Tetrahedral Layers Research Articles

Investigation of the effect of oxygen vacancies on the electronic properties of lizardite

Doping and chemical substitutions of clay minerals have been very successful recently in the design of new novel materials. The serpentine mineral, lizardite has attracted a lot of attention due to its abundance in nature across the world and its eco-friendly behavior. A detailed study of lizardite has been performed to understand the effects of the presence of vacancies placed strategically at three positions of the structure, thereby leading to six different configurations. Formation energy calculations exhibit the possibility of obtaining all the conformations considered in this work. Moreover, free energy calculations demonstrate the stability at higher temperatures. The presence of the oxygen vacancies in the site that binds the Si atoms and also that between the Si atom and the Mg atom decreases the gap. However, the oxygen vacancy on top of the tetrahedral layer of the clay mineral induces an insulator-metal transition. Energy-bands and the density of states display the modified electronic properties of the system with vacancies. Lowdin-charge analysis and the isolines of the charge distribution in different planes provide information on the modifications brought about by the vacancies. Hence, vacancies have a vital role in controlling the band-gap. Moreover, the modifications of the other electronic properties could provide a promising route towards to achieving valuable thermoelectric materials.

Cation and anion ordering in synthetic lepidolites and lithian muscovites: influence of the OH ∕ F and Li ∕ Al ratios on the mica formation studied by NMR (nuclear magnetic resonance) spectroscopy and X-ray diffraction

Abstract. A large number of lepidolites K(LixAl3−x)[Si2xAl4−2xO10](OH)yF2−y and Li-muscovites K(LixAl2-x/3□1-2x/3)[Si3AlO10](OH)yF2−y were synthesised by a gelling method in combination with hydrothermal syntheses at a pressure of 2 kbar and a temperature of 873 K. The nominal composition ranged between 0.0≤x≤2.0 and 0.0≤y≤2.0, i.e. from polylithionite K[Li2.0Al][Si4.0O10](OH)yF2−y over trilithionite K[Li1.5Al1.5][AlSi3.0O10](OH)yF2−y to muscovite K[Al2.0□][AlSi3.0O10](OH)yF2−y. 1H, 19F, 29Si and 27Al magic-angle spinning nuclear magnetic resonance (MAS NMR) and 27Al multiple-quantum magic-angle spinning (MQMAS) NMR spectroscopy has been performed to investigate the order and/or disorder state of Si and Al in the tetrahedral layers and of Li, Al, OH and F in the octahedral layer. The synthetic mica crystals are very small, ranging from 0.1 to 5 µm. With increasing Al content, the crystal sizes decrease. Rietveld structure analyses on 12 samples showed that nearly all samples consist of two mica polytypes (1M and 2M1) of varying proportions. In the case of lepidolites, the 1M / 2M1 ratio depends on the Li/Al ratio of the reaction mixture. The refinement of the occupancy factors of octahedral sites shows that lepidolites (1.5≤x≤2.0) represent a solid solution series with polylithionite and trilithionite as the endmembers. In the case of the Li-muscovites (0.0≤x≤1.5), the 1M / 2M1 ratio depends on the number of impurity phases like eucryptite or sanidine depleting the reaction mixture of Li or Al. There is no solid solution between trilithionite and muscovite; instead, the Li-muscovite crystals consist of domains differing in the relative proportions of muscovite and trilithionite. The overall composition of the synthesised micas which consist of two polytypes can be characterised by 29Si, 1H and 19F MAS NMR spectroscopy. The Si/Al ratio in the tetrahedral layers and thus the content of [4]Al were calculated by analysing the signal intensities of the 29Si MAS NMR experiments. The Li content xest was calculated from the measured tetrahedral Si/Al ratio of the 29Si MAS NMR signals. The calculated Li contents xest of samples between polylithionite and trilithionite agree with the expected values. The F-rich samples show slightly increased values and the OH samples lower values. Lepidolites with only F (x = 1.5 to 2.0, y = 0.0), but not lepidolites with only OH (x = 1.5 to 2.0 and y = 2.0), were observed after synthesis. With decreasing Li content, x≤1.2, Li-muscovites containing mostly hydroxyl (y>1.0) are formed. It was possible to synthesise fluorine containing micas with a Li content as low as 0.3 and y = 0.2 to 1.8. The 19F and 1H MAS NMR experiments reveal that F and OH are not distributed statistically but local structural preferences exist. F is attracted by Li-rich and OH by Al-rich environments. The quadrupolar coupling constant which represents the anisotropy of the Al coordination is low for polylithionite with CQ=1.5 MHz and increases to CQ=3.8 MHz for trilithionite. For tetrahedral Al a smaller increase of CQ from 1.7 to 2.8 MHz is observed. Advancing from trilithionite to muscovite both quadrupolar coupling constants decrease to 2.5 MHz for octahedral and 1.5 MHz for tetrahedral Al. In polylithionite there is the most isotropic environment for octahedral Al; there are only Li2Al sites coordinated by F in the octahedral sheets and O from the tetrahedral sheets which are regular, containing only Si. The distortion and anisotropy for Al in tetrahedral as well as octahedral sheets increases with rising Al content. The most anisotropic environment can be found in trilithionite, especially for octahedral Al.

