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The deviation of positions of atoms from their ideal lattice sites in crystalline solid state systems causes distortion and it causes variation in structural [1] and functional properties [2] . Severe lattice distortion has been proposed to be one of the core-effect in high-entropy alloys. But the fundamental mechanism of distortion at atomic scale is missing for real three-dimensional metallic systems. The present investigation aims to develop mechanistic understanding of atomic scale distortion in metallic systems in terms of the magneto-volume effects. The correlation between charge-disproportion, spin fluctuations, magneto-volume effects and Fermi surface nesting has been highlighted.

In this work, we studied the influence of lattice distortion on the initiation of plasticity in Ti-based (multi-principal element alloy) MPEAs at a loading rate of 500 μN/s. The surface dependence was observed in Ti20Al20Cr20V20Nb20 (Ti20) MPEA, where the lowest first burst load was determined in (110) oriented grain, which is the same as that in Ti60Al10Cr10V10Nb10 (Ti60). This implies this kind of crystallographic dependence is the intrinsic feature of present studied alloys and it is not covered by the lattice distortion effect. In spite of similar orientation dependence, a much higher load at first burst was identified in Ti20 compared with Ti60, which is attributed to the fact that the more severe lattice distortion causes a larger critical resolved shear stress (CRSS) to nucleate the dislocation and a greater lattice friction to overcome during dislocation multiplication and emission process. In addition, based on the activation volume value, the mechanism in Ti20 is regarded as the same as that in Ti60, inferring that altering the lattice distortion does not change the pop-in mechanism in MPEAs. Lastly, the lattice distortion influence on the homogeneous dislocation nucleation process was investigated and compared with the heterogeneous dislocation nucleation event.

Ceria and zirconia are very important for their thermal, mechanical, and chemical stability, and their thin films have attracted much attention for applications such as buffer layers for growing electric devices, thermal-shield or optical coatings, corrosion-resistant coatings, oxygen sensors and ionic conductors for fuel cells. To investigate and control the thin film orientation and phase is important to improve those performances. In this study, the reciprocal space maps of CeO2/YSZ/Si(001) were obtained at high temperature by adding a heater to the sample stage. CeO2 and YSZ thin films were epitaxially grown samples. By measuring lattice constants at high temperature, it was conducted that axes of CeO2 and YSZ thin films parallel to the substrate surface showed smaller thermal coefficients than bulk reference and axes perpendicular to the surface showed larger thermal coefficients due to the underlayer and Si substrate. The distortion rate of the lattice of each film was small around at the film deposition temperature. And it could be controled the lattice parameter at the film surface by the film thickness. Therefore, when another thin film, for example, SrTiO3 is deposited on the CeO2 layer, the lattice change of CeO2 with increasing temperature may differ from that before depositing the top layer.

Whereas exceptional mechanical and radiation performances have been found in the emergent body-centered cubic (BCC) refractory multi-principal element alloys (RMPEAs), the importance of their complex atomic environment, reflecting diversity in atomic size and chemistry, has been largely unexplored at the atomic level. Here, we adopt a local structure approach based on the atomic pair distribution function measurements in combination with density functional theory (DFT) calculations to investigate a series of BCC RMPEAs. Our results demonstrate that all the analyzed RMPEAs exhibit local lattice distortions (LLD) to some extent, but a severe LLD, a breakdown of the 15% atomic size difference in Hume-Rothery rules, occurs only in the Zr- and/or Hf-containing RMPEAs. In addition, through the DFT calculations we show that charge transfer among the elements profoundly reduces the size mismatch effect in average to stabilize this energy-unfavorable severe LLD. The observed competitive coexistence between LLD and charge transfer demonstrates the importance of the electronic effects on the local environments in RMPEAs.

Self-trapped excitons (STEs) have recently been observed in several metal halide perovskites (MHPs), especially in low-dimensional ones. Despite studies that have shown that factors like dopant, chemical composition, lattice distortion, and structural and electronic dimensionality may all affect the self-trapping of excitons, a general understanding of their mechanism of formation in MHPs is lacking. Here, we study the intrinsic and defect-induced self-trapping of excitons in three-, two-, and one-dimensional MHPs. We find that whether the free excitons could be trapped is simply determined by the competition of the energy-gap decrease and deformation-energy increase along with the lattice distortion. Both introducing halogen defects into the lattice and decreasing the dimensionality can tip the balance between them and thus facilitate the self-trapping of free excitons. This general picture of the mechanism of formation of STEs provides important insights into the design and development of high-performance white-light devices and solar cells with MHPs.

