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1.
Parallel electron energy-loss spectroscopy (PEELS) in a scanning transmission electron microscope (STEM) was used to record the Mn L 2,3-edges from a range of natural and synthetic manganese containing materials, covering valences 0, II, III, IV and VII, with an energy resolution of ca. 0.5 eV. The Mn L 2,3 electron-loss near-edge structure (ELNES) of these edges provided a sensitive fingerprint of its valence. The Mn 2+ L 2,3-edges show little sensitivity to the local site symmetry of the ligands surrounding the manganese. This is illustrated by comparing the Mn L 2,3-edges from 4-, 6- and 8-fold coordinated Mn 2+. In contrast, the Mn L 3-edges from Mn 3+ and Mn 4+ containing minerals exhibited ELNES that are interpreted in terms of a crystal-field splitting of the 3d electrons, governed by the symmetry of the surrounding ligands. The Mn L 3-edges for octahedrally coordinated Mn 2+, Mn 3+ and Mn 4+ showed variations in their ELNES that were sensitive to the crystal-field strength. The crystal-field strength (10Dq) was measured from these edges and compared very well with published optically determined values. The magnitude of 10Dq measured from the Mn L 3-edges and their O K-edge prepeaks of the manganese oxides were almost identical. This further confirms that the value of 10Dq measured at the Mn L 3-edge is correct. Selected spectra are compared with theoretical 2p atomic multiplet spectra and the differences and similarities are explained in terms of the covalency and site symmetry of the manganese. The Mn L 3-edges allow the valence of the manganese to be ascertained, even in multivalent state materials, and can also be used to determine 10Dq. 相似文献
2.
Crystals of the olivine minerals, tephroite (Mn 2SiO4) and fayalite (Fe 2SiO4) containing manganese(II) and iron (II and trace of III), respectively, were synthesized. Glasses were prepared from these crystalline materials by a splat-quench technique. Measurement of electron paramagnetic resonance (EPR) of all these powdered samples at room temperature show that the g-factors of Mn 2+ in both glassy and crystalline environments (g eff = 2.004) are the same, although the EPR linewidths (for glass, ΔH pp = 200 G; for crystals ΔH pp = 287 G) suggest less clustering of paramagnetic Mn 2+ ions in the glass. Mn 2+ probably occupies a distorted octahedral site in the tephroite crystal structure, although a four-fold coordination is suggested from other spectroscopic investigation on this glass. The EPR parameters of Fe 3+ in synthetic fayalite glass (g eff = 2.01 and 6.00; ΔH pp=150 and 1375 G, respectively, for the high and low field resonances) and powdered crystals (g eff = 3.31 and ΔH pp = 900 G) indicated that Fe 3+ ion in the crystals, is probably located in a distorted tetragonal site M2 and an axial environment has been proposed in the glassy system. 相似文献
3.
The use of ultrasonically modulated electron resonance (UMER) to study S-state ions in substitutional sites of mineral single crystals is discussed. Mn 2+ and Fe 3+ in natural single crystals of tremolite are used as examples. Combined electron paramagnetic resonance (EPR) and UMER measurements establish almost certainly that Mn 2+ enters predominantly into the distorted M4 sites occupied by Ca 2+ in the ideal tremolite structure and only to a minor extent into the M1, M2 and M3 sites normally occupied by Mg 2+. Fe 3+ in tremolite gives rise to the well known high spin resonance with g eff?4.3 but there is considerable uncertainty as to the site of the impurity ion. 相似文献
4.
Strong enrichments of cobalt occur in marine manganese nodules, soils, wads, and natural and synthetic minerals such as hollandite, cryptomelane, psilomelane, lithiophorite, birnessite, and δ-MnO 2. Previously, it was suggested that Co 3+ ions in these minerals replace either Mn 3+ or substitute for Fe 3+ in incipient goethite epitaxially intergrown with δ-MnO 2. Neither of these interpretations is now considered to be satisfactory on account of the large discrepancy of ionic radius between octahedrally coordinated low-spin Co 3+ and high-spin Mn 3+ or Fe 3+ in oxide structures. The close agreement between the ionic radii of Co 3+ and Mn 4+ suggests that some cobalt substitutes for Mn 4+ ions in edge-shared [MnO 6] octahedra in many manganese(IV) oxide mineral structures. It is proposed that hydrated cations, including Co 2+ ions, are initially adsorbed on to the surfaces of certain Mn(IV) oxides in the vicinity of essential vacancies found in the chains or sheets of edge-shared [MnO 6] octahedra. Subsequently, fixation of cobalt takes place as a result of oxidation of adsorbed Co 2+ ions by Mn 4+ and replacement of the displaced manganese by low-spin Co 3+ ions in the [MnO 6] octahedra or vacancies. 相似文献
5.
