A high resolution dilatometer for in situ studies of the electrointercalation of layered materials

A dilatometer with an estimated resolution of ?25 nm is described which allows a continuous recording of the crystal expansion during electrointercalation of layered materials. We report on two examples: the galvanostatic intercalation of $\text{HSO}{}_4{}^{\mathrm{?}}\text{H}{}_2\text{SO}{}_4$ into graphite and $\text{K}{}^{\mathrm{+}}\text{H}{}_2\text{O}$ into 2HTaS₂. In the graphite system, the dilatometer record confirms the pronounced staging phenomenon, whereas for TaS₂ no higher than a second stage shows up. For both systems, the overall behaviour of the crystal expansion during intercalation suggests that no coherent intercalation front exists. In the case of TaS₂ with a rather high stacking fault density in situ dilatometry turns out to be ideally suited for the investigation of the intercalation mechanism.     

Stability of the perovskite phase LaBO3 (B = V,Cr, Mn,Fe, Co,Ni) in reducing atmosphere I. Experimental results

The chemical stability of perovskites LaBO₃ where B = V, Cr, Mn, Fe, Co, Ni was studied by thermogravimetry at 1000°C in gas mixtures of $\text{CO}{}_2\text{H}{}_2$, $\text{O}{}_2\text{CO}{}_2$ and $\text{O}{}_2\text{Ar}$ at 1 bar.The stability limits of the perovskite phases expressed in terms of -log Po₂★ (Po₂★ = critical oxygen partial pressure in bar) were for LaCrO₃ and LaVO₃ (greater than 21.1), LaFeO₃ (16.95), LaMnO₃ (15.05), LaCoO₃ (7.0) and for LaNiO₃ (～0.6). The changes in standard enthalpy ΔH° and entropy ΔS° of the following reactions were obtained.$\text{LaVO}{}_4\text{=}\text{LaVO}{}_3\text{+}\text{1}\text{20}{}_2\text{δ=328}\text{kJ}\text{mol}\text{°=135}\text{J}\text{mol·deg.}$,$\text{LaMnO}{}_3\text{=}\text{1}\text{2}\text{La}{}_2\text{O}{}_3\text{+}\text{MnO}$     

Growth of Ca3Fe2Ge3O12 and Ca3Fe(Al,Cr) Ge3O12 garnets in molten bismuth germanate glasses

Additions of Fe₂O₃ to CaO·Bi₂O₃·2 GeO₂ cause Ca₃Fe₂Ge₃O₁₂ garnets to precipitate from the resultant melt at 1250°C. Garnets with the composition Ca₃Fe(Al, Cr) Ge₃O₁₂ are also precipitated by adding either $\text{Al}{}_2\text{O}{}_3\text{Fe}{}_2\text{O}{}_3$ or $\text{Cr}{}_2\text{O}{}_3\text{Fe}{}_2\text{O}{}_3$ mixtures. The well-formed crystals range from several to 100 μm in size and are obtained in 50 to 70% yields at $\text{Fe}\text{Bi}\text{= 0.4}$. Additions of Fe₂O₃ (up to $\text{Fe}\text{Bi}\text{= 1.0}$) to compositions containing ZnO, CdO, SrO, and BaO yield only dark glasses. The physical properties of these glasses suggest that Fe(III), in contrast to AL(III) & Ga(III), prefers octahedral coordination.     

Growth of YFe2O4 single crystals by floating zone method

The first successful growth of YFe₂O₄ single crystals was carried out by the floating zone method. The atmosphere to give suitable oxygen partial pressures for the crystal growth of YFe₂O₄ was determined. The mixtures of CO₂ and H₂ with the mixing ratio ranging over $\text{CO}{}_2\text{H}{}_2\text{= 0.65 – 0.95}$, or the equivalent CO₂CO mixtures, and the growth speed of 2 mm/hour or slower were found to be the essential conditions. The as-grown boules were aggregates of large single crystal grains with the c-axes perpendicular to the growth direction. A typical separated single crystal was a rectangular chip of 3mm × 1.5mm × 0.5mm. A slower growth speed is suggested for obtaining a bigger single crystal.     

