Ionic Radii Of Cations Research Articles

Different lanthanide ions and the pybox substituents induce the reverse of the sense of induction in the enantioselective Diels-Alder reaction between acryloyloxazolidinone and cyclopentadiene.

The Diels-Alder reaction of cyclopentadiene with acryloyl-1,3-oxazolidin-2-one is catalyzed by (R,R)-i-Pr- and (R,R)-Ph-pybox (5 and 6)/lanthanide(III) triflate complexes. The enantioselectivity of the reaction is influenced by 4 A molecular sieves; moreover, the absolute sense of the enantioselection was found to be a function of the nature of the substituents on the chiral ligand (e.g., aromatic vs alkyl groups) as well as of the specific cation employed. In particular, seven lanthanide triflates were tested and a regular variation of the enantioselectivity as a function of the cation ionic radius was evidenced. The different sense of induction can be rationalized by assuming two competitive reacting complexes with different coordination number, which favor the attack on the opposite heterotopic faces of the coordinated dienophile.

Electron detachment energies in high-symmetry alkali halide solvated-electron anions

We decompose the vertical electron detachment energies (VDEs) in solvated-electron clusters of alkali halides in terms of (i) an electrostatic contribution that correlates with the dipole moment (μ) of the individual alkali halide molecule and (ii) a relaxation component that is related to the polarizability (α) of the alkali halide molecule. Detailed numerical ab initio results for twelve species (MX)n− (M=Li,Na; X=F,Cl,Br; n=2,3) are used to construct an interpolation model that relates the clusters’ VDEs to their μ and α values as well as a cluster size parameter r that we show is closely related to the alkali cation’s ionic radius. The interpolation formula is then tested by applying it to predict the VDEs of four systems [i.e., (KF)2−, (KF)3−, (KCl)2−, and (KCl)3−] that were not used in determining the parameters of the model. The average difference between the model’s predicted VDEs and the ab initio calculated electron binding energies is less than 4% (for the twelve species studied). It is concluded that one can easily estimate the VDE of a given high-symmetry solvated electron system by employing the model put forth here if the α, μ and cation ionic radii are known. Alternatively, if VDEs are measured for an alkali halide cluster and the α and μ values are known, one can estimate the r parameter, which, in turn, determines the “size” of the cluster anion.

Magnetic, electrical and structural properties of some ternary and quaternary spinels with chromium

Spinel compounds with the general formulas ACr 2X 4 and ACr 2− x B x X 4 (where A=Cd, Zn, Hg, Ga, Cu; X=S, Se, Te, O; B=Ga, In, Sb), including also substitution of two different cations in the tetrahedral subarray, exhibit different correlations of the magnetic and electrical properties. These properties are correlated with the ionic radii of cations and anions. The solid solutions of the boundary compounds reveal, e.g. correlations of metallic conductivity and a semiconductor–metal phase transition. In some spinel solid solutions the latter phase transition is accompanied by the magnetic phase transitions, i.e. either AF-F or Fi-F. Magnetic and electrical properties and their correlations in different spinel series with chromium are discussed in the frames of the phase diagram of the spinel-type compounds with chromium. Different mechanisms leading to the spin-glass state are discussed and illustrated.