Summary The orange cathodoluminescence (CL) of calcite is known to be due to the presence of Mn 2+ cations. It has been demonstrated here using CL and electron paramagnetic resonance (EPR) crossed analysis from synthetic calcite that neither Fe 2+ nor Fe 3+ ions influence this luminescence emission. More complex natural calcium carbonates have been investigated to check whether or not this conclusion can be applied to them. For this purpose, different white marbles from Greek quarries were analysed with CL. The data are completed with neutron activation analysis (NAA) for manganese and iron contents. Again it is shown that only manganese plays a role in the orange CL of these white marbles. This result provides an important clue in the wide field of provenance determination of calcium carbonate used in ancient art.Received February 19, 2002; revised version accepted October 22, 2002
Published online March 10, 2003 相似文献
6.
Geological sedimentary dolomite samples from the Superior Proterozoic are studied using electron paramagnetic resonance (EPR)
spectroscopy. The complex spectra in the g=2.0 region is composed of Mn 2+ lines and signals due to crystallization and radiation-induced defects. Measurements in microwave frequencies of 9.5 GHz
(X-band) and 35 GHz (Q-band), and thermal and/or radiation treatments allowed identification of seven paramagnetic radicals
in the g=2.0 region: (1) isotropic organic radical; (2) axial SO 2
−; (3) axial PO 2
0 or PO 2
2−; (4) isotropic CO 2
−; (5) axial CO 2
−; (6) axial CO 3
3−; (7) isotropic unknown line. The use of these paramagnetic centres as indicators of geological events is discussed.
Received: 18 March 2002 / Accepted: 3 October 2002 相似文献
7.
The natural speciation of Mn (0.19 g/kg), Ni (46 mg/kg), and Zn (42 mg/kg) in the argillic horizon (120 cm depth, pH = 5.6) of an Ultisol from a paddy soil in northern Taiwan was investigated by advanced X-ray synchrotron techniques. Microchemical associations were imaged by synchrotron-based X-ray microfluorescence, host minerals were identified by standard and micrometer-resolved X-ray diffraction, and the local coordination environment of Mn, Ni, and Zn was probed using extended X-ray absorption fine structure (EXAFS) spectroscopy on a powdered sample and a soil thin section, and polarized EXAFS spectroscopy on a highly textured self-supporting clay film from the <2 μm fraction of the soil. Manganese was concentrated in Fe-Mn soft mottles (44.4 g/kg) as turbostratic hexagonal birnessite and lithiophorite having Mn 3+/Mn 4+ atomic ratios of ∼20% and 50%, respectively. Quantitative analysis of high-order scattering paths of the EXAFS spectrum for natural and synthetic lithiophorite revealed that Mn 3+ and Mn 4+ are ordered in the layer. A structural model is proposed, in which Mn 4+ and Mn 3+ are ordered similarly to Al and Li in the layer, with Mn 3+ cations being surrounded by six Mn 4+, and Mn 4+ cations by three Mn 3+ and three Mn 4+. Similar cation ordering in the manganese and aluminum layers likely provides a more homogeneous local balance of the excess and deficit of charges in each layer and increases the stability of lithiophorite. Ni ( r = 0.70 Å) substitutes for Mn (r(Mn 4+) = 0.54 Å, r(Mn 3+) = 0.65 Å) in the manganese layer in the natural lithiophorite. In contrast, Zn ( r = 0.74 Å) fills vacant sites in the gibbsitic layer of natural lithiophorite, in a similar manner as lithium ( r = 0.74 Å) in synthetic lithiophorite. The partitioning of Ni and Zn between the two layers is a result of the general preference of Ni, whose size is intermediate between those of Mn 3+ and Li +, for slightly smaller sites. In contrast with nickel, which is detected only where there is lithiophorite, the Zn-lithiophorite association found in Fe-Mn mottles is not representative of the bulk soil. The combined use of X-ray diffraction, and powder and polarized EXAFS spectroscopy revealed that Zn is predominantly bound to hydroxy-Al interlayers sandwiched between 2:1 vermiculite layers in the fine soil matrix. The incorporation of Zn in the gibbsitic layer of both lithiophorite and vermiculite helps increase the stability of these minerals by providing positive charge to balance the negative charge from the 2:1 phyllosilicate layer and the layer of lithiophorite. This binding environment for zinc is probably the main mechanism by which zinc is sequestered in acidic to near-neutral aluminum-rich clayey soils. 相似文献
8.
