Unit Cell Changes Research Articles

A novel analytical solution for determining the shear behavior of the lattice structure based on the Primitive unit cell considering the shear and bending effect

The lattice structure of Schwarz Primitive triply periodic minimal surfaces (P-TPMS) has recently attracted significant attention. This attention arises from its unique topological configuration and superior mechanical properties. This paper studied the effect of changing geometric parameters and the effect of the number of unit cells on the shear modulus of the P-TPMS structure. An analytical model considering the shear and bending effects was derived for the first time, which can efficiently and accurately determine the shear modulus of the P-TPMS lattice structure. Shear modulus was obtained for relative densities in the range of 0.24–0.76. The relative density was calculated by considering the geometric parameter of the surface size (k). The analytical expression was verified by carrying out finite element simulations. Based on the results of this investigation, the shear modulus of the Primitive unit cell changes significantly with different surface size values. Specifically, at k = 0.35, the normalized shear modulus value is 24 times greater than at k = 0.65. This characteristic of the Primitive unit cell extends the range of choices for designers. The completed Ashby diagram suggests that lattice structures based on Primitive unit cells could be one of the most appropriate choices for achieving high shear modulus compared to other structures.

Response of ZrC to swift heavy ion irradiation

Zirconium carbide (ZrC) is commonly used for energy sector research, as well as a surrogate for the proposed advanced nuclear fuel candidate uranium carbide. This study investigates structural modifications to nanocrystalline and microcrystalline ZrC resulting from dense electronic excitations induced by swift heavy ion exposure. Samples were irradiated with 946 MeV Au ions to various fluences up to 6 × 1013 ions cm−2 and characterized using synchrotron-based x-ray diffraction. The evolution of the unit-cell parameter and heterogeneous microstrain were evaluated as a function of fluence and compared with those of nanocrystalline and microcrystalline CeO2 (a surrogate for UO2 fuel) irradiated under identical conditions. Distinct differences were observed in the radiation responses of the carbide and oxide across both grain sizes. Most notably, microcrystalline ZrC exhibits swelling characterized by two distinct regimes, which does not result in saturation at the ion fluences achieved. This contrasts with CeO2, which exhibits the well-documented direct-impact defect accumulation mechanism, reaching a steady-state saturation of swelling at higher fluences. Nanocrystalline CeO2 undergoes more pronounced swelling compared with microcrystalline CeO2, in contrast to nanocrystalline ZrC, which exhibits only minimal unit-cell changes. These results demonstrate that swift heavy ion-induced structural changes can be quite different in carbides and oxides, which must be considered when extrapolating fission-fragment type damage in current fuels to advanced fuels.

Electronic and thermoelectric properties of the 2D Cu2FeSnS4: DFT study

Based on the density functional theory, the electronic, optical and thermoelectric properties of the Cu2FeSnS4 two-dimensional (2D) structure are investigated. The total energy of unit cell changes the curve in terms of its volume which indicates an equilibrium volume for this compound. The density of states and band structure show that the compound has half-metallic behavior with an electron gap of 0.7[Formula: see text]eV at up spin. The merit coefficient at high spin up to room temperature is in the range of 0.9 and is stable, making it a suitable option for thermoelectric applications.

Elastic Molecular Crystals: Their Deformation-Induced Reversible Unit Cell Changes with Specific Poisson Effect

Abstract Detailed investigation of macroscopic deformation and nanoscopic structural changes in flexible organic crystals poses challenges for investigators. Herein, applied stress and subsequent relaxation of elastic organic crystals resulted in reversible macroscopic crystal deformation. X-ray diffraction with a curved stage-jig revealed reversible nanoscopic structural unit cell changes in the crystal structure under the bending stress and relaxation. The crystal lattice changed quantitatively under the applied macroscopic stress-strain (%). This method enables quantitative monitoring of the dynamic nanoscopic structural changes in detail associated with crystal deformation through the use of standard laboratory X-ray diffraction analysis. Importantly, the developed method offers a way of quantitatively measuring reversible structural changes, without synchrotron X-ray analysis. Moreover, the analysis derives Poisson’s ratio, i.e., the ratio of the change in the width per unit width of materials. It is important in materials science, and normally has a positive value in the range of 0.2–0.5. However, the crystals show not only the “Poisson effect” but also the unusual “negative Poisson effect”. This novel approach for investigation generates unprecedented opportunities for understanding dynamic nano-structural unit cell changes in flexible organic crystals.

