Cesium Chloride Structure 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.

Physical properties of different polymorphs of sulfur doped ZnO studied in the framework of first-principles approaches

Various physical properties of pure and sulfur-doped zinc oxide in the germanium phosphide (GeP), cesium chloride (CsCl), and nickel arsenide (NiAs) type structures are studied using the first-principles approaches in this research. The structural characteristics of the ZnOS alloys in GeP, CsCl, and NiAs type polymorphs show a slight deviation from Vegard's law, which is consistent with the available literature. It is observed that the electronic band structures of the ZnOS alloys show an exciting impact of sulfur (S) substitution in the ZnO. The ZnOS alloys, in CsCl type structure, display their metallic character. The static dielectric constants of the GeP, CsCl, and NiAs type’s polymorphs demonstrate that with increasing S concentration, polarization is enhanced. Moreover, the CsCl type phase of the ZnOS alloys exhibits the maximum value of the static dielectric constant along with showing metallic character. The optical results highlight the potential of S-doped ZnO in these structures as the highest absorption, reflectivity, and conductivity peaks shift towards low photon energies. The examination of the absorption spectra demonstrates that GeP-type ZnOS alloys are suitable for infrared to visible regime applications. On the other hand, NiAs-type ZnOS alloys are appropriate for use in the visible light regime.

Ab initio study of structural, mechanical and electronic properties of 3d transitional metal carbide in cubic rocksalt (rs), zincblende (zb), and cesium chloride (cc) structures by using LDA and GGA Approximation.

This study rigorously investigates three 3d transition metal carbide (TMC) structures via LDA and GGA approximations. It examines cohesive energy (Ecoh), Vickers hardness (Hv), mechanical stability, and electronic properties. Notably, most 3d TMCs exhibit higher cohesive energy than nitrides, and rs-TiC demonstrates a Vickers hardness of 25.66 GPa, outperforming its nitride counterpart. The study employs theoretical calculations to expedite research, revealing mechanical stability in CrC and MnC (GGA) and CrC (LDA in cc structure), while all 3d TMCs in rs and seven in zb structures show stability. Charge transfer and bonding analysis reveal enhanced covalency along the series, influenced by the interplay between p orbitals of carbon and d orbitals of the metal. Most 3d TMCs exhibit metallic properties, excluding zb-TiC and zb-FeC in all phases. An inverse correlation between elastic constant C44 and electronic states near the Fermi level (EF) emerges, guiding applications and design. This study efficiently uncovers 3d TMC properties, offering insights for applications and design. We employed the Vienna ab initio Simulation software (VASP) to perform computations based on density functional theory (DFT). Our approach incorporated both the projector augmented wave (PAW) and PW91 general gradient approximation (GGA) methods within the local density approximation (LDA).

Correlating structure and orbital occupation with the stability and mechanical properties of 3d transition metal carbides

The development of novel transition metal carbides for improved hard coating technologies requires a detailed understanding of the factors influencing their stability and mechanical performance. To this end, we carried out first principles calculations based on density functional theory to tabulate the electronic structures, formation energies, and phonon dispersion curves of 3d transition metal carbides adopting zincblende, rocksalt, and cesium chloride structures. By analyzing the corresponding results, we outline a theoretical framework that describes how valence electron concentration and bonding configuration control the stability of these compounds. Many early transition metal carbides are predicted to be stable in the rocksalt and zincblende structures, enabled by filled bonding states, whereas the cesium chloride structure shows persistent instability. For compounds that are predicted to be stable, mechanical properties were investigated through calculation of elastic tensors, from which observable properties including Vicker’s hardness and ductility were derived. A robust mechanical performance is shown to be correlated with complete filling of bonding orbitals as illustrated for rocksalt TiC and VC, which have calculated hardnesses of 25.66 and 22.63 GPa respectively. However, enhanced ductility and toughness can be achieved by allowing partial occupation of the antibonding states as in CrC, which has a relatively low Pugh’s ratio of 0.51.

