Intergrowth Compounds Research Articles

Tutorial on Describing, Classifying, and Visualizing Common Crystal Structures in Nanoscale Materials Systems.

Crystal structures underpin many aspects of nanoscience and technology, from the arrangements of atoms in nanoscale materials to the ways in which nanoscale materials form and grow to the structures formed when nanoscale materials interact with each other and assemble. The impacts of crystal structures and their relationships to one another in nanoscale materials systems are vast. This Tutorial provides nanoscience researchers with highlights of many crystal structures that are commonly observed in nanoscale materials systems, as well as an overview of the tools and concepts that help to derive, describe, visualize, and rationalize key structural features. The scope of materials focuses on the elements and their compounds that are most frequently encountered as nanoscale materials, including both close-packed and nonclose-packed structures. Examples include three-dimensionally and two-dimensionally bonded compounds related to the rocksalt, nickel arsenide, fluorite, zincblende, wurtzite, cesium chloride, and perovskite structures, as well as layered perovskites, intergrowth compounds, MXenes, transition metal dichalcogenides, and other layered materials. Ordered versus disordered structures, high entropy materials, and instructive examples of more complex structures, including copper sulfides, are also discussed to demonstrate how structural visualization tools can be applied. The overall emphasis of this Tutorial is on the ways in which complex structures are derived from simpler building blocks, as well as the similarities and interrelationships among certain classes of structures that, at first glance, may be interpreted as being very different. Identifying and appreciating these structural relationships is useful to nanoscience researchers, as it allows them to deconstruct complex structures into simpler components, which is important for designing, understanding, and using nanoscale materials.

Topochemical Anionic Subunit Insertion Reaction for Constructing Nanoparticles of Layered Oxychalcogenide Intergrowth Structures.

Intergrowth compounds contain alternating layers of chemically distinct subunits that yield composition-tunable synergistic properties. Synthesizing nanoparticles of intergrowth structures requires atomic-level intermixing of the subunits rather than segregation into stable constituent phases. Here we introduce an anionic subunit insertion reaction for nanoparticles that installs metal chalcogenide layers between metal oxide sheets. Anionic [CuS]- subunits from solution replace interlayer chloride anions from LaOCl to form LaOCuS topochemically with retention of crystal structure and morphology. Sodium acetylacetonate helps extract Cl- concomitant with the insertion of S2- and Cu+ and is generalized to other oxychalcogenides. This topochemical reaction produces nanoparticles of ordered mixed-anion intergrowth compounds and expands nanoparticle ion exchange chemistry to anionic subunits.

Hydrides compounds for electrochemical applications

Hydrides have been used since a long time for solid-state hydrogen storage and electrochemical nickel-metal hydride batteries. Besides these applications, growing attention has been devoted to their development as anode materials, as well as solid electrolytes for Li-ion and other ion batteries. Herein, we review and summarize the recent advances of hydrides as negative electrodes for Ni- M H and A -ion batteries ( A = Li, Na), and as electrolyte for all solid-state batteries (ASSB). Metallic hydrides such as intergrowth compounds are highlighted as the best compromise up to now for Ni- M H. Regarding anodes of Li-ion batteries, MgH 2 , especially its combination with TiH 2 , provides very promising results. Complex hydrides such as Li-borohydride and related closo-borates and monovalent carborate boron clusters appear to be very attractive as solid electrolytes for Li-based ASSB, whereas closo-hydroborate sodium salts and closo-carboborates are investigated for Na- and Mg-ASSB. Finally, further research directions are foreseen for hydrides in electrochemical applications.

Quasi-Two-Dimensional Heterostructures (KM1 – xTe)(LaTe3) (M = Mn and Zn) with Charge Density Waves

