Amine intercalates of lamellar compounds NiPS3 and CdPS3

Layered compounds CdPS₃ and NiPS₃ were reacted with a variety of amines, of which only short-chain linear alkylamines gave stable intercalation products. NiPS₃ and CdPS₃ reacted by quite distinct mechanisms. The inserted amines were partly ionised, and there was a large transfer of electrons into the host crystal in the case of NiPS₃, but the material remained a semiconductor.     

Optical and electronic properties of the layered semiconductors NiPS3 and FePS3

From optical absorption data, the band-gaps for NiPS₃ and FePS₃ are found to have similar values of about 1.6 eV. A marked photoconductive effect is observed in NiPS₃, which supports this value for the energy-gap. It is confirmed by the temperature dependence of resistivity for NiPS₃, which shows intrinsic behaviour. The isostructural FePS₃ has a much lower resistivity and behaves extrinsically.     

High‐Yield Electrochemical Production of Large‐Sized and Thinly Layered NiPS3 Flakes for Overall Water Splitting

Achieving large‐sized and thinly layered 2D metal phosphorus trichalcogenides with high quality and yield has been an urgent quest due to extraordinary physical/chemical characteristics for multiple applications. Nevertheless, current preparation methodologies suffer from uncontrolled thicknesses, uneven morphologies and area distributions, long processing times, and inferior quality. Here, a sonication‐free and fast (in minutes) electrochemical cathodic exfoliation approach is reported that can prepare large‐sized (typically ≈150 µm²) and thinly layered (≈70% monolayer) NiPS₃ flakes with high crystallinity and pure phase structure with a yield ≈80%. During the electrochemical exfoliation process, the tetra‐n‐butylammonium salt with a large ionic diameter is decomposed into gaseous species after the intercalation and efficiently expands the tightly stratified bulk NiPS₃ crystals, as revealed by in situ and ex situ characterizations. Atomically thin NiPS₃ flakes can be obtained by slight manual shaking rather than sonication, which largely preserves in‐plane structural integrity with large size and minimum damage. The obtained high quality NiPS₃ offers a new and ideal model for overall water splitting due to its inherent fully exposed S and P atoms that are often the active sites for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Consequently, the bifunctional NiPS₃ exhibits outstanding performance for overall water splitting.     

Insertion de lithium la structure lamellaire NiPS3

Chemical and electrochemical intercalation of lithium in NiPS₃ has been performed. X Ray, NMR and the examination of open circuit potential as a function of discharged composition indicate retention of the initial lattice structure during the intercalation process and suggest that lithium intercalates in the octahedral voids of the host structure. NiPS₃ behaviour is compared with other MPX₃ compounds (M = Mn, Fe, X = S, Se and M = Zn, Cd and X = S).     

Intercalation of polyethylene oxide PEO in layered MPS3 (M = Ni, Fe) materials

The intercalation compounds Li_0.96(H₂O)_0.77(PEO)_0.63Ni_0.48PS₃ and Li_0.94(H₂O)_0.92(PEO)_0.94Fe_0.48PS₃ obtained by the insertion of PEO in MPS₃ form lithium-polyethylene oxide complexes containing Li⁺ exchangeable cation in the interlayer space. Polyethylene oxide (PEO) is able to associate interlayer cation increasing the ionic conductivity of NiPS₃ and FePS_3. These compounds constitute a new family of intercalates MPS₃ (M = Ni, Fe) host-layer materials.The new materials were characterized by powder X-Ray diffraction (XRD), Fourier-transformed infrared (FT-IR), differential thermal and thermogravimetric analyses (DTA/TG), energy dispersive X-Ray (EDX), inductively coupled plasma (ICP) and electrochemical impedance measurements. The intercalation compound Li_0.96(H₂O)_0.77(PEO)_0.63Ni_0.48PS₃ shows an ionic conductivity of 0.13 μS/cm, and dc electronic conductivity of ca. 0.1 μS/cm which is twice that of NiPS₃.     

Imperfections and impurity phases in flux grown RCrO3 (R = La,Yb) single crystals

Results of scanning electron microscopy (SEM) and energy dispersive X-ray analytical (EDAX) investigations, conducted on some elevated structures displayed by flux grown rare earth orthochromite, RCrO₃ (R = La, Yb) crystals, are presented. The peculiar structures exhibited by crystal surfaces indicate imperfections and impurity phases. EDAX of elevated structures reveals the various phases to be composed of lead associated materials which may probably be either Pb₂CrO₅ or Pb₂OF₂ (flux). Other secondary crystallization of impurity phases, ROF (R = La, Yb) is illustrated in the case of RCrO₃ (R = La, Yb) crystals. The elevated structures illustrate their non-stoichiometric behaviour. Precipitation of impurity phases and formation of imperfections during the growth of RCrO₃ (R = La, Yb) crystals and their effect on the crystalline quality is discussed.     