The present work investigates the change in the microstructure and the improvement in the microhardness in the Mo-modified Ti2AlNb alloys induced by solution treatment. Typical Widmanstatten O + B2 structure was observed in the alloys directly aged in the O + B2 phase region, with a lower hardness value compared to that of the alloy without Mo addition. Well-arranged O + B2 colonies were observed in the specimen solution treated in single B2 phase region, and it exhibited a favorable hardness performance of up to 620 HV. Besides the precipitation hardening of the O phase, the solution of Mo in B2 phase should be responsible for the enhancement of hardness. Further microstructural observation proved that the substitution of Mo for Nb in the lattice of B2 phase induced the lattice distortion mainly the (200) and (211) planes, and the induced entanglement of dislocations also contributed to the enhancement of hardness.

Low-temperature sintered (Na1/2Bi1/2)0.935Ba0.065Ti0.975(Fe1/2Nb1/2)0.025O3 (NBT-BT-0.025FN) lead-free incipient piezoceramics were investigated using high-purity Li2CO3 as sintering aids. With the ≤0.5 wt% Li2CO3 addition, the introduced Li+ cations precede to enter the A-sites of the perovskite lattice to compensate for the A-site deficiencies. Once the addition exceeds 0.5 wt%, the excess Li+ cations will occupy B-sites and give rise to the generation of oxygen vacancies, which accelerate the mass transport and thus lower the sintering temperature effectively from 1100 °C down to 925 °C. It was also found that a small amount of Li+ addition has little effect on the phase structure and electromechanical properties of the system, but overweight seriously disturbs these characteristics because of the large lattice distortion. The sintered NBT-BT-0.025FN incipient piezoceramics with 1.25 wt% Li2CO3 addition at 925 °C provides a large strain of 0.33% and a corresponding large signal piezoelectric coefficient d*33 of 550 pm/V at 60 kV/cm, indicating this system is a very promising candidate for lead-free co-fired multilayer actuator application. Keywords: Lead-free piezoceramics, (Na1/2Bi1/2)TiO3, Low-temperature sintering, Electric-field-induced strain

In commonly used Sn-based solder systems the η′-Cu6Sn5 phase, which develops during field operation, is of huge interest concerning solder joint reliability in electronic components. For all mentioned results in this paper, the η′-Cu6Sn5 was produced via solid state interdiffusion by employing an industrial like set up. The specimens were characterized via SEM, EDS and XRD measurements. The main focus was set on getting really precise lattice parameters, which gave rise to the problem of partially poor refinements during XRD evaluations. Strongly overlapping fundamental reflections of different occurring phases lead to the danger of getting trapped into false, local minima during refinement. For that reason an unusual refinement method was applied, which only considers the superstructure reflections of the η′-Cu6Sn5 phase. Thereby, the obtained precise lattice parameters could be used for calculating the spontaneous strain tensors of the η′-Cu6Sn5. The concept of the spontaneous strain initially introduced for ferroelastics was applied to quantify the metric distortion of the η′-Cu6Sn5 phase. The calculated eigenvectors of the corresponding strain tensors reveal the direction of the most prominent distortion, which concludes referred to the NiAs/Ni2In structure in a contraction in the [ 110 ] h and an expansion in a corresponding, perpendicular [ 1 1 ¯ 0 ] h direction. Therefore, the corresponding eigenvalues (−0.00088 and 0.00080) of η′-Cu6Sn5 are 5–6 times smaller than the ones from the comparable structure Ni3Sn2. Overall, a refinement strategy for evaluating lattice parameters based on XRD pattern of η′-Cu6Sn5 was worked out, which is also applicable for other problematic superstructures. Hence, the obtained really precise lattice parameters could be used to characterize for the first time the exact monoclinic metric and therefore the monoclinic distortion of the η′-Cu6Sn5 phase.

We report studies on the role of a ZnTe buffer in determining the crystalline phase of MBE-grown MnSe1−xTex alloy thin films. It was found that MBE growth of MnSe and MnTe directly onto a zincblende GaAs substrate usually result in their corresponding stable phases, which are rocksalt and hexagonal, respectively. A set of zincblende MnSe1−xTex alloy thin films with Te composition covering from 0.27 to 1 were fabricated on zincblende ZnTe buffer layers. We have addressed the lattice distortion issue due to thin film effect for these films. A combination of several structural characterizations demonstrates that a perfect lattice matched MnSe1−xTex/ZnTe heterostructure can indeed be realized. The results of this study pave the way for realizing a double-barrier MnSe1−xTex/ZnTe/MnSe1−xTex resonant tunneling diode structure with perfect lattice match as a candidate for a promising THz emitter.

