Preparation of Zn2+–Ni2+–Fe3+–CO32−LDHs and study of photocatalytic activities for decomposition of Methyl Orange solution

New type photocatalytic materials of Zn²⁺–Ni²⁺–Fe³⁺–CO₃^2?LDHs were prepared by complexing agent-assisted homogeneous precipitation technique and Zn(NO₃)₂·6H₂O, Ni(NO₃)·6H₂O, Fe(NO₃)₃·9H₂O used as raw materials in the case of molar ratio of Zn²⁺/Ni²⁺/Fe³⁺ = 1:6:2. Zn²⁺–Ni²⁺–Fe³⁺–CO₃^2?LDHs having a specific surface area of 96.5 m²/g. The structure and catalytic properties of the material were systematically studied. The experimental results show that the Zn²⁺–Ni²⁺–Fe³⁺–CO₃^2?LDHs has a higher adsorption performance and lower band gap which make it an excellent catalyst for reducing the degradation of the methyl orange. Study on the process of photocatalytic reaction shows that Methyl Orange was adsorbed to the layer of Zn²⁺–Ni²⁺–Fe³⁺–CO₃^2?LDHs, and then it was photodecomposed to inorganic molecules and ions by Zn²⁺, Ni²⁺, and Fe³⁺ on the surface of Zn²⁺–Ni²⁺–Fe³⁺–CO₃^2?LDHs.     

Study of hopeite coatings: II. Study of polycationic hopeites: structure and dehydration process

The structures and the dehydration processes of phosphates, formed on galvanized steel sheets treated in polycationic solutions containing Zn²⁺, Ni²⁺ and Mn²⁺ as dihydrogenophosphates, are studied using differential and gravimetric thermal analysis (DTA, TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The compounds constituting the phosphated layers, and the crystals precipitated in a stove at 70° C from the same solutions, are structurally substituted-hopeites, (Zn, Mn, Ni)₂(PO₄)₂·4H₂O. Their thermal behaviour is strongly influenced by the presence of Ni²⁺ and Mn²⁺ ions. The dihydrate (Zn₃(PO₄)₂·2H₂O), whose structure conformation has been determined at first, is identified as the main component in the dehydration products of these compounds. The knowledge of the dihydrate conformation allows the understanding of the specificity of the dehydration processes of substituted hopeites whose transformation temperatures and dehydration modes depend on the nature of the substituting cations.     

Absorption spectra of Ni2+ in (NH4)2Mg(SO4)2·6H2O and Co2+ in Na2Zn(SO4)2·4H2O

Optical absorption spectra of Ni²⁺ in (NH₄)₂Mg(SO₄)₂·6H₂O and Co²⁺ in Na₂Zn(SO₄)₂·4H₂O single crystals have been studied at room and liquid nitrogen temperatures. From the nature and position of the observed bands, a successful interpretation could be made assuming octahedral symmetry for both the ions in the crystals. The splitting observed for ${}^3\text{T}{}_{\mathrm{1g}}\text{(F)}$ band in Ni²⁺ and ${}^4\text{T}{}_{\mathrm{2g}}\text{(F)}$ band in Co²⁺ at liquid nitrogen temperature have been explained as due to spin-orbit interaction. The extra band observed at 16,325 cm^-1 in the case of Ni²⁺ at low temperature has been interpreted to be the superposition of vibrational mode of SO^2-₄ radical on ${}^3\text{T}{}_{\mathrm{1g}}\text{(F)}$ band. The observed band positions in both the crystals have been fitted with four parameters B, C, Dq and ζ.     

