The topography of nickel crystals during the reaction towards Ni(CO)4; A field ion microscope study

The structural aspect of the formation of Ni(CO)₄ by the reaction of CO with solid nickel has been studied. The nickel initial state was a nearly hemispherical single crystal as prepared by field evaporation of a nickel field emitter tip. Field-free reaction of CO with the clean nickel surface took place at pressures up to 2 mbar, reaction times up to 45 h, and at a temperature of 373 K, which as a result from work by others was found optimum for highest rates of Ni(CO)₄ formation. Neon field ion imaging at 80 K after reaction with CO showed the crystal always in an intermediate state, which had the features: (1) Areas of {;111} were increased; (2) at half angles between a central (111) and peripherical {111} planes there were {110} planes flanked by {210}, and {100} flanked by {511}, respectively; (3) with the exception of the planes mentioned in feature (2), the remaining surface area was more than mono-atomically stepped. From these results and in accordance with the theory of crystal growth (Kossel, Stranski) and the theory of crystal dissolution (Lacmann, Franke, Heimann) a pure octahedron is expected to be the final state of the crystal. This implies that nickel atoms removed by the reaction are most frequently taken from 〈110〉 atom chains of the {111} planes.     

Synthesis, crystal structure, Cu doped EPR, thermal and voltammetric studies of [Ni(isonicotinamide)2(H2O)4]·(sac)2 single crystal

The single crystal of [Ni(ina)₂(H₂O)₄]·(sac)₂, (NINS), (ina is isonicotinamide and sac is saccharinate) complex has been prepared and its structural, spectroscopic and thermal properties have been determined. The title complex crystallizes in monoclinic system with space group P2₁/c, Z=2. The octahedral Ni(II) ion, which rides on a crystallographic centre of symmetry, is coordinated by two monodentate ina ligands through the ring nitrogen and four aqua ligands to form discrete [Ni(ina)₂(H₂O)₄] unit, which captures two saccharinate ions in up and down positions, each through intermolecular hydrogen bands. The magnetic environment of copper(II) doped NINS crystal has also been identified by electron paramagnetic resonance (EPR) technique. The g and A values of Cu²⁺ doped NINS single crystal were calculated from the EPR spectra recorded in three mutually perpendicular planes. These values indicated that the paramagnetic centre has a rhombic symmetry with the Cu²⁺ ion having distorted octahedral environment. The complex exhibits only metal centred electroactivity in the potential range of −2.00, 1.25 V versus Ag/AgCl reference electrode.     

PbMoO4晶体生长基元和生长习性的高温拉曼光谱研究

应用高温拉曼光谱研究了PbMoO₄熔体中的生长基元.通过对不同温度下PbMoO₄晶体拉曼光谱和熔点温度附近熔体高温拉曼光谱的研究,发现PbMoO₄熔体中存在Pb²⁺阳离子和［MoO₄］^2－阴离子生长基元.进一步讨论了PbMoO₄晶体生长基元和各个低指数晶面间的相互作用,解释了晶体的生长习性和枝晶生长的原因,并指出:PbMoO₄晶体生 关键词： 钼酸铅晶体 枝晶 籽晶取向 拉曼光谱     

Calcium precipitation in NaCl monitored by the Eu2+ -fluorescence

Taking into account that the optical spectroscopy of the Eu²⁺ ion is quite sensitive to the crystalline environment in which this ion is located, in the present investigation the fluorescence of a small concentration (8 ppmm) of divalent europium incorporated into a NaCl crystal which was also doped with ≈4500 ppmm of Ca²⁺ has been systematically investigated as a function of different thermal treatments in order to study the calcium-precipitation processes in the host NaCl. The data presented in this paper strongly suggest that the annealing of quenched samples at 200°C produces the incorporation of Eu²⁺ into the stable dihalide phase CaCl₂, as well as into the metastable precipitated CaCl₂-like plate zones parallel to the {111} planes of the NaCl matrix. This fact is associated with the increase in intensity of two overlapping emission bands peaking at 430 and 432 nm. On the other hand, the aging of quenched samples at room temperature produces the growth of three emission bands peaking at 400, 414, and 447 nm. The former two emission bands have been associated with Eu²⁺ embedded into calcium precipitates, the structures of these precipitates being different from that of CaCl₂, while the band at 447 nm has been ascribed to europium ions incorporated into the metastable precipitated CaCl₂-like plate zones parallel to the {310} planes of the NaCl matrix. Some of the characteristics of the different calcium second phase precipitates have been obtained by measuring the crystal field splitting (10 Dq) of the 4f⁶5d configuration of the divalent europium ions when they were located inside them. Values for the 10 Dq splitting were determined from the excitation spectrum of each of the emission bands associated with the different calcium-precipitated phases.     