Defect engineering or lattice distortion is considered an efficient strategy to enhance the intrinsic activity of an electrocatalyst. Multishell, hollow NiCoFe alloy spheres were prepared with vacancies, gaps or defect, and tilting of an atomic plane with incorporated graphitic carbon derived from the surfactant. The extra gaps or defects in the lattice, which can be verified by high-resolution transmission electron microscope, provide additional active edge sites for the hydrogen evolution reaction. As a result, three-dimensional NiCoFe alloy poses a very low overpotential of 16 mV in 0.5 M H2SO4 for the hydrogen evolution reaction and an unexpectedly small Tafel slope of 38 mV dec−1. This work can therefore broaden horizons and provide a new dimension for the design of new, highly efficient electrocatalysts for hydrogen evolution in an acidic medium.

SrRuO3 (SRO) is an itinerant ferromagnet with strong coupling between the charge, spin, and lattice degrees of freedom. This strong coupling suggests that the electronic and magnetic behaviors of SRO are highly susceptible to changes in the lattice distortion. Here we show how the spin interaction and resultant magnon formation change with the modification in the crystallographic orientation. We fabricated SRO epitaxial thin films with (100), (110), and (111) surface orientations, to systematically modulate the spin interaction and spin dimensionality. The reduced spin dimensionality and enhanced exchange interaction in the (111)-oriented SRO thin film significantly suppresses magnon formation. Our study comprehensively demonstrates the facile tunability of magnon formation and spin interaction in correlated oxide thin films., 17 pages, 7 figures, 1 table, and 1 appendix

Multi-principal element alloys (MPEAs) are alloys that form solid solution phases and consist of three or more principal elements. Fundamental to the numerical study of mechanical properties of MPEAs are the calculations of their basic structural parameters such as lattice parameter and elastic constants. Due to the presence of multiple elements, calculation of each quantity should ideally consider multiple atomic configurations for each MPEA. However, direct calculations are sometimes expensive, and so some studies in the literature either considered only one atomic configuration or used an indirect method to provide an estimation. In this paper, we calculate the lattice parameters, cohesive energies, and elastic constants of 42 equal-molar refractory MPEAs using small atomistic models. For each quantity in each MPEA, four approaches are used: multiple direct calculations using the alloy potential, a single direct calculation using the A -atom potential, as well as estimations using two rules of mixtures. It is shown that the coefficient of variation based on the first approach positively scales with the lattice distortion of MPEAs. In addition, taking the mean values obtained via the first approach as references, we find that the other three approaches can overestimate or underestimate the basic structural parameters.

In this paper, a two-dimensional lattice-gas model is applied to study the stability and lattice distortion of sI clathrate hydrates of ethylene. Two levels of approximation are considered for the lateral interactions between the adsorbed molecules. By using Monte Carlo simulations, adsorption isotherm (coverage of the cavities as a function of the chemical potential), degree of deformation of the sI structure, and free energy of the adsorbed phase are obtained. A direct relationship between cell distortion and cell occupancy is observed. In addition, the minimum distortion coincides with the minimum value of the free energy. Accordingly, the stability phase diagram can be calculated from the values of the chemical potential at the minimum deformation. The obtained results indicate that the most stable condition of the system occurs for values of the cavity density ranging between 0.35 and 0.4. Finally, MC results are compared with data from experiments and more complex simulations. Fil: Longone, Pablo Jesus. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; Argentina Fil: Martín, Ángel. Universidad de Valladolid; España Fil: Ramirez Pastor, Antonio Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; Argentina

In this paper, based on ab initio molecular dynamics and the exchange-interaction model, the magnetic order transition phenomenon of ${\mathrm{Na}}_{2}{\mathrm{Co}}_{2}\mathrm{Te}{\mathrm{O}}_{6}$ material under different temperatures is investigated. Our results exclude the effect of lattice distortion as a factor for magnetic susceptibility under different temperatures in ${\mathrm{Na}}_{2}{\mathrm{Co}}_{2}\mathrm{Te}{\mathrm{O}}_{6}$. Furthermore, we found that the charge transfer is not a main factor to effectively explain the magnetic phase transition. We proposed a method based on radial distribution function to analyze the space-charge density (SCD) to explore the thermal fluctuations. Our analysis of SCD implies that the thermal fluctuations induced by the variation of atomic vibration under different temperatures are responsible for the anomalies of magnetic susceptibility in ${\mathrm{Na}}_{2}{\mathrm{Co}}_{2}\mathrm{Te}{\mathrm{O}}_{6}$ below the N\'eel temperature.

