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.     

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.     

On the pyrochlore type Ln2V2O7 (Ln: Rare-earth elements)

Pyrochlore type rare-earth vanadites (Ln₂V₂O₇) were prepared and some physical properties were investigated. Ln₂V₂O₇ (Ln:Tm, Yb or Lu) crystallized in the cubic space group $\text{O}{}_{\mathrm{<mtext>h</mtext>}}\text{=}\text{Fd}{}_3\text{m}\text{,}\text{a}{}_0\text{= 9.9575}\text{A}\text{?}\text{, 9.9346}\text{A}\text{?}\text{and}\text{9.9231}\text{A}\text{?}$ for Tm₂V₂O₇, Yb₂V₂O₇ and Lu₂V₂O₇, respectively. These compounds were all n-type semiconductors and paramagnets in the temperature range 90–300K.     

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.     

Diagramme d'equilibre solide-liquide du systeme Ce(PO3)3 — AgPO3

The Ce(PO₃)₃ — AgPO₃ system was investigated by differential thermal analysis (DTA) and X-ray diffraction. Its phase equilibrium diagram was established by recording heating curves on a M5 Setaram μ-DTA aparatus. This diagram shows that the Ce (PO₃)₃—AgPO₃ system forms only one compound, AgCe(PO₃)₄, which melts in a peritectic reaction at 788°C. The chemical preparation, powder diagram and main crystallogrophic characteristics of this compound are given. AgCe(PO₃)₄, a polyphosphate isotypic with NaNd(PO₃)₄, has a monoclinic unit cell with a space group $\text{P2}{}_1\text{n}$ and parameters a = 9.717(4), b = 12.959(5), c = 7.242(2) Å, β = 91.07(2)°, Z = 4, V = 911.79 ų, d_x = 4.11. The different structure types of binary poly and metaphosphates, M₂O.Ln₂O₃.4P₂O₅, are regrouped and a correlation between each crystalline form and the corresponding M³ and Ln³⁺ cation size is dicussed.     

Crystal chemistry of γ-(Zn, Me)3(PO4)2 solid solutions

A number of γ-(Zn,$\text{Me}$)₃(PO₄)₂ solid solutions with the “γ-Zn₃(PO₄)₂” structure have been prepared and equilibrated at about 1070 K ($\text{Me}\text{= Mg, Mn, Fe, Co, Ni, Cu, and Cd}$). Approximate homogeneity ranges are given. The monoclinic unit cell dimensions have been accurately determined from Guinier-Hägg photographs. The structure contains five- and six-coordinated cations. Correlations between homogeneity ranges, unit cell dimensions, cation radii and cation distributions are pointed out, and the phases are also compared with isotypic (Mg,$\text{Me}$₃(PO₄)₂ and (Co,$\text{Me}$)₃(PO₄)₂ solid solutions.     

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.     

The crystal structure of a new high -Nd- concentration laser material: Na3Nd(PO4)2

The crystal structure of Na₃Nd(PO₄)₂ has been determined from three-dimensional Mo-Kα diffractometer data. The space group is Pbc2₁, the lattice constants are: $\text{a}\text{= 15.874(8)}\text{A}\text{?}$$\text{b}\text{= 13.952(8)}\text{A}\text{?}$$\text{c}\text{= 18.470(9)}\text{A}\text{?}$ and there are 24 formula units per unit cell, giving a Nd concentration of 5.8 10²¹cm^?3. The final R-factor with 2329 independent reflections is 0.060. The structure of Na₃Nd(PO₄)₂, very closely related to that of Na₃La(VO₄)₂, is made up of isolated PO₄ tetrahedra and of sodium and neodymium atoms arranged in an ordered way. The tripling of the a parameter results only from the distortion of the PO₄ tetrahedra. The NdO_y polyhedra are isolated from one another and the shortest Nd-Nd distance is 4.65 Å.     

Crystal chemistry of (Cd,Me)3(PO4)2 solid solutions

A number of solid solutions of $\text{Me}$₃(PO₄)₂ in Cd₃(PO₄)₂ have been prepared and equilibrated at 1070 K ($\text{Me}\text{=}\text{Mg, Mn, Fe, Co, Ni, Cu, Zn, or Ca}$). The respective ($\text{Cd}{}_{\mathrm{<mtext>1?</mtext><mtext>z</mtext>}}\text{Me}{}_{\mathrm{<mtext>z</mtext>}}\text{)}{}_3\text{(}\text{PO}{}_4\text{)}{}_2$ phases are either isotypic with β′-Cd₃(PO₄)₂ or with the mineral graftonite, both with five- and six- (or even seven)-coordinated cations. The monoclinic unit cell dimensions have been accurately determined from Guinier-Hägg photographs, and complete X-ray powder diffraction data are given for β′-Cd₃(PO₄)₂. The cell volumes are strongly correlated to the size and amount of incorporated $\text{Me}$²⁺ cation. The homogeneity regions and structures of the (Cd,$\text{Me}$)₃(PO₄)₂ phases, though, seem rather to be controlled by the $\text{Cd}{}^{\mathrm{2+}}\text{Me}{}^{\mathrm{2+}}$ cation ordering.     