α[sbnd]Ag2WO4 under microwave, electron beam and femtosecond laser irradiations: Unveiling the relationship between morphology and photoluminescence emissions

In this study, the α-Ag2WO4 samples were successfully synthesized combined two methods, co-precipitation and microwave-assisted hydrothermal. Later, two different irradiation processes: electron beam and femtosecond laser are applied. Unit cell changes were shown by X-ray measurements and Rietveld analysis and compared with the results obtained for first-principle calculations. The formation of oxygen vacancies on the surface of the particles after the irradiation process was revealed by XPS measurements. Electron beam and femtosecond laser irradiations were found to cause expansion of the unit cell, form oxygen vacancies on the surface, change the angle and distance between OAg and OW bonds, and modify the particle morphology to rod-, cube- and sphere-like. The XANES measurements confirm that the local order of the W atoms is maintained along the different irradiation processes. Based on the theoretical analysis of surfaces investigation and Wulff construction, the contribution of (010) and (101) surfaces at the emission centers in 550 and 733 nm associated with the PL spectrum of α–Ag2WO4, was established

Depolarization-mediated monoclinic states in ultrathin [111] PbTiO3 epitaxial films

Stress-depolarization field phase stability map is constructed for ultrathin [111]-PbTiO3 epitaxial films coherently grown on SrTiO3. Despite a large compressive strain imposed by the substrate, rhombohedral to monoclinic transition can be induced so that the polarization vector is confined in a symmetry plane. We investigate competition of phase stability and evolution of monoclinic states by inspecting the flattened energy surface, and show that in the presence of depolarization field the critical stress for inducing low-symmetry states can be remarkably lowered. The influence of vertical stress and depolarization field on polarization, monoclinic shear strain, and volume change of unit cell are calculated for the coherent [111]-PbTiO3, and boundary conditions allowing for considerable enhancement in dielectric and piezoelectric responses are revealed.

Configuration of phosphorus doping in silicene nanoribbons in the presence of an external electric field

Silicene nanoribbons have been studied a lot in recent years, it is a nanostructure with enormous applications. The doping of another element into the unit cell changes the electrical and magnetic properties of the material, which creates new research directions in materials science. Based on the DFT theory, this work studies the doping phosphorus atoms and in silicene nanoribbons in the presence of an external electric field of about 0.1 V/Angstrom. The work also limited the doping study in two cases: The doping case of one phosphorus atom and the 100% doping configuration. There are two doping positions of a phosphorus atom, the top position, and the valley position, and the formation energy will find the optimal position. The energy band structure and state density will also be drawn, examined, and compared.

Exploration of crystal structure, magnetic and dielectric properties of titanium-barium hexaferrites

The BaFe12-xTixO19 hexaferrites up to x = 3.00 were extended. XRD patterns were Rietveld fitted for P63/mmc (no.194) space group and the unit cell parameters were defined. The a parameter and V volume of unit cell change non-monotonically with × while the c parameter has linear behavior. The Ti4+ cations substitute the Fe3+ cations in the 2a, 4fVI and 12 k octahedral positions. This is confirmed by the Mössbauer spectroscopy. Ms spontaneous magnetization was determined with the law of approach to saturation from field magnetization at 5 K and 300 K. The ε/ real part of the permittivity increases constantly with increasing temperature and decreases with frequency. The main objective of this study is an interpretation of the magnetic and dielectric properties of the titanium-barium hexaferrites which has performed in frame of breakdown of Fe3+-O2–-Fe3+/2+(Ti4+) indirect superexchange interactions taking into account the positions occupation.