The interplay between interlayer van der Waals interaction and intralayer lattice distortion can lead to structural reconstruction in slightly twisted bilayer graphene (TBG) with the twist angle being smaller than a characteristic angle θ_{c}. Experimentally, the θ_{c} is demonstrated to be very close to the magic angle (θ≈1.08°). Here we address the transition between reconstructed and unreconstructed structures of the TBG across the magic angle by using scanning tunneling microscopy (STM). Our experiment demonstrates that both structures are stable in the TBG around the magic angle. By using a STM tip, we show that the two structures can be changed to each other and a triangular network of chiral one-dimensional states hosted by domain boundaries can be switched on and off. Consequently, the bandwidth of the flat band, which plays a vital role in the emergent strongly correlated states in the magic angle TBG, is tuned. This provides an extra control knob to manipulate the exotic electronic states of the TBG near the magic angle.

We have studied the compression behavior of ${\mathrm{H}}_{2}\text{\ensuremath{-}}\mathrm{He}$ mixtures in comparison with pure ${\mathrm{H}}_{2}$ and He using powder synchrotron x-ray diffraction, and we present the pressure-volume (PV) compression data of ${\mathrm{H}}_{2}\text{\ensuremath{-}}\mathrm{He}$ mixtures to 160 GPa. The results indicate that both ${\mathrm{H}}_{2}$ and He in ${\mathrm{H}}_{2}\text{\ensuremath{-}}\mathrm{He}$ mixtures remain in hcp to the maximum pressure studied, yet they develop a substantial level of lattice distortion in the (100) plane, most profound in He-rich solids and below 66 GPa. The measured PV data also indicate the softening of an He (or ${\mathrm{H}}_{2}$) -rich lattice upon increasing the level of the guest ${\mathrm{H}}_{2}$ (or He) concentration. We suggest that the observed softening and lattice distortion are due to a substitutional incorporation of ${\mathrm{H}}_{2}$ (guest) molecules into the basal plane of the hcp-He (host) lattice, and thereby reflect the miscibility between ${\mathrm{H}}_{2}$ and He in ${\mathrm{H}}_{2}\text{\ensuremath{-}}\mathrm{He}$ mixtures. Interestingly, solid He exhibits a lesser degree of preferred orientation in ${\mathrm{H}}_{2}\text{\ensuremath{-}}\mathrm{He}$ mixtures than in pure He, likely due to the presence of solid ${\mathrm{H}}_{2}$ disturbing the crystalline ordering of He-rich solids. Finally, the present PV compression data of ${\mathrm{H}}_{2}$-rich and He-rich solids to 160 GPa deviate from those of pure ${\mathrm{H}}_{2}$ and pure He above \ensuremath{\sim}70 and 45 GPa respectively, providing new constraints for the development of the equation of state for ${\mathrm{H}}_{2}\text{\ensuremath{-}}\mathrm{He}$ mixtures for planetary models.

The phase transformation mechanism leading to the formation of intragranular α precipitates in Ti−16Nb (at.%) alloy was investigated by TEM. Spinodal decomposition of the β matrix acts as the uniformly distributed heterogeneous nucleation sites for such α precipitates upon annealing at 550 °C. An α-like atomic arrangement with severe lattice distortion forms in the bcc lattice at the early stage of phase transformation and it transforms to the perfect hcp atomic structure gradually in a displacive mode.

The authors identify the modalities enabling an electronically induced distortion, which is identical across the board of 3d elements showing electronic degenerate states in the high symmetry cubic cell. This constitutes the fingerprint of a Jahn-Teller effect. Materials without electronic instabilities such as LaMnO3 display an alternate lattice distortion simply resulting from lattice mode couplings with the sterically induced distortions.

Statistical mechanics harmonizes mechanical and thermodynamical quantities, via the notion of local thermodynamic equilibrium (LTE). In absence of external drivings, LTE becomes equilibrium tout court, and states are characterized by several thermodynamic quantities, each of which is associated with negligibly fluctuating microscopic properties. Under small driving and LTE, locally conserved quantities are transported as prescribed by linear hydrodynamic laws, in which the local material properties of the system are represented by the transport coefficients. In 1-dimensional systems, on the other hand, the transport coefficients often appear to depend on the global state, rather than on the local state of the system at hand. We interpret these facts within the framework of boundary driven 1-dimensional Lennard-Jones chains of $N$ oscillators, observing that they experience non-negligible $O(N)$ lattice distortions and fluctuations. This implies that standard hydrodynamics and certain expressions of energy flow do not apply in these cases. One possible modification of the energy flow is considered., 8 pages, 7 figures

