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.     

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.     

Contribution a l'etude du systeme Na3PO4-Na2SO4 et proprietes de conduction ionique des materiaux de type γ-Na3PO4: Na3−xP1−xSxO4 (0<x≤0,58)

The study of the Na₃PO₄Na₂SO₄ system at 1050°C has proved the existence of the solid solution Na_3?xP_1?xS_xO₄ (0<x≤0.58) for which the cubic symmetry (Li₃Bi-type structure) of the “high temperature” form γ-Na₃PO₄ is maintained. The room temperature variation of the parameter of the unit cell as a function of doping level and the homogeneity range are discussed. The replacement of PO^3?₄ ions by SO^2?₄ ions in Na_3?xP_1?xS_xO₄ leads to better ionic conductivity. The results are explained on the bases of structural and size considerations. A conduction mechanism is proposed.     

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.     

Contribution a l'etude de la conductivite ionique de l'orthophosphate Na3PO4

The present work is concerned with the ionic conductivity of pure trisodium orthophosphate Na₃PO₄, devoid of any trace of hydroxide NaOH. At the allotropic transition (330°C), we observe a jump of the ionic conductivity and a slight decrease in the activation energy (ΔE = 0,70 ± 0,02 eV for the quadratic variety and ΔE = 0,60 ± 0,04 eV for cubic γ-Na₃PO₄). Na₃PO₄ can be considered to be an electrolytic solid with medium conductivity ($\text{σ = 1.10}{}^{\mathrm{?4}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ at 370°C).     

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.     

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.     

Fast Na+-ion transport in skeleton structures

Skeleton structures have been explored experimentally for fast Na⁺-ion transport. A skeleton structure consists of a rigid skeletal array of atoms stabilized by electrons donated by alkali ions partially occupying sites in a three dimensionally linked interstitial space. Fast Na⁺-ion transport was demonstrated in several structures, and the system Na_1+xZr₂P_3?xSi_xO₁₂ has a Na⁺-ion resistivity at 300°C of $\text{?}{}_{300}\text{? 5Ω-}\text{cm}$ for x ≈ 2, which is competitive with the best β″-alumina. An activation energy ε_a ≈ 0.29 eV is about 0.1 eV larger than that of β″-alumina.     

The sodium ytterbium orthophosphate Na3(1+x)Yb(2-x)(PO4)3

A new sodium ytterbium orthophosphate with general formula Na_3(1+x)Yb_(2-x)(PO₄)₃ (0.07 ? x ? 0.50) has been prepared and characterized. Its crystal structure has been determined from a single crystal for x = 0.50. The space group is R3?c, the lattice constants are : $\text{a}\text{= 9.12(1)}\text{A}\text{?}$, $\text{c}\text{= 21.81(6)}\text{A}\text{?}$. The structure of Na_4.50Yb_1.50(PO₄)₃ is related to that of NaZr₂(PO₄)₃. The PO₄ tetrahedra and the (Yb,Na)O₆ octahedra form a three-dimensional skeleton in which the remaining sodium atoms are inserted. This structural type is also found for the phases Na_4.50Ln_1.50(PO₄)₃ (Ln = Tm, Lu) and Na_4.50Ln_1.50(AsO₄)₃ (Ln = Er, Tm, Yb, Lu).     

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.     

Synthese et etude cristallochimique et magnetique des solutions solides LaxHo1−xB6

La_xHo_1?xB₆ solid solutions of CaB₆ type have been prepared by borothermal reduction in the range 0.2 ? x < 1. For $\text{La}\text{Ho+La}\text{< 0.2}$ the corresponding solid solution coexists with a HoB₄ and HoB₁₂ mixture. HoB₆ could not be obtained : the ionic radius of Ho³⁺ seems to be a border value for the stability of the CaB₆ structure. Extrapolation of the magnetic properties of La_xHo_1?xB₆ solid solutions allows to confer to an eventual HoB₆ an interaction mechanism of the RKKY type.     