Crystal growth,structure, electron paramagnetic resonance and magnetic properties of (NH4)2V3O8

A method to grow single crystals of ammonium vanadate (IV, V) (NH₄)₂V₃O₈ has been devised. The crystal structure is tetragonal P4bm; residual factor is R = 0.030. Cell parameters are $\text{a = 8.891 ± 0.004}\text{A}\text{?}$ and $\text{c = 5.582 + 0.002}\text{A}\text{?}$. The V⁵⁺ atom lies at the center of a triangular pyramide (VO₄ tetrahedron) while the V⁴⁺ atom is on A 4-fold rotation axis at the center of a square-based pyramide VO₅ whose symmetry point group is almost C_4v with the short V = O bond lying along the 4-fold axis parallel to the c edge of the tetragonal cell. Crystals are thin platlets with (001) cleavage planes. The platlets have very often a square or rectangular shape limited by {100} or {110} planes. Each single crystal was not large enough to record a good e.p.r. spectrum, but by sticking on the same quartz plate a score of them it was possible to gather enough crystals so to record correct spectra and by orienting the plate to obtain resonance lines separately for g_∥ = 1.9263 et g_τ = 1.9755. Measurements at 283 K on powder samples gave times for spin-spin relaxation T₂ = 0.4 × 10^?7s and for spin-lattice relaxation T₁ = 1.6 × 10^?7s. The magnetic structure is characterized by an exchange narrowing ω_e = 3 × 10¹⁰rad/s which corresponds to a transition temperature of about 0.5 K. Static susceptibility measurements at high magnetic field show a paramagnetic behaviour with an antiferromagnetic interaction which is interpreted in the magnetic space group P_2c4bm as the interaction between V⁴⁺ ions from consecutive planes parallel to (001).     

EPR and optical absorption studies of Cu<Superscript>2+</Superscript> ions in [ZnPd(CN)<Subscript>4</Subscript>(C<Subscript>4</Subscript>H<Subscript>12</Subscript>N<Subscript>2</Subscript>O<Subscript>2</Subscript>)] single crystals

A Cu²⁺-doped single crystal of catena-trans-bis(N-(2-hydroxyethyl)-ethylenediamine) zinc(II)-tetra-m-cyanopaladate(II) [ZnPd(CN)₄(C₄H₁₂N₂O₂)] complex has been investigated by electron paramagnetic resonance (EPR) technique at room temperature. EPR spectra indicate that Cu²⁺ ions substitute for magnetically equivalent Zn²⁺ ions and form octahedral complexes in [ZnPd(CN)₄(C₄H₁₂N₂O₂)] hosts. The crystal field affecting the Cu²⁺ ion is nearly axial. The optical absorption studies show two bands at 322 nm (30864 cm⁻¹) and 634 nm (15337 cm⁻¹) which confirm the axial symmetry. The spin Hamiltonian parameters and the relevant wave function are determined.     