Isomorphous substitution of silicon in the erionite-like structure AIP04-17 and acidity of SAPO-17

$\text{AlP0}{}_4\text{SAPO-17}$ samples were prepared and characterized by X-ray diffraction, adsorption isotherms, light/electron microscopy, adsorption calorimetry, temperature-programmed NH₃ desorption, and i.r. spectroscopy. Especially, the isomorphous substitution of silicon was studied, and the number of generated Bronsted centers was determined from the NH₃ chemisorption. It was found that the number of bridging hydroxyls generated by monomeric incorporation of silicon is limited strictly to one atom per unit cell. When the $\text{SiO}{}_2\text{Al}{}_2\text{0}{}_3$ ratio in the reaction mixtures is higher than 0.1, the main part of silicon is incorporated in the erionite-like structure as polymeric species.     

Les oxydes ATiMO5 : Echangeurs cationiques

The ion-exchange properties of the ATiMO₅ oxides (M = Ta, Nb), with a layer structure, are shown for the first time. By action of an acid solution on the ATiMO₅ compounds, the HTiMO₅ oxides were synthesized. The ion-exchange properties of the HTiMO₅ compounds were used to prepare new oxides which could not be obtained by direct action of the oxides - Tl Ti TaO₅, NH₄ Ti MO₅ - and hydrated compounds - ($\text{Na}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{(}\text{H}{}_3\text{O}\text{)}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$) TiMO₅.H₂O, ($\text{Li}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{(}\text{H}{}_3\text{O}\text{)}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$) $\text{TiMO}{}_5\text{.}\text{4}\text{3}\text{H}{}_2\text{O}$. The reversibility of the exchange properties was observed in every case. The crystallographical properties of these oxides were determined and discussed.     

Verres fluores au tetrafluorure de zirconium proprietes optiques d'un verre dope au Nd3+

Glass formation has been observed in the ZrF₄BaF₂NaF system around the composition 50 % ZrF₄, 25 % BaF₂, 25 % NaF. A Nd³⁺ doped glass obtained by dissolving NdF₃ in the previous material has been studied. Absorption spectra in the region ${}^4\text{I}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{→}{}^2\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, I.R. fluorescence spectra and lifetime measurement of the ${}^4\text{F}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ level show a good protection of Nd³⁺ against the fluorescence quenching.     

New phase with K2NiF4 structure in the LaLiFeO system

The existence has been proved, for the first time, in the LaLiFeO system of the phase (La_1.75Li_.25) (Fe_.5Li_.5)O_4?x with tetragonal symmetry ($\text{a}{}_{\mathrm{o}}\text{=3.765±0.001}\text{A}\text{?}$; $\text{c}{}_{\mathrm{o}}\text{=12.918±0.01}\text{A}\text{?}$; $\text{c}{}_{\mathrm{o}}\text{a}{}_{\mathrm{o}}\text{=3.43}$) and K₂NiF₄-type structure.This phase gives probably the first example of lithium distribution in both A and B sites of A₂BO₄-type mixed oxides. The high $\text{c}{}_{\mathrm{o}}\text{a}{}_{\mathrm{o}}$ ratio suggests a strong elongation of FeO₆ octahedra induced by a high spin Fe(IV) d⁴ configuration. The results of structural studies and of Mössbauer analysis, confirming the above conclusions, are reported.     

Nonstoichiometry and phase transition in NdMnO3

The nonstoichiometry of neodymium manganite NdMnO₃ phase has been studied by a gravimetric method at 1273 K. The oxygen partial pressures were controlled by using flowing $\text{O}{}_2\text{Ar}$ or $\text{H}{}_2\text{CO}{}_2$ mixtures. The existence of hyperstoichiometric phase and the homogeneity range of the phase NdMnO_3+x from x = 0 to 0.065 at 1273 K under various oxygen partial pressures has been revealed. And also the effect of oxygen nonstoichiometry on the phase transition at high temperature has been studied by electrical conductivity and DTA measurements. The transition temperature decreases with increasing oxygen content.     

Hydrothermal synthesis of zeolites from rhyolitic pumice of different geological origins

Twelve samples of rhyolitic pumice from widely different origins were subjected to zeolitization in standard hydrothermal conditions (solid/liquid ratio, $\text{1}\text{5}$; T, 95°C; reaction time, 5 h; alkaline solution 5 N NaOH). The $\text{Si}\text{Al}$ ratio of the starting material was of special importance in that zeolites formed with $\text{Si}\text{Al}$ ratios similar to or smaller than that of the parent material. Pumice with low $\text{SiO}{}_2\text{Al}{}_2\text{O}{}_3$, and high Fe content, preferentially gave rise to zeolites with lower $\text{SiO}{}_2\text{Al}{}_2\text{O}{}_3$ ratio than in the case of lower Fe and higher $\text{SiO}{}_2\text{Al}{}_2\text{O}{}_3$ ratio.     