It is a longstanding notion that alloying different sized elements can cause lattice distortion and phase transition in chemically complex alloys. However, a quantitative understanding of it remains difficult for traditional alloys, and becomes even more challenging for equimolar multicomponent alloys, also known as “high entropy alloys”, which recently emerged as a promising structural/functional material and have been attracting tremendous research interest due to their unique properties. In this work, we carried out extensive first-principles calculations on a series of equimolar complex alloys with a chemically disordered crystalline structure, and characterized their atomic-scale lattice distortions in terms of the local residual strains. Albeit the confounding chemical/geometric complexities, we are able to show that the average attributes of such an atomic-scale distorted lattice, such as the lattice constant and the overall magnitude of the distortion induced residual strains, can be predicted very well by a simple physical model taking into account the efficient packing of different sized atoms interacting in an effective elastic medium. The findings of our current research unveils the details of locally distorted atomic packing in chemically disordered complex alloys, which sheds quantitative insights into the unusual strengthening mechanism as recently discovered in high entropy alloys.

By first-principles calculation, elastic properties of seven single phase high-entropy alloys (HEAs) with excellent properties are presented in our work. A new method Maximum Entropy (MaxEnt) was adopted. The method is an algorithm that can be used to study the lattice distortion effect of HEAs. CP2K first-principles simulation package was employed for calculation. The comparison of calculated elastic properties of TaNbHfZrTi with experimental data is made and the agreement is found to be quite good. Elastic properties of AlMoNbTiV are close to the calculated data from Coherent Potential Approximation (CPA), and the reasons were discussed. The influence of lattice distortions on elastic properties were also studied. Furthermore, elastic properties of a series of refractory HEAs were predicted. These results demonstrate that MaxEnt model can properly describe HEAs.

We investigate the electronic structures, magnetic properties and half-metallicity of Heusler compounds Hf2VZ (Z = Ga, In, Tl, Si, Ge, Sn and Pb) with Hg2CuTi-type structure by using the first-principle calculations based on density-functional theory. It is found that the equilibrium lattice constants of Hf2VZ (Z = Ga, In, Tl, Si, Ge, Sn and Pb) compounds are 6.68, 6.88, 6.91, 6.57, 6.63, 6.85 and 6.94 A, respectively. Hf2VZ (Z = Ga, In, Tl, Si and Sn) compounds exhibit half-metallicity at their respective equilibrium lattice constants. Hf2VGe and Hf2VPb do not exhibit half-metallicity at their equilibrium lattice constants but can present the half-metallicity when the lattice constant decreases to 6.51 and 6.71 A, respectively. In case of the lattice thermal expansion, the half-metallicity can be kept in the range of 6.30∼ 7.27, 6.36∼ 7.80, 6.46∼ 7.35, 6.00∼ 6.70 and 6.10∼ 6.95 A (lattice constant) for Hf2VZ (Z = Ga, In, Tl, Si and Sn). Under the unaxial strain, the half-metallicity can still be kept for Hf2VZ (Z = Ga, In, Tl) when the lattice distortion is up to ± 10% (c/a) and be kept for Hf2VZ (Z = Si, Sn) when the lattice distortion is 0.88∼ 1.09, 0.91∼ 1.09 (c/a). For the Hf2VZ compounds with half-metallicity, the total magnetic moment is 2 μB when Z is the third main group elements and is 1 μB when Z is the fourth main group elements. The Hf2VZ compounds with half-metallicity obey the Slater-Pauling formula: Mt = 18 − Zt rule.

Tc-based oxides are of interest because of their complex crystalline structures. In this work, the phonon dispersions, lattice distortions, and elastic constants of TcO2 at external pressures up to 120 GPa were comprehensively studied using first-principles calculations. It is found that the lattice dynamic stability of TcO2 can be assessed by fitting the Γ-Z acoustical phonon branch. The applied external pressure can be divided into three ranges: the low-pressure stable range, the middle-pressure buckling range, and the high-pressure unstable range. Interestingly, the variation tendency of the low-pressure stable range is very close to that of the high-pressure unstable range. On the other hand, the TcO2 lattice responds intensely to external pressure in the middle-pressure buckling range, which can be sustained under about 71 GPa pressure. More importantly, we have unraveled the pressure-induced lattice distortion in TcO2, which leads to anomalous behaviors for the lattice constants, Tc-O bond lengths, and elastic constants at 10 and 20 GPa external pressures.