Synthesis and characterization of Ca2Sn1-xCexO4 with blue luminescence originating from Ce^4＋ charge transfer transition

Ce^4＋-doped Ca2SnO4 with a one-dimensional structure, which emits bright blue light, is prepared by using a solid-state reaction method. The x-ray diffraction results show that the Ce^4＋ ions doped in Ca2SnO4 occupy the Sn^4＋ sites. The excitation and emission spectra of Ca2Sn1-xCexO4 appear to have broad bands with peaks at - 268nm and -442nm, respectively. A long excited-state lifetime （-83μs） for the emission from Ca2Sn1-xCexO4 suggests that the luminescence originates from a ligand-to-metal Ce^4＋ charge transfer （CT）. The luminescent properties of Ca2Snl_xCexO4 have been compared with those of Sr2CeO4, which is the only material reported so far to show Ce^4＋ CT luminescence. More interestingly, it is observed that the emission intensity of Ca2Sn1-xCexO4 with a small doping concentration （x - 0.03） is comparable to that of Sr2CeO4 in which the concentration of active centre is 100%.     

Theoretical investigations of the local distortion and electron paramagnetic resonance parameter for CdCl2：V^2＋ and CsMgX3：V^2＋（X=Cl,Br） systems

This paper systematically investigates the local distortion and electron paramagnetic resonance (EPR) parameter for CdCl 2 :V 2+ and CsMgX 3 :V 2+ (X=Cl, Br) systems on the basis of the complete energy matrix, in which not only the contributions due to the spin–orbit coupling of the central ions but also that of the ligands are considered. To describe the difference of overlapping between d-orbits and p orbit, two spin–orbit coupling coefficients are introduced. By simulating the crystal field parameter and EPR parameter, the local distortion parameters are studied and the relationships between the EPR parameter and the spin–orbit coupling coefficients as well as divergent parameter are discussed. These results show that the local structures exhibit compression distortion for CdCl 2 :V 2+ and elongation distortions for CsMgX 3 :V 2+ (X=Cl, Br), respectively. It notes that the empirical formula R ≈ R H + (r i-r h )/2 is not suitable for CdCl 2 :V 2+ and CsMgX 3 :V 2+ (X=Cl, Br) systems. The contributions of ligand to spin–orbit coupling interaction cannot be neglected for strong covalent systems, especially for V 2+ doped in CsMgBr 3 :V 2+ .     

Bi12GeO20晶体的位错蚀斑与对称群

用化学浸蚀法系统的研究了Bi₁₂GeO₂₀晶体{100},{100},{111}等晶面独特浸蚀斑规律并用对称群理论进行分析.理论预示的蚀斑形态与实验结果符合很好.显示位错蚀斑是由{112}晶面组成,即晶体的惯态面为{112}.     

Si{111}晶面粒子堵塞坑的新现象

本文报道了从粒子背散射堵塞效应的实验中所发现的单晶Si的{111}晶面粒子堵塞坑的新现象。单晶Si的{111}晶面有两个面间距d_{(111)^(a)和d(111)^(b),而{110}晶面只有一个面间距d(110)。由此导致两者的堵塞坑是不同的,我们已从α粒子和质子的Si单晶堵塞效应的实验得到了证实。并由此估计了d(111)^(a)和d(111)^(b)以及d(110)的2ψ1/2角。据作者了解,到目前为止,国内外还没有人发现此现象。此现象的发现对复杂晶体的堵塞和沟道效应的研究开阔了前景。 关键词：}     

Influence of Copper(II) Ions on Radicals in DOPA–Melanin

DOPA–melanin (DOPA = 3,4-dihydroxyphenyl-alanine) complexes with Cu(II) cations were studied by electron paramagnetic resonance (EPR) spectroscopy. After the addition of metal cations to the melanin polymer, the EPR spectra parameters were measured. The axial g-factor values are g _|| = 2.20 and g _^ = 2.0 5 g_{ \bot } = 2.0 5 . Since $ g_{||} > g_{ \bot } > 2 $ g_{||} > g_{ \bot } > 2 , the ground state orbital of the unpaired electron of the Cu(II) complex is | x ²  -   y ² ñ \left| {{{x}}^{ 2} } \right. \, - \, \left. {{{y}}^{ 2} } \right\rangle . Square coordination of these cations in melanin is proposed. The influence of the Cu(II) concentration in solution used during synthesis on the concentration of melanin radicals was investigated. Cu(II) cations causes the decrease in the paramagnetic center concentration in melanin. The Cu(II) EPR spectra are not saturated within the microwave power range of 0.7–70 mW used in our experiment.     