Fabrication of Moisture-Responsive Crystalline Smart Materials for Water Harvesting and Electricity Transduction.

It is of profound significance with regard to the global energy crisis to develop new techniques and materials that can convert the chemical potential of water into other forms of energy, especially electricity. To address this challenge, we built a new type of energy transduction pathway (humidity gradients → mechanical work → electrical power) using moisture-responsive crystalline materials as the media for energy transduction. Single-crystal data revealed that a flexible zeolitic pyrimidine framework material, ZPF-2-Co, could undergo a reversible structural transformation (β to α phase) with a large unit cell change upon moisture stimulus. Dynamic water vapor sorption analysis showed a gate-opening effect with a steep uptake at as low as 10% relative humidity (RH). The scalable green synthesis approach and the fast water vapor adsorption-desorption kinetics made ZPF-2-Co an excellent sorbent to harvest water from arid air, as verified by real water-harvesting experiments. Furthermore, we created a gradient distribution strategy to fabricate polymer-hybridized mechanical actuators based on ZPF-2-Co that could perform reversible bending deformation upon a variation of the humidity gradient. This mechanical actuator showed remarkable durability and reusability. Finally, coupling the moisture-responsive actuator with a piezoelectric transducer further converted the mechanical work into electrical power. This work offers a new type of moisture-responsive smart material for energy transduction and provides an in-depth understanding of the responsive mechanism at the molecular level.

Stabilization of monoclinic distortion in [111] epitaxial PbTiO3 films

Monoclinic distortion stabilized in a compressively strained [111] PbTiO3, for which the polarization vector is confined in a symmetry plane, is investigated using a phenomenological model. Rhombohedral to monoclinic transitions can be induced by stress normal to the film surface when flattening of energy surface reaches a critical barrier level. Two types of monoclinic states close in free energy exhibit opposite direction of induced polarization rotation. The impact of compressive stress on polarization, monoclinic shear strain, and volume change of unit cell is calculated and compared with experimental reports in the literature. Dielectric and piezoelectric anomalies are predicted in the stabilized monoclinic phase.

High-pressure synthesis and thermodynamic stability of PdH1±ε up to 8 GPa

Palladium hydride alloys are superconductors and hydrogen storage materials. One synthesis route is compression of Pd to high pressure in a hydrogen-rich environment. Here we report the evolution of the unit cell volume of ${\mathrm{PdH}}_{x}$ synthesized by compressing Pd in a pure ${\mathrm{H}}_{2}$ medium to pressures from 0.2 to 8 GPa in a diamond anvil cell at room temperature. The volume of the face-centered cubic unit cell changes nonmonotonically with pressure, increasing upon compression from 0.2 to 1 GPa and decreasing upon compression from 1 to 8 GPa. Volume is reversible upon decompression and is independent of whether the sample was heated to 600 K at low pressure ($P<2$ GPa). The x-ray diffraction data show no evidence for a phase transition between 0.2 and 8 GPa. The volume maximum at 1 GPa must be caused by progressive hydrogenation from 0 to 1 GPa. Assuming a pressure-volume-composition equation of state derived from previously published data, the [H]:[Pd] ratio in this study increases to a maximum value of $x=1\ifmmode\pm\else\textpm\fi{}0.02$ at $2\ifmmode\pm\else\textpm\fi{}0.5$ GPa and remains stable upon further compression to and from 8 GPa. These results add to a mounting body of evidence that ${\mathrm{PdH}}_{1\ifmmode\pm\else\textpm\fi{}\ensuremath{\epsilon}}$ is in thermodynamic equilibrium with pure ${\mathrm{H}}_{2}$ at room temperature from 2 GPa to at least 8 GPa. The simplest interpretation is that H atoms occupy all octahedral sites and no tetrahedral sites in face-centered cubic ${\mathrm{PdH}}_{1.0}$.

