Mass spectrometry of a silane glow discharge during plasma deposition of a-Si: H films

We undertook a mass spectrometric investigation of the ionic and neutral species present during the deposition of a-Si: H using an r.f. glow discharge in silane (mixed with helium or hydrogen). A correlation between the neutral composition of the plasma and the nature of the IR vibrational modes in the deposited film is proposed. The ionic species extracted from the silane discharge are not characteristic of the direct ionization of SiH₄. The predominance of the SiH₃⁺ ion is attributed to the ion-molecule reaction $\text{SiH}{}_2{}^{\mathrm{+}}\text{+ SiH}{}_4\text{→ SiH}{}_3{}^{\mathrm{+}}\text{+ SiH}{}_3$ Secondary ions Si₂H_n⁺ (n = 1?7) are also observed. Mass spectrometry of the ionic species resulting from the interaction of a hydrogen plasma with the a-Si: film suggests that atomic hydrogen plays an active role during the growth of the film.     

The precipitation and characterization of cobalt (II) oxalate tetrahydrate

Mixing of solutions of Co²⁺ and C₂O₄^2? ions can lead to crystallization of cobalt (II) oxalate both as a tetrahydrate and a dihydrate. Up to about 60°C acicular crystallites of a greyish pink tetrahydrate initially result. In a period depending mainly on the temperature and to a lesser extent on the degree of supersaturation and the $\text{[}\text{C}{}_2\text{O}{}_4{}^{\mathrm{2?}}\text{]}\text{[}\text{Co}{}^{\mathrm{2+}}\text{]}$ ratio, the precipitated tetrahydrate recrystallizes to β-cobalt (II) oxalate, a bright pink dihydrate. The two cobalt (II) oxalates have been distinguished by means of X-ray diffraction (XRD), (electron)microscopy and thermal analysis. The d-values and relative peak heights of the most pronounced maxima of the XRD-pattern of the tetrahydrate are presented, as these are not available in standard reference works.     

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.     

High temperature standard gibbs free energy determinations for Co-o systems by e.m.f. measurements. A statistical approach to evaluate the reliability of the current methods

The standard Gibbs free energies of the following reactions: $\text{Co +}\text{1}\text{2}\text{O}{}_2\text{? CoO}$ (1) and $\text{3CoO +}\text{1}\text{2}\text{O}{}_2\text{? Co}{}_3\text{O}{}_4$ (2) have been calculated from the e.m.f. measurements carried out using a simple compartment solid state galvanic cell, as well for the reaction: 3Co + 20₂ ? Co₃O₄ (3) The temperature-equilibrium oxygen partial pressure relationship has been evaluated. A phase diagram for Co, CoO and Co₃O₄ is proposed in the temperature range 600–900 °C. A statistical analysis on reported ΔG_f⁰ values at 1100 K for reaction (1) has been performed and the results are discussed.     

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.     

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.     

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.     

Oxidation-reduction reactions of CeMO4+x (M = Ta or Nb) phases

Phase equilibrium methods, single crystal and powder x-ray diffraction analyses, thermogravimetric analysis and magnetic susceptibility measurements were utilized to define subsolidus phase relations $\text{in air}$ for the systems cerium oxide - Ta₂O₅ and cerium oxide - Nb₂O₅. Stoichiometric CeTaO₄ is stable in air (P_O2 = 0.21 atm) only above 1265°C. At 1265°C, the reversible reaction, $\text{3}\text{CeTaO}{}_4\text{+}\text{1}\text{2}\text{?}$CeTa₃O₉ + 2CeO₂ is established. If CeTaO₄ is quenched to room temperature and $\text{reheated}$ below 1000°C, or, if the material is rapidly cooled from above 1265°C to below 1000°C it absorbs oxygen according to, . The x parameter is variable and temperature dependent. Using a thermal microbalance, three distinct complex reaction series involving a homogeneity range in x were established, (a) 0.50 ≥ × ≥ 0.48 (<350°–600°C), (b) 0.17 ≥ × ≥ 0.06 (600°–950°C), (c) 0.40 ≥ × ≥ 0.34 (950°-room temperature). CeNbO₄ (not isostructural with CeTaO₄) also absorbs oxygen below ≈700°C in air to yield CeNbO_4+x materials.     