First-principles studies on electronic structures of superatomic compounds [Co6Se8(PMe3)6][C60] in several cubic structures

Structural features, electronic structures, and optical properties of superatomic compounds [Co6Se8(PMe3)6][C60] with rock-salt, cesium chloride, and zinc-blende structures were investigated from first principles. Partial electronic density of states, highest occupied molecular orbital, and lowest unoccupied molecular orbital were given and used to discuss the detailed electronic structures. Dielectric function, refractive index, reflectivity, absorption coefficient, and energy loss functions under several pressures were calculated and used to investigate the optical properties. We found that Co6Se8(PMe3)6 transfers electrons and C60 receives electrons, making contributions to electron communications between the positive and negative counterparts on the basis of electrostatic interactions. The superatomic structures are made from assemblies of charge-rich and charge-poor molecular precursors. In the solid state, charge is transferred between the components, with a net reduction of C60 by less than one electron (0.75 electron approximately).

Structural, Mechanical, Electronic, and Magnetic Properties of LiO in Cesium Chloride, Rocksalt and Zinc-blende Structures

The structural, mechanical, electronic, lattice dynamic and magnetic properties of LiO in the Cesium Chloride (CsCl), Rocksalt (Rs) and Zinc-blende (ZB) structures is presented. The firstprinciples calculations was implemented using the spin-polarized (DFT) approach. It was observed that LiO compound exhibits ferromagnetic (FM) character at the equilibrium lattice constants in the three phases. Applying the stability conditions for cubic phases, the calculations reveal that the compound is mechanically unstable. The study also confirmed that except for the ZB structure which exhibits the brittle property, the others portray ductile nature and they are of good plasticity. We find also that the LiO structures can be synthetized, and their half-metallic property can be preserved over a broad ambit of the lattice contraction which offers the possibility to epitaxially grow such compound on a wide range of semiconductors.Keywords: Half-metallic ferromagnetism; Spin-polarization; Band structure; Density of state

Insight into the structural, electronic, elastic and optical properties of the alkali hydride compounds, XH (X = Rb and Cs)

The equilibrium structural parameters, electronic and optical properties of the alkali hydrides RbH and CsH compounds in rock-salt (RS) and cesium chloride (CsCl) structures have been studied using the full-potential linearized augmented plane-wave (FP-LAPW) method. Wu and Cohen generalized gradient approximation (WC-GGA) was used for the exchange-correlation potential to compute the equilibrium structural parameters, such as the lattice constant (a0), the bulk modulus (B) and bulk modulus first order pressure derivative (B'). In addition to the WC-GGA, the modified Becke Johnson (mBJ) scheme has been also used to overcome the underestimation of the band gap energies. RbH and CsH compounds are found to be semiconductors (wide energy-band gap) using the WC-GGA method, while they are insulators using the mBJ-GGA method. Elastic constants, mechanical and thermodynamic properties were obtained by using the IRelast package. RbH and CsH compounds at ambient pressure are mechanically stable in RS and CsCl structures; they satisfy the Born mechanical stability criteria. Elastic constants (Cij), bulk modulus (B), shear modulus (S) and Debye temperatures (θD) of RbH and CsH compounds decrease as the alkali radius increases. The RS structure of these compounds at ambient conditions is mechanically stronger than CsCl structure. RbH and CsH in RS and CsCl structures are suitable as dielectric compounds. The wide direct energy band gap for these compounds make them promising compounds for optoelectronic UV device applications. Both RbH and CsH have a wide absorption region, on the other hand RbH absorption is very huge compared to the CsH absorption, RbH is an excellent absorbent material, maximum absorption regions are located in the middle ultraviolet (MUV) region and far ultraviolet (FUV) region. The absorption coefficient α (w), imaginary part of the dielectric constant ε2(w) and the extinction coefficient k(w) vary in the same way. The present calculated results are in good agreement with the experimental data, indicating the high accuracy of the performed calculations and reliability of the obtained results.

High-pressure structural phase transitions and electronic properties of the alkali hydride compounds XH (X=K, Rb and Cs)

The equilibrium structural parameters, structural phase transition as well the electronic properties of XH compounds have been computed by using the first-principles calculations based on density-functional theory (DFT) and the full-potential linearized augmented plane-wave (FP-LAPW) method. The generalized gradient approximation (GGA) has been used for the exchange-correlation potential. The equilibrium structural parameters such as the lattice constant, the bulk modulus and the pressure-induced phase transition were calculated for rocksalt (RS), cesium chloride (CsCl), zincblende (ZB) and wurtzite (WZ) structures. The GGA, modified Becke-Johnson (mBJ-GGA) and Yukawa screened hybrid functional (YS-PBE0) schemes have been used to calculate the electronic properties. The mBJ-GGA and YS-PBE0 schemes have been found to be more accurate than GGA in computing the energy-band gap. An agreement of our results with the experimental and results of the other theoretical work indicate its reliability. The compounds under our investigation are found to be wide band gap semiconductors within the GGA, and insulators using the mBJ-GGA and YS-PBE0 approaches.