First‐Principles Study of the Structure and Electronic Properties of Ti‐Doped LiCoO2

Herein, the structure and electronic properties of Ti‐doped LiCoO2 have been studied systematically using the first‐principles projector augmented wave (PAW) method based on density functional theory (DFT). The structure is distorted due to the presence of Co2+ after Ti doping. When the concentration of dopant Ti is less than 5.6%, the volume change of unit cell is independent of the Ti‐doped concentration, but at higher dopant Ti concentration, the volume of unit cell increases with increase of dopant Ti concentration. Meanwhile, it is also found that the Li‐ion diffusion rate and electronic conductivity are improved, and the concentration of dopant Ti has little effect on the redox potential. These results can promote Ti‐doped layered Li transition metal oxide cathode materials’ studies and improve layered Li transition metal oxide cathode materials design for Li‐ion batteries (LIBs).

Origin of the isostructural electronic states of the topological insulator Bi2Te3

The novel physics, such as the pressure-induced electronic topological transition (ETT), topological superconductivity and Majorana fermions in the isostructural $R\text{\ensuremath{-}}3m$ phase of three-dimensional topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$, holds considerable interest in condensed-matter physics. We carried out a combined investigation of single-crystal x-ray diffraction, high-quality x-ray absorption fine structure, and first-principles theoretical calculations to decipher the puzzling origin of the intriguing electronic states in the isostructural $R\text{\ensuremath{-}}3m$ phase of ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ at high pressure. Three distinct regions with two isostructural phase transitions (IPTs) in the $R\text{\ensuremath{-}}3m$ phase have been identified. The first IPT, which is known as the ETT, occurs at the boundary of region I (0--2 GPa) and region II (2--5 GPa) with a sharp minimum in the $c/a$ ratio of $R\text{\ensuremath{-}}3m$ structure, while the second IPT happens as pressure increases from region II (2--5 GPa) to region III (5--7 GPa). The positions of the Bi ($6c$) and Se ($6c$) sites in the unit cell change rapidly in region II (2--5 GPa), but there is little change at these sites in region III (5--7 GPa). The band-gap closure in region I reflects the pressure-induced metallization. At higher pressures, the band gap opens in region II but remains almost constant after the second IPT in region III, which agrees well with the topological superconductivity of ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$. Our results demonstrate that the combination of local structure, long-range crystal structure, and first-principles calculation is critically important for understanding the isostructural electronic states and the connection between the structure and function as in ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ at high pressure.

Macro-Micro Relationship of Dimensional Changing Behavior of Aluminum Matrix Composite

Accuracy and stability have always been the eternal pursuit of inertial navigation. Among them, the dimensional stability of inertial instrument materials is a key factor in determining the accuracy level of equipment. The dimensional changing(DC) behavior is a material problem extracted from the common accuracy drift problem in engineering technology. The DC behavior of 45vol% SiC P /2024Al composite under no load at constant temperature was systematically studied in-depth using in-situ heating XRD and double Cs-corrected transmission electron microscopy. The trend and magnitude of lattice constant and strain mapping of matrix near SiC/Al interface were both tracked and examined. A high-resolution thermal dilatometer was used to measure the macroscopic DC. Thermal mismatch residual stress has a decisive effect on the DC of SiC P /2024Al composite. The effect of exsolution on the DC of SiC P /2024Al composite was also discussed. Different dominant mechanism of DC between aluminum alloy and composites leads to the difference in the magnitude, rate, and stabilization of the dimensional change. In order to verify the validity of the mechanism, the DC results of different matrix and different heat treatment states were compared and explained. The estimation method of DC based on the volume change of unit cell could accurately predict the trend of DC and the magnitude of SiC P /2024Al composite. This provides instructive guidance for deeply understanding the DC behavior of aluminum matrix composites, and enriches the research work of micro-plastic deformation.

