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![The crystal structures in three projections of: initial elpidite from the Lovozero alkaline massif (a-c), initial elpidite from Khan Bogdo (drawn after [3]) (d-f) and Ag-exchanged form of elpidite from Khan Bogdo [only the main Ag sites are shown] (g-i). The unit cells are outlined.](profile/Vladislav-Kostov/publication/334387988/figure/fig1/AS:779321874587648@1562816222040/The-crystal-structures-in-three-projections-of-initial-elpidite-from-the-Lovozero.jpg)
The crystal structures in three projections of: initial elpidite from the Lovozero alkaline massif (a-c), initial elpidite from Khan Bogdo (drawn after [3]) (d-f) and Ag-exchanged form of elpidite from Khan Bogdo [only the main Ag sites are shown] (g-i). The unit cells are outlined.
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Elpidite from the Lovozero alkaline complex, Kola Peninsula, Russia, and Ag-exchanged forms of elpidite from two different localities (Lovozero and Khan Bogdo, Mongolia) were studied by means of single-crystal X-ray diffraction, electron microprobe analysis, thermogravimetry and IR spectroscopy. All studied samples retain the heteropolyhedral frame...
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![Figure 3. Crystal structure of the Ag-exchanged form of Na6Zr3[Si9O27]...](publication/339796175/figure/fig1/AS:867190458814464@1583765725130/Crystal-structure-of-the-Ag-exchanged-form-of-Na6Zr3Si9O27-with-all-Ag-sites-marked-in_Q320.jpg)
![Chemical composition of the Ag-exchanged form of Na6Zr3[Si9O27].](publication/339796175/figure/tbl3/AS:867190458826752@1583765725221/Chemical-composition-of-the-Ag-exchanged-form-of-Na6Zr3Si9O27_Q320.jpg)
The crystal structure of the Ag-exchanged form of the zirconosilicate with the simplified formula (Na6-2xCaxx)Zr3[Si9O27] with x < 1 (the idealized formula Na6Zr3[Si9O27]), a product of thermal transformation of catapleiite, ideally Na2Zr[Si3O9]·2H2O, was studied using single crystal X-ray diffraction data. The crystal structure of Na6Zr3[Si9O27] i...
Citations
... The silicon-oxygen radical has the designation 3 T 6 , where T means "tetrahedron", 3 is the connectivity of the tetrahedron and 6 is the number of such tetrahedra in the geometrical repeat unit [3]. The same type of ribbon ( 3 T 6 ) can be found in the crystal structures of minerals of the epididymite group, which include epididymite, Na 2 Be 2 [Si 6 [7]. It is interesting to note, that in armstrongite, CaZr[Si 6 O 15 ]·2H 2 O [8], and dalyite, (K,Na) 2 Zr[Si 6 O 15 ] [9], the radical [Si 6 O 15 ] does not form a ribbon. ...
... A number of experiments on the dehydration and thermal stability of elpidite (for example, [6,7,11,[13][14][15]) yielded that diffusion within the elpidite structure proceeds via a zigzag track along the c axis. As it is stated in [11,15], at about 100 • C, the crystal structure of elpidite undergoes changes from Pbcm to Cmce with the doubled a parameter. ...
... The average compositions (determined over 6-10 spots) are reported in Table 2. [14]; ElKhB (c) -elpidite from Khan Bogdo (Mongolia) [7]. ...
Elpidite belongs to a special group of microporous zirconosilicates, which are of great interest due to their capability to uptake various molecules and ions, e.g., some radioactive species, in their structural voids. The results of a combined electron probe microanalysis and single-crystal X-ray diffraction study of the crystals of elpidite from Burpala (Russia) and Khan-Bogdo (Mongolia) deposits are reported. Some differences in the chemical compositions are observed and substitution at several structural positions within the structure of the compounds are noted. Based on the obtained results, a detailed crystal–chemical characterization of the elpidites under study was carried out. Three different structure models of elpidite were simulated: Na2ZrSi6O15·3H2O (related to the structure of Russian elpidite), partly Ca-replaced Na1.5Ca0.25ZrSi6O15·2.75H2O (close to elpidite from Mongolia), and a hypothetical CaZrSi6O15·2H2O. The vibration spectra of the models were obtained and compared with the experimental one, taken from the literature. The strong influence of water molecule vibrations on the shape of IR spectra of studied structural models of elpidite is discussed in the paper
... Subsequently, Jale et al. reported three zirconoosilicate minerals (elpidite, umbite, and gaidonnayit), which Surfaces 2021, 4 42 contain SiO 4 in tetrahedral coordination and ZrO 6 in octahedral coordination [11]. On the other hand, the isomorphous substitutions of various ions as metal dopants into the zeolitic frameworks have also attracted interest over the last decade [12][13][14][15][16][17][18][19]. These metal dopants can be incorporated into the zirconosilicates frameworks, either as guest species in a solid solution or as separate phases encapsulated in the zeolite frameworks [19][20][21]. ...