Defect Structure of Nanocrystalline NiO Oxide Stabilized by SiO2

In this paper, structural features of the NiO-SiO2 nanocrystalline catalyst synthesized by the sol-gel method were studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (TEM), and differential dissolution (DD). The XRD pattern of NiO-SiO2 significantly differs from the “ideal” NiO pattern: the peaks of the NiO-like phase are asymmetric, especially the 111 diffraction peak. The NiO-SiO2 nanocrystalline catalyst was investigated by means of XRD simulations based on two approaches: conventional Rietveld analysis and statistical models of 1D disordered crystals. Through a direct simulation of XRD profiles, structural information is extracted from both the Bragg and diffuse scattering. XRD simulations showed that the asymmetry of all the diffraction peaks is due to the presence of two NiO-like oxides with different lattice constants and different average sizes: ~90 wt% of mixed Ni-Si oxide (Ni:Si = 0.14:0.86) with average crystallite sizes (D ~ 27.5 Å) and ~10 wt% of pure NiO (D ~ 50 Å). The high asymmetry of the 111 diffraction peak is due to the appearance of diffuse scattering caused by the inclusion of tetrahedral SiO2 layers between octahedral NiO layers. Such methods as TEM and DD were applied as independent criteria to prove the structural model, and the results obtained confirm the formation of mixed Ni-Si oxide.

High thermoelectric performance of layered LaAgXO (X=Se,Te) from electrical and thermal transport calculations

The present paper reports the electronic structure, thermal and electronic transport properties of layered oxychalcogenides $\mathrm{LaAg}X\mathrm{O}$ $(X=\mathrm{Se},\mathrm{Te})$ using density functional theory. Different scattering mechanisms, such as acoustic deformation scattering (ADP), ionized impurity scattering (IMP), and polar optical scattering (POP) are included to calculate the scattering rates at various doping concentrations and temperatures. The calculated scattering rates are used in the Boltzmann transport equation to get the absolute values of thermoelectric coefficients. The Seebeck coefficient of both the compounds is nearly $400 \ensuremath{\mu}\mathrm{V}/\mathrm{K}$ for optimal $p$-type doping. The lattice thermal conductivity of both $\mathrm{LaAg}X\mathrm{O}$ is ultralow with values around 0.20 W/mK along the ``$c$'' axis at 300 K due to low lifetime and low group velocity. This is lower than other well-known thermoelectric materials, such as PbTe and SnSe. Rattling motion observed in the Ag-Te tetrahedral layer might be the reason for the significant suppression of ${\ensuremath{\kappa}}_{l}$. We predict huge $ZT$ values of 1.63 for $p$-type and 2.8 for $n$-type LaAgTeO at 900 K, which are higher than that of promising thermoelectric materials, such as BiCuSeO (1.4) and LaCuSeO (2.71). There is a crossing in phonon band dispersion which forms a nodal line on the 001 plane that may lead to topological behavior. This study highlights $\mathrm{LaAg}X\mathrm{O}$ as potential thermoelectric materials for future device applications.