Small Dopant Effect on Static Grain Growth and Flow Stress in Superplastic TZP

Static grain growth behavior in 1 mol% of GeO2, TiO2, MgO or BaO-doped ZrO2-3 mol%Y2O3 (3Y-TZP) was examined at 1400 � C with a special interest in dopant effect on superplastic flow stress in fine-grained 3Y-TZP. The static grain growth can be described as normal grain growth in single-phase ceramics, and growth constant K for each material is in the order of 10% flow stress of the superplastic flow. The value of K in cation-doped TZP is correlated well with dopant cation's ionic radius. Assuming activation energy for diffusivity of constituent ion can be given as a linear function of strain caused by difference in the ionic size of dopant cation, the dependence of the growth constant and the flow stress on the ionic radius can be described as a function of the ionic radius of the dopant cation. The activation energy for the diffusivity in cation- doped TZP estimated from the calculation is in good agreement with the experimental data. The small dopant effect on the superplastic flow stress is well described by the activation energy as the function of the dopant cation's ionic size. is the grain growth exponent, and K is the growth constant. The reported data of the parameters are scattered, but in the case of normal grain growth in single-phase TZP, m ¼ 2 is often used for the phenomenological analysis. 13,15,17) The detailed mechanism of the grain growth in TZP has not been classified yet, but it is supposed that matter transport by diffusion in the vicinity of the grain boundaries is the rate- controlling mechanism for the normal grain growth. The growth constant K thus must be related to the diffusivity in TZP, and estimation of K value is expected to produce an important information about the dopant effect on the super- plastic flow stress in TZP. In the present study, the static grain growth behavior was investigated in ZrO2-3 mol%Y2O3 (3Y-TZP) and 1 mol% of cation-doped 3Y-TZP. The dopant effect on the grain growth behavior and the superplastic flow stress will be discussed from the viewpoint of ionic radius dependence of activation energy for the diffusivity. 2. Experimental Procedure The materials used in this study were tetragonal ZrO2- 3 mol%Y2O3 polycrystal (3Y-TZP) and 1 mol% of BaO, MgO, TiO2, or GeO2-doped 3Y-TZP. 3Y-TZPpowder (TZ3Y; Tosoh Co., Ltd.), barium oxide (BaO, Soekawa chemical Co., Ltd.), magnesium oxide (MgO, Ubekosan, Japan), titanium oxide (TiO2, Sumitomo Cement Co., Ltd.) and germanium oxide (GeO2, Rare Metallic Co., Ltd.) were used as starting materials. 3Y-TZP powders and the oxide powders were mixed, ball-milled in ethanol together with 5 mm diameter high-purity (>99:9%) zirconia balls for 24 h, dried and shifted through a 60 mesh sieve for granulation. The green compacts were prepared by pressing the mixed powders into bars with a cemented carbide die under a pressure of 33 MPa, and then isostatically-pressed under a pressure of 100 MPa. The green compacts were sintered at a temperature in the range 1400 or 1450 � C for 2 h in air to obtain an average grain size of about 0.4 mm and relative density of about or more than 99% for theoretical value in all samples. The sintering temperature is listed in Table 1. Heat treatment for investigation of grain growth behavior was conducted at 1400 � C for the annealing time in the range of 5-

Ion Beam-Induced Amorphization of the Pyrochlore Structure-Type: A Review

ABSTRACTThis paper reviews the recent developments in the understanding of the radiation-damage processes in A2B2O7 (Fd3m; Z=8) pyrochlore-structure compounds. Pyrochlore structure compounds display a wide range of behaviors in response to ion beam irradiation. Some compositions, such as Gd2Ti2O7, are amorphized at relatively low doses (∼0.2 dpa at room temperature) while other compositions, such as Gd2Zr2O7, do not amorphize (even at doses of 36 dpa at 25 K) and instead disorder to a defect fluorite structure. The response to ion beam irradiation is highly dependent on compositional changes that affect both the structural distortion from the ideal fluorite structure and the associated energetics of the disordering process. Generally, the ionic size of the cations plays a dominant role in determining the radiation response of different pyrochlore compositions. However, the cation ionic radius ratio criteria cannot be applied all-inclusively in predicting the radiation “tolerance” of a pyrochlore. Systematic irradiation studies of the radiation response of rare-earth (A-site) pyrochlores in which B = Ti, Zr, and Sn have shown that the behavior of the pyrochlore also depends on the cation electronic structure, i.e., the type of bonding, which is closely related to the polyhedral distortion and structural deviation from the ideal fluorite structure. These structural changes affect the dynamic defect recovery process directly linked to the material's response to and recovery from irradiation.

Phase Relations Between a Fluorite and a Pyrochlore Structure in the System of Actinides and Zirconium Oxides

Cubic stabilized zirconia (CSZ) exhibits the fluorite structure and zirconium pyrochlores form a special structure. Because of slight difference in crystallographic symmetry, local structures are formed in the pyrochlores: a distorted coordination of eight oxygen around a large dopant cation, and a symmetric coordination of six oxygen around Zr+. A similar local structure is confirmed in the Np-doped yttria stabilized zirconia (YSZ) solid solutions by means of 237Np Mössbauer spectroscopy. The Mössbauer study shows that small amounts of Np5+ are formed in the solid solution, and are distributed statistically on the available cation sites. Based o n these findings, a mean cation ionic radii model is developed to evaluate the lattice parameter change with composition in the Pu- and Np-doped YSZ solid solutions. An effect of the oxygen vacancy is treated as reducing the oxygen coordination number arouid Zr4+ from eight to seven in the model. The model represents successfully the observed lattice parameters. A phase transformation from the fluorite to the pyrochlore structure is considered to results in at average Zr coordination number of seven. Suggestions for further studies in this field are also provided.