Layered heterostructure materials with two different functional building blocks can teach us about emergent physical properties and phenomena arising from interactions between the layers. We report the intergrowth compounds KLa$M$$_{1-x}$Te$_{4}$ ($M$ = Mn, Zn; $x\approx$ 0.35) featuring two chemically distinct alternating layers [LaTe$_3$] and [K$M$$_{1-x}$Te]. Their crystal structures are incommensurate, determined by single X-ray diffraction for the Mn compound and transmission electron microscope (TEM) study for the Zn compound. KLaMn$_{1-x}$Te$_{4}$ crystallizes in the orthorhombic superspace group $Pmnm$(01/2${\gamma}$)$s$00 with lattice parameters $a$ = 4.4815(3) {\AA}, $b$ = 21.6649(16) {\AA} and $c$ = 4.5220(3) {\AA}. It exhibits charge density wave (CDW) order at room temperature with a modulation wave vector $\mathbf{q}$ = 1/2$\mathbf{b}$* + 0.3478$\mathbf{c}$* originating from electronic instability of Te-square nets in [LaTe$_{3}$] layers. The Mn analog exhibits a cluster spin glass behavior with spin freezing temperature $T_{\mathrm{f}}$ $\approx$ 5 K attributed to disordered Mn vacancies and competing magnetic interactions in the [Mn$_{1-x}$Te] layers. The Zn analog also has charge density wave order at room temperature with a similar $\mathbf{q}$-vector having the $\mathbf{c}$* component ~ 0.346 confirmed by selected-area electron diffraction (SAED). Electron transfer from [K$M_{1-x}$Te] to [LaTe$_{3}$] layers exists in KLa$M_{1-x}$Te$_{4}$, leading to an enhanced electronic specific heat coefficient. The resistivities of KLa$M_{1-x}$Te$_{4}$ ($M$ = Mn, Zn) exhibit metallic behavior at high temperatures and an upturn at low temperatures, suggesting partial localization of carriers in the [LaTe$_{3}$] layers with some degree of disorder associated with the $M$ atom vacancies in the [$M_{1-x}$Te] layers.

Self-assembly of designed precursors: A route to crystallographically aligned new materials with controlled nanoarchitecture

Modulated elemental reactants is a method by which new and complex intergrowth compounds can be synthesized by the self-assembly of designed precursors prepared by physical vapor deposition. Careful calibration of the composition and thickness of the precursors ensures the formation of the desired product by precise control of local composition and diffusion lengths. Superstructures of increasing complexity can be realized using binary and ternary systems as starting points. The synthesis of systems based on three different binary compounds, either alloyed together or separated into distinct layers, expands the number of possible superstructures that can be formed using this technique, but provides analytical challenges. The synthesis of [(SnSe)1.15]1([TaxV1−x]Se2)1[(SnSe)1.15]1([VyTa1−y]Se2)1 compound is used to illustrate the preparation of precursors and the challenges in both measuring and limiting the interdiffusion of layers during self-assembly. Systematic changes in the electrical properties of (SnSe)1+δ(TaxV1−x)Se2 alloys are observed as x is varied. The electrical resistivity of [(SnSe)1.15]1([TaxV1−x]Se2)1[(SnSe)1.15]1([VyTa1−y]Se2)1 can be modeled as the two constituent layers in parallel.

Influence of interstitial V on structure and properties of ferecrystalline ([SnSe]1.15)1(V1+xSe2)n for n=1, 2, 3, 4, 5, and 6

A series of ferecrystalline compounds ([SnSe]1.15)1(V1+xSe2)n with n=1–6 and a thin film V1+xSe2 were synthesized utilizing the modulated elemental reactant technique. The effect of interstitial V-atoms ranging from 0.13≤x≤0.42 in different compounds on structure and electrical properties of these intergrowth compounds is reported. The presence of the interstitial V-atoms for n>1 was confirmed by Rietveld refinements as well as HAADF-STEM cross sections. The off-stoichiometry in the thin film V1.13Se2 causes a suppression of the charge density wave, similar to the effect of non-stoichiometry observed for the bulk compound. The charge density wave of ([SnSe]1.15)1(V1+xSe2)1, however, is not affected by the non-stoichiometry due to its incorporation as volume inclusions or due to the quasi 2-dimensionality of the isolated VSe2 layer. In the compounds ([SnSe]1.15)1(V1+xSe2)n with n=2–6, the temperature dependence of the electrical resistivity approaches bulk-like behavior.

Structure, stability, and properties of the intergrowth compounds ([SnSe]1+δ)m(NbSe2)n, where m = n = 1-20.