Structural transformation induced twinning for enhanced conversion reaction of vacancy-ordered metal oxides with Li ions

Metal oxide anode materials based on conversion reaction usually deliver a capacity much higher than that of commercial graphite anodes in lithium-ion batteries (LIBs), and the porous forms of the materials can effectively alleviate volume change associated with (de)lithiation. In this work, tetragonal γ-Fe2O3, which is a vacancy-ordered superstructure containing large vacancy clusters, is studied as the representative of intrinsic nanoporous metal oxide anode materials of LIBs. γ-Fe2O3 exhibits a reversible capacity higher than the theoretical value in initial cycles, but a steady capacity same as that of α-Fe2O3. In lithiation, γ-Fe2O3 first transforms irreversibly to an ordered rock salt Li1-xFe1+xO2 (LiTiO2 type), and the Li1-xFe1+xO2 is converted reversibly into Li2O and Fe0 upon further lithiation: γ-Fe2O3+Li→Li1-xFe1+xO2+Li ↔ Fe0+Li2O. The alternate stacking of dense tetrahedral layers and porous octahedral layers in γ-Fe2O3 enables the simultaneous formation of Li1-xFe1+xO2 phases with different Li contents in a single particle and triggers structure twinning, accounting for fast reaction and likely high capacity in initial cycles. The structural evolution disclosed in γ-Fe2O3 not only updates the understanding of conversion reactions of vacancy-ordered metal oxides, but also offers an innovative approach for the fabrication of twinning structures in metal oxides including cathode materials.

A new melilite-type rare-earth borate CdTbGaB2O7 and multicolor tunable emission in the CdTb1-xSmxGaB2O7 (0 ≤ x ≤ 0.2) phosphors.

A new mixed metal borate, CdTbGaB2O7, was successfully synthesized using the high-temperature solution method and its crystal structure was determined by single-crystal X-ray diffraction with the following unit-cell data: P4̄21m, a = b = 7.3487(1) Å, c = 4.7247(1) Å, V = 255.150(9) Å3, and Z = 2. It belongs to a new member of the melilite family, which features a 3D framework consisting of alternately stacked [Ga(B2O7)]n5n- tetrahedral layers and (Cd2+/Tb3+) cationic layers that are interconnected via B(Ga)-O-(Cd/Tb) bridges. In addition, the solid solutions of CdTb1-xSmxGaB2O7 (0 ≤ x ≤ 0.2) were prepared via the solid-state reaction method. The combined techniques of XRD, SEM, IR/Raman, XPS and PLE/PL were employed to characterize the products. It was found that the CdTb1-xSmxGaB2O7 phosphors simultaneously showed green emission of Tb3+ at 545 nm and orange emission of Sm3+ at 603 nm under excitation at 370 nm. The emission color can be adjusted from green to orange-red by varying the Sm3+ doped content via an energy transfer mechanism. For CdTb0.995Sm0.005GaB2O7, a QY of 13.22% was obtained, and its emission intensity at 423 K was 94% of that at 303 K. These results show that the prepared materials can act as potential color-tunable phosphors for UV w-LEDs.

B-site mixed cationic tetrahedral layer confined the concentration and mobility of interstitial oxygen in mellite family

The subtle difference in the cationic size and covalent bonding between Ga and Ge enables B-site mixed Ga/Ge tetrahedral centers to confine the concentration and mobility of interstitial oxygen in mellite family.