X-ray study of the deficient perovskite La23TiO3

The A-site deficient perovskite $\text{La}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{TiO}{}_3$ was synthesized under the controlled atmosphere of CO₂H₂ mixed gas at 1350°C, and the structure was investigated by the powder X-ray diffraction method. The product is slightly oxygen deficient ($\text{La}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{TiO}{}_{\mathrm{3?\lambda }}$, where 0.007 ≦ λ ≦ 0.079), and the structure is dependent on λ: when λ is small, the perovskite cell is distorted to orthorhombic symmetry and the unit cell is doubled along the c′ (> b′, a′) axis, while a cubic perovskite structure is facilitated with the increase of λ. A structural model, which calls for an ordered arrangement of the A-site vacancies along the c′-axis, is proposed and its order parameter is calculated from the intensities of the superstructure lines.     

Preparing new extremely difficult-to-form crystal structures

Simple ways have been found to prepare CaTi₃Al₈O₁₉ and LaTi₂Al₉O₁₉ as prototypes of difficult-to-prepare compounds. The structures are monoclinic with very large unit cells. The new technique has been successfully tried on $\text{Na}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{Ca}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{Al}{}_{11.5}\text{Ti}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{O}{}_{19}$.     

The low temperature magnetic properties of austenitic Fe-Cr-Ni alloys: 2. The prediction of Néel temperatures and maximum susceptibilities

The compositional dependence of the Néel temperature has been studied, from data derived by different techniques and by various authors, for 30 austenitic stainless steels or special Fe-Cr-Ni alloys whose compositions fall near the range of the AISI 300 series. A linear relationship enables the predicted Néel temperature, T_N to be evaluated with an rms deviation of 3.5 K on the basis of the wt % of alloy constituents. The effect of alloying elements in lowering $\text{T}{}_{\mathrm{N}}{}^1$ increases in the order Cr, Ni, Mo, and Si, while Mn is unique in raising $\text{T}{}_{\mathrm{N}}{}^1$. By comparing this equation for $\text{T}{}_{\mathrm{N}}{}^1$ with previous equations to predict the onset of a martensitic phase change at a temperature M_s, it is concluded that isotherms for M_s in ternary Fe-Cr-Ni alloys should also be parallel to the tangent to the boundary between fcc and bcc phases calculated from thermodynamic data. This conclusion throws doubt on the applicability of the Eichelman and Hull equation to the 300 series of stainless steels. If γ phase stability is achieved by adding Cr, Ni, Mo, or Si, the alloys are likely to be ferromagnetic at low temperatures, but if structural stability is due to C, N, or Mn, then the alloys should be antiferromagnetic or superparamagnetic. A logarithm plot of the maximum initial susceptibility versus Ni content can be used to estimate X_v max in the AISI 300 series stainless steels. This relationship does not apply to alloys with Mn > 2 wt %, but in these the value of X_v max is lowered. The significance of these observations is discussed in terms of the application of stainless steel in magnetic environments at low temperatures.     

Spectres vibrationnels,transitions electroniques et structures a courtes distances dans les verres: Sulfures de terres rares - sulfure de gallium

Absorption spectra of chalcogenide glasses of general formula Ln₂S₃-1,8 Ga₂S₃ (Ln = La⁺³, Ce⁺³, Pr⁺³, Nd⁺³, Gd⁺³ were investigated continously from far infrared to ultra-violet region. Raman spectra were recorded in the 5cm^?1–600 cm^?1 range. Vibrational spectra of glasses have been compared to those of polycrystalline compounds $\text{Ln}{}_{\mathrm{<mtext>10</mtext><mtext>3</mtext>}}\text{Ga}{}_6\text{S}{}_{14}$ (Ln = La⁺³, Ce⁺³) and $\text{Ln}{}_6\text{Ga}{}_{\mathrm{<mtext>10</mtext><mtext>3</mtext>}}\text{S}{}_{14}\text{(}\text{Ln = La}{}^{\mathrm{+3}}\text{to Gd}{}^{\mathrm{+3}}\text{)}$.From the observed spectra it could be concluded that the short distance order around gallium atom is strongly modified in going from crystalline to glassy state.Electronic transitions of Ce⁺³, Pr⁺³ and Nd⁺³ ions have been also identified in the visible region and in the mid infrared absorption spectra.     