To investigate the carbothermic reduction behaviors of xFeTiO3·(1 − x)Fe2O3 solid solutions, the solid solutions with different x values were synthesized and used in the corresponding reactions. With an increase in x, the temperature pertaining to the onset of carbothermic reduction increased, while the rate of reduction of the solid solutions, α, decreased. The lattice parameters calculated from XRD patterns indicated that the solid solution with a higher x led to a larger lattice distortion. The non-isothermal kinetics were calculated, and an average activation energy E value of 3.0 × 102 kJ/mol was obtained.

Dependence of structural and luminescence properties of nano-crystalline ZnGa2O4 phosphors on the synthesis conditions such as concentration of precursor metal ions and nature of solvents were investigated in detail. Based on XRD and luminescence studies carried out on samples prepared with high and low concentrations of precursor metal ions in ethylene glycol medium, it is established that distortion of structural units along with defects/traps in the lattice, and not the particle size, is responsible for the observed blue shift in emission maxima with decrease in precursor concentrations. Unlike this, a red shift is observed when the synthesis is carried out under identical conditions in water medium. This has been explained based on difference in particle size distributions as confirmed by TEM studies.

Many recent efforts have been made to apply traditional theories for solid solution strengthening to explain the strength increase in concentrated equiatomic alloys (or high-entropy alloys), but always faced the challenge of differentiating solvent from solute atoms. In this report, we conducted a systematical analysis of Ni-based equiatomic alloys with a face-centered cubic structure and found that the lattice distortion in this alloy system could be simply described by the parameter of atomic size mismatch. It was found that lattice friction stresses of these alloys were well correlated with the lattice distortion. Dislocation core width in this Ni-based alloy system was also estimated and compared with that in the pure nickel. The intrinsically high strength in high-entropy alloys was probably resulted from a high lattice friction stress.

Periodic chemically homogenized high-entropy alloy structures are constructed according to maximum entropy principle. The method can efficiently generate equimolar and non-equimolar high-entropy alloy atomic structures. Nine high-entropy alloys are simulated based on the constructed models using density functional theory techniques. The calculated lattice parameters are consistent with the available experimental data. The calculated enthalpies of mixing are more negative than the values estimated by using Miedema model, due to severe lattice distortion. The lattice distortion parameters were calculated. The results showed that fcc structure tend to stable with smaller and bcc structure with larger. The bulk modulus of Al1.5CoCrNiFe high-entropy alloys was fitted and the value is consistent with the available experimental data.

Low thermal conductivity is the key property dominating the heat insulation ability of thermal barrier coatings (TBC). Reducing the intrinsic thermal conductivity is the major topic for developing advanced TBCs. Defect engineering has attracted much attention in seeking better TBC materials since lattice defects play a crucial role in phonon scattering and thermal conductivity reduction. Oxygen vacancies and substitutions are proven to be the most effective, while the accompanying lattice distortion is also of great importance. In this paper, recent advances of reducing the thermal conductivity of potential thermal barrier coating materials by defect engineering are comprehensively reviewed. Effects of the mass and size mismatch between the defects and the host lattice are quantitatively estimated and unconventional thermal conductivity reduction caused by the lattice distortions is also discussed. Finally, challenges and potential opportunities are briefly assessed to further minimize the thermal conductivity of TBC materials in the future.

Nematic states are characterized by rotational symmetry breaking without translational ordering. Recently, nematic superconductivity, in which the superconducting gap spontaneously lifts the rotational symmetry of the lattice, has been discovered. In nematic superconductivity, multiple superconducting domains with different nematic orientations can exist, and these domains can be controlled by a conjugate external stimulus. Domain engineering is quite common in magnets but has not been achieved in superconductors. Here, we report control of the nematic superconductivity and their domains of SrxBi2Se3, through externally-applied uniaxial stress. The suppression of subdomains indicates that it is the Δ4y state that is most favoured under compression along the basal Bi-Bi bonds. This fact allows us to determine the coupling parameter between the nematicity and lattice distortion. These results provide an inevitable step towards microscopic understanding and future utilization of the unique topological nematic superconductivity., Nematic superconductors, exhibiting rotational-symmetry breaking, can form domains; a counterpart of common magnetic domains. Here, the authors report control of nematic superconductivity and their domains of SrxBi2Se3 by uniaxial deformation, a step toward superconductive domain engineering.