Minerals of the arctite supergroup from the Bellerberg volcano xenoliths, Germany

AbstractThe recently defined arctite supergroup contains nine mineral members defined as hexagonal intercalated antiperovskites, most of which have been found in pyrometamorphic rocks of the Hatrurim Complex, Israel. Three members of this supergroup: nabimusaite, gazeevite and zadovite, were identified for the first time in altered carbonate–silicate xenoliths from the Caspar and Scherer quarries, Bellerberg volcano in Germany. Present work focuses on the chemical, structural and spectroscopic investigation of these minerals and their correlation with holotype counterparts. The apparent differences are mainly related to the chemical composition, types of substitution in the tetrahedral and antiperovskite layers within the crystal structure, and position of bands in the Raman spectra. In the Bellerberg volcano xenoliths, the crystallisation of nabimusaite and gazeevite is caused by high-temperature alteration of early mineral associations (clinker-like phases) and their reaction with melt or gas generated by volcanic activity. In turn, the formation of zadovite is related to the Ba-rich silicate melt that filled the intergranular space between the rock-forming minerals.

Mullite production: phase transformations of kaolinite, thermodynamics of the process

The growing demand for mullite raw materials, which meet industrial requirements originates the search for new and alternative sources, as well as efficient technologies for obtaining the target products (nanocomposites). The article suggests a method for obtaining mullite from kaolinite experimentally (Vezhayu-Vorykvinsky deposit, Russia). Structural kaolinite transformations (Al-Si-O-Me system), mineral phases transformations, and thermodynamics of the process have been studied. Based on the estimation of the thermodynamics of the reactions, the preferable reaction of mullite formation was determined. The article shows, that formation of the target product, mullite nanocomposite, has several intermediate phases (metakaolinite, pseudomullite). The transformations of the initial kaolinite structure include the removal of structural water and separation of the silica-oxygen tetrahedral and alumina-oxygen octahedral layers, the decomposition into free oxides, breaking of bonds between the silica-oxygen tetrahedrons and the partial increase in the coordination number of aluminium ions, the formation of mullite and cristobalite from free oxides. The proposed approach controls the ratio of Al2O3 and SiO2 phases at certain stages, which will further improve the mechanical and other properties of the matrix of the obtained raw materials for the target prototypes of industrial products.

Highly efficient two-dimensional Ag2Te cathode catalyst featuring a layer structure derived catalytic anisotropy in lithium-oxygen batteries

Two-dimensional (2D) materials have recently become one of the most suitable candidates as cathode catalysts for lithium-oxygen batteries (LOBs) due to their unique electronic properties and good stability. However, the variation of the layer structures will trigger catalytic anisotropy leading to different performance in LOBs. In this work, narrow gap telluride Ag2Te with a chemical bonded 2D layer structure composed by Ag-Te tetrahedral stacking layer was applied as the highly efficient catalyst for LOBs. Ag2Te nanowires (NWs) were synthesized and exhibited superior specific capacity over 15,000 mAh g−1, outstanding rate capabilities, and ultralong high-rate cycle stability over 300 cycles at 500 mA g−1 and 220 cycles at 1000 mA g−1 with the fixed capacity of 1000 mAh g−1 when used as the cathode catalyst in LOBs. Experimental studies and DFT calculations reveal that Ag2Te with a chemical bonded 2D layer structure exhibited outstanding catalytic capability and weak structure derived catalytic anisotropy in LOBs, in which the 2D stacking surface (200) plane and side edge planes both exhibit superior catalytic activity. For comparison, the Ag-terminated 2D stacking surface (200) plane exhibits high active catalytic capability with low overpotentials during ORR/OER process derived from the appropriate adsorption energy for the adsorbates, stable surface, and highly efficient charge transfer during the growth of discharge products. The current contribution provides an in-depth insight to understanding the 2D structure derived elusive catalytic mechanism in LOBs.

Tetrahedral Tilting and Oxygen Vacancy Stabilization and Migration in La1-xSr2+x(GaO4)O1-0.5x Mixed Electronic/Oxide Ionic Conductors.

