New solid ionic conductors

A new class of solid Li⁺ ionic conductors has been found, related to the compound LiZr₂(PO₄)₃. Solid solutions of the type Li_1?xZr_2?xTa_x(PO₄)₃ and Li_1?xHf_2?xTa_x(PO₄)₃ have conductivities of about 10^?3ohm^?1 cm^?1 at 200°C, which are relatively independent of composition. These systems are compared with the recently discovered class of Na⁺ conductors Na_1+xZr₂P_3?xSi_xO₁₂. Other solid solutions are also discussed.     

Thermal expansion of NZP-family alkali-metal (Na, K) zirconium phosphates

The thermal expansion of the A _x Zr_2.25-0.25x(PO₄)₃ phosphates with A = Na(x = 0.5,1.0,2.0,3.0,4.0, 5.0) and K(x = 1.0, 3.0, 5.0), crystallizing in structures of the NaZr₂(PO₄)₃ type (sp. gr.R3c or C2/c), was studied by high-temperature x-ray powder diffraction in the range 20–700‡C. The lattice parametersa and c and thea- andc-axis thermal expansion coefficients (α_a and α_c) were determined. The thermal expansion of the phosphates was found to be highly anisotropic (α_a < 0, α_c > 0). The strongest anisotropy was found in NaZr₂(PO₄)₃ (α_a = -4.89 x 10^-6 K^-1, α_c = 22.02 x 10^-6 K^-1), KZr₂(PO₄)₃ (α_a =-5.30 x 10^-6 K^-1, α_c = 5.41 x 10^-6 K^-1), and Na₅Zr(PO₄)₃ (α_a = -5.82 x 10^-6 K^-1, α_c = 20.73 x 10^-6 K^-1). K₅Zr(PO₄)₃ exhibited the smallest thermal expansion and weak anisotropy (α_a = -2.14 x 10^-6 K^-1, α_c = 2.65 x 10^-6 K^-1). The effects of M(l) and M(2) site occupancies on α_a, α_c,a, and c were assessed. The relative magnitudes of crystal-chemical and thermal expansion in the Na and K compounds were analyzed.     

Superprotonic CsH<Subscript>2</Subscript>PO<Subscript>4</Subscript>-CsHSO<Subscript>4</Subscript> solid solutions

We have performed partial HSO₄⁻ substitution in CsH₂PO₄ and studied the associated structural changes and the proton conductivity of the resultant (CsH₂PO₄)_{1 − x} (CsHSO₄) _x solid solutions in the range x = 0.01–0.3. The results indicate that, at room temperature, the solid solutions are disordered. In the range x = 0.01–0.1, they are isostructural with the low-temperature phase of CsH₂PO₄ (sp. gr. P2₁/m), and their unit-cell parameters increase with x, whereas in the range x = 0.15–0.3 the solid solutions are isostructural with the high-temperature, cubic phase of CsH₂PO₄ (Pm3m), and their unit-cell parameter decreases. The conductivity of the (CsH₂PO₄)_{1 − x} (CsHSO₄) _x solid solutions with x ≤ 0.3 depends significantly on their composition and increases at low temperatures by up to four orders of magnitude, approaching that of the superionic phase of CsH₂PO₄ in the range x = 0.15–0.3 because of the hydrogen bond weakening and increased proton mobility. The conductivity of the superionic phase decreases with increasing x by no more than a factor of 1.5–2, and the superionic phase transition, which occurs at 231°C in CsH₂PO₄, shifts to lower temperatures and disappears for x ≥ 0.15. The activation energy for low-temperature conduction decreases with increasing x: from 0.9 eV in CsH₂PO₄ to 0.48 eV at x = 0.1.     

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.     

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.     

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.     

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.     