EPR of 3d 5 and 3d 8 Ions in Crystals With Perchlorate Structure at High Pressure

EPR spectra for ions Ni 2+ (3d 5 ) and Mn 2+ (3d 5 ) substituting Zn 2+ in crystals Zn(BF 4 ) 2 ·6H 2 O are studied within a wide range under hydrostatic pressure in X and Q bands. It is shown that the pressure changes to a considerable extent the spectrum parameters of ion Mn 2+ , reducing axial parameter b_{2}^{0} and increasing cubic one b_{4}^{0} at 9 kbar pressure, there is no temperature dependency of parameter b_{2}^{0} . Hydrostatic pressure changes linearly the initial splitting of ion Ni 2+ and results to a change in D(b_{2}^{0}) sign, which means the spin levels inversion at 3.5 kbar.     

Electrochemical Studies on Substituted Iron-Hexacyanoiron(III) Bi-Layered Thin Films at Glassy Carbon Electrode/Electrolyte Interface

Thin films (30–50 nm) of bilayered HCM (hexacyanometalates) were prepared using direct electrodeposition or electrochemically driven insertion-substitution of PB (Prussian Blue) or InHCF (Indium Hexacyanoferrate) or K..In _x [Fe{CN}₆] _y , as starting material. The redox behavior of the immobilized counter/central ions at GCE/electrolyte interface have been investigated in aqueous KCl (pH 1) electrolytes using dynamic voltammetric techniques. Studies show that when the counter Fe or In ion is replaced by expandable partially filled d orbits elements such as Ru³⁺ a redox wave of the inserted counter ion is observed. Furthermore, the substitution of Fe as a counter ion with other poly-valent cations was found to be reversible if PB was the starting material. Studies were extended to include the EC (electrochemical) behavior of related HCM compounds such as K...Al _x [Fe{CN}₆] _y K, Ni _x [Fe{CN}₆] _y Cu _x [Fe{CN}₆] _y , K..Zn _x [Fe{CN}₆] _y and, K..Ru[Fe{CN}₆]₃. Unlike studied 3d cations, GCE modified with thin films of copper-hexacyanoiron (III) KCu _x [Fe{CN}₆] _y or CHF showed two redox waves with E^o _f 0.6, 0.9 V vs Ag/AgCl. Studies showed that even immobilized Cu ions were capable of catalyzing the oxidation of hydrazine and sulfite. The mechanism for electro-oxidation is also included.     

Time-resolved photoelectron spectroscopy on small tungsten cluster anions

We have studied the dynamics of photoexcited tungsten cluster anions W_n^-\mathrm{W}_{n}^{-} (n=3,4,…,14) by means of time-resolved two-photon photodetachment spectroscopy. At an excitation energy of h ν _pump=1.56 eV the photoinduced dynamics is mainly dominated by fast electronic relaxation processes. For the smallest clusters, i.e., W₃^-\mathrm{W}_{3}^{-}, W₄^-\mathrm{W}_{4}^{-}, and W₅^-\mathrm{W}_{5}^{-}, individual relaxation channels have been identified and resolved on a timescale well below 100 fs. The time constants for the decay of nascent and secondary electrons have been deduced from a Bloch model. Complete thermalization takes place for all clusters on a timescale of ∼1 ps.     

Plasma with two-negative ions and immobile dust particles: planar and non-planar ion-acoustic wave propagation

