Sodium deintercalation from α-NaFeO2

Chemical deintercalation was investigated on α-NaFeO₂ using bromine as oxidizing agent. The product had a composition about Na_0.9FeO₂ keeping the host layer structure as it was. The crystal lattice was hexagonal and the lattice parameters were $\text{a}\text{=2.997}\text{A}\text{?}$, $\text{c}\text{=16.32}\text{A}\text{?}$. Mössbauer spectrum showed the presence of Fe⁴⁺ in the product. Electrical resistivity was higher than 10⁸Ωcm at room temperature. Na_0.9FeO₂ decomposed to a mixture of α-NaFeO₂ and Fe₃O₄-like ferromagnetic materials above 130°C.     

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.     

Fluorite-related phases in the system CaO-HfO2

Three ordered fluorite-related phases which occur in the system CaOHfO₂ are described. Ca₂Hf₇O₁₆ (Ø) is rhombohedral, with $\text{a}\text{= 9.527}\text{A}\text{?}\text{, α = 38.80°}$. CaHf₄O₉ (Ø₁) is monoclinic, with $\text{a}\text{=17.698,}\text{b}\text{= 14.500,}\text{c}\text{= 12.021}\text{A}\text{?}\text{, β = 119.47°}$. Ca₆Hf₁₉O₄₄ (Ø₂) is rhombohedral, with $\text{a}\text{= 12.059}\text{A}\text{?}\text{,}\text{α}\text{= 98.31°}$.     

Proche environnement du fer et conductivite electrique de verres du systeme Na2O|SiO2|Fe3O4Iron environment and electrical conductivity of glasses in the Na2O|SiO2|Fe3O4 system

Glasses have been synthesized in the system x Fe₃O₄ (1?x) (0.33 Na₂O–0.67 SiO₂). The different valence ratios and coordinations of iron (II) and iron (III) have been determined by Mössbauer spectroscopy. A limitation of Fe(III) in tetrahedral sites seems to appear at 0.2 $\text{Fe}{}_{\mathrm{Td}}\text{Na}$. Electrical conductivity measurements have been performed, using complex impedance spectroscopy. The results are compared with glasses of the systems Al₂O₃|Na₂O|SiO₂ and Na₂O|SiO₂. It is shown that Fe₂O₃ plays a role closer to SiO₂ than to Al₂O₃.     

A series of rare earth silicates RE3+2M3+[SiO4]2 (OH)

A series of isotypic silicates of composition RE₂M[SiO₄]₂ (OH) with RE = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, and M = Al³⁺, Fe³⁺ has been synthesized under hydrothermal conditions. Lattice constants of two members as determined from single crystal X-ray diffraction data are: La₂Al[SiO₄]₂ (OH) (La₂Fe[SiO₄]₂ (OH)) $\text{a}{}_{\mathrm{o}}\text{= 7.401 (7.346)}\text{A}\text{?}$, $\text{b}{}_{\mathrm{o}}\text{= 5.702 (5.862)}\text{A}\text{?}$, $\text{c}{}_{\mathrm{o}}\text{= 17.072 (97.196)}\text{A}\text{?}$, gb = 112.4 (112.5°), $\text{P}\text{2}{}_1\text{c}$, Z=4.     

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.     

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.     

Fluorite related ordered compounds in the ZrO2CaO and ZrO2Y2O3 systems

ZrO₂:CaO and ZrO₂:Y₂O₃ systems have been examined for possible ordered compounds. Fluorite related ordered compounds CaZr₄O₉ and Zr₃Y₄O₁₂ have been successfully prepared and identified. While it is believed that the former is monoclinic with $\text{a}\text{= 17.813 ± 0.005}\text{A}\text{?}$, $\text{b}\text{= 14.612 ± .004}\text{A}\text{?}$, $\text{c}\text{= 12.065 ± .003}\text{A}\text{?}$ and β = 119.5 ± .02° and isostructural with CaHf₄O₉, the latter appears to be isostructural with M₇O₁₂ type of compounds with $\text{a}\text{= 9.723 ± .001}\text{A}\text{?}$ and $\text{c}\text{= 9.090 ± 0.002}\text{A}\text{?}$, which is formed commonly in compounds containing tri and tetravalent cations and is characterized by a chain oxygen vacancy along a 〈111〉 of the original fluorite. No other fluorite related ordered compound could be detected in these systems.     

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).     