Mn 2+Sb 2S 4, a monoclinic dimorph of clerite, and benavidesite (Mn 2+Pb 4Sb 6S 14) show well-individualized single chains of manganese atoms in octahedral coordination. Their magnetic structures are presented
and compared with those of iron derivatives, berthierite (Fe 2+Sb 2S 4) and jamesonite (Fe 2+Pb 4Sb 6S 14). Within chains, interactions are antiferromagnetic. Like berthierite, MnSb 2S 4 shows a spiral magnetic structure with an incommensurate 1D propagation vector [0, 0.369, 0], unchanged with temperature.
In berthierite, the interactions between identical chains are antiferromagnetic, whereas in MnSb 2S 4 interactions between chains are ferromagnetic along c-axis. Below 6 K, jamesonite and benavidesite have commensurate magnetic structures with the same propagation vector [0.5, 0, 0]:
jamesonite is a canted ferromagnet and iron magnetic moments are mainly oriented along the a-axis, whereas for benavidesite, no angle of canting is detected, and manganese magnetic moments are oriented along b-axis. Below 30 K, for both compounds, one-dimensional magnetic ordering or correlations are visible in the neutron diagrams
and persist down to 1.4 K. 相似文献
9.
A quantitative analysis of the distortion of octahedral and tetrahedral coordination polyhedra with respect to perfect symmetry in crystal structures is presented. The distortion of a polyhedron is defined by all the fourfold and threefold pseudo-symmetries. Tests on the significance of the pseudo-symmetries are presented. In forsterite the results are compared to ones previously proposed, based on the pseudo-symmetry of fourth order expansion of the crystal field, and also compared to the pseudo-symmetries of the environment of Mn 2+ and Gd 3+ that were determined by electron paramagnetic resonance (EPR) measurements. Agreements and differences between these results are given. 相似文献
10.
Eighty ferromanganese nodules from a wide variety of marine and fresh-water environments have been analyzed by electron spin resonance spectroscopy. The purpose has been to gain information on the forms in which the major constituents of manganese nodules are present. Contributions to ESR spectra of the nodules come mainly from Mn 2+ and Fe 3+. Deep-sea samples generally showed only broad resonance lines, and those with larger peaks close to g = 2.0 are believed to contain more Mn 2+ than others. Some Antarctic and fresh-water nodules lack a strong Mn 2+ resonance and have a peak around g = 4.0 which is most likely tetrahedral Fe 3+. A number of smaller peaks in several samples could not be readily interpreted in terms of contributions from individual ionic species because of fundamental problems in preparing standards having the ion of interest in the same micro-environment as it experiences in the nodules. 相似文献
11.
X-ray absorption spectroscopy, including extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) techniques, have been used to determine the structure and speciation of complexes for Fe 2+ and Fe 3+ chloride solutions at a variety of pH's, ionic strengths, and chloride/iron ratios.Low intensity K-edge transition features and analysis of modified pair correlation functions, derived from Fourier transformation of EXAFS spectra, show a regular octahedral coordination of Fe(II) by water molecules with a first-shell Fe 2+-O bond distance, closely matching octahedral Fe 2+-O bonds obtained from solid oxide model compounds. Solution Fe 2+-O bond distances decrease with chloride/iron ratio, pH, and total FeCl 2 concentration. A slight intensification of the transition with increasing FeCl 2 concentration suggests that chloride may begin to mix with water as a nearest-neighbor octahedral ligand. Fe 3+ solutions show a pronounced increase in the transition intensities between 1.0 M FeCl 3/7.8 M Cl ? to 1.0 M FeCl 3/ 15 M Cl ?, indicating a coordination change from octahedral to tetrahedral complexes. EXAFS analyses of these solutions show an increase in first-shell Fe 3+-ligand distances despite this apparent reduction in coordination number. This can be best explained by a change from regular octahedral complexes of ferric iron (either Fe(H 2O) 63+ or trans-Fe(H 2O) 4Cl 2 or both; Fe 3+-O bond distances of 2.10 Å) to tetra-chloro complexes [Fe 3+-Cl bond distances of 2.25 Å]. 相似文献
12.