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.     

Un nouveau conducteur protonique [H(H2O)n]12Sb12O36 (n ⩽ 1)

Single crystals of K₁₄Sb₁₂O₃₆F₂ undergo rapid ion exchange in 9N sulfuric acid to produce “hydronium” compound (H(H₂O)_n)₁₂Sb₁₂O₃₆ (n ? 1). Between 30 and 140°C this phase undergoes a partial and reversible dehydratation in which approximately 85 % of its “H₃O⁺” content is converted to H⁺.The structures of hydrated and dehydrated phases have been refined by full-matrix least squares, respectively to factor R = 0.030 and 0.047. The conductivity of $\text{(H(H}{}_2\text{O)}{}_{\mathrm{<mtext>n</mtext>}}\text{)}{}_{12}\text{Sb}{}_{12}\text{O}{}_{36}\text{(σ}{}_{20}\text{? 1O}{}^7\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$) increases in an Arrhenius relationship with an activation energy of 8.8 kcal.mole^?1, the dehydrated compound (H(H₂O)_0.33)₁₂Sb₁₂O₃₆ has a much lower conductivity but the same activation energy.     

Acceleration effect of hydrogen storage alloys for the catalytic dehydrogenation of cyclohexane

The dehydrogenation of cyclohexane was carried out at temperatures between 120 and 200°C over the mixture of a $\text{Pt}\text{Al}{}_2\text{O}{}_3$ catalyst and a hydrogen storage alloy in order to test the function of the alloy for the acceleration of the dehydrogenation reaction at lower temperatures. Among the alloys examined (iron-, nickel- and magnesium-based alloys), CaNi₅ showed the highest acceleration effect. The higher the initial rate of hydrogen absorption, the higher the acceleration effect of the alloy. The effect decreased with time, but was recovered when the gaseous phase was purged with nitrogen at 150°C. No catalytic activity was observed on the alloys. The effect was much higher at lower temperatures.     

Structural changes with composition and temperature in rhombohedral Li1−xHxNbO3

Polycrystalline Li_1?xH_xNbO₃ (0.07≤x≤0.87) has been prepared by exchange of LiNbO₃ in benzoic acid/lithium benzoate and $\text{Mg}\text{(}\text{NO}{}_3\text{)}{}_2\text{·6}\text{H}{}_2\text{O}\text{LiNO}{}_3$ melts. X-ray diffraction measurements for these materials show complex structural behavior, with three distinct rhombohedral (LiNbO₃ structure) phases in the range x≤0.75. Samples with 0.65<x<0.75 were found to undergo a reversible phase transition at ～ 150°C. These results explain why proton-exchanged LiNbO₃ waveguides made in neat benzoic acid are prone to refractive index instabilities, and show how such problems can be avoided by limiting the maximum value of x in the guides.     

Crystal structure and fluorescence lifetime of NdAl3(BO3)4, a promising laser material

The structure of NdAl₃(BO₃)₄, determined by single-crystal x-ray analysis, is rhombohedral with space group R32 and cell parameters $\text{a}\text{= 9.3416 (6)}\text{A}\text{?}$, $\text{c}\text{= 7.3066 (8)}\text{A}\text{?}$, Z = 3. A full-matrix, least-squares refinement gives R = 0.033 and R_w = 0.037. The Nd atoms, Al atoms and B atoms occupy trigonal prisms, octahedra, and triangles of oxygen, respectively. Edge-shared Al octahedra form helices along the c-axis. These helices are connected by isolated B triangles and isolated Nd trigonal prisms. The fluorescence lifetime of the ${}^4\text{F}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{→}{}^4\text{I}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ transition of Nd⁺³ is reported for the system Nd_xGd_1?xAl₃(BO₃)₄. The lifetime of NdAl₃(BO₃)₄ is 19us, and concentration quenching is reduced in the series, as happens in NdNa₅(WO₄)₄ (85μs) and NdP₅O₁₄ (115μs). The shorter lifetime is attributed to noncentrosymmetry; the reduced concentration quenching to isolation of Nd polyhedra.