Crystal chemistry of lithium in octahedrally coordinated structures III. A new structure-type in the system K2O:Li2O:TiO2 (KxLixTi4−x2O8)

A new compound in the system K₂O:Li₂O:TiO₂ corresponding to the formula $\text{K}{}_{\mathrm{<mtext>x</mtext>}}\text{Li}{}_{\mathrm{<mtext>x</mtext>}}\text{Ti}{}_{\mathrm{<mtext>4?</mtext><mtext>x</mtext><mtext>2</mtext>}}\text{O}{}_8$ was found to be orthorhombic with a=3.821, b=15.921, c=2.973A space group Cmcm. The similarity between this unit cell and those of Rb_xMn_xTi_2?xO₄ and FeO(OH) has been used to predict the structure of this new phase. From the composition of this phase and that of the hollandite and ramsdellite phases in this system, it can be deduced that some of the Li⁺ ions occur in the tunnels as well as in octahedral coordination substituting for titanium.     

Luminescence of some oxygen-octahedric ferroelectrics exposed to an electron beam

Spectral and temperature dependence of cathodo luminescence (CL) was studied in oxygen-octahedric ferroelectrics Ba_XSr_1-XNb₂O₆, $\text{PbMg}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{O}{}_3$, LiNbO₃, SrTiO₃, Ba₂NaNb₅O₁₅, and PLZT-ceramics. CL in these materials is of admixture type. In the region of ferroelectric phase transition (PT) of Ba_XSr_1-XNb₂O₆ and $\text{PbMg}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{O}{}_3$ an anomaly in CL is observed. Redistribution of recombination flows between the centers of radiative and non-radiative recombinations in PT region due to variation of dielectric constant is proposed to account for this phenomenon.     

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.$\text{LaVO}{}_4\text{=}\text{LaVO}{}_3\text{+}\text{1}\text{20}{}_2\text{δ=328}\text{kJ}\text{mol}\text{°=135}\text{J}\text{mol·deg.}$,$\text{LaMnO}{}_3\text{=}\text{1}\text{2}\text{La}{}_2\text{O}{}_3\text{+}\text{MnO}$     

The role of TiO2 and ZrO2 in Na2OMO2SiO2 glasses

The glass transition temperatures of $\text{(1?x)}\text{Na}{}_2\text{O}\text{·}\text{1}\text{2}\text{x}\text{MO}{}_2\text{·2}\text{SiO}{}_2$ and Na₂O·xMO₂·(2 ?x)SiO₂ glasses, with M = Ti or Zr, have been related to the structural role and coordination of Ti and Zr. The role of network-former, intermediate or modifier of a cation has been fundamentally linked to ionic field strength; T_g values depend on ionic field strength and coordination. Titanium behaves like an intermediate oxide; its coordination ranges between four and six, depending on $\text{Ti}\text{Si}$ ratio. The role of zirconium changes according to the degree of substitution for Na or Si and progressively approaches that of a modifier ion.     

ESR evidence for the existence of rutile-type,nonstoichiometric vanadium antimonate

A nonstoichiometric vanadium antimonate has been synthesized from a high temperature solid state reaction of V₂O₅ and Sb₂O₃. Powder-X-ray diffraction data of this phase could be indexed on a tetragonal basis with $\text{a}\text{= 4.60}\text{A}\text{?}$, $\text{c}\text{= 3.02}\text{A}\text{?}$. The phase exhibits a well resolved hyperfine ESR spectrum at 298 K due to V(4+)(3d′) ions interacting with ${}^{51}\text{V}\text{(}\text{I}\text{=}\text{7}\text{2}\text{)}$, thus establishing its identity as a rutile type phase postulated earlier. The ESR parameters are $\text{g}{}_{\mathrm{}}\text{= 1.933±0.002}$, g_⊥ = 1.984±0.002, $\text{A}{}_{\mathrm{}}\text{= 193±3}\text{G}$, A_⊥ = 75±3G. Present results are discussed in relation to ESR of V(4+) in other rutile-type hosts.     