On the Relation of the ro/ra versus rt/ra Plot with Direct and RKKY Exchanges in the Compounds Containing Chromium

An attempt was made to explain the physical sense of the special r o /r a vs. r t /r a plot being a phase diagram for the variety of chromium compounds, especially spinels, Krok-Kowalski et al., J. Alloys Compd. 315, 62 (2001). Here r t is the ionic radius of cations in the tetrahedral positions, r o the ionic radius of cations in the octahedral positions, r a the ionic radius of anions. Therefore, a model was proposed in which only the direct and RKKY exchanges were taken into account. The predictions of the presented model are adequate to the experimental data contained in this plot.

FT-IR and Raman Spectroscopic Characterization of the Major Oilfield Sulfate Scale Forming Minerals

Sulfate minerals commonly form in the oilfield environment due to secondary recovery operations. Two essential tools for identification of these minerals are Fourier transform infrared (FT-IR) and Raman spectroscopies. In this paper, a comprehensive database of the FT-IR and Raman spectra of these minerals has been composed. The symmetry of the sulfate tetrahedra in the various sulfate molecules has been assigned from observation of the vibrational degeneracy. Force constant calculations show that cation mass and polarizability are the dominant influences upon sulfate symmetry. Studies of the vibrational peak positions have demonstrated a direct relationship between properties of the associated sulfate cation and the positions of both the infrared and Raman v1 and v3 vibrations. The major influences were found to be cation electronegativity, cation mass, and cation ionic radius. These observations were confirmed from force constant calculations. It has been concluded that both FT-IR and Raman spectroscopies are valid techniques for identification of oilfield scale minerals. Raman spectroscopy is particularly useful as it can be applied to aqueous systems and the in situ measurements of scale formation.

Correlations of the magnetic and electrical properties with the ionic radii of cations and anions for the series of ternary and quaternary spinel-type chromium compounds

For the compounds ACr 2X 4 (where: A=Cd, Zn, Hg, Ga, Cu; X=O, S, Se, Te), ACr 2 x B 2−2 x X 4 (where: A=Cd, Zn; B=Ga, In; X=S, O), ZnCr 2− x In x Se 4 and Cr 2V 4− x Mo x O 13+0.5 x correlations were observed of the magnetic and electrical properties with the ionic radii of their cations and anions, whereas for the solid solutions of the boundary compounds ACr 2X 4 (where: A=Cd, Zn; X=S, Se, Te) and CuCr 2X 4 (were X=S, Se, Te) not only such correlations but also the metallic conductivity and a semiconductor–metal phase transition were observed. In particular for Zn 1− x Cu x Cr 2Se 4 this phase transition is accompanied by the magnetic AF-F phase transition, while for Cd 1− x Cu x Cr 2Se 4 one deals with the accompanying Fi-F phase transition. In the latter spinel series there exists the ferrimagnetic ordering at low copper concentrations, whereas at high copper concentrations one deals with the ferromagnetic ordering.

Cation incorporation into zirconium oxide in LiOH, NaOH, and KOH solutions

To investigate the cation incorporation into zirconium oxide, SIMS analysis was performed on the specimens prepared to have an equal oxide thickness in LiOH, NaOH, and KOH solutions. Even though they have an equal oxide thickness in LiOH, NaOH, and KOH solutions, the penetration depth of cation into the oxide decreased with an increase in the ionic radius of cation. The cation is considered to control the corrosion in alkali hydroxide solutions and its effect is dependent on the concentration of alkali and the oxide thickness. The slight enhancement of the corrosion rate at a low concentration is thought to be caused by cation incorporation into oxide, while the significant acceleration at a high concentration is due to the transformation of oxide microstructures that would be also induced by cation incorporation into oxide.