... On the other hand, the isomorphous substitutions of various ions as metal dopants into the zeolitic frameworks have also attracted interest over the last decade [12][13][14][15][16][17][18][19]. These metal dopants can be incorporated into the zirconosilicates frameworks, either as guest species in a solid solution or as separate phases encapsulated in the zeolite frameworks [19][20][21]. It has been shown that the dopants lead to changing ion-exchange activities of zeolite materials, in which the isomorphous substitutions of some ions with others have different oxidation states through incorporations into tetrahedral positions [13,15]. ...
... It was also found that various cationic forms of synthetic titanosilicates can remove trace amounts of Cs(II) and Sr(II) from aqueous solutions [1]. Elpidite mineral (Na 2 ZrSi 6 O 15 ·3H 2 O) is an example of zirconosilicate phases characterized by its active ion-exchange behavior [19]. ...
Decontamination of water from radionuclides contaminants is a key priority in environmental cleanup and requires intensive effort to be cleared. In this paper, a microporous iron-doped zeolite-like sodium zirconosilicate (F@SZS) was designed through hydrothermal synthesis with various Si/Zr ratios of 5, 10, and 20, respectively. The synthesized materials of F@SZS materials were well characterized by various techniques such as XRD, SEM, TEM, and N2 adsorption–desorption measurements. Furthermore, the F@SZS-5 and F@SZS-10 samples had a crystalline structure related to the Zr–O–Si bond, unlike the F@SZS-20 which had an overall amorphous structure. The fabricated F@SZS-5 nanocomposite showed a superb capability to remove cesium ions from ultra-dilute concentrations, and the maximum adsorption capacity was 21.5 mg g–1 at natural pH values through an ion exchange mechanism. The results of cesium ions adsorption were found to follow the pseudo-first-order kinetics and the Langmuir isotherm model. The microporous iron-doped sodium zirconosilicate is described as an adsorbent candidate for the removal of ultra-traces concentrations of Cs(I) ions.
... Wide channels inside the heteropolyhedral framework contain Nа + cations and H 2 O molecules (Neronova and Belov, 1964;Cannillo et al., 1973). The presence of the threedimensional system of these channels causes distinct zeolitic properties of elpidite: this mineral readily exchanges Na + in aqueous solutions for other large cations (K + , Rb + , Cs + , Ag + and Pb 2+ ) and demonstrates reversible dehydration in thermal experiments (Turchkova et al., 2006;Grigor'eva et al., 2011;Zubkova et al., 2011Zubkova et al., , 2019Cametti et al., 2016). Elpidite is an orthorhombic mineral. ...
... For different samples of elpidite and its laboratory-modified (cation-substituted or dehydrated) forms, a variety of space groups (Pbmm, Pbm2, Pbcm, Bba2, Cmce) was reported and doubling of the a and/or c unit-cell parameters was found in some cases. Crystal chemical data on all structurally studied samples of elpidite, its monoclinic (C2/m) dimorph yusupovite and modified forms of elpidite were recently summarised and reviewed by Zubkova et al. (2019). ...
... The lowering of symmetry to Pma2 means splitting can be avoided: the O atom almost fully occupies one site (89%) and the Na1 site is not split and occupied fully by statistically substituting Na cations and H 2 O molecules. The same symmetry lowering to Pma2 was found for the elpidite sample studied by Neronova and Belov (1964), for Ca-enriched variety of elpidite (Sapozhnikov and Kashaev, 1978) and for elpidite from Lovozero reported by Zubkova et al. (2019) but in the latter only the Ow2 site was finally not split while the Na site was split. ...