Theoretical investigation on the high-pressure physical properties of ZnN in cubic zinc blende, rock salt, and cesium chloride structures

In the current work, the aim is to report systematic results from first-principles calculations with density functional theory (DFT) on three cubic structures, rock salt (NaCl-type), zinc blende (ZnS-type), and cesium chloride (CsCl-type), of ZnN under high pressure. From the enthalpy versus pressure relations, we find that the NaCl-type phase of ZnN is more stable than the ZnS-type phase when the pressure higher than 2.55 GPa and high-pressure NaCl-type phase will stabilize up to 150 GPa. Through the careful evaluation with the quasi-harmonic Debye model, a complete set of thermodynamic data up to 2000 K, including PVT equation of state, isothermal bulk modulus, Debye temperature, Grüneisen parameter, thermal expansivity, heat capacity, and entropy for the ZnN with high-pressure NaCl-type structure is achieved. This set of data is considered as the useful information to understand the high-temperature and high-pressure properties of ZnN.

Indirect phase transition of refractory nitrides compounds of: TiN, ZrN and HfN crystal structures

The static and dynamical phase stabilities of refractory nitrides based on plane wave calculation in the framework of generalised gradient approximation (GGA) are reported in this work. The calculation reveals that the postulated zinc blende (B3) phase is statically and dynamically stable unlike the cesium chloride (B2) because of an appearance of imaginary modes in the phonon spectra which prevents the formation of this crystal phase similar to the corresponding carbides. The soft modes of the phonon bands were explored over a temperature range of 280–350K. The indirect phase transition pressures from the zinc blende to the cesium chloride structure are about 10-, 8-, and 7-fold lower compared with the direct transformation from the ground state rock-salt structure to the B2 phase of TiN, ZrN and HfN respectively. The calculated electronic partial density of states show strong hybridization at the gap region and that all the crystal phases are metallic. Again, the phonon calculation showed an appearance of phonon gap for the rock salt and the zinc blende phases but collapsed in the B2.

High-pressure structural phase transition and electronic properties of the alkali hydrides compounds XH (X = Li, Na)

ABSTRACTFirst principle calculations based on the density functional theory using the full-potential linearized augmented plane wave method have been carried out to determine the structural stability of different crystallographic phases, the pressure-induced phase transition and the electronic properties of LiH and NaH compounds. The rocksalt, zincblende, cesium chloride (CsCl) and wurtzite structures are considered. The exchange and correlation potential is treated by using the improved generalized-gradient approximation Moreover, the modified Becke–Johnson (mBJ) scheme is also applied to optimize the corresponding potential for the band structure calculations. The calculated ground state parameters for these compounds in each structure are well compared with the available theoretical and experimental results. The calculated band structures using the mBJ-GGA approach have an insulating nature for both compounds in all the considered structures, except the LiH for CsCl structure which shows a semi-conducting behavior. The results are in good agreement with other calculations and experimental measurements.

English

Using first principles total-energy calculations within the framework of density functional theory, the relative stability and the structural and electronic properties of a VN/GaN/VN interlayer in sodium chloride (NaCl), cesium chloride (CsCl), nickel arsenide (NiAs), zinc-blende, and wurtzite structures were studied. The calculations were carried out using a method based on pseudopotential, employed exactly as implemented in Quantum-ESPRESSO code. From total energy minimization, it was found out that the global energy minimum of VN/GaN/VN is obtained for the wurtzite structure. Additionally, at high pressure, our calculations show the possibility of phase transition from the wurtzite to the NaCl structure. For the wurtzite phase, the density of states analyses revealed that the interlayer exhibits a half-metallic behavior with a magnetic moment of 2.0 µβ/V-atom. This property essentially comes from the polarization of states V-d and N-p crossing of the Fermi level. Due this property, the interlayer can potentially be used in the field of spintronics as spin injectors.   Key words: Density functional theory (DFT), interlayers, structural and electronic properties.