La structure cristalline de Ca4Fe9O17: Des feuillets “hexagonaux” d'octaedres FeO6 et de bipyramides FeO5 lies par des tetraedres FeO4

The new calcium ferrite Ca₄Fe₉O₁₇, belonging to the CaFe_2+nO_4+n family ($\text{n}\text{=}\text{1}\text{4}$), has not the same stacking process of “FeO” blocks in “CaFeO₄” blocks, as the others terms of the series.It crystallizes in the monoclinic system, space group C2 with the parameters: $\text{a}\text{= 10,441}\text{A}\text{?}$, $\text{b}\text{= 6,025}\text{A}\text{?}$, $\text{c}\text{= 11,384}\text{a}\text{?}$ and β = 98°80. Its structure is characterized by the presence of iron atoms in oxygen octahedra and trigonal based bipyramides stacking in hexagonal layers along $\text{c}$.These layers are linked by iron atoms on tetrahedral sites. Calcium atoms are hexagonaly located around each tetrahedron.     

The many phases of HUP, (UO2)[HPO4] · 4H2O. An electron-optical investigation

The prompt recrystallization of the tetragonal phyllophosphate HUP, (UO₂)[HPO₄] · 4H₂O, when rinsed with distilled water at ambient temperature, has been studied by TEM, SEM and SAD. In course of the rinsing process, to remove excess phosphorous acid, HUP underwent an orthorhombic phase change, which produced two orthorhombic phases O₁ and O₂. O₁ has $\text{a = 7.6(3)}\text{A}\text{?}$, $\text{c = 7.0(4)}\text{A}\text{?}$, and 001 absent for l odd. O₂ has $\text{a = 7.3(2)}\text{A}\text{?}$, $\text{c = 6.8(2)}\text{A}\text{?}$ and no systematic absent reflections. O₁ and O₂ are metastable and by spinodal decomposition modulate into monoclinic phases through a string of intermediate and disordered phases with the β-angle increasing from 90.0° (orthorhombic phases) to 91.3(3)°, 95(2)° and 97.7(2)° for M_2.2, M_2.1, and M_1.1 respectively, where M_1.1 is the monoclinic derivative ($\text{a = 6.9(4)}\text{A}\text{?}$, $\text{c = 6.4(4)}\text{A}\text{?}$, β = 97.7(3)°) of O₁ and M_2.1 ($\text{a = 7.3(4)}\text{A}\text{?}$, $\text{c = 12.1(3)}\text{A}\text{?}$, β = 95(2)°) together with M_2.2 ($\text{a = 14.22(4)}\text{A}\text{?}$, $\text{c = 13.08(4)}\text{A}\text{?}$, β = 91.3(3)°) are the derivatives of O₂. The crystallographic b axis could not be determined. All the abovementioned phases exhibit a striking epitaxial relationship which presumably gives the clue to the fact that these phase findings are at variance with X-ray findings given in literature. It is suggested that the phases are isomeric polymorphs of HUP.     

Alkali ion exchange reactions with RbA1SiO4: A new metastable polymorph of KA1SiO4

A new metastable polymorph of KA1SiO₄ has been prepared by K⁺ ion exchange of orthorhombic RbA1SiO₄ (a=9.215±.001, b=5.329±.001, $\text{c}\text{=8.742±.001}\text{A}\text{?}$). The new phase is pseudo-orthorhombic with a=18.151±.003, b=10.551±.002, $\text{c}\text{=8.490±.001}\text{A}\text{?}$ with apparent Cc★★ symmetry but may be monoclinic. This new polymorph is metastable at temperatures up to approximately 1100°C where it transforms to normal “low” orthorhombic KA1SiO₄.     

Syntheses and magnetic properties of Eu3B2O6 and Sr3B2O6

Europium orthoborate and strontium orthoborate crystallize in the rhombohedral system with two formula units in a cell of dimensions $\text{a}{}_{\mathrm{R}}\text{=6.697}\text{A}\text{?}$, α_R=85.17° for Eu₃B₂O₆, and $\text{a}{}_{\mathrm{R}}\text{=6.695}\text{A}\text{?}$, α_R=85.00° for Sr₃B₂O₆. The equivalent hexagonal lattice parameters are $\text{a}{}_{\mathrm{H}}\text{=9.069}\text{A}\text{?}$, $\text{c}{}_{\mathrm{H}}\text{=12.542}\text{A}\text{?}$, and $\text{a}{}_{\mathrm{H}}\text{=9.046}\text{A}\text{?}$, $\text{c}{}_{\mathrm{H}}\text{=12.566}\text{A}\text{?}$ respectively. Eu₃B₂O₆ appears to be ferromagnetic below 7.5K.     

Preparation and structure of EuIINb4O11

The occurrence of compound in the system has been studied by means of X-ray powder diffraction. A compound, Eu^IINb₄O₁₁, was found. The X-ray powder diffraction data for Eu^IINb₄O₁₁ could be indexed on a tetragonal cell with $\text{a}\text{=52.52}\text{A}\text{?}$, $\text{C}\text{=7.69}\text{A}\text{?}$. The temperature dependence of the magnetic susceptibility for this compound is expressed by the equation, $\text{X}{}_{\mathrm{M}}\text{=}\text{7.10}\text{(}\text{T}\text{+0.20)}$. This compound is oxidized at about 290°C or above in air.     