An unusual highly hydrated and Na-depleted variety of elpidite was identified in a hydrothermally altered peralkaline pegmatite at Mt. Yukspor in the Khibiny alkaline complex, Kola Peninsula, Russia. It differs from ‘ordinary’ elpidite, ideally Na 2 ZrSi 6 O 15 ⋅3H 2 O, in its crystal chemical features, infrared spectrum and optical characteristics. The chemical composition (wt.%, electron microprobe, H 2 O by TGA) is: Na 2 O 5.45, K 2 O 0.67, CaO 0.05, SiO 2 60.32, TiO 2 1.34, ZrO 2 18.43, Nb 2 O 5 0.65, H 2 O 12.80, total 99.71. The empirical formula calculated on the basis of 6 Si and 15 O atoms is [(Na 1.05 K 0.08 Ca 0.01 ) Σ1.14 (H 3 O) 0.74 ] Σ1.88 (Zr 0.89 Ti 0.10 Nb 0.03 ) Σ1.02 Si 6 O 15 ⋅3.47H 2 O; the H 2 O:H 3 O ratio was calculated from the charge balance requirement, taking into account the results of crystal structure refinement. The highly hydrated variety of elpidite is orthorhombic, Pma 2, a = 14.5916(6), b = 7.3294(3), c = 7.1387(2) Å, V = 763.47(5) Å ³ and Z = 2. The crystal structure was solved from single-crystal X-ray diffraction data, R 1 = 3.43%. The structure is based upon an elpidite-type heteropolyhedral Zr–Si–O framework with Na ⁺ and H 3 O ⁺ cations and H 2 O molecules in the zeolitic channels. Hydronium cations substitute for water molecules in one of the extra-framework sites. This variety of elpidite could be considered as an intermediate product of natural ion-exchange reaction between ‘ordinary’ elpidite and a low-temperature hydrothermal fluid.
... The crystal structure of elpidite was first solved in 1963 by Neronova and Belov [2] in the space group Pbmm on sample from the Lovozero alkaline complex, Kola peninsula, Russia. Later on, the structure of this mineral from another locality in the same Lovozero complex was re-refined by different authors, in some cases in the acentric space group (S.G.) Pbm2 (No. 28) [3,4] or in the space group Pbcm (No. 57) with one unit-cell parameter doubled [5]. Rietveld powder diffraction analysis has been applied in the second case. ...
... Among many natural and synthetic zirconosilicates, elpidite got particular attention because of its pronounced cation-exchange properties which occur both in laboratory conditions [10,7,4] and in nature [11]. The mineral exhibits high exchange capacity for K and Rb, accompanied by pronounced dehydration and structural modification, resulting in the doubling of the a-parameter (~7 Å) and change of symmetry from Pbcm (No. 57) to Cmce (No. 64) [7]. ...
... The mineral exhibits high exchange capacity for K and Rb, accompanied by pronounced dehydration and structural modification, resulting in the doubling of the a-parameter (~7 Å) and change of symmetry from Pbcm (No. 57) to Cmce (No. 64) [7]. Recently, similar structural conversions were reported for natural samples of elpidite from: (i) Lovozero, Kola peninsula, Russia and (ii) Khan Bogdo, Mongolia upon ion-exchange on Ag [4]. In both cases a high exchange capacity to Ag has been registered as the cation exchange is accompanied by a significant distortion of the heteropolyhedral framework, which results in the doubling of the ~7 Å parameters of the unit cell and the change in symmetry from space groups Pma2 (No. 28) (Lovozero) or Pbcm (No. 57) (Khan Bogdo) to Cmce (No. 64). ...
Elpidite is a natural microporous zirconosilicate with ideal formula Na2ZrSi6O15.3H2O. It attracts much attention due to its pronounced cation-exchange properties which occur both in laboratory conditions and in nature. The mineral exhibits high exchange capacity for K Rb, and Ag accompanied by pronounced structural modification, resulting in the doubling of some of the ~7 Å unit cell parameters and change of symmetry from Pma2 or Pbcm to Cmce. Similar modifications of its framework has also been observed when this material is subjected to dehydration. This work focuses attention to the amazing framework flexibility of elpidite subjected to ion-exchange and dehydration procedures. Various geometric parameters such as rotation and tilt angles, channels apertures, and distortion indices have been introduced in order to quantify the occurring structural modifications. Analysis of their measured values has allowed elucidation of the mechanism through which the elpidite structure responds to the applied laboratory modifications.
... The crystal structure of elpidite was first solved in 1963 by Neronova and Belov [2] in the space group Pbmm on sample from the Lovozero alkaline complex, Kola peninsula, Russia. Later on, the structure of this mineral from another locality in the same Lovozero complex was re-refined by different authors, in some cases in the acentric space group (S.G.) Pbm2 (No. 28) [3,4] or in the space group Pbcm (No. 57) with one unit-cell parameter doubled [5]. Rietveld powder diffraction analysis has been applied in the second case. ...