Relative phase and physical properties of CrN/AlN multilayer: A DFT study

Using first principles total-energy calculations within the framework of density functional theory, we studied the relative stability and the structural and electronic properties of multilayer CrN/AlN in the sodium chloride (NaCl), cesium chloride (CsCl), nickel arsenide (NiAs), zinc-blende, and wurtzite structures. The calculations were carried out using the method based on pseudopotentials, employed exactly as implemented in Quantum-ESPRESSO code. Based on total energy minimization, we found that the minimum global energy of CrN/AlN is obtained for the zincblende structure. Additionally, at high pressure our calculations show the possibility of a phase transition from the zincblende to NaCl structure. For the zincblende phase, the density of states analysis reveals that the multilayer exhibits a half-metallic behavior with a magnetic moment of 3.0^p/Cr-atom. These properties come essentially from the polarization of Cr-d and N-p states that cross the Fermi level. Due to these properties, the multilayer can potentially be used in the field of spintronics or spin injectors.

The Half-metallic Properties of (001) and (110) Surfaces of CsSe from the First-principles

We investigated the half-metallicity and magnetism at the (001) and (110) surfaces of CsSe in cesium chloride and zinc-blende structures by using the all-electron full-potential linearized augmented plane wave method within the generalized gradient approximation. From the calculated local density of states, we found that all the surfaces preserve the half-metallicity of the bulk structures. The surfaces with a greater polarity have stronger ferromagnetic properties when terminated with Se atoms; the non-polar surfaces do not change their electronic or magnetic properties considerably as compared with the bulk structures.

Pressure-induced localisation of the hydrogen-bond network in KOH-VI.

Using a combination of ab initio crystal structure prediction and neutron diffraction techniques, we have solved the full structure of KOH-VI at 7 GPa. Rather than being orthorhombic and proton-ordered as had previously be proposed, we find that this high-pressure phase of potassium hydroxide is tetragonal (space group I4/mmm) and proton disordered. It has an unusual hydrogen bond topology, where the hydroxyl groups form isolated hydrogen-bonded square planar (OH)4 units. This structure is stable above 6.5 GPa and, despite being macroscopically proton-disordered, local ice rules enforce microscopic order of the hydrogen bonds. We suggest the use of this novel type of structure to study concerted proton tunneling in the solid state, while the topology of the hydrogen bond network could conceivably be exploited in data storage applications based solely on the manipulations of hydrogen bonds. The unusual localisation of the hydrogen bond network under applied pressure is found to be favored by a more compact packing of the constituents in a distorted cesium chloride structure.

Electronic band structure, optical, dynamical and thermodynamic properties of cesium chloride (CsCl) from first-principles

The geometric structural optimization, electronic band structure, total density of states for valence electrons, density of states for phonons, optical, dynamical, and thermodynamical features of cesium chloride have been investigated by linearized augmented plane wave method using the density functional theory under the generalized gradient approximation. Ground state properties of cesium chloride are studied. The calculated ground state properties are consistent with experimental results. Calculated band structure indicates that the cesium chloride structure has an indirect band gap value of 5.46 eV and is an insulator. From the obtained phonon spectra, the cesium chloride structure is dynamically stable along the various directions in the Brillouin zone. Temperature dependent thermodynamic properties are studied using the harmonic approximation model.

Stability and Half-Metallicity of the (001) and (111) Surfaces of RbN with Cesium Chloride Structure

Using the full-potential local orbital minimum-basis method, we study the electronic and magnetic properties of relaxed (001) and (111) surfaces of the bulk RbN within the framework of density functional theory. It is shown that the Rb(N)-terminated (001) surfaces as well as the N-terminated (111) surface are the half-metallicity, while the Rb-terminated (111) surface loses the half-metallicity. The atomic magnetic moments at the N-terminated (001) and Rb(N)-terminated (111) surfaces increase considerably with respect to the corresponding bulk values. In addition, calculations reveal the half-metallicity of the N-terminated (111) surface is more robust than the bulk RbN due to its larger half-metallic gap. Finally, we discuss the stability of the surface. The positive formation energy in the bulk RbN indicates the surfaces unstable, and non-equilibrium growth techniques may be required for the realization of RbN thin films.