By using the hydrodynamic equations of positive and two negative ions, Boltzmann electron density distribution, and Poisson equation with immobile positive/negative dust particles, a cylindrical Korteweg-de Vries (CKdV) equation is derived for small but finite amplitude ion-acoustic waves. At the critical total negative ion concentration and/or the critical density rate of the second-negative ions, the pulses collapse at this limit as nonlinearity fails to balance dispersion. Then the CKdV equation is not appropriate to describe the system. Therefore, the modified CKdV (MCKdV) and extended CKdV (ECKdV) equations are derived at the critical plasma compositions and in the vicinity of the critical plasma compositions, respectively. The physical parameters of two plasma environments (e.g., Xe⁺–F^-–SF₆^-_{6}^{-} and Ar⁺–F^-–SF₆^-_{6}^{-} plasmas) are examined on the wave phase velocity and the nonlinear localized pulse profile. The latter should satisfy necessary condition to exist. The localized pulse of Ar⁺–F^-–SF₆^-_{6}^{-} plasma is much spiky than Xe⁺–F^-–SF₆^-_{6}^{-} plasma. Thus, the mass ratio of the negative-to-positive ions is focused upon and it emphasizes to play an important role on the pulse profile. Dependence of the geometrical divergence on the pulse profile is also investigated, which indicates that the localized pulse damps with time. The implications of our results agrees with the experimental observations.     

Twinned EPR spectra of Fe centers in ternary layered TlGaS2 crystal

TlGaS₂ single crystal doped by paramagnetic Fe³⁺ ions has been studied by electron paramagnetic resonance (EPR) technique. The fine structure of EPR spectra of paramagnetic Fe³⁺ ions was observed. The spectra reveal a nearly orthorhombic symmetry of the crystal field (CF) on the Fe³⁺ ions. Two groups each consisting of four equivalent Fe³⁺ centers were observed in the EPR spectra. The local symmetry of the crystal field on the Fe³⁺ centers and CF parameters were determined. Experimental results indicate that the Fe ions substitute Ga at the center of the GaS₄ tetrahedrons. The rhombic distortion of the sulfur ligand CF is attributed to the effect of Tl ions located in the trigonal cavities between the tetrahedral complexes. The observed twinning of the resonance lines indicates a presence of two non-equivalent positions of Tl ions that confirms their zigzag alignment in the TlGaS₂ crystal structure.     

Crystallographic anisotropy in chemisorption: Nitrogen on tungsten single crystal planes

A molecular beam technique for the determination of sticking probabilities and surface coverages was used in earlier work to investigate the adsorption of nitrogen on tungsten {110}, {111} and {100} single crystal planes. In the present paper these studies have been extended to the {310}, {320} and {411} planes. Absolute sticking probabilities and adatom surface coverages are reported for crystal temperatures between 90 K and 960 K. Crystallographic anisotropy in this system is exemplified by zero coverage sticking probabilities with the crystal at room temperature: {110}, 1&#x0303;0^?2; {111}, 0.08; {411}, 0.4; {100}, 0.59; {310}, 0.72; {320}, 0.73. Results for planes on the [001] zone are quantitatively described by a general model developed for adsorption on stepped planes as an extension to the precursor-state order-disorder model for adsorption kinetics of King and Wells. It is shown that nitrogen dissociation only takes place at vacant pairs of {100} sites, but that subsequently the chemisorbed adatoms so formed may migrate out onto {110} terraces. The results are critically analysed in terms of the available LEED and work function data for nitrogen on tungsten single crystal planes, and the general model developed by Adams and Germer.     

Physisorption and dissociative chemisorption of H2 on sub-nanosized Al$_{13}^{-}$ anion cluster: ab initio study

We have studied the interaction of Al₁₃^-_{13}^{-} anion cluster with H₂. Both the long range interaction and dissociative adsorption have been examined using the established correlated ab initio methods, MP2 and CCSD(T), in conjunction with the augmented correlation consistent basis sets up to aug-cc-pVTZ. The formation of the weakly bound (physisorbed) end-on anion complex Al₁₃^-_{13}^{-}...H₂ is predicted for the interacting Al...H distances of 3.95 ? with the H-H axis pointing towards the ‘hollow’ site of Al₁₃^-_{13}^{-} and binding energy (D_e)D_{e}) of 0.7 kcal/mol at the estimated complete basis set (CBS) limit of CCSD(T). The barrier height for H₂ dissociation on Al₁₃^-_{13}^{-} of 41.6 (42.9) kcal/mol calculated at the ZPVE-corrected CCSD(T)/aug-cc-pVTZ (estimated CCSD(T)/CBS) level is at least twice as large as that evaluated by us for a dissociative adsorption of H₂ on an open-shell Al₁₃ neutral cluster. To our knowledge, this report presents the first “benchmark” quality study of the physisorption and dissociative chemisorption of molecular hydrogen on Al₁₃^-_{13}^{-} anion cluster.     