Boolean AND/OR mechanical logic using multi-plane mechanical metamaterials

In recent years, and with the continual development of additive manufacturing technologies, mechanical metamaterials have been explored for their programmable nature. This has opened a new design space into mechanical devices that utilise the structure of a material to perform a function, otherwise known as functional materials. Several examples of functional materials performing mechanical Boolean logic have been successfully demonstrated in the past. Previous designs were shown to have a limited number of gate configurations due to device operation occurring in a single plane. In this paper, a novel approach in performing AND and OR mechanical logic is successfully demonstrated. The proposed mechanical metamaterial controls the buckling response of a biased Von Mises Truss through actuation of anisotropic 3D unit cells to perform Boolean logic. It is shown, by changing the separation distance between unit cells, the functional material can behave as an AND/OR gate. Actuation of the unit cell changes the effective beam length of the bistable system, allowing a snap-through response to occur. By changing the orientation of the 3D unit cells, the input direction must also be considered for a snap-through response. The mechanical logic gates demonstrated are multi-plane, as the correct plane of actuation and input sequence are required for an output to occur.

Study of bandgap property of a bilayer membrane-type metamaterial applied on a thin plate

This work is aimed to study the bandgap property of a thin plate structure with periodically attached bilayer membrane-type resonators. An analytical method based on the Plane Wave Expansion (PWE) method combined with the Rayleigh method, is proposed to predict the bandgap property of bilayer membrane-type metamaterials. The accuracy of the proposed method is verified by the finite element analysis, and a parametric analysis is conducted to reveal the effect of parameters on the bandgap performance. It is found that such a metamaterial can generate two separated bandgaps through the contribution of its two layers of membranes. It is observed that the increase of membrane tensile stress or the magnitude of attached mass can lead to the broadening of bandgaps, whilst the change of unit cell's periodicity has the opposite effect. In addition, if compared with the corresponding single layer membrane-type metamaterials, it is shown that the bilayer membrane-type's first bandgap is suppressed while the second one is extended. However, by applying proper membrane tensile stress and mass magnitude, the suppression of the first bandgap can be weakened whilst allowing the tuning of the bandgap location. These characteristics reveal the benefits of using bilayer membrane-type metamaterial as it possesses higher agility in bandgap tuning. The proposed method can provide an effective tool for the bilayer membrane-type metamaterial design and optimisation.

Group-IV monochalcogenide monolayers: Two-dimensional ferroelectrics with weak intralayer bonds and a phosphorenelike monolayer dissociation energy

We performed density functional theory calculations with self-consistent van der Waals corrected exchange-correlation (XC) functionals to capture the structure of black phosphorus and twelve monochalcogenide monolayers and find the following results: (a) The in-plane unit cell changes its area in going from the bulk to a monolayer. The change of in-plane distances implies that bonds weaker than covalent or ionic ones are at work within the monolayers themselves. This observation is relevant for the prediction of the critical temperature $T_c$. (b) There is a hierarchy of independent parameters that uniquely define a ground state ferroelectric unit cell (and square and rectangular paraelectric unit cells as well): only 5 optimizable parameters are needed to establish the unit cell vectors and the four basis vectors of the ferroelectric ground state unit cell, while square and rectangular paraelectric structures are defined by only 3 or 2 independent optimizable variables, respectively. (c) The reduced number of independent structural variables correlates with larger elastic energy barriers on a rectangular paraelectric unit cell when compared to the elastic energy barrier of a square paraelectric structure. This implies that $T_c$ obtained on a structure that keeps the lattice parameters fixed (for example, using an NVT ensemble) should be larger than the transition temperature on a structure that is allowed to change in-plane lattice vectors (for example, using the NPT ensemble). (d) The dissociation energy (bulk cleavage energy) of these materials is similar to the energy required to exfoliate graphite and MoS$_2$. (e) There exists a linear relation among the square paraelectric unit cell lattice parameter and the lattice parameters of the rectangular ferroelectric ground state unit cell. These results highlight the subtle atomistic structure of these novel 2D ferroelectrics.