... Among many natural and synthetic zirconosilicates, elpidite got particular attention because of its pronounced cation-exchange properties which occur both in laboratory conditions [10,7,4] and in nature [11]. The mineral exhibits high exchange capacity for K and Rb, accompanied by pronounced dehydration and structural modification, resulting in the doubling of the a-parameter (~7 Å) and change of symmetry from Pbcm (No. 57) to Cmce (No. 64) [7]. ...
... The mineral exhibits high exchange capacity for K and Rb, accompanied by pronounced dehydration and structural modification, resulting in the doubling of the a-parameter (~7 Å) and change of symmetry from Pbcm (No. 57) to Cmce (No. 64) [7]. Recently, similar structural conversions were reported for natural samples of elpidite from: (i) Lovozero, Kola peninsula, Russia and (ii) Khan Bogdo, Mongolia upon ion-exchange on Ag [4]. In both cases a high exchange capacity to Ag has been registered as the cation exchange is accompanied by a significant distortion of the heteropolyhedral framework, which results in the doubling of the ~7 Å parameters of the unit cell and the change in symmetry from space groups Pma2 (No. 28) (Lovozero) or Pbcm (No. 57) (Khan Bogdo) to Cmce (No. 64). ...
Elpidite is a natural microporous zirconosilicate with ideal formula Na2ZrSi6O15.3H2O. It attracts much attention due to its pronounced cation-exchange properties which occur both in laboratory conditions and in nature. The mineral exhibits high exchange capacity for K Rb, and Ag accompanied by pronounced structural modification, resulting in the doubling of some of the ~7 Å unit cell parameters and change of symmetry from Pma2 or Pbcm to Cmce. Similar modifications of its framework has also been observed when this material is subjected to dehydration. This work focuses attention to the amazing framework flexibility of elpidite subjected to ion-exchange and dehydration procedures. Various geometric parameters such as rotation and tilt angles, channels apertures, and distortion indices have been introduced in order to quantify the occurring structural modifications. Analysis of their measured values has allowed elucidation of the mechanism through which the elpidite structure responds to the applied laboratory modifications.
... The crystal structure of elpidite was first solved in 1963 by Neronova and Belov [2] in the space group Pbmm on a sample from the Lovozero (L) alkaline complex, Kola Peninsula, Russia. Subsequently, the structure of this mineral from the Lovozero complex was re-refined by different authors, in some cases in the acentric space group Pbm2 [3,4] or in Pbcm with one of the unit-cell parameters doubled [5]. Rietveld powder diffraction analysis has been applied in the latter case. ...
... In 1973, Cannillo et al. [8] and in 2016, Cametti et al. [9] determined the elpidite crystal structure on samples from Mont Saint-Hilaire (MSH), Québec, Canada in space group (S.G.) Pbcm. Despite the observed differences in the space groups of different samples belonging to one mineral species and taken from the same or various localities, all studied compounds retain an equal structural topology that can be presented as a heteropolyhedral framework consisting of double Si 6 O 15 chains (ribbons) connected by isolated ZrO 6 octahedra [4]. ...
... In this study, twist-, tiltand azimuth-angles have also been measured for the crystal structures determined by single crystal X-ray diffraction of the initial unprocessed elpidite samples from Lovozero (Pma2) [4], Khan Bogdo (Pbcm) [7], and Mont Saint-Hilaire (Pbcm) [9], as well as for all reliable crystal structure refinements performed here. Later in this work, they will be used to track the structural evolution and to evaluate the framework flexibility of these materials occurring upon heating. ...
The present study demonstrates the capabilities of the Rietveld procedure to track the structural transformations and framework flexibility on the example of the natural water-containing zirconosilicate elpidite, subjected (in bulk) to thermal treatment from room temperature to 300 • C. The methodological approach to the performed refinements and the obtained results are in accordance with the previously reported data from in situ single crystal X-ray diffraction studies on heated samples of the same mineral. More light has been drawn on the temperature interval in which the non-reconstructive topotactic phase transition occurs upon partial dehydration. The framework flexibility observed as a response to the water loss and subsequent thermal expansion was evaluated in terms of intentionally introduced set of geometric parameters characterizing the spatial orientation of symmetrically related zirconium octahedra in the structure, the coordination polyhedra volumes, their distortion indices, and bond angle variances.
... Silver cations replace sodium; however, calcium cations remain practically unreplaced. As well as in the recently reported results of Ag exchange in another zirconosilicate elpidite, ideally Na2ZrSi6O15⋅3H2O [21], the incorporation of Ag+ in the structure of Na6Zr3[Si9O27] causes a significant distortion of the heteropolyhedral framework resulting in the doubling of a parameter of the hexagonal unit cell and the change of the space group from centrosymmetric P63/mcm (Na6Zr3[Si9O27]) to acentric P63cm (its Ag-exchanged form); in elpidite, the cation exchange accompanied by a significant distortion of the framework results in the doubling of the parameters of the orthorhombic unit cell and the change in symmetry from space groups Pma2 or Pbcm (characteristic to the initial elpidite samples from different localities) to Cmce. Funding: This work was supported by the Russian Foundation for Basic Research, grants nos. ...