Etude du systeme KPO3-LaP3O9. Donnees cristal lographiques sur K2La(PO3)5 et (NH4)2La(PO3)5

The system KPO₃-LaP₃O₉ has been studied for the first time by differential thermal analysis and X ray diffraction. The system shows two compounds KLa(PO₃)₄ and K₂La(PO₃)₅ which melt in a peritectic decomposition at 880°C and 770°C respectively. An eutectic point appears at 705°C; The eutectic point corresponds to a concentration of 10% molar LaP₃O₉.Infra Red absorption spectra are typical of chain phosphates.The new compound K₂La(PO₃₅ is isotypic whith (NH₄)₂La(PO₃)₅ which has been synthetized for the first time. They belong to the triclinic system whith space group P1 and Z = 2. The parameters of the unit cell are: $\text{a = 7.309(4)}\text{A}\text{?}$$\text{b = 13.35(2)}\text{A}\text{?}$$\text{c = 7.155(7)}\text{A}\text{?}$α = 90°3(1) β = 109°17(7) γ = 89°90(4) for K₂La(PO₃)₅ and: $\text{a = 7.174(8)}\text{A}\text{?}$$\text{b = 13.38(2)}\text{A}\text{?}$$\text{c = 7.35(2)}\text{A}\text{?}$α = 90°6(2) β = 107°4(1) γ = 89°82(7) for (NH₄)₂La(PO₃)₅.     

Ionic conductivity in low carnegieite compositions based on NaAlSiO4

Carnegieite compositions of the type Na_1+xAl_1+xSi_1?xO₄ with x = 0 to ～0.7 were prepared. Na ion conductivities, measured with Na and Au electrodes at ～10³ Hz, range from $\text{4×10}{}_{\mathrm{?5}}\text{(Ω-}\text{cm}\text{)}{}^{\mathrm{?1}}$ for NaAlSiO₄ to $\text{5×10}{}^{\mathrm{?3}}\text{(Ω-}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 300 C for Na_1.7Al_1.7Si_0.3O₄. Substitutions of Li, K, Ca, or Sr for Na lowered σ whereas substitution of Ti for Si raised σ. Na aluminum silicates with the nepheline structure had lower σ than carnegieite compositions.     

Ionic conductivity and crystallographic data for Na2-xCa1-xAlxSiO4 and Na2-xCaSi1-xPxO4 carnegieite phases

Single crystals of Na₂CaSiO₄ prepared at 30 kbar and 1500°C are cubic with $\text{a}\text{= 22.456}\text{A}\text{?}$. The polycrystalline compositions Na_1.9Ca_0.9Al_0.1SiO₄ and Na_1.8CaSi_0.8P_0.2O₄ can also be indexed using $\text{a}\text{= 22.458}\text{and}\text{22.471}\text{A}\text{?}$, respectively. The Ca carnegieites Na₂CaSiO₄, Na_1.9Ca_0.9Al_0.1SiO₄, and Na_1.8CaSi_0.8P_0.2O₄ have Na ion conductivities of only 5?8 × 10^?6 (ω-cm)^?1 at 300°C.     

Synthese et etude de la conductivite anionique des phases du systeme NaF - BiF3

A definite NaBiF₄ phase and a solid solution Na_1?xBi_xF_1+2x (0,60 ? x ? 0,70) of fluorite derived type have been obtained at 430°C in the NaF - BiF₃ system. Investigation of the electrical properties of these materials shows that Na_0,40 Bi_0,60 F_2,20 is the best anionic conductor of the system, with a conductivity of about 10^?3 Ω^?1 cm^?1 and 100°C and an activation energy of 0,46 e v. The results are discussed in comparison with those previously obtained for the KF - BiF₃ and RbF - BiF₃ systems.     