Intergrowth compounds of ([SnSe]1+δ)m(NbSe2)n, where 1 ≤ m = n ≤ 20, with the same atomic composition but different c-axis lattice parameters and number of interfaces per volume were synthesized using the modulated elemental reactant technique. A c-axis lattice parameter change of 1.217(6) nm as a function of one unit of m = n was observed. In-plane X-ray diffraction shows an increase in distortion of the rock salt layer as a function of m and a broadening of the NbSe2 reflections as n increases, indicating the presence of different coordination environments for Nb (trigonal prismatic and octahedral) and smaller crystallite size, which were confirmed via scanning transmission electron microscopy investigations. The electrical resistivities of all 12 compounds exhibit metallic temperature dependence and are similar in magnitude as would be expected for isocompositional compounds. Carrier concentration and mobility of the compounds vary within a narrow range of 2-6 × 10(21) cm(-3) and 2-6 cm(2) V(-1) s(-1), respectively. Even at a thickness of 12 nm for the SnSe and NbSe2 blocks, the properties of the intergrowth compounds cannot be explained as composite behavior, due to significant charge transfer between them. Upon being annealed at 500 °C, the higher order m = n compounds were found to convert to the thermodynamically stable phase, the (1,1) compound. This suggests that the capacitive energy of the interfaces stabilizes these intergrowth compounds.

Solution‐Based Synthesis of Layered Intergrowth Compounds of the Homologous PbmBi2nTe3n+m Series as Nanosheets

AbstractLayered intergrowth compounds in the homologous PbmBi2nTe3n+m family are interesting because they are examples of natural heterostructures. We present a simple solution‐based synthesis of two‐dimensional nanosheets of PbBi2Te4, Pb2Bi2Te5, and PbBi6Te10 layered intergrowth compounds, which are members of the PbmBi2nTe3n+m [that is, (PbTe)m(Bi2Te3)n] homologous series. Few‐layer nanosheets exhibit narrow optical band gaps (0.25–0.7 eV) with semiconducting electronic‐transport properties.

Solution-Based Synthesis of Layered Intergrowth Compounds of the Homologous Pbm Bi2n Te3n+m Series as Nanosheets.

Layered intergrowth compounds in the homologous Pbm Bi2n Te3n+m family are interesting because they are examples of natural heterostructures. We present a simple solution-based synthesis of two-dimensional nanosheets of PbBi2 Te4 , Pb2 Bi2 Te5 , and PbBi6 Te10 layered intergrowth compounds, which are members of the Pbm Bi2n Te3n+m [that is, (PbTe)m (Bi2 Te3 )n ] homologous series. Few-layer nanosheets exhibit narrow optical band gaps (0.25-0.7 eV) with semiconducting electronic-transport properties.

Carrier dilution in TiSe2 based intergrowth compounds for enhanced thermoelectric performance

Synthesis and electrical properties of kinetically stabilized (PbSe)1+δ(TiSe2)n thin-film intergrowths are reported for 1 ≤ n ≤ 18. The carriers donated to the TiSe2 from PbSe are diluted with increasing n, leading to a systematic increase in the Seebeck coefficient and thermoelectric power factor.

Preparation, formation, and structure of [(SnSe)1.04]m(MoSe2)n intergrowth compounds (0 < m and n < 32) from designed precursors.

A detailed synthetic approach, using the method of modulated elemental reactants, is described for the preparation of MX-TX(2) (M = metal, X = chalcogen, and T = transition metal) solid-state intergrowths with m and n values significantly larger than previously reported. As a specific example, we demonstrate the ability to synthesize more than 500 distinct intergrowth compounds in a single ternary system, Sn-Mo-Se. A simple method for determination of the chemical composition of the constituent layers in the precursor and product is described for cases in which both structural components contain one or more common elements. X-ray reflectivity, laboratory and synchrotron X-ray diffraction, scanning transmission electron microscopy, and high-resolution transmission electron microscopy imaging, and electron microprobe analysis provide conclusive evidence of the formation of layered intergrowths with well-defined structure and composition. The ability to access a large range of monochalcogenide thicknesses allows a size-dependent structural transition in the SnSe component to be controlled and tracked and indicates that intergrowth materials such as those described here comprise novel material systems in which size-dependent phenomena can be precisely controlled.

