and biocompatibility of calcium- and lanthanide-containing NaZr2(PO4)3-type compounds

Ca_0.5Zr₂(PO₄)₃:Er/Yb and Ca_0.75Zr₂(PO₄)_2.5(SiO₄)_0.5:Er/Yb compounds have been prepared and their luminescence properties and biocompatibility have been investigated. We found synthesis conditions that ensured phase homogeneity and formation of nanopowders. Their luminescence properties have been studied. Under IR excitation, emission was observed at ?? = 0.525 ??m. Cells (neutrophil granulocytes) were shown to retain viability in the presence of the compounds studied.     

On a new hydrogenated Cu (I) nasicon-type phosphate H0.5CuI0.5Zr2(PO4)3

Absorption of hydrogen in Cu^II_0.5Zr₂(PO₄)₃ gives rise to a new Cu (I) Nasicon-type derived phosphate H_0.5Cu^I_0.5Zr₂(PO₄)₃ as the result of an intercalation process. Various physical properties have been investigated. The copper (I) luminescence has been explained on hand of the position of the lowest levels of the Cu (I) 3d⁹4s¹ electronic configuration within the forbidden gap.     

Nanostructured Li3V2(PO4)3 Cathodes

To further increase the energy and power densities of lithium‐ion batteries (LIBs), monoclinic Li₃V₂(PO₄)₃ attracts much attention. However, the intrinsic low electrical conductivity (2.4 × 10^?7 S cm^?1) and sluggish kinetics become major drawbacks that keep Li₃V₂(PO₄)₃ away from meeting its full potential in high rate performance. Recently, significant breakthroughs in electrochemical performance (e.g., rate capability and cycling stability) have been achieved by utilizing advanced nanotechnologies. The nanostructured Li₃V₂(PO₄)₃ hybrid cathodes not only improve the electrical conductivity, but also provide high electrode/electrolyte contact interfaces, favorable electron and Li⁺ transport properties, and good accommodation of strain upon Li⁺ insertion/extraction. In this Review, light is shed on recent developments in the application of 0D (nanoparticles), 1D (nanowires and nanobelts), 2D (nanoplates and nanosheets), and 3D (nanospheres) Li₃V₂(PO₄)₃ for high‐performance LIBs, especially highlighting their synthetic strategies and promising electrochemical properties. Finally, the future prospects of nanostructured Li₃V₂(PO₄)₃ cathodes are discussed.