Electrical properties of sintered EuZrO3  EuNbO3 and EuNbO3

Electrical resistivity of two-phase products [yEuZrO₃ + (1 ? y) EuNbO₃] increased continuously with y, and a transition from a metallic to semiconducting characteristic occured at y = 0.14. The resistivity varied almost linearly with temperaure in the range y = 0 to y = 0.24, and thermal coefficients of resistivity at 300 K for the products decreased from +5.9 × 10^?4 K^?1 to ?7.4 × 10^?4 K^?1 according to the value of y. At y = 0.14, the thermal coefficient was almost zero. Thermal coefficients of electrical resistivity for the niobates with various oxygen contents were all positive in the range $\text{2.55 <}\text{O}\text{Nb}\text{< 3.24}$ and exhibited a sharp minimum at $\text{O}\text{Nb}\text{= 2.92}$. In all these niobates, Eu_xNbO₃ was a major phase and Eu₃NbO₆ or EuNbO₂ was detected as a second phase in the range $\text{O}\text{Nb}\text{> 3}$ or $\text{O}\text{Nb}\text{< 3}$ respectively. Peaks in the resistivity curves were correlated with a magnetic ordering temperature for samples with an overall ratio $\text{O}\text{Nb}\text{> 3}$.     

Phase diagram of the LISICON,solid electrolyte system,Li4GeO4Zn2GeO4

The phase diagram of the system Li₄GeO₄Zn₂GeO₄ is fairly similar to the corresponding silicate system and contains a wide range of solid solutions that extend to either side of the composition Li₂ZnGeO₄. These solid solutions are polymorphic. The high temperature ^γII solid solutions have a crystal structure derived from that of ^γII Li₃PO₄ and a formula, Li_{2 + 2x}Zn_1?xGeO₄ : ?0.36 < x < +0.87. LISICON, x = 0.75, is one member of the ^γII solid solution series. The compositional extent of the ^γII solid solutions is temperature dependent and eg. the LISICON composition is stable as a single phase γII structure only ? 630°C. On annealing LISICON and other lithiumrich, ^γII solid solutions in the range ～100 to 600°C, various reactions occur, including 1) precipitation of Li₄GeO₄, 2) phase transition(s) to metastable low temperature, γ-derivative structure(s) and 3) atmospheric attack to give Li₂GeO₃, Li₂CO₃ and other phases. The low temperature ^βII, ^βII′ solid solutions occur over a much smaller range of compositions to either side of Li₂ZnGeO₄ and have a crystal structure derived from that of ^βII Li₃PO₄. Li₄GeO₄ forms a short range of solid solutions.     

High pressure synthesis and structural evolution of new compounds of formulation NaNb1−xWxO3

Solid solutions of formula NaNb_1?xW_xO₃ (0 ? x ? 1) have have been prepared using a high pressure technique and their structural evolution observed as Nb⁵⁺ is substituted by W⁵⁺. Five phases with perovskite-related structures have been identified: two orthorhombic phases with space group Pbma (0 ? x ? 0.16 and 0.20 ? x ? 0.40), another orthorhombic phase whose b axis is approximately one quarter of the former (0.40 < x < 0.52) and two cubic phases ($\text{x}\text{? 0.16}$ and 0.52 ? x ? 1). An attempt is made to correlate the complex evolution with x of the lattice parameters in the orthorhombic phases with the change of octahedron size and tilting angles.     

Temperature dependence of critical stress and phase diagram of ferroelastic Pb3 (PO4)2 Pb3 (VO4)2

The temperature dependence of the critical stress in ferroelastic Pb₃ (PO₄)₂ reveals a Curie-Weiß law ($\text{ß =}\text{1}\text{2}$) up to 145°C. Between 160°C and the transition point at 180°C a crossover to a $\text{ß =}\text{1}\text{3}$ regime was found. For mixed crystals Pb₃ (PO₄)₂ ? Pb₃ (VO₄)₂ a phase diagram is suggested from optical, dielectric and Raman spectroscopical experiments.