Na-doped β-tricalcium phosphate: physico-chemical and in vitro biological properties

Synthetic calcium phosphate ceramics as β-tricalcium phosphate (Ca₃(PO₄)₂; β-TCP) are currently successfully used in human bone surgery. The aim of this work was to evaluate the influence of the presence of sodium ion in β-TCP on its mechanical and biological properties. Five Na-doped-β-TCP [Ca_10.5−x/2Na _x (PO₄)₇, 0 ≤ x ≤ 1] microporous pellets were prepared via solid phase synthesis, and their physico-chemical data (lattice compacity, density, porosity, compressive strength, infrared spectra) denote an increase of the mechanical properties and a decrease of the solubility when the sodium content is raised. On the other hand, the in vitro study of MC3T3-E1 cell activity (morphology, MTS assay and ALP activity) shows that the incorporation of sodium does not modify the bioactivity of the β-TCP. These results strongly suggest that Na-doped-β-TCP appear to be good candidates for their use as bone substitutes.     

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.     

Structure of Cs<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Rb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>H<Subscript>2</Subscript>PO<Subscript>4</Subscript> solid solutions

Cs_{1 − x} Rb _x H₂PO₄ solid solutions have been synthesized for the first time in a broad composition range, x = 0.03–0.9. At room temperature, the Cs_{1 − x} Rb _x H₂PO₄ solid solutions are isostructural with the low-temperature phase of CsH₂PO₄ over the entire composition range studied. In the CsH₂PO₄-based solid-solution series, the unit-cell parameters and volume decrease with increasing Rb content. At high temperatures, the Cs_{1 − x} Rb _x H₂PO₄ solid solutions exist in the range x = 0–0.4, are isostructural with cubic CsH₂PO₄, and have a smaller unit-cell parameter.     

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.     

Carbon-coated nano-sized LiFe1?xMnxPO4 solid solutions (0?≤?x?≤?1) obtained from phosphate–formate precursors

LiFe_1−x Mn _x PO₄ solid solutions in the whole concentration range (0 ≤ x ≤ 1) are obtained at 500 °C by a phosphate–formate precursor method. The method is based on the formation of homogeneous lithium–iron–manganese phosphate–formate precursors by freeze-drying of aqueous solutions containing Li(I), Fe(II), Mn(II), phosphate, and formate ions. Thermal treatment of the phosphate–formate precursors at temperatures at 500 °C yields nano-sized LiFe_1−x Mn _x PO₄ coated with carbon. The structure and the morphology of the LiFe_1−x Mn _x PO₄ compositions are studied by XRD, IR spectroscopy, and SEM analysis. The in situ formed carbon is analyzed by Raman spectroscopy. The electrochemical performance of LiFe_1−x Mn _x PO₄ is tested in model lithium cells using a galvanostatic mode. All LiFe_1−x Mn _x PO₄ compositions are characterized with an ordered olivine-type structure with a homogeneous Fe²⁺ and Mn²⁺ distribution in the 4c olivine sites. The morphology of LiFe_1−x Mn _x PO₄ consists of plate-like aggregates which are covered by in situ formed carbon. Inside the aggregates nano-sized isometric particles with narrow particles size distribution (between 60 and 100 nm) are visible. The structure of the deposited carbon presents a considerable disordered graphitic phase and does not depend on the Fe-to-Mn ratio. The solid solutions LiFe_1−x Mn _x PO₄ deliver a good reversible capacity due to the Fe²⁺/Fe³⁺ and Mn²⁺/Mn³⁺ redox-couples at 3.5 and 4.1 V, respectively.     

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.     

High-pressure synthesis of metastable ternary solid solutions between tetrahedral semiconductors

Amorphous Ge-GaSb, Ge-InSb, and GaSb-InSb solid solutions were prepared by high-pressure liquid quenching followed by solid-state amorphization. In the eutectic systems Ge-GaSb and Ge-InSb at 8–9.5 GPa, continuous series of solid solutions are obtained. It is shown, using the Ge-GaSb system as an example, that complete miscibility of the components occurs in the stability field of high-pressure phases. Amorphous Ge-GaSb materials were obtained at Ge concentrations from 0 to 80 at. %. In the (Ge₂)_1-x (InSb) _x and (GaSb)_1-x (InSb) _x solid-solution systems, the composition range of amorphization is narrower, 0.2 ≤x ≤ 0.8. Melt quenching and pressure release at 160 K yield crystalline (Ge₂)_1-x (GaSb) _x (x = 0.1 and 0.15) solid solutions with an unidentified structure similar to that ofR8 Si.     