The La2O3/SrO/Ga2O3 ternary system contains several compounds with remarkable oxide or proton ionic conduction. Among them, the layered LaSr2(GaO4)O compound is a less commonly studied material. Here, the crystal structure, electrical conduction properties, and ionic migration mechanism of the La1-xSr2+x(GaO4) O1-0.5x (0 ≤ x ≤ 0.3) system are thoroughly analyzed. Diffraction methods indicate that the system crystallizes in the tetragonal space group P4/ncc, which is compatible with the presence of a subtle GaO4 tetrahedral tilting along the c axis, leading to a slight deviation of the body-centered tetragonal structure previously reported. This feature is essential to further understanding the mixed p electronic/oxide ion-conducting behavior of the system. Upon La3+ for Sr2+ substitution, oxygen vacancies arise at the loosely bound oxide sublattice, which at high temperature go through the GaO4 tetrahedral layer, leading to the formation of intermediate corner-sharing Ga2O7 tetrahedral dimers, and migrate via the continuous breaking and re-formation of the dimers, assisted by the synergic rotation and deformation of neighboring GaO4 tetrahedra. The unique structural and electrical features of La1-xSr2+x(GaO4)O1-0.5x materials within the La2O3/SrO/Ga2O3 ternary system emphasize their potential application as cathode materials in LaGaO3-based fuel cells.

From Three-Dimensional Clathrates to Two-Dimensional Zintl Phases AMSb2 (A = Rb, Cs; M = Ga, In) Composed of Pentagonal M-Sb Rings.

Three new antimonide Zintl phases, RbGaSb2, CsGaSb2, and CsInSb2, were discovered during exploration of corresponding A-M-Sb (A = Rb, Cs; M = Ga, In) ternary systems while searching for new clathrates. The AGaSb2 phases crystallize in the tetragonal space group P42/nmc (No. 137) in the LiBS2 structure type, while CsInSb2 crystallizes in lower symmetry in the orthorhombic space group Cmce (No. 64) in the KGaSb2 structure type with additional disorder of one of the Cs sites. The crystal structures of all three reported AMSb2 compounds are composed of two-dimensional [MSb2]- tetrahedral layers separated by Rb+ or Cs+ cations. [MSb2]- layers are built from fused M-Sb pentagons and hexagons, which are also the main structural units for A8M27Sb19 clathrate cages. The semiconductor nature of AMSb2 was suggested by band structure calculations and confirmed by transport property characterization. CsGaSb2 is a rare example of an n-type pnictide Zintl phase. All reported compounds exhibit low thermal conductivity typical for complex antimonides of heavy elements.

Iridate Li8IrO6: An Antiferromagnetic Insulator.

A polycrystalline iridate Li8IrO6 material was prepared via heating Li2O and IrO2 starting materials in a sealed quartz tube at 650 °C for 48 h. The structure was determined from Rietveld refinement of room-temperature powder neutron diffraction data. Li8IrO6 adopts the nonpolar space group R3̅ with Li atoms occupying the tetrahedral and octahedral sites, which is supported by the electron diffraction and solid-state 7Li NMR. This results in a crystal structure consisting of LiO4 tetrahedral layers alternating with mixed IrO6 and LiO6 octahedral layers along the crystallographic c-axis. The +4 oxidation state of Ir4+ was confirmed by near-edge X-ray absorption spectroscopy. An in situ synchrotron X-ray diffraction study of Li8IrO6 indicates that the sample is stable up to 1000 °C and exhibits no structural transitions. Magnetic measurements suggest long-range antiferromagnetic ordering with a Néel temperature (TN) of 4 K, which is corroborated by heat capacity measurements. The localized effective moment μeff (Ir) = 1.73 μB and insulating character indicate that Li8IrO6 is a correlated insulator. First-principles calculations support the nonpolar crystal structure and reveal the insulating behavior both in paramagnetic and antiferromagnetic states.