The crystal structure of the Ag-exchanged form of the zirconosilicate with the simplified formula (Na6-2xCaxx)Zr3[Si9O27] with x < 1 (the idealized formula Na6Zr3[Si9O27]), a product of thermal transformation of catapleiite, ideally Na2Zr[Si3O9]·2H2O, was studied using single crystal X-ray diffraction data. The crystal structure of Na6Zr3[Si9O27] is based on a heteropolyhedral framework built by nine-membered tetrahedral rings [Si9O27] and isolated [ZrO6] octahedra. This zirconosilicate demonstrates high exchange capacity to Ag (experiment with 1 M AgNO3 aqueous solution, 250 °C, 30 days). Its Ag-exchanged form with the simplified formula (Ag5Ca0.5)Zr3[Si9O27] is characterized by a significant distortion of the heteropolyhedral framework and strongly disordered arrangement of extra-framework cations (Ag) which results in the doubling of a parameter of the hexagonal unit cell [a = 23.3462(3), c = 10.10640(10) Å, V = 4770.45(13) Å3] and space group P63cm. Ag+ cations preferably occupy the sites that are close to the Na sites in Na6Zr3[Si9O27].
Flexible crystal(水晶) structures, which exhibit(展览) single-crystal(水晶)-to-single-crystal(水晶) (SCSC) transformations(转型), are attracting attention(注意) in many applied aspects: magnetic(磁) switches, catalysis, ferroelectrics and sorption. Acid treatment(治疗) for titanosilicate material(材料) AM-4 and natural(自然) compounds with the same structures led to SCSC transformation(转型) by loss(损失) Na+, Li+ and Zn2+ cations with large structural(结构) changes (20% of the unit(单位)-cell(细胞) volume(体积)). The conservation(保育) of crystallinity through complex(复杂) transformation(转型) is possible due(由于) to the formation(形成) of a strong hydrogen bonding(债券) system(系统). The mechanism(机制) of transformation(转型) has been characterized using single-crystal(水晶) X-ray(射线) diffraction analysis(分析), powder(粉) diffraction, Rietvield refinement, Raman spectroscopy and electron microscopy. The low migration(迁移) energy(能源) of cations in the considered materials(材料) is confirmed using bond(债券)-valence and density(密度) functional(功能) theory(理论) calculations, and the ion conductivity of the AM-4 family’s materials(材料) has been experimentally verified.
The modular approach is a powerful tool in current inorganic crystal chemistry. It enables not only a more detailed analysis of the known structures and the determination of structural relationships between them, but also the prediction of potentially novel structures that can be applied in modern materials science. A large number of examples of compounds with modular structures allows us to state that structural modularity is a widely spread phenomenon among natural and synthetic compounds. The use of the formalism of OD theory makes it possible to analyze the symmetry of polytypes with different crystal structures. In this review, we collected new data published in the last 15 years about OD structures and phenomena of polytypism and modularity in inorganic compounds, as well as the topological approach to the analysis of crystal structures.
Topological analysis of the heteropolyhedral MT framework (where M and T are octahedral and tetrahedral cations, respectively) in the eudialyte-type structure and its derivatives was performed based on a natural tiling analysis of the 3D cation. To analyze the migration paths of sodium cations in these structures, the Voronoi method was used. The parental eudialyte-type MT framework is formed by isolated ZO6 octahedra, six-membered [M(1)6O24] rings of edge-sharing M(1)O6 octahedra, and two kinds of rings of tetrahedra, [Si3O9] and [Si9O27]. Different occupancies of M(2), M(3) and M(4) sites with variable coordination numbers by the additional Q, T* and M* cations, respectively, result in 12 different types of the MT framework. Based on the results of natural tilings calculations as well as theoretical analysis of migration paths, it is found that Na⁺ ions can migrate through six- and seven-membered rings, while all other rings are too small for the migration. In eight types of MT frameworks, Na⁺-ion migration and diffusion is possible at ambient temperature and pressure, while in four other types cages are connected by narrow windows and, as a result, the Na⁺ diffusion in them is complicated at ambient conditions because of the window diameter, but may be possible either at higher temperatures or under mild geological conditions for long periods of time.