Effect of the ionic radius on jump frequencies of alkaline earth cations in NaCl crystals

By comparing diffusion coefficientsD of bivalent cations Ba²⁺, Ca²⁺, Sr²⁺ in NaCl crystals it was shown that in the temperature range above 550 °CD (Ba²⁺)>D (Sr²⁺)>D (Ca²⁺) is valid. Temperature dependences of jump frequenciesw ₂ of these cations are described byw ₂ (Ba²⁺)=(2·15±0·55) × 10¹² × exp {?(0·817±0.007)/kT};w ₂ (Sr²⁺)=(2·9±1·1) × 10¹² × exp {?(0·84±0.02)/kT} andw ₂ (Ca²⁺)=(5·5±6·5) × 10¹⁰ × exp {?(0·51±0·07)/kT}. It was demonstrated that in NaCl crystals the activation enthalpy and the preexponential factor of the jump frequencyw ₂ increase with increasing ionic radius and mass of the bivalent alkaline earth cation.     

准一维反铁磁体CsMnCl3·2D2O中激子的能量转移

在2—300K温度范围,研究了纯的及掺Mg²⁺,Ni²⁺和Co²⁺的准一维反铁磁体CsMnCl₃·2D₂O(CMC)中Mn²⁺离子的⁴T₁激子的能量转移动力学过程,发现在2—10K范围,激子的荧光强度和寿命随温度很快下降,较高浓度的杂质离子将进一步加快荧光的减弱和寿命的缩短。这种现象被归结为与磁相互作用和自旋有序相关联的多声子无辐射跃迁及施主—受主之间的能量转移。在更高的温度,能量转移速率增高,但由于仍然存在的自旋短程有序和Jahn-Teller效应,施主之间的能量迁移受到一定限制,出现非指数衰减过程。各种不同的杂质离子在某种程度上显示出不同的陷落作用和弛豫特性。 关键词：     

Inversion of spin levels in Ni2+: Zn(BF4)2 · 6H2O under uniform compression and the effect of transition coincidence

The electron paramagnetic resonance (EPR) spectra of Ni²⁺ ions substituting for Zn²⁺ ions in Zn(BF₄)₂ · 6H₂O crystals are studied over a wide range of temperatures under uniform compression. Measurements are performed in the X-and Q-bands. The parameter D, which characterizes the initial splitting, undergoes considerable variations with changes in temperature and pressure, whereas the g factor remains virtually unchanged. An increase in the temperature is accompanied by a nonlinear increase in D. Under uniform compression, the initial splitting varies linearly and the parameter D changes its sign at 3.5 kbar, which indicates inversion of the spin levels. The coincidence of the EPR lines associated with different transitions leads to the appearance of line-profile dips in the spectra due to cross-relaxation inside the spin system.     

Optical and electrical properties of some sulphates doped with cobalt

Doubly ionized cobalt ion which has a ⁴F ground state exhibits several optical bands in orthorhombic sulphates. In view of the low symmetry, many degenerate states split and at low temperature (77°K) well resolved bands have been observed which enable the detailed calculation of the crystal field parameters in orthorhombic symmetry.Electrical conductivity measurements in pure potassium and ammonium sulphates show only the extrinsic unassociated region while in cobalt doped crystals, extrinsic as well as association regions are observed. Three distinct regions with slopes 0·86, 1·2 and 0·5 eV are obtained in cobalt doped K₂SO₄.X-irradiated pure crystals give two prominent bands at 2200 and 3300 Å which are attributed to SO₃^? and SO₂^?. Divalent cobalt doped crystals give additional bands at 2100 and 3100 Å. These bands are attributed to Co⁺ in different surroundings. Three ESR lines with ‘g’ values 2·042, 2·02 and 2·004 are obtained in support of the assignments.     

Investigation on the Local Structure of Nickel II–Doped Sodium Phosphate Glasses by Their Optical Spectra and Electron Spin Resonance g Factor

ABSTRACT

The optical spectra and electron spin resonance (ESR) g factor of Ni²⁺-doped sodium phosphate glasses are uniformly studied on the basis of both the complete (energy matrix) diagonalization procedure (CDP) and the two spin-orbit coupling parameters model. The bond length of Ni²⁺-O^2? of Ni²⁺-doped sodium phosphate (Na₂O · P₂O₅) glasses has been determined by fitting their optical spectra and ESR g factor to the experimental values. Theoretical results are in good agreement with experimental data.     