Electrical conduction in the solid solution La1 −x Na x Co1 −x Nb x O3 (0·01 ⩽x ⩽ 0·99)

Seebeck coefficient and DC resistivity of the solid solution La_{1 −x} Na _x Co_{1 −x} Nb _x O₃ (0·01 ⩽x ⩽ 0·99) have been measured in the temperature range 300–900 K. Seebeck coefficient is positive for all compositions over the temperature range of measurements. Conduction is due to 3d electrons of cobalt ions in the compositions withx ⩽ 0·60. Conduction occurs among localized sites for compositions withx ⩾ 0·70.     

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.     

Structure and dielectric properties of (1 − <Emphasis Type="Italic">x</Emphasis>)BiFeO<Subscript>3</Subscript> · <Emphasis Type="Italic">x</Emphasis>(KBi)<Subscript>1/2</Subscript>TiO<Subscript>3</Subscript> perovskite solid solutions

(1 − x)BiFeO₃ · x(KBi)_1/2TiO₃ ceramics have been prepared by solid-state reactions. The system has been shown to contain a continuous series of perovskite solid solutions. In the composition ranges x < 0.4, 0.4 < x < 0.9, and x > 0.9, the solid solutions have rhombohedral, orthorhombic, and tetragonal structures, respectively. The observed compositional phase transitions are accompanied by sharp changes in unit-cell volume. We describe the dielectric properties of the orthorhombic solid solutions, which demonstrate that these materials exhibit relaxor behavior.     

Coprecipitation synthesis and optical absorption property of Zn2TixSn1–xO4 (0?≤?x?≤?1) solid solutions

We report a coprecipitation method for the preparation of solid solutions in the Zn₂Ti _x Sn_1–x O₄ (0 ≤ x ≤ 1) series. The precipitates obtained from the coprecipitation were calcined using different temperatures and then characterized with X-ray diffraction (XRD), Raman scattering (RS), scanning electron microscopy (SEM), and surface area measurements to gain insights into the solid-state reaction and phase transformation during the calcinations. Formation of the Zn₂Ti _x Sn_1–x O₄ solid solutions was observed after the calcination up to 1000 °C, which is much lower than the temperature (1300 °C) required in the conventional solid-state reaction method. The optical absorption property of the Zn₂Ti _x Sn_1–x O₄ solid solutions, measured by ultraviolet-visible diffuse reflectance spectroscopy (UV–Vis DRS), was shown to change according to the composition of the solid solutions.     

Preparation of Pb(Zr,Ti)O<Subscript>3</Subscript>–Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> piezoelectric ceramics by dry–dry method

Ternary perovskite ceramics of Pb[(Zr_0.5Ti_0.5)_0.8−x (Mg_1/3Nb_2/3)_0.2+x]_0.98Nb_0.02O_3.01 (PZTMN, x = −0.075, −0.05, −0.025, 0, 0.025, 0.05, and 0.075 ), are synthesized via dry–dry method. B-site precursors of PZTMN ([(Zr_0.5Ti_0.5)_0.8−x (Mg_1/3Nb_2/3)_0.2+x ]_0.98Nb_0.02O_2.01, ZTMN) can be synthesized via a two-step solid state reaction method. The first calcination temperature is 1,300 °C, and the second is not higher than 1,360 °C. Incorporation of magnesium and niobium ions promotes the formation of the single phase solid solution with ZrTiO₄ structure. Single phase perovskite PZTMN is formed at 780 °C, much lower than that in conventional process. Dense ceramics can be sintered at about 1,260 °C with dielectric and piezoelectric properties comparable to that of wet–dry method and higher than that of conventional method. It seems that B-site precursor method is cost effective in preparation of ternary piezoelectric ceramics.     

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.