To improve the photovoltaic performance (both efficiency and stability) in hybrid organic-inorganic halide perovskite solar cells, perovskite lattice distortion is investigated with regards to residual stress (and strain) in the polycrystalline thin films. It is revealed that residual stress is concentrated at the surface of the as-prepared film, and an efficient method is further developed to release this interfacial stress by A site cation alloying. This results in lattice reconstruction at the surface of polycrystalline thin films, which in turn results in low elastic modulus. Thus, a "bone-joint" configuration is constructed within the interface between the absorber and the carrier transport layer, which improves device performance substantially. The resultant photovoltaic devices exhibit an efficiency of 21.48% with good humidity stability and improved resistance against thermal cycling.

High entropy alloys (HEAs) have attracted great attention due to their impressive properties induced by the severe lattice distortion in comparison to the conventional alloys. However, the effect of severe lattice distortion on the mechanical properties in face-centered-cubic (FCC) and body-centered-cubic (BCC) structured HEAs is still not fully understood, which are critically important to the fundamental studies as well as the industrial applications. Herein, a theoretical model for predicting the lattice-friction resistance and the yield stress in the FCC and BCC HEAs accounting for the lattice distortion is presented. Both the calculated lattice-friction resistance and the yield strength are compared to the experimental results, to verify the rationality of the built theoretical model. Moreover, the effect of the grain-size distribution on the yield strength is theoretically considered, which reveal the origin of multistage grain structure strengthening. The numerical predictions considering the severe lattice-distortion effect agree well with the experimental results for both FCC and BCC HEAs, in terms of the yield strength and the lattice-friction resistance. The grain-boundary strengthening dominates the yield strength in the FCC Al0.3CrCoFeNi HEA. The yield strength is governed by the lattice-friction resistance in the BCC TaNbHfZrTi HEA, agreeing with the previous work. In AlxCrCoFeNi HEAs, the Al concentration dominates the lattice-friction resistance, and the atomic-radius mismatch and shear-modulus mismatch induced by other four-principal-elements govern the lattice-friction lattice. The atomic-size mismatch dominates the lattice distortion in HEAs, and this viewpoint differs from the traditional knowledge that the increasing incorporated principal element controls the lattice distortion. These results provide the insight into the effect of the severe lattice distortion on the yield strengths in HEAs from the theoretical perspective, for discovering advanced high-strength HEAs.

In the present study, we have revealed that (NiCoFeCr)100&minus, xPdx (x= 1, 3, 5, 20 atom%) high-entropy alloys (HEAs) have both local- and long-range lattice distortions by utilizing X-ray total scattering, X-ray diffraction, and extended X-ray absorption fine structure methods. The local lattice distortion determined by the lattice constant difference between the local and average structures was found to be proportional to the Pd content. A small amount of Pd-doping (1 atom%) yields long-range lattice distortion, which is demonstrated by a larger (200) lattice plane spacing than the expected value from an average structure, however, the degree of long-range lattice distortion is not sensitive to the Pd concentration. The structural stability of these distorted HEAs under high-pressure was also examined. The experimental results indicate that doping with a small amount of Pd significantly enhances the stability of the fcc phase by increasing the fcc-to-hcp transformation pressure from ~13.0 GPa in NiCoFeCr to 20&ndash, 26 GPa in the Pd-doped HEAs and NiCoFeCrPd maintains its fcc lattice up to 74 GPa, the maximum pressure that the current experiments have reached.

Strain induced by lattice distortion is one of the key factors that affect the photovoltaic performance via increasing defect densities. The unsatisfied power conversion efficiencies (PCEs) of solar cells based on antimony chalcogenides (Sb‐Chs) are owing to their photoexcited carriers being self‐trapped by the distortion of Sb2S3 lattice. However, strain behavior in Sb‐Chs‐based solar cells has not been investigated. Here, strain tuning in Sb‐Chs is demonstrated by simultaneously replacing Sb and S with larger Bi and I ions, respectively. Bi/I codoped Sb2S3 cells are fabricated using poly[2,6‐(4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b;3,4‐b']dithiophene)‐alt‐4,7‐(2,1,3‐enzothiadiazole)] as the hole‐transporting layer. Codoping reduced the bandgap and rendered a bigger tension strain (1.76 × 10−4) to a relatively smaller compression strain (−1.29 × 10−4). The 2.5 mol% BiI3 doped Sb2S3 cell presented lower trap state energy level than the Sb2S3 cell; moreover, this doping amount effectively passivated the trap states. This codoping shows a similar trend even in the low bandgap Sb2(SxSe1‐x)3 cell, resulting in 7.05% PCE under the standard illumination conditions (100 mW cm−2), which is one of the top efficiencies in solution processing Sb2(SxSe1‐x)3 solar cells. Furthermore, the doped cells present higher humidity, thermal and photo stability. This study provides a new strategy for stable Pb‐free solar cells., Strain tuning in Sb‐Chs was demonstrated by simultaneously replacing Sb and S with larger Bi and I ions, respectively. This strategy has been applied in Sb2(SxSe1– x)3 solar cells, and the champion cell exhibits a PCE of 7.05% under the standard illumination conditions (100 mW cm−2), which is one of the top efficiencies in solution processing Sb2(SxSe1– x)3 solar cells.