Study of divalent and trivalent chromium in forsterite by high-frequency EPR spectroscopy

Divalent and trivalent chromium ions Cr²⁺ and Cr³⁺ replacing magnesium ions at octahedral positions in Mg₂SiO₄: Cr and Mg₂SiO₄: Cr: Li crystals are investigated by submillimeter EPR spectroscopy in the frequency range 65–230 GHz. The crystals are grown from the melt by the Czochralski method. The content of mixed-valence chromium species in forsterite is analyzed. It is demonstrated that, in crystals grown in argon (the oxygen partial pressure is \(P_{O_2 } \) = 0.01 kPa), approximately half of the chromium ions are in the divalent form. The Cr²⁺ ions are distributed over the M1 and M2 positions in a ratio of approximately 2: 1. A change in the oxygen partial pressure \(P_{O_2 } \) and the chromium concentration, as well as an additional doping with lithium, does not lead to substantial changes in the distribution of divalent chromium ions over the positions. It is shown that an increase in the oxygen partial pressure \(P_{O_2 } \) from 0.01 to 2.00 kPa results in a decrease in the coefficient of divalent chromium distribution between the crystal and the melt. Doping with lithium also decreases the concentration of Cr²⁺ centers. In crystals grown without lithium, approximately half of the trivalent chromium ions are associated with magnesium vacancies. The addition of lithium leads to the destruction of these associates, an increase in the concentration of individual Cr³⁺ centers, and the formation of lithium associates with trivalent chromium ions. The conditions for the formation of associates of trivalent chromium ions with lithium ions are optimum when the crystal contains approximately identical amounts of Cr³⁺ and Li⁺ ions. Doping with lithium increases the concentration of Cr³⁺ ions and, thus, decreases the fraction of Cr²⁺ and Cr⁴⁺ ions in the total content of chromium centers.     

Nuclear orientation and NMR/ON of205,207Po

^205,207Po have keen implanted with an isotope separator on-line into cold host matrices of Fe, Ni, Zn and Be. Nuclear magnetic resonance of oriented²⁰⁷Po has been observed in Fe and Ni, of²⁰⁵Po in Fe. The resonance frequencies for zero external field are $$\begin{gathered} v_L (^{207} Po\underline {Fe} ) = 575.08(20)MHz \hfill \\ v_L (^{207} Po\underline {Ni} ) = 160.1(8)MHz \hfill \\ v_L (^{205} Po\underline {Fe} ) = 551.7(8)MHz. \hfill \\ \end{gathered} $$ From the dependence of the resonance frequency on external magnetic field theg-factor of²⁰⁷Po was derived as $$g(^{207} Po) = + 0.31(22).$$ Using this value the magnetic hyperfine fields of Po in Fe and Ni were obtained as $$\begin{gathered} B_{hf} (Po\underline {Fe} ) = + 238(16)T \hfill \\ B_{hf} (Po\underline {Ni} ) = 66.3(4.6)T. \hfill \\ \end{gathered}$$ Theg-factor of²⁰⁵Po follows as $$g(^{205} Po) = + 0.304(22).$$ From the temperature dependence of the anisotropies ofγ-lines in the decay of^205,207Po the multipole mixing of several transitions was derived. The electric interaction frequenciesv _Q=eQV_zz/h in the hosts Zn and Be were measured as $$\begin{gathered} v_Q (^{207} Po\underline {Zn} ) = + 42(3)MHz \hfill \\ v_Q (^{207} Po\underline {Be} ) = - 70(20)MHz \hfill \\ v_Q (^{205} Po\underline {Be} ) = - 42(17)MHz. \hfill \\ \end{gathered}$$