Application of the multiband -models to quantum transport in quasi-periodic crystals

We consider the quantum transport of a particle in a crystal where the global three-dimensional translation symmetry is removed. Our analysis concerns solid state structures where the microscopic potential of the ions is no longer periodic. This includes materials with variable chemical composition, intergrowth compounds and abrupt junctions. The application of the kp multiband envelope function models to the description of the quantum mechanical motion in such a quasi-periodic structure is investigated. By using a spectral decomposition technique, we show that when the interatomic distance is asymptotically small, the particle probability density can be obtained by the envelope kp model with variable coefficients.

Diffuse scattering and phase transitions in aperiodic inclusion compounds

Small molecules, such as urea, thiourea, perhydrotriphenylene can be co-crystallised with long-chain hydrocarbon molecules to form inclusion compounds. The guest chains are confined to narrow, approximately cylindrical, channels created by the host small-molecule lattice. The stoichiometry and the conformations of the chains included inside the channels are function of internal interactions such as intra-chain interaction, but also of overall co-operative properties of the resulting three dimensionally ordered single crystal. These intergrowth compounds may form incommensurate composite crystals. A prototype example of such uniaxial intergrowth aperiodic crystals is n-alkane (CnH2n+2)/urea (CO(NH2)2). In these supra-molecular systems, urea molecules are connected by H-bonds and form helical ribbons, which repeat every six urea molecules to form a series of linear, hexagonal tunnels that can accommodate linear alkanes. Because the channels (~0.53 nm) are larger than the hydrocarbon chains, guests are held loosely and can undergo substantial motions. A significant amount of diffuse scattering of the first and second kinds can be depicted in scattering experiments, static or dynamic. These materials undergo a large variety of continuous or weakly first order structural phase transitions when changing the alkane molecule length and giving place to large pre-transitional effects. The talk will give an overview of the diffuse scattering in these compounds and will focus on connection with aperiodicity.

Homogenization limit for a multiband effective mass model in heterostructures

We study the homogenization limit of a multiband model that describes the quantum mechanical motion of an electron in a quasi-periodic crystal. In this approach, the distance among the atoms that constitute the material (lattice parameter) is considered a small quantity. Our model include the description of materials with variable chemical composition, intergrowth compounds, and heterostructures. We derive the effective multiband evolution system in the framework of the kp approach. We study the well posedness of the mathematical problem. We compare the effective mass model with the standard kp models for uniform and non-uniforms crystals. We show that in the limit of vanishing lattice parameter, the particle density obtained by the effective mass model, converges to the exact probability density of the particle.

Synthesis of [(SnSe)1.15]m(TaSe2)n Ferecrystals: Structurally Tunable Metallic Compounds

A modification of the modulated elemental reactants synthetic technique was developed and used to synthesize eleven members of the [(SnSe)1.15]m(TaSe2)n family of compounds, with m and n equal to integer values between 1 and 6. Each of the intergrowth compounds contained highly oriented intergrowths of SnSe bilayers and TaSe2 monolayers with abrupt interfaces perpendicular to the c-axis. The c-lattice parameter increased 0.579(1) nm per SnSe bilayer and 0.649(1) nm per Se–Ta–Se trilayer (TaSe2) as m and n were varied. ab-plane X-ray diffraction patterns and transmission electron microscope images revealed a square in-plane structure of the SnSe constituent, a hexagonal in-plane structure for the TaSe2 constituent, and rotational disorder between the constituent layers. Temperature dependent electrical resistivity, measured on several specimens, revealed metallic behavior, and a simple model is presented to explain the differences in resistivity as a function of m and n.

Effect of Nd substitution on the microstructure and electrical properties of Bi7Ti4NbO21 piezoceramics

Abstract Neodymium (Nd) doped intergrowth bismuth layer-structured ferroelectric compounds Bi 7− x Nd x Ti 4 NbO 21 ( x = 0, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75 and 2.0) were synthesized through a solid-state method. The influence of the Nd 3+ substitution of Bi 3+ on the lattice, microstructure and electrical properties of these compounds were investigated. The X-ray diffraction and Raman scattering analyses demonstrate that a phase transition from orthorhombic to pseudo-tetragonal occurs in these compounds, relying on substitution proportions and sites of Nd 3+ for Bi 3+ . With the increasing Nd 3+ dopants, the growth of plate-like grains along the a – b plane and a secondary intergranular metallic Bi phase were retarded which resulted in the increases of sintering temperature, density and electrical resistance of the doped ceramics. The resultant ceramic with x = 1.25 possesses a piezoelectric coefficient d 33 up to 16.3 pC/N with a Curie temperature T C above 750 °C were obtained for the compound.