Characterization of magnetism and electronic properties of a ternary transition metal chalcogenide Rb2Ni3S4

The process of preparing specimens of Rb₂Ni₃S₄ single crystals grown by the flux method was reconsidered to clarify the magnetic and electronic properties of this nickel sulfide. Specimens obtained by removing fluxes with water were confirmed to have a residual ferromagnetic moment, as previously reported by the present authors. Specimens peeled a surface of as-grown crystals off by taking advantage of the quadratic layer characteristic of this crystal were ascertained to be diamagnetic and to exhibit magnetic properties intrinsic to Rb₂Ni₃S₄. However, the temperature dependence of the specific resistivity of the latter sample is similar to that of the former. Through examination of the experimental results, Rb₂Ni₃S₄ was identified as a nonmagnetic semiconductor in a low spin 3d⁸ configuration of Ni²⁺.     

Quantum efficiencies of near-infrared emission from Ni-doped glass-ceramics

A systematic method to evaluate potentials of Ni²⁺-doped transparent glass-ceramics as a new broadband optical gain media is presented. At first, near-infrared emission of various ceramics were investigated to explore the suitable crystalline phase to be grown in the glass-ceramics. The quantum efficiency of Ni²⁺ near-infrared emission estimated by the Struck-Fonger analysis was higher than 95% for spinel-type structure gallate crystals MgGa₂O₄ and LiGa₅O₈ at room temperature. Transparent glass-ceramics containing Ni²⁺:LiGa₅O₈ could be prepared and the quantum efficiency for the glass-ceramics was measured to be about 10%. This value shows a potential of Ni-doped transparent glass-ceramics as a broadband gain media.     

The structure of Ni(II)−Fe(III) hydroxy-chloride green rusts by Mössbauer spectroscopy and X-ray diffraction

The crystallographic structure of Ni(II)?Fe(III) hydroxy-chloride green rusts obtained by oxidation of a Fe_xNi_1?x(OH)₂ precipitate is isomorphous with that of the ferrousferric green rust one and independent of the value of P=Fe/Ni. Mössbauer spectra exhibit two quadrupole doublets after further oxidation of the compounds which correspond to a formula (3-x)Ni(OH)₂ · xFeOOH · Fe(OH)₂Cl. The Fe³⁺ ions are found to occupy preferentially the sites close to the Cl^? ions and the Ni²⁺ those far from them. However the ordering of the Fe³⁺ ions is not perfect.     

Etude par diffraction neutronique de l'ilmenite ferrimagnetique NiMnO3

The magnetic structure of ferrimagnetic ilmenite Ni²⁺Mn⁴⁺O₃ has been investigated by neutron diffraction. Below the Curie temperature (164°C), the spins are oriented into two kinds of ferromagnetic planes perpendicular to the [111] rhomboedral axis, one containing Mn⁴⁺ and the other Ni²⁺ cation. Two successive planes are coupled antiferromagnetically. The experimental magnetic moments are respectively found equal to 1.8 and 2.2 μ_B for Ni²⁺ and Mn⁴⁺ at room temperature. The positional atomic parameters have been redetermined from nuclear diffraction data taken above the Curie temperature.     

Comparative study of crystal field effects for Ni ion in LiGa5O8, MgF2 and AgCl crystals

Exchange charge model (ECM) of crystal field was used to calculate the crystal field parameters (CFPs) and model the energy levels for Ni²⁺ ion in LiGa₅O₈, MgF₂ and AgCl crystals. Calculated energy levels (including splitting of the orbital triplets) are in good agreement with experimental absorption spectra. Covalent effects were shown to play an important role in all considered crystals. Bilinear forms built up from the overlap integrals between (Ni²⁺-Cl⁻)→(Ni²⁺-O²⁻)→(Ni²⁺-F⁻) pairs were considered a quantitative measure of the covalent (nephelauxetic) effects.     