Dynamic SFM with true atomic resolution on alkali halide surfaces

Large-amplitude dynamic force microscopy is used to study alkali halide surfaces. The {001} cleavage faces of NaF, RbBr, LiF, KI and NaCl could be atomically re- solved with excellent stability. In all cases the observed lattice periods correspond to the bulk lattice of equally charged ions. The resonance frequency shift and the atomic corruga- tion amplitude tend to increase after successive tip crashes. This behaviour is explained by analogy with scanning tun- nelling microscopy. In addition, the mean atomic corrugation is found to be comparable to the difference between the anion and cation ionic radii.

The effect of salts on the electrochemical polymerization of aniline

Aniline is electrolysed by repeated potential cycling between 0 and 1.1 V (versus SCE); a current plateau instead of a current peak is observed on the I- E curve for the first cycle during electrolysis of aniline in aqueous acid solution in the presence of NaCl. The occurrence of the current plateau plays an important role in extending the potential range of electrolysis of aniline at a high rate. The polymerization rate of aniline in a solution containing a given HCl concentration increases with increasing concentration of sodium chloride; the potential range of the intermediate generated at the disk electrode is also extended with increasing concentration of NaCl. The potential necessary for the formation of the soluble intermediate is at least 0.75 V. The hydrochloric acid concentration necessary for an autocatalytic polymerization of aniline decreases from 0.6 to 0.4 M in the presence of NaCl. The conductivity of polyaniline prepared in a solution containing 0.2 M aniline, 0.4 M HCl and 1 M NaCl is about 30 times higher than that of polyaniline prepared in a solution containing 0.2 M aniline and 0.4 M HCl. The oxidation potential of aniline in the presence of the salts shifts toward negative potentials, depending on the ionic radius of cations and the concentration of the different salts.

A simple model for the estimation of electronegativities of cations in different electronic states and coordinations

A simple relation exists between electronegativities, oxidation states and ionic radii of cations. An empirical law x ≈ 0.274 z − 0.15 zr i − 0.01 r i + 1 + α is proposed, where z is the oxidation number, r i is the ionic radius and α is a term dependent on the atomic number. This relation permits the calculation of an electronegativity scale covering a large set of electronic and crystallographic situations. An application to the calculation of the acidic strength of cations is presented.

Influence of Metal Ions on the Order‐Disorder Transition Temperature of the Ba‐M‐O (M: La, Y, In, or Ga) System

Preparation of BaLa2O4, Ba3,Y4O9, Ba,In2O5, and Ba3Ga2O6 powders and their sintering were investigated in Ar or air. These sintered bodies with perovskite‐related structure were synthesized by reaction sintering, using mixed powders in the atomic ratios of Ba/La = 1, Ba/Y = 0.75, Ba/In = 1, and Ba/Ga = 1.5. The order‐disorder transition temperatures of the BaLa2O4, Ba3Y4O9, Ba2In2O5, and Ba3Ga2O6 sintered bodies were 270°, 350°, 880°, and 123OoC, respectively. It was found that the temperatures were influenced by the ionic radius of cations in B sites, and the transition temperatures decreased with increasing ionic radius.

Infrared reflectance investigation of alkali diborate glasses

Alkali diborate glasses have been investigated by infrared reflectance spectroscopy to demonstrate the potential of this technique for a quantitative description of the glass structure. Kramers-Krönig transformation was performed on the reflectance data to obtain the optical and dielectric properties of glasses over a broad and continuous spectral range (30–4000 cm −1). Analysis of the mind infrared spectra shows that the normalized absorption area attributed to boron-oxygen tetrahedra decreases upon increasing alkali cation ionic radius, and scales linearly with the fraction of four-coordinated boron atoms determined recently from NMR spectra. The far infrared asymmetric absorption profiles were deconvoluted into two broad bands and attributed to vibrations of alkali cations in two distinct network environments. Cation effective charges were calculated from the integrated absorption of the bands due to cation vibrations, and were found to increase with alkali ionic radius.