Evolution structurale et proprietes physiques des phases AXMO2 (A = Na,K; M = Cr,Mn, Co) (x ⩽ 1)

The structures of the A_XMO₂ (x ? 1) phases may be classified in three main groups. The layer structures are the most common, their anionic packing varies with the nature of the alkali element and its insertion rate. The tunnel structures are observed only for manganese and small values of x. Cristobalite derived structures characterize the KMO₂ oxides for small size M³⁺ cations. Whereas the A_xCrO₂ and A_xMnO₂ phases are semi-conductors, the A_xCoO₂ oxides have a metallic behaviour, the small Co-Co distances allowing t_2g orbital overlaping through the common edges of adjacent octahedra. The influence of the structure on magnetic properties is discussed.     

Phase composition of ceramics in systems with oxides of rare-earth elements, manganese, and titanium

Ceramics based on systems with oxides of rare-earth elements (REE: Y₂O₃, Sm₂O₃, Gd₂O₃), manganese, and titanium, considered as hosts for immobilization of REE- and actinide-containing radioactive wastes (RAW), were prepared by cold pressing and sintering at 1300–1400°C, and also by plasma treatment. Phases of the pyrochlore-murataite series are prevalent in the ceramics, and perovskite-pyrophanite-type phases are impurity phases, as well as the hibonite-loveringite- and garnet-type phases revealed in the ceramics prepared with addition of iron and aluminum oxides. The formation of murataite or, more precisely, of structures consisting of murataite and pyrochlore modules is more typical of the yttrium-containing systems. With an increase in the radius of the REE ion, the tendency toward formation of pyrochlore-type phases is enhanced, and the presence of large REE cations (La) stimulates formation of a perovskite-type phase.     

Magnetic,morphological and structural investigations of CoFe/Si interfacial structures

CoFe/Si interfacial structures have been realised by electron beam evaporation of CoFe magnetic alloy on p- and n-Si substrates. These realised interfacial structures have been characterised from X-ray diffraction (XRD), atomic force microscopy (AFM), magnetic force microscopy (MFM) and magnetisation (M–H) characteristics. XRD data have shown the presence of CoFe (bcc phase) and β-FeSi₂ phases for CoFe/p-Si interfacial structures, whereas CoFe/n-Si interfacial structures have shown the presence of CoFe (bcc and fcc) phases along with Fe₃Si, ?-FeSi and β-FeSi₂ silicide phases having nanodimension crystallites. The M–H characteristics have shown the superparamagnetic type behaviour for CoFe/p-Si structure, whereas CoFe/n-Si structure shows a feature of interfacial antiferromagnetic (AF) coupling. The observed magnetic behaviour has been understood due to the presence of various magnetic phases and their nanosized grains. The MFM data of domain size have also been correlated with the observed magnetic behaviour. CoFe/n-Si structures have shown a significant feature of giant magnetoresistance (GMR) as compared to CoFe/p-Si structures. It has been found that CoFe/p-Si structures show a distinctly different behaviour than CoFe/n-Si structures for their chemical structure, morphology and magnetic behaviour.     

Hard and superhard carbon phases synthesized from fullerites under pressure

A review has been presented on the structural and mechanical properties of hard carbon phases synthesized from fullerite C₆₀ under pressure. The density and nanostructure have been recognized as the key parameters defining the mechanical properties of hard carbon phases. By suggesting a version of the transitional high-pressure diagram of C₆₀ (developed up to 20 GPa), the three areas of the formation of hard carbon phases have been highlighted. The corresponding phases of superhard carbon are (1) disordered sp₂-type atomic structures at moderate pressures and high temperatures (> 1100 K), (2) three-dimensionally polymerized C₆₀ structures at moderate temperatures and high pressures (> 8 GPa), and (3) sp₃-based amorphous and nanocomposite phases at high pressures and temperatures. First region can be in turn separated into 2 subparts with different peculiarities of sp² structures and properties: low pressure part (0.1–2 GPa) and high-pressure part (2–8 GPa). Temperature can be recognized as a factor responsible for the formation of nanostructures by the partial destruction of molecular phases, whereas pressure is a factor responsible for stimulating the formation of rigid polymerized structures consisting of covalently bonded C₆₀ molecules, whereas the combination of both factors leads to the formation of atomic-based phases with dominating sp³ bonding.     