Models for the effect of chemisorbed gases on the electrical resistance of metal films

Three hypotheses are considered for the proportionate change of resistance $\text{ΔR}\text{R}{}_1$ when a continuous metal film of resistance R₁ adsorbs gas: (a) a loss of metallic properties at the surface; (b) a change in the electron scattering parameter at the surface; and (c) a change in the electron concentration throughout the film. Two models of the film structure are used to compare the predictions of these hypothesis with our experimental data for the systems $\text{O}{}_2\text{Er}$, $\text{CO}\text{Er}$, $\text{CO}\text{Ti}$ and $\text{O}{}_2\text{Ti}$. The flat plate model accounts for neither R₁ nor $\text{ΔR}\text{R}{}_1$. A simple version of the columnar model accounts for $\text{ΔR}\text{R}{}_1$ by either (a) or (b) for the first three systems and by (c) for the fourth, but it does not explain all the properties of the clean films. The linear approximation given by Mola and Heras for the columnar model of Mayadas and Shatzkes accounts satisfactorily for R₁ and $\text{ΔR}\text{R}{}_1$ for $\text{O}{}_2\text{Er}$, $\text{CO}\text{Er}$ and $\text{CO}\text{Ti}$ by increases in the electron scattering coefficient at the grain boundaries. It does not account for $\text{ΔR}\text{R}{}_1$ with $\text{O}{}_2\text{Ti}$ because that system incorporates gas into the metal lattice.     

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.     

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.     

Author index of volume 8

The $\text{Zr}\text{ZrO}{}_2$ electrode was prepared by the electrolytic oxidation of molten KNO₃ on zirconium. This electrode can be used as indicator electrode in potentiometric acid-base titrations. It behaves reversibily and responds theoretically to the oxide-ion concentration in molten KNO₃. Its potential varies linearly with the logarithm of [O^2?] and the slope of the line amounts to 67 mV at 350°C. The standard potential of $\text{Zr}\text{ZO}{}_2$, O^2? electrode, i.e. the potential at [O^2?] = 1, is computed as ?1698 mV relative to the Ag/Ag(I) reference electrode.     

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.     

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.     

Control of the growth-induced magnetic anisotropy in ferrimagnetic garnet films grown by liquid-phase epitaxy

The influence of melt composition and growth temperature T_g on the growth-induced magnetic anisotropy constant K^g_u in Bi substituted LPE ferrimagnetic garnet films has been investigated. In films grown from Bi₂O₃ based and from $\text{PbO}\text{B}{}_2\text{O}{}_3$ based melts the value of K^g_u increased upon decreasing T_g, associated with an increasing incorporation of B1. However, at given Bi content the films grown from Bi₂O₃ based fluxes generally exhibited smaller values of K^g_u than those from $\text{PbO}\text{B}{}_2\text{O}{}_3$ based melts. The addition of small amounts of Ca²⁺ to the Bi₂O₃ based melts resulted in (Y,Bi)-garnet films changing from n- to p-type electrical conductivity at a minimum value of K^g_u. Additions of Si⁴⁺ to a $\text{PbO}\text{B}{}_2\text{O}{}_3$ based melt reduced the uniaxial magnetic anisotropy of La-YIG-Ga films accompanied by a change from p- to n-type conductivity. Similarly, (Gd,Bi)-garnet films from $\text{PbO}\text{B}{}_2\text{O}{}_3$ based melts changed from n- to p-type conductivity upon decreasing T_g where K^g_u changes sign from negative to positive. From the temperature dependence of the electrical conductivity the electron and hole concentrations in some of these films were estimated suggesting that the sign change of K^g_u in the investigated (Gd,Bi)-garnet films and the minimum of K^g_u in the investigated (Y,Bi)-garnet films and (La,Y)-garnet films occur at donor-acceptor compensation. This experimental evidence led us to conclude that the growth induced magnetic anisotropy may be correlated with the presence of donor and acceptor centers in the garnet structure.