ζ-potential of synthetic chrysotile asbestos in aqueous simple salt solutions

The ζ-potential of synthetic chrysotile asbestos in aqueous alkali halide MX (M = Li, Na, K, Cs; X = F, Cl, Br, I) solutions was measured by a microelectrophoretic method. The ζ-potential of chrysotile in water was a minimum at pH 6.3 and its isoelectric point (IEP) was 12.3. This variation of ζ-potential with pH is interpreted as due to the formation of a complex oxide composed of silica and brucite due to Mg 2+ -leaching from outer brucite surfaces. The positive ζ values at pH 6.3 more than 8 increased with salt concentration. The ζ-potential increased with increase in ionic radius of cations with decrease in ionic radius of anions. This ζ-potential increase is interpreted as a specific effect of cations on the outer surface. The titration of chrysotile in aqueous solution gave the point of zero charge (PZC) of chrysotile, 10.5. The difference between the PZC the IEP may arise from the tubular structure of chrysotile, i.e., the existence of both acidic inner (silica) basic outer (brucite) surfaces.

Rare earth element distribution in some hydrothermal minerals: evidence for crystallographic control

Rare earth element (REE) abundances were measured by neutron activation analysis in anhydrite (CaSO 4), barite (BaSO 4), siderite (FeCO 3) and galena (PbS). A simple crystal-chemical model qualitatively describes the relative affinities for REE substitution in anhydrite, barite, and siderite. When normalized to ‘crustal’ abundances (as an approximation to the hydrothermal fluid REE pattern), log REE abundance is a surprisingly linear function of (ionic radius of major cation—ionic radius of REE) 2 for the three hydrothermal minerals, individually and collectively. An important exception, however, is Eu, which is anomalously enriched in barite and depleted in siderite relative to REE of neighboring atomic number and trivalent ionic radius. In principle, REE analyses of suitable pairs of co-existing hydrothermal minerals, combined with appropriate experimental data, could yield both the REE content and the temperature of the parental hydrothermal fluid. The REE have only very weak chalcophilic tendencies, and this is reflected by the very low abundances in galena—La, 0.6 ppb; Sm, 0.06 ppb; the remainder are below detection limits.

ChemInform Abstract: VIBRATIONAL SPECTROSCOPY OF CATION‐SITE INTERACTIONS IN PHOSPHATE GLASSES

Abstract30 Verschiedene Gläser mit Metaphosphatzusammensetzung (M20°C P2O5, M0 ‐ P2O5 , M203 ′3 P2O5 oder M02 ‐ 2 P2O5) werden nach Literaturmethoden dargestellt.

Vibrational spectroscopy of cation-site interactions in phosphate glasses

Thirty different binary metal oxide glasses having the metaphosphate composition have been prepared containing cations from the following groups: alkali metals, alkaline earths, transition metals, and lanthanide and actinide metals. Far infrared absorption assigned to the cation vibration in its oxygen cage has been measured for these glasses. Empirical ionic models are proposed correlating the absorption maximum with the cation mass, charge, and ionic radius. Discrepancies between the observed and predicted vibrational frequency indicate a more covalent interaction between the metal cation and the glass network. Raman intensities and vibrational frequencies of the network metaphosphate vibrations have been obtained and provide additional evidence about the cation–site interaction.

Crystal chemistry of kosmochlor-diopside solid solutions.

Crystal structure parameters have been determined for Ko75 (NaCrSi2O6; 75 mol%) Di25 (CaMgSi2O6; 25mol%), Ko50 Di50 and Ko25 D75 synthesized at 1200°C and 20 kb. Refinements in space group C2/c using anisotropic temperature factors and over 600 unrejected reflections for each set of data resulted in weighted R-factors ranging from 0.020 to 0.025. The nearest M1-M1 distances of Ko-Di solid solutions are significantly shorter than those expected from the averaged ionic radii of cations occupying the M1 sites. The longest M1-M1 distances werer found for the crystals having the compositions corresponded to the both sides of the misibility gap at high pressure. It is expected that Cr+3 within Ko solid solutions form Cr-O-Cr coupling and Cr+3 within Di solid solutions are completely disordered. Ko75 Di25 and Ko50 Di50 being stable only at high pressure have smaller cell volumes than those expected from the values of Ko, Ko25 Di75 and Di. They have shorter M1-O distances than those expected from the averaged ionic radii of cations occupying the M1 sites. Their mean 8 (M2-O) and (M2-0) distances are longer than those expected from the values of Ko, Ko25 Di75 and Di. The characteristic structures of Ko75 Di25 and Ko50 Di50 may suggest at least party those at high pressure.