A new topological semimetal candidate: SmMnBi2

The new compound SmMnBi2 has been synthesized by the self-flux method and shown to crystallize in space group I4/mmm with a = 4.5054 (4) Å, c = 20.5914 (19) Å and Z = 4. Its structure comprises two-dimensional square Mn-nets layers, puckered rock-salt-like SmBi slabs and two-dimensional square Bi-nets layers, alternating along the c axis in an …Mn-net–SmBi slab–Bi-net–SmBi slab–Mn-net… sequence. Surprisingly, the atomic arrangement differs from its neighboring compound EuMnBi2 which has similar layers but with a different stacking arrangement. This gives rise to edge-shared square planar MnBi4 polyhedral layers in SmMnBi2 while EuMnBi2 has edge-shared MnBi4 tetrahedral layers. The MMnX 2 (M = alkaline earth/rare earth metals, X = Sb/Bi) family has emerged as topological Dirac or Weyl semimetal candidates, all of them sharing similar structural features. Although SmMnBi2 has a different stacking arrangement to EuMnBi2, its layer structure still makes it a topological Dirac or Weyl semimetal candidate.

Layered quaternary chalcogenides KMgCuSe2 and KMgCuTe2 with paramagnetic semiconducting behavior

Here we report the synthesis of two new quaternary chalcogenides KMgCuSe2 and KMgCuTe2. Both single-crystal and polycrystalline samples have been obtained using self-flux method and high temperature reaction. These two compounds adopt ThCr2Si2-type structure which is composed of edge-sharing [Mg0.5Cu0.5Se4] and [Mg0.5Cu0.5Te4] tetrahedral layers separated by K+ ions. Single-crystal refinement reveals the random distribution of Mg and Cu with ratio of 1:1 in the centre of tetrahedron motifs. The Mg-Se and Mg-Te bond lengths in KMgCuSe2 and KMgCuTe2 are markedly shorter than those in binary MgSe and MgTe, but are comparable with the Cu-Se and Cu-Te bond lengths in binary Cu chalcogenides. In addition, the tetrahedral configurations in KMgCuSe2 and KMgCuTe2 are highly distorted with strong compression along c axis. These two new Mg chalcogenides are semiconductors with the indirect band gaps estimated from optical absorption spectra as 1.26 and 1.36 eV for KMgCuSe2 and KMgCuTe2. Magnetic susceptibility measurements indicates the paramagnetic behavior of KMgCuSe2 and KMgCuTe2 with small effective magnetic moment ueff (0.35 and 0.31 μB per Mg/Cu).

Nomenclature and Classification of the Arctite Supergroup.Aravaite, Ba2Ca18(SiO4)6[(PO4)3(CO3)]F3O, a New Arctite Supergroup Mineral from Negev Desert, Israel

ABSTRACT The crystal structure of arctite, (Na5Ca)Ca6Ba(PO4)6F3 (Rm, a = 7.904 Å, с = 41.320 Å), was refined in 1984 by E. Sokolova. According to modern concepts, this mineral belongs to the intercalated antiperovskites and is characterized by intercalation of triple antiperovskite layers {[F3(Ca7Na5)](PO4)4}4+ and tetrahedral layers Ba(PO4)24–. The pyrometamorphic rocks of the Hatrurim Complex, which are distributed along the Dead Sea Rift, are the origin of eight new minerals with intercalated antiperovskite structures, all discovered within the last five years. Therefore, an update and improvement of the classification and nomenclature was required. The new classification of the arctite supergroup was approved by the CNMNC IMA (Memorandum 95–SM20). The arctite supergroup combines the arctite group (minerals with triple antiperovskite layers), which includes arctite, (Na5Ca)Ca6Ba(PO4)6F3; nabimusaite, KCa12(SiO4)4(SO4)2O2F; dargaite, BaCa12(SiO4)4(SO4)2O3; and ariegilatite, BaCa12(SiO4)4(PO4)2F2O, with the zadovite group (minerals with single antiperovskite layers), which includes zadovite, BaCa6[(SiO4)(PO4)](PO4)2F; aradite, BaCa6[(SiO4)(VO4)](VO4)2F; gazeevite, BaCa6(SiO4)2(SO4)2O; and stracherite, BaCa6(SiO4)2[(PO4)(CO3)]F. Another ungrouped member of the arctite supergroup is aravaite, Ba2Ca18(SiO4)6[(PO4)3(CO3)]F3O – a unique mineral which is formed by the ordered intercalation of super-modules of ariegilatite and stracherite. In addition, a description of aravaite as a new mineral is presented in this paper. The crystal structure has been previously published (Krüger et al. 2018). Furthermore, preliminary data for potentially new minerals of the arctite supergroup, found in rocks of the Hatrurim Complex, are discussed.