High resolution electron microscopic studies of HoAl3, Er0·5Gd0·5Al3 and Y0·91Er0·09Al3 in thin film form

Rare earth trialuminides (RAl₃) exhibit an interesting series of structures changing from 2H to 3C in the bulk form. Many of the rare earth trialuminides have been recently found to exhibit curious structural characteristics such as the occurrence of the modulated phases. A detailed investigation of the formation synthesis and characterization of some binary and ternary alloys of the rare earth-aluminium system has been carried out. High resolution microscopic technique has been employed to study the modulated phases for some alloyse.g. HoAl₃, Er_0·5Gd_0·5Al₃ and Y_0·91Er_0·09Al₃. With the help of lattice imaging technique, several new modulated phases have been investigated. A possible mechanism for the formation of these phases has been suggested. The details of the results obtained by lattice imaging technique are discussed.     

A study of the microstructure, phase composition, and mechanical properties of extruded Mg–9Er–6Y–xZn–0.6Zr magnesium alloys

The microstructure, phase composition, and mechanical properties of Mg–9Er–6Y–xZn–0.6Zr (x = 1, 3, 5 wt%; nominal chemical composition) series alloys were investigated through optical microscopy, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometry, transmission electron microscopy, and tensile tests. Numerous granular Mg₂₄(Er, Y, Zn)₅ phases were distributed in a discontinuous network mainly along the grain boundaries in the alloy with 1 wt% Zn. With increasing Zn content, the Mg₂₄(Er, Y, Zn)₅ phases in the alloys gradually disappeared, the amount of block Mg₁₂Zn(Y, Er) phases increased, and the block size became larger. In addition, a few lamellar phases grew parallel with one another from the grain boundaries to the grain interior in the alloys. The crystallographic structures of the Mg₁₂Zn(Y, Er) and Mg₂₄(Er, Y, Zn)₅ phases were confirmed as 18R-type long-period stacking ordered structures and body-centered cubic structures, respectively. The Mg₁₂Zn(Y, Er) phases with long-period stacking ordered structures increased the strength and toughness of the alloys more than the Mg₂₄(Er, Y, Zn)₅ phases with body-centered cubic structures.     

Solid solutions between ettringite, Ca6Al2(SO4)3(OH)12·26H2O, and thaumasite, Ca3SiSO4CO3(OH)6·12H2O

A series of solid solution phases between ettringite, Ca₆Al₂(SO₄)₃(OH)₁₂·26H₂O, and thaumasite, Ca₃SiSO₄CO₃(OH)₆·12H₂O, have been prepared and analysed by X-ray powder diffraction and full pattern fitting. Solid solutions were shown to exist with both the ettringite structure (space group P31c) and the thaumasite structure (space group P6₃, c-axis halved). A possible discontinuity was identified, characterised by a gap in the a-dimension of the solid solution phases produced. This discontinuity is believed to correspond to a switch between the ettringite space group and the thaumasite space group. It is suggested that any discontinuity in the solid solution is caused by differences in the hydrogen bonding of the two structures.     

Formation of secondary phases and microdiscs on flux-grown HoFeO3 crystals

Results of optical and scanning electron microscopic and EDAX studies, carried out on structures exhibited by HoFeO₃ crystals grown from the PbO-PbF₂-B₂O₃ flux system, are reported. Aluminium and silicon are present as impurities in the crystals studied. EDAX of certain structures indicate formation of magnetoplumbite (PbO · 6Fe₂O₃) during the flux growth of HoFeO₃. Crystallization of HoOF on the HoFeO₃ crystal surfaces is also indicated; the process taking place almost at the end of HoFeO₃ crystal growth. A variety of microdisc patterns on HoFeO₃ crystal surfaces are illustrated. Their formation is attributed to the covering process of impurity phases by the rapidly advancing growth fronts on the HoFeO₃ crystal surfaces. Experimental evidence in support of this is offered by exposing the impurity phase buried under the microdisc. Precipitation of the secondary phases during the flux growth of HoFeO₃ crystals and their influence on the latter is discussed.     

Crystal structure,electron-to-atom ratio and hydrogen storage capacity of zirconium based intermetallic laves phases

Laves phases of the type AB₂, where A is zirconium, have potential for use as hydrogen storage materials. These Laves phases have one of two different crystal structures, namely the C15 (cubic MgCu₂-type) or the C14 (hexagonal MgZn₂-type) Strukterbericht types. Data are presented on the lattice parameters for the two phases and relationships are developed between the lattice parameters of the two phases both for the binary (ZrB₂) and the pseudobinary (Zr(B′_xB″_1?x)2) Laves phases. Electron-to-atom ratios are calculated for both the binary and pseudobinary Laves phases and these are related to hydrogen storage capacity (hydrogen-to-metal ratio, H/M). The hydrogen-to-metal ratio is shown to decrease with increasing electron-to-atom ratio.     