A new type of phase transition in M(ClO4)2(H2O)6M = Fe,Co, Ni and Mn

Mössbauer studies on Fe(ClO₄)₂(H₂O)₆ salt showed anomalous quadrupole splitting around (230 ± 15)°K which we have established to be due to a new type of phase transition from pseudohexagonal to monoclinic system. Exactly similar type of transition was observed magnetically in all the isomorphous Ni²⁺, Co²⁺ and Mn²⁺ perchlorate hexahydrate single crystals at different critical temperatures.     

Absorptionsspektrum des Ce3+-Ions und Schwingungsspektrum im CeCl3·7H2O und CeCl3·7D2O

The absorption spectra of CeCl₃·7 H₂O, LaCl₃·7 H₂O, CeCl₃·7 D₂O and LaCl₃·7 D₂O have been measured at low temperatures in the region of the 4 f→4 f infrared transitions. The energy levels of the Ce³⁺-ion in these compounds have been derived. The infrared phonon transitions have also been determined from the reflection spectra of these crystals measured in the region between 4000 cm^?1 and 50 cm^?1. Some of the energy levels of the Ce³⁺-ions in the deuterated crystals are shifted for about 10 wavenumbers against those in CeCl₃·7 H₂O. These shifts are probably due to an interaction of the electronic levels with resonant phonon-states in one or the other of the two compounds.     

Spectral and scintillation characteristics of compound x-ray detectors based on calcium iodide crystals

The results of an investigation of the spectral and scintillation properties of pure and Tl⁺, Eu²⁺, Fe²⁺, Co²⁺, and Ni²⁺ activated calcium iodide crystals as well as the results of measurements of the scintillation characteristics of compound x-ray detectors based on calcium iodide crystals are reported. It is shown that paired CaI₂ and CaI₂:Tl crystals can be used to fabricate compound detectors with different fluorescence times. On account of their high light output and good energy resolution CaI₂ and CaI₂:Eu crystals are suitable for compound detectors with different technical light output. CaI₂ or CaI₂:Eu scintillators together with scintillators based on calcium iodide with iron-group luminescence quenching impurity (Fe²⁺, Co²⁺, and Ni²⁺) can be used to obtain compound detectors with different physical light output. Zh. Tekh. Fiz. 68, 71–73 (September 1998)     

Ni2+:BeAl2O4晶体发光性质的研究

用时间分辨的激光诱导荧光光谱方法测量了10—300K温度范围内Ni²⁺:BeAl₂O₄晶体的红外荧光光谱和荧光寿命。通过荧光寿命的温度变化特性分析,得出³T_2g态的内禀辐射衰减寿命为123±7.2μs。无辐射弛豫的Mott激活能为1147cm^-1,并导出了此晶体发光量子效率随温度的变化关系式。Ni²⁺:BeAl₂O_{4关键词：}     

Mossbauer study of ferrite systems Co x Mn1−x Fe2O4 and Ni x Mn1−x Fe2O4

Mössbauer spectra of Co _x Mn_1?x Fe₂O₄ and Ni _x Mn_1?x Fe₂O₄ ferrites withx values ranging from 0·1 to 0·8 in steps of 0·1 have been recorded at room temperature. All spectra exhibit well-defined Zeeman hyperfine patterns. It has been observed that hyperfine field at Fe³⁺ nucleus increases more rapidly by nickel substitution than by cobalt substitution. This has been explained in terms of exchange interactions and cation distribution in the spinels. Hyperfine fields, isomer shifts and quadrupole splittings have been determined.     

EPR observation of a high temperature phase transition in Zn(ClO4)2·6H2O:Mn2+

The electron paramagnetic resonance of Mn²⁺ doped in single crystals of Zn(ClO₄)₂·6H₂O has been studied at X-band in the temperature range 300–380 K. A phase transition, observed at ～ 346 K, is reported for the first time.