Conductivity of Zr-doped Na3PO4: A new Na+ ion conductor

Na₃PO₄ forms an extensive range of solid solutions with the replacement mechanism, 4Na⁺ ? Zr⁴⁺ and formula Na_3–4xZr_xPO₄:0 < x < 0.20. With increasing x, the conductivity increases markedly and passes through a maximum at $\text{x ? 0.13}$ with a value of 2.5 × 10^?2 ohm^?1cm^?1 at 300°C. The solid solutions are thermodynamically stable, easily prepared and sinter into dense ceramics at ～1000°C.     

The dependence of structure and conductivity in three-dimensional phosphate ionic conductors on composition

Two series of solid solutions, Na _x Ca_(1−x)/2Zr₂(PO₄)₃ (NCZP(x), 0⩽x⩽1) and Na _x Nb_1-x Zr_1+x (PO₄)₃(NNZP(x), 0⩽x⩽1), were synthesized. They were examined by powder X-ray diffraction, infra-red (i.r.) absorption and Raman scattering. Ionic conductivities of graphite coated samples were measured. A complete series of solid solutions was formed for NCZP(x), while a second phase was found forx<0.1 for NNZP(x). The i.r. and Raman spectra of their solid solutions consistently showed the formation of PO₄ tetrahedra with different geometries. The composition dependence of conductivity is interpreted on the basis of a structural change around Na⁺.     

Conductivite ionique dans les systems Na1+xZr2−xLx(PO4)3 (L = Cr,Yb)

Ionic conductivity measurements in the solid solution Na_1+xZr_2?xL_x(PO₄)₃ (L = Cr, Yb) have been carried out. The materials have a Nasicon-type structure in a 0 ? x ? x^max._L range (x^max._Cr = 2.0 and x^max._Yb = 1.9). A small monoclinic distortion appears at low temperature for Na₃Cr₂(PO₄)₃. As in the Na_1+xZr₂P_3?xSi_xO₁₂ system a strong increase of the conductivity with rising x has been observed. The results are discussed in connection with temperature and structural parameters.     

Crystal chemistry of the Na1+xZr2−xLx(PO4)3 (L = Cr,In, Yb) solid solutions

A crystal chemistry study of the three solid solutions Na_1+xZr_2?xL_x(PO₄)₃ (L = Cr, In, Yb) has been carried out. A Nasicon-type phase is obtained in the range 0 ? x ? x^max._L with x^max._Cr = 2.0, x^max._In = 1.85, x^max_Yb = 1.90 at 950°C. All phases have rhombohedral symmetry except Na₃Cr₂(PO₄)₃, where a small monoclinic distortion appears at low temperature. Influence of cationic size, electrostatic repulsion and sodium distribution is discussed.     

Lithium ion conductivity and mobility in the Li0.12Na0.88Ta0.4Nb0.6O3 solid solution

Lithium ion mobility and the superionic phase transition in the Li_0.12Na_0.88Ta_0.4Nb_0.6O₃ solid solution have been studied using temperature-dependent ionic conductivity measurements and Raman spectroscopy. From the temperature dependences of the conductivity and the width of a Raman line corresponding to Li⁺ and Na⁺ vibrations in the AO _x (A = Na⁺, Li⁺) polyhedra, the average lifetime of the Li⁺ ion in its equilibrium position and the height of the barrier to hopping have been estimated at ?3.9 × 10^?13 s and ?16 kJ/mol, respectively.     

Ionic conductivity of the Na1+xM x III Zr2−x(PO4)3 systems (M = Al,Ga, Cr,Fe, Sc,In, Y,Yb)

The existence and ionic conductivity of solid solutions Na_1+xM _x ^III Zr_2–x(PO₄)₃ with Nasicon-like structure have been investigated and the results compared with literature data. A limited range of solid solutions is formed with M^III = aluminium, gallium, yttrium, ytterbium, whereas a continuous series is obtained for M^III = chromium, iron, scandium, indium. The pure end member Na₃ln₂(PO₄)₃ is reported for the first time; according to powder diffraction data, it is hexagonal witha = 0.8966(1) andc = 2.2104(4) nm. The small monoclinic distortion already known for M^III = chromium, iron and scandium is restricted tox values very close to 2. Ionic conductivity measurements show that for a given value ofx, the mobility of the Na⁺ ions is strongly influenced both by the ionic radius and the type of electronic structure of the M^III ion. However, no simple correlation can be found.     