Etude cristallochimique et dielectrique des oxyfluorures de terres rares Na4Ln(WNb2)O9F5

Six new compounds with formula Na₄Ln(WNb₂)O₉F₅ (Ln = Y, Nd, Eu, Gd, Dy, Lu) have been synthetized. The corresponding room temperature phases have a tetragonal symmetry and a chiolite-type structure. At low temperature a ferroelectric-paraelectric transition is detected for each compound. The Curie temperature increases with the size of the Ln³⁺ ion.     

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.     

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 and crystal chemistry of some rare earth vanadium (IV) pyrochlores (RE)2V2O7; RE = Lu,Yb, Tm,Lu1−xYx, Lu1−xScx

The preparation of the phases (RE)₂V₂O₇ where RE = Lu, Yb, Tm, and the solid solutions Sc_xLu_1?x (x = .10 → .50) and Y_xLu_1?x (x = .20 and .40), using a $\text{CO}\text{CO}{}_2$ buffer system are described. Precision lattice constants were determined and compared with previous work, finding good agreement with (1) but not with (2). The solid solution (Sc_xLu_1?x)₂V₂O₇ exists as a pyrochlore to x = .30, compared with x = .55 for the similar (Sc_xLu_1?x)₂ Ti₂O₇ system. Chemical analysis on the members x = .40 and x = .50 indicate significant amounts of V(III) and X-ray data show a diminishing intensity for the “ordering” reflections (h, k, l all odd). These results suggest that Lu(III), Sc(III), V(III) and V(IV) are partially disordered over both cation sites tending toward a C-type (RE)₂O₃ structure or a defect fluorite structure with increasing x.     

Hydrothermal phase equilibria studies in Ln2O3H2O systems and synthesis of cubic lanthanide oxides

Phase diagrams for the systems Ln₂O₃H₂O (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y) studied at 5000 to 10,000 psi and temperature range of 200–900°C, show that Ln(OH)₃ hexagonal and LnOOH monoclinic are the only stable phases from Nd to Ho. The cubic oxide phase (CLn₂O₃) is stable for systems of Er, Tm, Yb and Lu, with no evidence of its equilibrium in the systems of lighter lanthanides. Using strong acids, HNO₃ and HCOOH, as mineralisers the cubic oxides could be stabilised from Eu down to Lu. Solid solution phases of CeO₂Y₂O₃ and Eu₂O₃Y₂O₃ have also been synthesised with HNO₃ as mineraliser, since these compounds have promising use as solid electrolyte and phosphor materials respectively.     

Crystal growth and precision lattice constants of some Ln2(WO4)3-type rare earth tungstates

Single crystals of the title compounds with Ln = La, Ce, Pr, Nd, Sm, and Eu have been grown by the Czochralski technique, and their cell parameters and melting points were determined accurately. All compounds crystallize in the prototype $\text{C}\text{2}\text{c}$ symmetry, and apparently only La₂(WO₄)₃ exhibits a phase transition between room temperature and the melting point. Cell volumes vary linearly with (ionic radius)³.     

Crystal data on ytterbium chlorosilicate,Yb3(SiO4)2Cl

Ytterbium chlorosilicate, Yb₃(SiO₄)₂Cl, was obtained in the form of single crystals up to 1.5 × 1.5 × 0.5 mm³ as by-product of the synthesis of ytterbium oxychloride. The compound has orthorhombic symmetry (space group Pnma - D_2h¹⁶). The unit cell parameters are: $\text{a}\text{= 6.753}\text{A}\text{?}\text{, b}\text{= 17.583}\text{A}\text{?}\text{, c}\text{= 6.137}\text{A}\text{?}$. The substance is characterized by means of morphology and X-ray powder data.     

Une structure derivee de celle du spinelle la structure de Fe0.76 Yb2.16 S4

Single crystals of so-called “FeYb₂S₄ spinel” were prepared and their crystal structure was solved. The cubic cell, space group Fd3m, has a lattice constant $\text{a}\text{= 10.69}\text{A}\text{?}$. From X-rays determinations, its content is (Fe_0.76 Yb_2.16 S₄) × 8. Iron is divalent and ytterbium is trivalent. Ytterbium is in two series of octahedral sites, which are partially filled : 0.96 Yb and 0.04 ? on every 16d position, 0.12 Yb and 0.88 ? on every 16c position. Only 0.76 iron atom is in every 8a position of the spinel.     

The cation distribution between five- and six-coordinated sites in some (Mg,Me)3(PO4)2) solid solutions

Approximate homogeneity ranges at about 1073 K have been determined for some (Mg,$\text{Me}$)₃(PO₄)₂ solid solutions. X-ray powder diffraction data are given and the observed changes in unit cell dimensions are discussed. The Mg₃(PO₄)₂ structure, isotypic with γ-Zn₃(PO₄)₂, contains five- and six-coordinated cation sites, M1 and M2 respectively. The M1 site preference order is Zn²⁺ > Co²⁺ > Fe²⁺ > Mg²⁺ > Mn²⁺.     

Preparation and properties of the Pb3(VO4)2Pb3(PO4)2 system

Single crystals of the pseudobinary system Pb₃(V_1?xP_xO₄)₂ were grown via the Czochralski technique and were studied over wide ranges of x, particularly with regard to the influence of substitution on the $\text{3}\text{?}\text{mF}\text{2}\text{m}$ transition as a function of temperature.