Hyaluronic Acid/Laponite Clay Nanocomposites‐Based Hydrogels for 3D Bioprinting Applications

Hyaluronic acid (HA) is a glycosaminoglycan with excellent physicochemical and biological properties and represents a potential component to constitute inks used in tissues and organs 3D bioprinting process. On the other hand, it does not have an adequate degree of rigidity necessary for the structural maintenance of printed components. Laponite (Lap) is a synthetic nanoclay capable of increasing the rheological properties of polymeric hydrogels. The present study aimed to develop and characterize HA/Lap clay nanocomposites-based hydrogels for the constitution of inks for 3D bioprinting, considering the Lap potential to improve the rheological characteristics of HA. For this, HA (12 mg/mL) and Laponite-XLG (50 mg/mL) hydrogels were initially produced. Three additional hydrogels, composed from the association of different percentages of HA and Lap samples (w/w), were manufactured (HA/Lap 75:25%, 50:50%, and 25:75%). After constitution, all hydrogels samples were characterized by rheological and spectrophotometric analysis (Fourier-Transform Infrared Spectroscopy-FTIR). Finally, they were submitted to an in vitro cytotoxicity test, with cell viability (human fibroblasts-GM07492) established by a spectrophotometric Resazurin/Resorufin method. The rheological analysis results demonstrate a directly proportional increase in hydrogel viscosity concerning the increase in Lap percentage. The values of HA, Lap, and experimental HA/Lap clay nanocomposites-based hydrogels samples (75:25%, 50:50%, and 25:75%) were 4.9, 12.7, 4.0, 9.4, and 12.0 Pa.s, respectively. In FTIR analysis, bands (wavenumber 1000.7 cm-1) were identified in the Lap and HA/Lap samples, corresponding to the stretching of the Si-O interaction of Lap's tetrahedral layer. The viability tests demonstrated the non-toxic profile of the HA, Lap, and the hydrogels resulting from their associations. Such results demonstrate the biological safety of HA/Lap samples and the rheological modifying role from Lap on developed hydrogels. The viscosity levels achieved, especially in the proportions of HA/Lap of 50:50% and 25:75%, demonstrate its potential in the constitution of inks for use in 3D bioprinting. Further research should contribute to establishing the ideal composition (percentage of HA and Lap) and the printability characteristics of the HA/Lap clay nanocomposites-based hydrogels.

Rb1.66Cs1.34Tb[Si5.43Ge0.57O15]·H2O, a New Member of the OD-Family of Natural and Synthetic Layered Silicates: Topology-Symmetry Analysis and Structure Prediction