Structure cristalline de Mn0, 4Er4, 6S7

The crystal structure of Mn₀, ₄Er₄, ₆S₇ ($\text{a}\text{= 12,573 (4)}\text{A}\text{?}$, $\text{b}\text{= 11,390 (4)}\text{A}\text{?}$, $\text{c}\text{= 3,777 (4)}\text{A}\text{?}$, γ = 105,45°, space group B2/m, Z = 2) has been refined by a least square method to a final R = 0,045, with 1431 independant reflections. The octahedral positions are occupied either by Er and Mn atoms or by Er atoms only and the prismatic sites by Er atoms.     

Nouvelles phases multiples obtenues par intercroissance des reseaux “M6X4O26” et “M8O21”: Les oxydes K10(M8O21)2·M6X4O26

New oxides K₁₀(M₈O₂₁)₂·M₆X₄O₂₆ (M = Nb, Ta; X = Si, Ge) were synthesized. These compounds were investigated by electron diffraction and microscopy, the symmetry is hexagonal, space group P62m, with $\text{a}\text{? 9}\text{A}\text{?}$, $\text{c}\text{? 20}\text{A}\text{?}$. They show an intergrowth of two structural types: (M₈O₂₁) and (M₆X₄O₂₆) layers. Results of structural study by X-ray powder diffraction are discussed in terms of the stabilization of A₃M₈O₂₁ and A_6?xM₆Si₄O₂₆ structures.     

Etude des transformations allotropiques de Mg2NiH4

Three allotropic varieties of Mg₂NiH₄ with monoclinic, orthorhombic and cubic symmetry have been identified. The unitcell dimensions are : $\text{a}\text{= 12.99}\text{A}\text{?}$, $\text{b}\text{= 6.390}\text{A}\text{?}$, $\text{c}\text{= 6.598}\text{A}\text{?}$ and $\text{β = 93.22}\text{A}\text{?}$ for the monoclinic form. The orthorhombic structure whose parameters are : $\text{a}\text{= 6.499}\text{A}\text{?}$, $\text{b}\text{= 6.415}\text{A}\text{?}$ et $\text{c}\text{= 6.589}\text{A}\text{?}$, represents a slight distortion from the cubic one. Under pressure, an irreversible transformation from the monoclinic to the cubic variety has been observed. The transition temperature is 245°C at 1 bar. On the other hand, the orthorhombic form transforms reversibly into the cubic one about 235°C under 1 bar pressure. The orthorhombic-monoclinic transition occurs only at very high pressure.     

New tetrahedrally coordinated A2CdBr4 compounds (A = Cs,CH3NH3)

(CH₃NH₃)₂CdBr₄ and Cs₂CdBr₄ are two compounds with a tetrahedral CdBr₄-coordination. Their room temperature structures are determined. (CH₃NH₃)₂CdBr₄: monoclinic, $\text{P}\text{2}{}_1\text{c}$, $\text{a}\text{= 8.1227(13)}\text{A}\text{?}$, $\text{b}\text{= 13.4355(16)}\text{A}\text{?}$, $\text{c}\text{= 11.4194(13)}\text{A}\text{?}$, β = 96.194(11) °, z = 4. Cs₂CdBr₄: orthorhombic, Pnma, $\text{a}\text{= 10.235(5)}\text{A}\text{?}$, $\text{b}\text{= 7.946(3)}\text{A}\text{?}$, $\text{c}\text{= 13.977(5)}\text{A}\text{?}$, z = 4.     

CuTa2O6 - crystal growth and characterization

The compound CuTa₂O₆ has been prepared as crystals from a Cu/O melt and found to be tetragonal ($\text{a}\text{= 7.510}\text{A}\text{?}$, $\text{c}\text{= 7.526}\text{A}\text{?}$) rather than cubic as reported in the literature. The coefficient of thermal expansion between room temperature and 1000°C was found to be 8.0 × 10^?6°C^?1. Electrical resistivity measurements on a crystal showed semiconductor behavior between room temperature ($\text{? = 2 × 10}{}^3\text{Ω}\text{cm}$) and 140°K ($\text{? = 7 × 10}{}^6\text{Ω}\text{cm}$) with an activation energy of E_A = 0.2 eV. Magnetic measurements between 4.2°K and room temperature showed Curie-Weiss behavior with a change in μeff at 120°K. For T>120°K, μeff = 1.76μ_B and θ_p = 0°K while for T<120°K μeff = 1.91 μB and θ_p = ?15°K.