Synthesis and crystal structure of RMgSi 2 compounds ( R=La, Ce, Pr, Nd), a particular example of linear intergrowth

A new series of rare earth compounds with stoichiometry RMgSi 2 ( R=La, Ce, Pr, Nd) is reported. The single crystal X-ray diffraction showed that CeMgSi 2, which melts congruently at 1200 °C, crystallizes in a new tetragonal structure type ( I4 1/ amd, tI32, a=4.2652(4) Å, c=36.830(4) Å, Z=8; w R 2=0.042 (19 parameters, 393 F 0 2), R 1=0.018 (297 F 0>4 σF 0). The crystal structure of CeMgSi 2 can be formally built up by alternating along the z direction four CeMg 2Si 2-type CeMg 2Si 2 slabs with four AlB 2-type CeSi 2 slabs, one after the other. The structural model obtained from a CeMgSi 2 single crystal has been confirmed for the La, Pr and Nd homologous compounds by means of Rietveld refinement. The trend of the unit-cell parameters, plotted versus the R 3+ ionic radius, shows a linear behaviour, which strongly suggests a trivalent state for the Ce atoms. An analysis of the features of this new structure is reported, in comparison with the other known CeMg 2Si 2/AlB 2-type linear intergrowth compounds.

Improvement on the temperature coefficient of resonant frequency of hexagonal perovskites through intergrowth structures

Cation-deficient hexagonal perovskites Ba5Nb4O15, Ba6Nb4TiO18, and their intergrowth compounds were prepared by solid-state reaction method. Dielectric measurements showed that the intergrowth compounds had a relatively low temperature coefficient of resonant frequency (τf) compared to that of the simple terms Ba5Nb4O15 and Ba6Nb4TiO18. On the basis of the structure data, the authors proposed a structural parameter d, the degree of atomic displacements, to evaluate the structural dependence of the temperature coefficient of resonant frequency. The reduced τf value of intergrowths was considered to be resulted from the decreased degree of atomic displacements in the hexagonal perovskite structure.

Zn1− x Pd x ( x =0.14–0.24): a missing link between intergrowth compounds and quasicrystal approximants

Our investigations in the Zn-rich portion of the Zn–Pd system are related to the idea that a prototypic 1-dimensional (1D) quasicrystal, as defined by the Fibonacci sequence, can be regarded both as a quasicrystal and as an incommensurately modulated crystal. Consequently, there are two different ways to achieve the atomic structure. Six different new structures, closely related to the γ-brass structure, in the Zn1−x Pd x system have been synthesized and contain Pd-centred Zn icosahedra. A misfit character of all structures with two distinct main subsets and satellite reflections is clear from the diffraction patterns. Among these six structures, two specific examples, Zn10.65Pd2.35 (Zn0.819Pd0.181) and Zn212Pd64 (Zn0.768Pd0.232), have been refined by single crystal X-ray diffraction using traditional refinement methods but also using the (3 + 1)D formalism (superspace group Xmmm(00γ)0s0). Analogies with the Fibonacci sequence are possible if we identify dimers of Pd-centred Zn icosahedra (DI) as short segments, S, and trimers of Pd-centred Zn icosahedra (TI) as long segments, L. By defining these S and L segments, Zn11Pd2 and Zn212Pd64 correspond to the two first simplest approximants of a hypothetical 1D quasicrystal.

不規則性をもつ結晶，超イオン導電体，非晶質，ガラス，融体の構造解析―不規則系・ランダム系の結晶学―１．周期系における不規則性の解析 インコメンシュレート相の構造解析

Four-dimensional approach for incommensurate structures was briefly reviewed. Recent developments of the method using discontinuous modulation functions were explained, which enabled us to get the 4-dimensional description of structures forming the homologous series such as intergrowth compounds and crystallographic shear (CS) structures. An example of the incommensurate CS structure was given, in which domain boundaries were aperiodically inserted in contrast to the usual CS structures.