The incommensurate solid solution phase Na5−4x Zr1+x(PO4)3:0.04 <x <0.15

The orthophosphate solid solution phase, Na_5?4x Zr_1+x(PO₄)₃:0.04 ? x ? 0.15 has trigonal symmetry with an apparent one dimensional incommensurate superstructure parallel to c_HEX. Using selected area electron diffraction patterns as a guide, an indexing scheme for the powder X-ray data has been devised. The parameter $\text{k = c}{}_{\mathrm{<mtext>supercell</mtext>}}\text{c}{}_{\mathrm{<mtext>subcell</mtext>}}$ varies smoothly with composition from ～ 10.4 at x = 0.04 to ～4.4 at x = 0.11 and is believed to originate in ordering of the extra interstitial Zr⁴⁺ ions. The Na⁺ ion conductivity increases gradually with x and for x = 0.108 varies from ～5×10^?8 ohm^?1 cm^?1 at 25°C to ～1×10^?3 ohm^?1 cm^?1 at 300°C.     

Preparation of sodium zirconium phosphates of the type Na1+4xZr2−x (PO4)3

Sodium zirconium phosphates of the type Na_1+4x Zr_2?x (PO₄)₃ were prepared from mixtures of Na₃PO₄-ZrO₂-ZrP₂O₇ in sealed platinum tubes at temperatures of 900 – 1200°C. Stoichiometric NaZr₂ (PO₄)₃ (x = 0) was found not to exist. Instead, a solid solution in the range x = 0.02 ? 0.06 was found, with a slight difference in unit cell dimensions obtained. A second solid solution region was found with x = 0.88 – 0.93. At still higher values of x, a stoichiometric phase with hexagonal unit cell dimensions of $\text{a}\text{= 9.152(1)}\text{A}\text{?}$ and $\text{c}\text{= 21.844(1)}\text{A}\text{?}$ was obtained. Finally a phase of composition Na₇Zr_0.5 (PO₄)₃ was synthesized at the highest values of x. Attempts to prepare Na_5+x ZrSi_x-P_3?xO₁₂ always yielded NASICON and Na₇Zr_0.5 (PO₄)₃.     

Solid-state reactions in the system Li<Subscript>2</Subscript>CO<Subscript>3</Subscript>-Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript>

The formation mechanisms of Li _x Na_{1 ?x} Ta _y Nb_{1 ? y} O₃ perovskite solid solutions in the Li₂CO₃-Na₂CO₃-Nb₂O₅-Ta₂O₅ system have been studied by x-ray diffraction, differential thermal analysis, thermogravimetry, IR spectroscopy, and mass spectrometry at temperatures from 300 to 1100°C. The results indicate that the synthesis of Li _x Na_{1 ? x} Ta _y Nb_{1 ? y} O₃ solid solutions involves a complex sequence of consecutive and parallel solid-state reactions. An optimized synthesis procedure for Li _x Na_{1 ? x} Ta _y Nb_{1 ? y} O₃ solid solutions is proposed.     

New rutile solid solutions,Ti1−4xLixM3xO2: M = Nb,Ta, Sb

Three extensive new rutile solid solution series have been prepared in which Ti⁴⁺ is replaced by a combination of Li⁺ and a pentavalent cation: Nb⁵⁺, Ta⁵⁺, Sb⁵⁺. The formulae are Ti_1?4xLi_xM_3xO₂: 0 < x ? 0.15, M = Ta; 0 < x ? 0.17, M = Nb; 0 < x ? 0.12, M = Sb. The solid solutions were characterised by X-ray powder diffraction and density measurements. In addition to the rutile solid solutions, LiNb₃O₈ forms a limited range of solid solutions, Li_1?yNb_3?3yTi_4yO₈: 0 < y ? 0.06.     