The rate of crystal growth of Mn 3O 4 (hausmannite) and βMnOOH (feitknechtite) in aerated aqueous manganous perchlorate systems, near 0.01 M in total manganese, was determined at pH levels ranging from 7.00 to 9.00 and at temperatures from 0.5 to 37.4°C. The process is autocatalytic, but becomes psuedo first-order in dissolved Mn 2+ activity when the amount of precipitate surface is large compared to the amount of unreacted manganese. Reaction rates determined by titrations using an automated pH-stat were fitted to an equation for precipitate growth. The rates are proportional to surface area of oxide and degree of supersaturation with respect to Mn 2+. The oxide obtained at the higher temperature was Mn 3O 4, but at 0.5° C only βMnOOH was formed. At intermediate temperatures, mixtures of these solids were formed. The rate of precipitation of hausmannite is strongly influenced by temperature, and that of feitknechtite much less so. The difference in activation energy may be related to differences in crystal structure of the oxides and the geometry of polymeric hydroxy ion precursors. 相似文献
13.
The role of manganese in the chemical composition and coloring of tourmaline is discussed. It is shown that manganese tourmaline-tsilaisite is similar to tourmaline-elbaite in composition and condition formation. The miscibility in the sherlite-elbaite-tsilaisite system is complete, but in the sherlite-dravite-tsilaisite system there is a gap between the dravite and tsilaisite, similar to the relationship between dravite and elbaite. Manganese may be present in tourmaline in the form of Mn 2+ and Mn 3+. The pink coloring of the tourmaline is caused by Mn 3+. This conclusion has been drawn from data provided by many authors on the nature of pink coloring of tourmaline, the dyeing properties of Mn 2+ and Mn 3+, the possibility of the existence of Mn 3+ during the crystallization of pink tourmaline, and the distribution of manganese in differently colored tourmaline. --auth. 相似文献
14.
The local structures of divalent Zn, Cu, and Pb sorbed on the phyllomanganate birnessite (Bi) have been studied by powder and polarized extended X-ray absorption fine structure (EXAFS) spectroscopy. Metal-sorbed birnessites (MeBi) were prepared at different surface coverages by equilibrating at pH 4 a Na-exchanged buserite (NaBu) suspension with the desired aqueous metal. Me/Mn atomic ratios were varied from 0.2% to 12.8% in ZnBi and 0.1 to 5.8% in PbBi. The ratio was equal to 15.6% in CuBi. All cations sorbed in interlayers on well-defined crystallographic sites, without evidence for sorption on layer edges or surface precipitation. Zn sorbed on the face of vacant layer octahedral sites (□), and shared three layer oxygens (O layer) with three-layer Mn atoms (Mn layer), thereby forming a tridentate corner-sharing (TC) interlayer complex (Zn-3O layer-□-3Mn layer). TCZn complexes replace interlayer Mn 2+ (Mn inter2+) and protons. TCZn and TCMn inter3+ together balance the layer charge deficit originating from Mn layer4+ vacancies, which amounts to 0.67 charge per total Mn according to the structural formula of hexagonal birnessite (HBi) at pH 4. At low surface coverage, zinc is tetrahedrally coordinated to three O layer and one water molecule ( [IV]TC complex: (H 2O)- [IV]Zn-3O layer). At high loading, zinc is predominantly octahedrally coordinated to three O layer and to three interlayer water molecules ( [VI]TC complex: 3(H 2O)- [VI]Zn-3O layer), as in chalcophanite ( [VI]ZnMn 34+O 7·3H 2O). Sorbed Zn induces the translation of octahedral layers from − a/3 to + a/3, and this new stacking mode allows strong H bonds to form between the [IV]Zn complex on one side of the interlayer and oxygen atoms of the next Mn layer (O next): O next…(H 2O)- [IV]Zn-3O layer. Empirical bond valence calculations show that O layer and O next are strongly undersaturated, and that [IV]Zn provides better local charge compensation than [VI]Zn. The strong undersaturation of O layer and O next results not only from Mn layer4+ vacancies, but also from Mn 3+ for Mn 4+ layer substitutions amounting to 0.11 charge per total Mn in HBi. As a consequence, [IV]Zn,Mn layer3+, and Mn next3+ form three-dimensional (3D) domains, which coexist with chalcophanite-like particles detected by electron diffraction. Cu 2+ forms a Jahn-Teller distorted [VI]TC interlayer complex formed of two oxygen atoms and two water molecules in the equatorial plane, and one oxygen and one water molecule in the axial direction. Sorbed Pb 2+ is not oxidized to Pb 4+ and forms predominantly [VI]TC interlayer complexes. EXAFS spectroscopy is also consistent with the formation of tridentate edge-sharing ( [VI]TE) interlayer complexes (Pb-3O layer-3Mn), as in quenselite (Pb 2+Mn 3+O 2OH). Although metal cations mainly sorb to vacant sites in birnessite, similar to Zn in chalcophanite, EXAFS spectra of MeBi systematically have a noticeably reduced amplitude. This higher short-range structural disorder of interlayer Me species primarily originates from the presence of Mn layer3+, which is responsible for the formation of less abundant interlayer complexes, such as [IV]Zn TC in ZnBi and [VI]Pb TE in PbBi. 相似文献
15.