Interactions of hydrogen with Tb3Ni6M2 (M= Al,Ga, or Si) alloys with structures of Ce3Ni6Si2 type

Summary A crystallochemical analysis has been performed on the structures of Tb₃Ni₆M₂ (M = Al, Ga, Si), which crystallize in the Ce₃Ni₆Si₂ structure type, as they are potential hydrogen absorbers. There are seven types of cavity suitable for hydrogen atoms. When the Tb₃Ni₆M₂ intermetallides interact with hydrogen, hydride phases are formed that contain 0.32-0.95 mass % H and which decompose completely in the range 20–300°C. The hydrogen contents in the hydrides and the thermal stabilities decrease in the aluminide-gallide-silicide sequence. Hydrogenation produces isotropic expansion in the initial body-centered cubic structures. Neutron diffraction indicates that the deuterium atoms in Tb₃Ni₆Al₂D_6.5 occupy the Tb₃Al, TbNi₃, and Ni₄ cavities.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 27, No. 4, pp. 22–25, July–August, 1991.     

Mechanochemical synthesis, phase composition, and properties of Pb(Zn1/3Nb2/3)O3-based ferroelectric ceramics

Pb-containing relaxor ferroelectric ceramics are prepared by mechanochemical ceramic processing. Mechanochemical reactions in binary and ternary mixtures of the PbO-ZnO-Nb₂O₅ system are studied by x-ray diffraction. Disordered compounds with the columbite, changbaiite, and pyrochlore structures are prepared. The perovskite and pyrochlore phases in 0.9Pb(Zn_1/3Nb_2/3)O₃ + 0.1ABO₃ morphotropic phase boundary materials are shown to be in mechanochemical equilibrium. Among the ABO₃ additives studied, BaMnO₃ is the most effective for stabilizing the perovskite structure. The mechanochemical synthesis path has a strong effect on the phase composition of the resulting material. Conventional synthesis through a columbite phase leads to the predominant formation of a pyrochlore phase. Firing conditions also have a profound effect on the phase composition of the ceramics, but the disordered perovskite phase retains cubic symmetry.     

Strain on ferroelectric thin films

Strain engineering aims to take advantage of the stress field imposed by substrates on thin films. It requires an understanding of the consequences of stress fields on the physical properties of the deposited materials. This is achieved in ferroelectric thin films through the use of misfit-strain phase diagrams that show the stability regions for the possible phases. These encompass bulk phases as well as new ones exhibiting symmetries that are not present in the bulk. For the solid solution lead zirconate–lead titanate, Pb(Zr_1−x Ti _x )O₃, monoclinic phases found in the bulk morphotropic phase boundary region and associated to concentrations exhibiting the highest properties can be stabilized on a wider range of composition in thin films. In addition, phases of lower symmetry can be stabilized through the use of anisotropic biaxial stress fields, generated by orthorhombic substrates for example. Another crucial aspect of the influence of biaxial stress fields is the generation of domain structures. Theoretical tools as well as experimental verifications have provided much insight on the underlying physics. We, therefore, present here an overview of the influence of both iso- and anisotropic biaxial stress fields on the structures and properties of ferroelectric thin films exemplified on Pb(Zr_1−x Ti _x )O₃.     

LaNi5- and RT3-based (R = Ce, Nd, Gd, Er; T = Co, Ni, Fe) hydrides prepared at low temperatures and H2 pressures

Hydride phases based on the intermetallic compounds LaNi₅, CeCo₃, NdNi₃, GdFe₃, DyCo₃, and ErNi₃ have been synthesized at a hydrogen pressure of 10 MPa and a temperature of 273 K. The phase composition of the synthesized materials and the lattice parameters of the hydride phases have been determined by X-ray diffraction. During storage in air at room temperature, the hydrides decompose more slowly than do their analogs synthesized at low pressure. The hydrogen content of the hydrides is higher than or similar to that of hydride phases synthesized at high pressure. X-ray diffraction results for the low-temperature RT₃-based intermetallic hydrides demonstrate that their lattice is expanded to a lesser extent than that of their high-pressure analogs.     

Structural adaptability in the system Bi2O3  WO3 : Higher members of the homologous series Bi2WnO3n+3

The ultramicrostructure of phases with n = 1, 2 and 3 in the hypothetical series Bi₂W_nO_3n+3 has been investigated by high resolution electron microscopy and energy dispersive X-ray emission spectroscopy. For n = 1 and 2, well ordered phases with the predicted compositions have been obtained, but for n = 3, a severely disordered assemblage containing intergrowths of the two known structures and strips of the n = 3 member is produced. No evidence for ordered structures with n > 2 has yet been obtained.