A nasicon-type phase as intercalation electrode: NaTi2(PO4)3

Reversible intercalation of sodium in NaTi₂(PO₄)₃ at room temperature can be achieved either chemically or electrochemically. Na₃Ti₂(PO₄)₃ is obtained as final product via a two phase mechanism. The non-existence between both extreme compounds of a Na_1+xTi₂(PO₄)₃ solid solution seems to result from a topotactic demixtion reaction which requires only Na⁺ and e⁻ transfers without skeleton bond breaking and recombination.     

Electrochemical Investigation of Calcium Substituted Monoclinic Li3V2(PO4)3 Negative Electrode Materials for Sodium- and Potassium-Ion Batteries

Herein, the electrochemical properties and reaction mechanism of Li_3‒2xCa_xV₂(PO₄)₃/C (x = 0, 0.5, 1, and 1.5) as negative electrode materials for sodium-ion/potassium-ion batteries (SIBs/PIBs) are investigated. All samples undergo a mixed contribution of diffusion-controlled and pseudocapacitive-type processes in SIBs and PIBs via Trasatti Differentiation Method, while the latter increases with Ca content increase. Among them, Li₃V₂(PO₄)₃/C exhibits the highest reversible capacity in SIBs and PIBs, while Ca_1.5V₂(PO₄)₃/C shows the best rate performance with a capacity retention of 46% at 20 C in SIBs and 47% at 10 C in PIBs. This study demonstrates that the specific capacity of this type of material in SIBs and PIBs does not increase with the Ca-content as previously observed in lithium-ion system, but the stability and performance at a high C-rate can be improved by replacing Li⁺ with Ca²⁺. This indicates that the insertion of different monovalent cations (Na⁺/K⁺) can strongly influence the redox reaction and structure evolution of the host materials, due to the larger ion size of Na⁺ and K⁺ and their different kinetic properties with respect to Li⁺. Furthermore, the working mechanism of both LVP/C and Ca_1.5V₂(PO₄)₃/C in SIBs are elucidated via in operando synchrotron diffraction and in operando X-ray absorption spectroscopy.     

Mn-doped Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> nanocrystal with enhanced electrochemical properties based on aerosol synthesis method

Mn-doped Li₃V_2?x Mn _x (PO₄)₃ nanocrystals with enhanced electrochemical properties for lithium-ion batteries were synthesized by aerosol process successfully. The nanocrystals synthesized from aerosol-assisted spray process have an average particle size smaller than 500 nm, with some initial particle size of about 100 nm. The Mn-doped Li₃V₂(PO₄)₃ cathode materials show higher capacity and coulombic efficiency than pure Li₃V₂(PO₄)₃ materials. Especially, the Mn-doped Li₃V_1.94Mn_0.06(PO₄)₃ shows a capacity of 130 mAh/g in the voltage range of 3.0–4.4 V and a coulombic efficiency of 99.5 % at 1C. The results from XRD, SEM, HRTEM, and EIS suggested that lattice changes of Li₃V₂(PO₄)₃ due to Mn doping and the fine particles enabled by aerosol-assisted spray process can significantly reduce the charge-transfer resistance and improve the apparent Li⁺ diffusion coefficient of insertion/desertion in the electrodes, which were the critical reason of better electrochemical performance of Mn-doped Li₃V₂(PO₄)₃ cathode materials.     

Electrical conductivity of Cs<Subscript>3</Subscript>PO<Subscript>4</Subscript> doped with trivalent cations

Cs_{3 ? 3x} M _x PO₄ (M = Sc, Y, La, Sm, Nd) solid electrolytes have been synthesized, their phase composition has been determined, and their electrical conductivity has been measured as a function of temperature. In all of the systems, we have identified cesium orthophosphate based solid solutions. Above ～550°C, the solid solutions are isostructural with the high-temperature, cubic phase of Cs₃PO₄. They offer high cesium ion conductivity owing to the formation of cesium vacancies via 3Cs⁺ → M³⁺ substitutions and the decrease in phase transition temperature. The conductivity of the synthesized solid solutions, (4.8?5.6) × 10^?3 S/cm at 300°C and (1.6?1.9) × 10^?1 S/cm at 800°C, is at the level of earlier studied Cs_{3 ? 2x} M _x ^II PO₄ solid electrolytes.     