Cu- and Mn-bearing tourmalines from Brazil and Mozambique were characterised chemically (EMPA and LA-ICP-MS) and by X-ray single-crystal structure refinement. All these samples are rich in Al, Li and F (fluor-elbaite) and contain significant amounts of CuO (up to ~1.8 wt%) and MnO (up to ~3.5 wt%). Structurally investigated samples show a pronounced positive correlation between the < Y-O> distances and the (Li + Mn 2+ + Cu + Fe 2+) content (apfu) at this site with R 2 = 0.90. An excellent negative correlation exists between the < Y-O> distances and the Al 2O 3 content ( R 2 = 0.94). The samples at each locality generally show a strong negative correlation between the X-site vacancies and the (MnO + FeO) content. The Mn content in these tourmalines depends on the availability of Mn, on the formation temperature, as well as on stereochemical constraints. Because of a very weak correlation between MnO and CuO we believe that the Cu content in tourmaline is essentially dependent on the availability of Cu and on stereochemical constraints. 相似文献
16.
The formation of authigenic manganese minerals and ores in the pelagic regions of the ocean is related to oxidation of Mn 2+ extracted from basalts and other rocks with heated seawater. For littoral parts of the ocean and lakes mobilization of Mn 2+ and Fe 2+ is admitted finding its way to the bottom sediments (along with the organic substances) from land in the form of Mn 4+. The main manganese mineral of oceanic and continental basins is vernadite. Its deposition is considered a result of the activity of microorganisms. 相似文献
17.
Polarized absorption spectra of natural piemontite (Ca1.802Mn
2+0.178
Mg0.025) (Mn
3+0.829
Fe
3+0.346
Al1.825) [(Si2.992Al0.008) O12OH], viridine (Al1.945Mn
3+0.033
Fe
3+0.063
Mg0.003) [O|Si0.970 O4], and kanonaite (Al1.291Mn
3+0.682
Fe
3+0.019
) [O|Si1.006 O4] were measured at 295 and ca. 100 K. For piemontite, lowering the temperature resulted in a sharpening of broad bands in the 10 000–25 000 cm−1 region supporting their assignment to single ion Mn3+ in M3 non-centrosymmetric sites. Alternatively, in kanonaite, temperature behaviour pointed to a slightly stronger influence of vibronic coupling on strong bands near 16 000 and 22 000 cm−1, which supported an interpretation of Mn3+ in nearly centrosymmetric M1 sites. Measurements at ca. 100 K show pronounced fine structure in the viridine spectra which is attributed to Fe3+. The ɛ values for Mn3+ spin-allowed bands in the three minerals lie in the range 18 to 227 [1·g-atom−1·cm−1]. For the same band and polarisation, ɛ values in Mn3+-bearing andalusite-type minerals viridine and kanonaite are the same, which indicates an absence of strong magnetic coupling effects between Mn3+ ions in the andalusite type structure down to ca. 100 K. In silicates, the high ɛ values for Mn3+ spin-allowed bands, in comparison to those obtained for Fe2+ spin-allowed bands from sites of “similar distortion”, is attributed to a higher degree of covalency in the Mn3+-O bonds compared to the Fe2+-O bonds, as a result of the higher valence state of manganese. 相似文献
18.