Structural Properties of CaS<sub>1-x</sub>Se<sub>x</sub> Mixed Crystal under High Pressure

The mixed ionic crystals are formed by the mixing of pure components and are truly crystalline and their lattice constants change linearly with concentration from one pure member to another. The present work is intended to investigate structural properties of CaS1-xSexunder high pressure. The structural properties of mixed compound CaS1-xSex(0≤x≤1) under high pressures have been evaluated using three body potential model (TBPM). This interaction potential has been calculated by using three model parameters. For this mixed compound, the experimental data has been generated by the application of Vegard’s law to experimental values available for pure end-point members.The Structure of CaS and CaSe has been Rock Salt (B1) at ambient pressure and with increasing pressure Rock Salt (B1) structure undergo a transition in Cesium Chloride (B2) at 40GPa and 38 GPa respectively and CaS1-xSexunder goes Rock Salt to Cesium Chloride (B1→B2) structure. The difference in phase transition pressure in end-point members is low. In the present work we have investigated structural properties at high pressure for five different concentration x (x=0, 0.25, 0.50, 0.75, 1) for CaS1-xSex. Phase transition pressure and relative volume collapse at different phase transition pressure for different values of x has been calculated. Predicted phase transition pressure and relative volume collapse are found in good agreement with experimental and other theoretical data. Linear variation of phase transition pressure and lattice constant of different composition show that Vegard’s law is valid for this alloy. We have evaluated the phase transition pressure from graphical analysis where the Gibb’s free energy difference ΔG [G(B1)-G(B2)] have been plotted against pressure (P) for CaS1-xSexfor different concentration x. The pressure at which ΔG approaches zero corresponds to phase –transition pressure (Pt). The relative volume changes, ΔV(Pt)/V(0), associated with the above mentioned compression have also been computed and plotted against pressure to get the phase diagram for CaS1-xSexin different concentration.

Laser-Based Dynamic Compression of Solids to Ultrahigh Pressures

Laser-based dynamic compression provides new opportunities to study the structures and properties of materials to ultrahigh pressure conditions. In this technique, high-powered laser beams are used to ablate a sample surface and by reaction a compression wave is generated and propagate through the sample. By controlling the shape and duration of the laser pulse, either shock or ramp (shockless) compression can be produced. Diagnostics include velocity interferometry (from which the stress-density response of the material can be determined) and x-ray diffraction from which structural information is obtained. Magnesium oxide is a fundamental ionic solid which has been extensively examined at high pressures. Theoretical studies predict a change in MgO from a rocksalt (B1) crystal structure to a cesium chloride (B2) structure at pressures of about 400–600 GPa but diamond anvil cell experiments have not been able to reach these pressures. Here we present dynamic X-ray diffraction measurements of ramp-compressed magnesium oxide. We show that a solid–solid phase transition, consistent with a transformation to the B2 structure occurs near 600 GPa. On further compression, this structure remains stable to 900 GPa. Our results provide an experimental benchmark to the equations of state and transition pressure of magnesium oxide, and may help constrain interior properties of super-Earth extrasolar planets. We have also examined the high-pressure behavior of molybdenum under both shock and ramp loading. The melting curves and high-pressure phase diagrams of transition metals have been controversial, and Mo is an excellent test case for resolving these discrepancies. We have conducted shock compression experiments on Mo with an X-ray diffraction diagnostic to address previous claims of high-pressure phase transitions and to determine the location of the Hugoniot melting point. We have also carried out ramp compression experiments to test predictions of phase transitions in Mo at ultrahigh pressures and low temperatures.

High-pressure phase transition of cesium chloride and cesium bromide.

The high-symmetry cubic cesium chloride (CsCl) structure with a space group of Pm3¯m (Z = 1) is one of the prototypical AB-type compounds, which is shared with cesium halides and many binary metallic alloys. The study of high-pressure evolution of the CsCl phase is of fundamental importance in helping to understand the structural sequence and principles of crystallography. Here, we have systematically investigated the high-pressure structural transition of cesium halides up to 200 GPa using an effective CALYPSO algorithm. Strikingly, we have predicted several thermodynamically favored high-pressure phases for cesium chloride and cesium bromide (CsBr). Further electronic calculations indicate that CsCl and CsBr become metallic via band-gap closure at strong compression. The current predictions have broad implications for other AB-type compounds that likely harbor similar novel high-pressure behavior.