Etude cristallochimique,dielectrique et pyroelectrique de la solution solide Na1−xLix(Nb0,6Ta0,4)O3 (0,02 ⩽ x ⩽ 0,20)

A solid solution with formulation Na_1?xLi_x(Nb_0.6Ta_0.4)O₃ (0.02 ? x ? 0.20) and a perovskite related structure has been prepared by substituting sodium by lithium in Na(Nb_0.6Ta_0.4)O₃. The ferroelectric Curie temperature increases with x from 308 to 428 K. The pyroelectric properties have been investigated. The high performances may lead to appropriate applications.     

Dielectric properties and electrical conductivity of LixNa1?xTa0.1Nb0.9O3 ferroelectric solid solutions

We have studied the dielectric properties and electrical conductivity of Li _x Na_{1 − x} Ta_0.1Nb_0.9O₃ (x = 0.03−0.135) ferroelectric solid solutions at temperatures from 290 to 700 K and frequencies from 25 to 10⁶ Hz. The results demonstrate that charge transport in these materials is due to the Li⁺ ion and that their conductivity is dominated by volume ion transport. In the temperature range studied, the Li _x Na_{1 − x} Ta_0.1Nb_0.9O₃ solid solutions undergo a first-order ferroelectric phase transition close to second order. Increasing the lithium content enhances features characteristic of second-order transitions.     

Preparation of powders and films of the lithium ion conducting solid electrolyte Li1.3Al0.3Ti1.7(PO4)3

This paper describes a process for the preparation of powders and films of the lithium ion conducting solid electrolyte Li_1.3Al_0.3Ti_1.7(PO₄)₃ from peroxide solutions. The use of peroxide solutions ensures the preparation of Li_1.3Al_0.3Ti_1.7(PO₄)₃ with a room-temperature electrical conductivity of (4?C5) × 10^?4 S/cm by calcining a precursor at 800°C. The synthesized Li_1.3Al_0.3Ti_1.7(PO₄)₃ powders were characterized by X-ray diffraction, thermal analysis (DTA/TG), and ionic and electronic conductivity measurements. The growth of Li_1.3Al_0.3Ti_1.7(PO₄)₃ solid electrolyte films is described.     

Intercalation properties and electrochemical reduction of chromium oxide chloride

Intercalation complexes M_x(DMSO)_y[Cr_1?x⁺³ Cr_x⁺²OCl] have been obtained by cathodic reduction of chromium oxide chloride in a solution of M⁺ (Li⁺, Na⁺, K⁺) in dimethyl-sulfoxide (DMSO). From galvanostatic experiments upper limits for x were determined to be x = 0.12 for Li⁺ and x = 0.05 for Na⁺ and K⁺. Correlations between the degree of reduction (x), ionic radii of M⁺, amount of solvent intercalation (y), lattice expansion and M⁺-coordination are discussed.Chromium oxide chloride samples with either chloride deficiency or Cl^? by O^2? replacement showed a degree of reduction of only x = 0.05 upon Li⁺-intercalation.     

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.     

Resorption of Ca<Subscript>3 – <Emphasis Type="Italic">x</Emphasis></Subscript>M<Subscript>2<Emphasis Type="Italic">x</Emphasis></Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> (M = Na,K) Calcium Phosphate Bioceramics in Model Solutions

The resorbability of bioceramics in the Ca₃(PO₄)₂–CaNaPO₄–CaKPO₄ system is evaluated in an approach involving thermodynamic assessment of solubility and investigation of the dissolution kinetics in model media, in particular in citric acid solutions. Thermodynamic calculation indicates high solubility of the Ca₅Na₂(PO₄)₄, α-CaМPO₄, β-CaKPO₄, and β-СаK_0.6Na_0.4PO₄ phases. Investigation of the dissolution kinetics of ceramics has made it possible to identify two distinct types of behavior of resorbable materials in weakly acidic solutions: with fast resorption kinetics in the case of the phases based on nagelschmidtite solid solutions and α-CaМPO₄ disordered high-temperature solid solutions, and with a nearly constant, relatively low dissolution rate and a high solubility limit in the case of β-СaK_{1 – x}Na _x -based phases.