Structural interaction between dissolved fluorine and silicate glass (25°C) and melt (to 1400°C) has been examined with 19F and 29Si MAS NMR and with Raman spectroscopy in the system Na 2O-Al 2O 3-SiO 2 as a function of Al 2O 3 content. Approximately 3 mol.% F calculated as NaF dissolved in these glasses and melts. From 19F NMR spectroscopy, four different fluoride complexes were identified. These are (1) Na-F complexes (NF), (2) Na-Al-F complexes with Al in 4-fold coordination (NAF), (3) Na-Al-F complexes with Al in 6-fold coordination with F (CF), and (4) Al-F complexes with Al in 6-fold, and possibly also 4-fold coordination (TF). The latter three types of complexes may be linked to the aluminosilicate network via Al-O-Si bridges.The abundance of sodium fluoride complexes (NF) decreases with increasing Al/(Al + Si) of the glasses and melts. The NF complexes were not detected in meta-aluminosilicate glasses and melts. The NAF, CF, and TF complexes coexist in peralkaline and meta-aluminosilicate glasses and melts.From 29Si-NMR spectra of glasses and Raman spectra of glasses and melts, the silicate structure of Al-free and Al-poor compositions becomes polymerized by dissolution of F because NF complexes scavenge network-modifying Na from the silicate. Solution of F in Al-rich peralkaline and meta-aluminous glasses and melts results in Al-F bonding and aluminosilicate depolymerization.Temperature (above that of the glass transition) affects the Q n-speciation reaction in the melts, 2Q 3 ⇔ Q 4 + Q 2, in a manner similar to other alkali silicate and alkali aluminosilicate melts. Dissolved F at the concentration level used in this study does not affect the temperature-dependence of this speciation reaction. 相似文献
19.
Extended X-ray absorption fine-structure (EXAFS) spectroscopy is used to characterize the local coordination of selected rare-earth elements (Nd 3+, Sm 3+, Dy 3+, Yb 3+) coprecipitated with calcite in minor concentrations from room-temperature aqueous solutions. Fitting results confirm substitution in the Ca site, but first-shell Nd-O and Sm-O distances are longer than the Ca-O distance in calcite and longer than what is consistent with ionic radii sums for sixfold coordination in the octahedral Ca site. In contrast, first-shell Dy-O and Yb-O distances are shorter than the Ca-O distance and are consistent with ionic radii sums for sixfold coordination. Comparison of Nd-O and Sm-O bond lengths with those in lanthanide sesquioxides and with ionic radii trends across the lanthanide series suggests that Nd 3+ and Sm 3+ have sevenfold coordination in a modified Ca site in calcite. This would require some disruption of the local structure, with an expected decrease in stability, and possibly a different charge compensation mechanism between Nd and Sm vs. Yb and Dy. A possible explanation for the increased coordination for the larger rare-earth elements involves bidentate ligation from a CO 3 group. Because trivalent actinides such as Am 3+ and Cm 3+ have ionic radii similar to Nd 3+, their incorporation in calcite may result in a similar defect structure. 相似文献
20.
It is shown the possibility to determine the coordination of paramagnetic ions in disordered solid structures, e.g., in barium
borate glasses. For this purpose the electron paramagnetic resonance (EPR) method was used to study α-and β-BaB 2O 4 crystals and glasses of 45·BaO × 55·B 2O 3 and 40·BaO × 60·B 2O 3 (mol%) composition activated by Ag + and Pb 2+ ions. After the samples were exposed to X-rays at 77 K, different EPR centers were observed in them. In α-and β-BaB 2O 4 crystals and glasses the EPR centers Ag 2+, Ag 0, Pb +, Pb 3+, and hole centers of O − type were studied. The EPR parameters of these centers and their arrangement in crystal structure were determined. It is
shown that Pb 3+ ions in β-BaB 2O 4 crystals occupy Ba 2+ position in an irregular polyhedron from the eight oxygen, whereas in α-BaB 2O 4 crystals they occupy Bа 2 position in a sixfold coordination. Pb + ions in α-BaB 2O 4 crystals occupy Bа 1 position in a ninefold coordination from oxygen. In barium borate glasses, Pb 3+ ions were studied in coordination polyhedron from six oxygen atoms and in a polyhedron from nine to ten oxygen atoms. It
is assumed that the established difference in the structural position of Pb 3+ ions in glasses is due to their previous incorporation in associative cation–anion complexes (AC) and “free” structure-forming
cations (FC). Computer simulations have been performed to analyze the stability of specific associative complexes and to compare
their bond lengths with experimental data. 相似文献
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