Crystals of new silicate-germanate Rb1.66Cs1.34Tb[Si5.43Ge0.57O15]·H2O have been synthesized hydrothermally in a multi-component system TbCl3:GeO2:SiO2 = 1:1:5 at T = 280 °C and P = 100 atm. K2CO3, Rb2CO3 and Cs2CO3 were added to the solution as mineralizers. The crystal structure was solved using single crystal X-ray data: a = 15.9429(3), b = 14.8407(3), c = 7.2781(1) Å, sp. gr. Pbam. New Rb,Cs,Tb-silicate-germanate consists of a [Si5.43Ge0.57O15]∞∞ corrugated tetrahedral layer combined by isolated TbO6 octahedra into the mixed microporous framework as in synthetic K3Nd[Si6O15]·2H2O, K3Nd[Si6O15] and K3Eu[Si6O15]·2H2O with the cavities occupied by Cs, Rb atoms and water molecules. Luminescence spectrum on new crystals was obtained and analysed. A comparison with the other representatives of related layered natural and synthetic silicates was carried out based on the topology-symmetry analysis by the OD (order-disorder) approach. The wollastonite chain was selected as the initial structural unit. Three symmetrical ways of forming ribbon from such a chain and three ways of further connecting ribbons to each other into the layer were revealed and described with symmetry groupoids. Hypothetical structural variants of the layers and ribbons in this family were predicted.

Glauconite authigenesis during the onset of the Paleocene-Eocene Thermal Maximum: A case study from the Khuiala Formation in Jaisalmer Basin, India

Biological and ecological changes across the Paleogene hyperthermal events were accompanied by dramatic shifts in sedimentation systems in both marine and continental environments. This study investigates the formation of authigenic glauconite within a biostratigraphically constrained section encompassing the Paleocene-Eocene Thermal Maximum (PETM). Paleogene transgressive shelf deposits in the Jaisalmer Basin in western India are represented by the Khuiala Formation, consisting of grey shale, limestone, and glauconitic shale. Foraminiferal assemblage not only constrains the age of the glauconitic shale to planktic zone E1 but also indicates the deposition of sediments in an oxygen-depleted mid-shelf environment. A detailed geochemical and mineralogical characterization of the authigenic glauconite within the mid-shelf deposits reveals the highest glauconite content within the maximum flooding zone, immediately below the negative carbon isotope excursion representing the PETM, followed by its steady decrease. The geochemical signature of the glauconite is unusual for its high Al2O3 and MgO and medium Fe2O3 and SiO2 contents. The K2O content suggests the ‘evolved’ nature of the glauconite, which is confirmed by the X-ray diffractional parameters and the presence of the ‘rosette’ texture in FEG-SEM images. The glauconite evolved by Al-for-Fe substitution in the octahedral site and subsequent fixation of K+ into the interlayer sites. The high alumina content of the glauconite corresponds to the high Al3+ in the tetrahedral layer, inherited from an aluminous substrate. Mössbauer spectroscopy suggests the dominance of Fe3+ compared to Fe2+ in the octahedral site of glauconite pellets. The unusual variety of glauconite formed by the transformation of continent-derived kaolinite and iron oxide in oxygen-depleted porewater conditions. Glauconite authigenesis in the Khuiala Formation is strongly influenced by the warm climatic condition, oxygen-depletion in the mid-shelf environment, and sharp marine transgression promoting sediment starvation associated with the PETM.

Capturing functional two-dimensional nanosheets from sandwich-structure vermiculite for cancer theranostics

Clay-based nanomaterials, especially 2:1 aluminosilicates such as vermiculite, biotite, and illite, have demonstrated great potential in various fields. However, their characteristic sandwiched structures and the lack of effective methods to exfoliate two-dimensional (2D) functional core layers (FCLs) greatly limit their future applications. Herein, we present a universal wet-chemical exfoliation method based on alkali etching that can intelligently “capture” the ultrathin and biocompatible FCLs (MgO and Fe2O3) sandwiched between two identical tetrahedral layers (SiO2 and Al2O3) from vermiculite. Without the sandwich structures that shielded their active sites, the obtained FCL nanosheets (NSs) exhibit a tunable and appropriate electron band structure (with the bandgap decreased from 2.0 eV to 1.4 eV), a conductive band that increased from −0.4 eV to −0.6 eV, and excellent light response characteristics. The great properties of 2D FCL NSs endow them with exciting potential in diverse applications including energy, photocatalysis, and biomedical engineering. This study specifically highlights their application in cancer theranostics as an example, potentially serving as a prelude to future extensive studies of 2D FCL NSs.