Structural studies and exchange bias interaction in Sr+2 doped LaFeO3 synthesised via PVA based sol-gel method

Modification in the crystal structure often exhibits different functionalities and characteristics. In the present study it is demonstrated that Sr2+ modified lanthanum ferrite La(1-x)SrxFeO3 (x = 0, 0.02, 0.04 and 0.06) prepared using PVA based sol gel method shows unique structure and magnetic properties. Structural analysis and phase formation study was performed using X-ray diffraction data and various structural parameters were calculated using Rietveld refinement. It is observed that with the increase in Sr2+ content the structural parameters of LaFeO3 unit cell change. The FESEM and TEM studies were used to study the size and morphology of La(1-x)SrxFeO3 nanoparticles. Magnetic hysteresis measurement reveals the appearance of zero field cooled exchange bias in La(1-x)SrxFeO3, originating due to the interfacial exchange coupling between AFM/FM. In addition, the magnetization increases while exchange bias vanishes at higher strontium concentration. These results help in understanding the in-depth interfacial coupling interaction mechanism.

Fe1-xS/reduced graphene oxide composite as anode material for aqueous rechargeable Ni/Fe batteries

Owing to the abundant resources of Ni and Fe elements, aqueous Ni/Fe battery has emerged as an attractive electrochemical energy storage device. However, the performance of the Ni/Fe battery is largely limited by the low specific capacity and poor discharge rate capacity of the Fe electrodes. Herein, we report a new Fe1-xS/reduced graphene oxide composite (Fe1-xS@rGO composite) as anode material for high performance Ni/Fe batteries. In the composite, the highly conductive rGO sheets wrap the Fe1-xS particle sheets, creating a compact sheet-particle interface and thereby greatly improving the conductivity of the anode electrode. Moreover, the Fe1-xS particle sheets of nanosized architectures and the rGO sheets can effectively prevent the crystal unit cell changes and the aggregation/dissolution of the Fe1-xS particle sheets. Consequently, the resultant Fe1-xS@rGO electrode delivers a specific capacity of ∼320, 282, 270 and 120 mAh g−1 at a current density of 0.3, 0.6, 1, and 10 A g−1, respectively, exhibiting high specific capacity and high rate capacity. Moreover, the Fe1-xS@rGO electrode exhibits a long cycling stability, with 83.3% of initial capacity retained after 100 cycles at 1 A g−1. These results suggest that the Fe1-xS@rGO composite is a promising anode material for practical Ni/Fe battery.

In Situ Cs and H Exchange into Gaidonnayite and Proposed Mechanisms of Ion Diffusion.

The microporous mineral gaidonnayite Na2ZrSi3O9·2H2O was studied to better understand its ion-exchange mechanisms, specifically for Cs+ and H+ ions. In situ Raman spectroscopy, in situ X-ray diffraction (XRD), simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), and in situ X-ray fluorescence were used to determine the exchange processes involved. The Raman spectra contain strong peaks that can be attributed to the vibrational modes for the 3MR symmetric stretch at 500 cm-1, Si-O-Zr-O chain stretches at 938 cm-1, and Si-O stretching in the 1000-1100 cm-1 range. The most prominent Raman shift during ion exchange is found near the 520 cm-1 peak, which corresponds to distortions of the 3MR substructure of gaidonnayite. In all instances of this study, the 3MR exhibited the highest amount of distortion during ion exchange, and the evolution of this distortion is compared to unit-cell changes as measured from XRD data and elemental changes via XRF. The correlations between the Raman, XRD, and XRF data show rapid deformation of the 3MR during the onset of H+ ion exchange in the Na form of gaidonnayite. Even when unit-cell volume changes were small (<3 Å3) as in the cases for Cs+ into Na-gaidonnayite and Cs+ into H-gaidonnayite, significant changes in the ≈520 cm-1 peak were measured. By comparing XRD data and Raman data, and verifying the cation uptake by XRF, we were able to identify and confirm conformational changes and distortions in the crystal structure before, during, and after Cs+ and H+ exchange. Cs exchange occurred the fastest and with the greatest capacity when starting in the H-form at room temperature, and at elevated temperatures when starting in the Na-form.