We investigate the dynamics of an active particle in two-dimensional spherical crystals, which provide an ideal environment to illustrate the interplay of active particle and crystallographic defects. A moving active particle is observed to be surrounded by localized topological defects, becoming a dressed active particle. Such a physical picture characterizes both the lattice distortion around the moving particle and the healing of the distorted lattice in its trajectory. We find that the dynamical behaviors of an active particle in both random and ballistic motions uniformly conform to this featured scenario, whether the particle is initially a defect or not. We further observe that the defect pattern around a dressed ballistic active particle randomly oscillates between two well-defined wing-like defect motifs regardless of its speed. The established physical picture of dressed active particles in this work partially deciphers the complexity of the intriguing nonequilibrium behaviors in active crystals, and opens the promising possibility of introducing the activity to engineer defects, which has strong connections with the design of materials., Comment: 8 pages, 5 figures

It is demonstrated that thermally induced atomic displacements from ideal lattice positions can produce considerable effect on magnetic exchange interactions and, consequently, on the Curie temperature of Fe. Thermal lattice distortion should, therefore, be accounted for in quantitatively accurate theoretical modeling of the magnetic phase transition. At the same time, this effect seems to be not very important for magnetic exchange interactions and the Curie temperature of Co and Ni.

We study the response of the antiferromagnetism of CeAuSb$_2$ to orthorhombic lattice distortion applied through in-plane uniaxial pressure. The response to pressure applied along a $\langle 110 \rangle$ lattice direction shows a first-order transition at zero pressure, which shows that the magnetic order lifts the $(110)/(1\bar{1}0)$ symmetry of the unstressed lattice. Sufficient $\langle 100 \rangle$ pressure appears to rotate the principal axes of the order from $\langle 110 \rangle$ to $\langle 100 \rangle$. At low $\langle 100 \rangle$ pressure, the transition at $T_N$ is weakly first-order, however it becomes continuous above a threshold $\langle 100 \rangle$ pressure. We discuss the possibility that this behavior is driven by order parameter fluctuations, with the restoration of a continuous transition a result of reducing the point-group symmetry of the lattice., 6 pages, 7 figures

Exploration of advanced anode materials is a highly relevant research topic for next generation lithium-ion batteries. Here, we report severe lattice distorted MoS2 nanosheets with a flower-like morphology prepared with PEG400 as additive, which acts not only as surfactant but importantly, also as reactant. Notably, in the absence of a carbon-related incorporation/decoration, it demonstrates superior electrochemical performance with a high reversible capacity, a good cycling stability, and an excellent rate capability, originated from the advantages of synthesized MoS2 including enlarged interlayer spacing, 1T-like metallic behavior, and coupling of Mo–O–C (and Mo–O) hetero-bonds. PEG-assisted synthesis is believed applicable to other anode materials with a layered structure for lithium-ion batteries.

Superconductivity in BaFe2(As1-xPx)2 iron pnictides emerges when its in-plane two-dimensional (2D) orthorhombic lattice distortion associated with nematic phase at Ts and three-dimensional (3D) collinear antiferromagnetic (AF) order at TN (Ts = TN) are gradually suppressed with increasing x, reaching optimal superconductivity around x = 0.30 with Tc $\approx$ 30 K. Here we show that a moderate uniaxial pressure along the c-axis in BaFe2(As0.70P0.30)2 spontaneously induces a 3D collinear AF order with TN = Ts > 30 K, while only slightly suppresses Tc. Although a ~ 400 MPa pressure compresses the c-axis lattice while expanding the in-plane lattice and increasing the nearest-neighbor Fe-Fe distance, it barely changes the average iron-pnictogen height in BaFe2(As0.70P0.30)2. Therefore, the pressure- induced AF order must arise from a strong in-plane magnetoelastic coupling, suggesting that the 2D nematic phase is a competing state with superconductivity., 13 pages, 5 figures

The effect of interaction of low-index atomic planes, (100), (110), and (111) terminating CdSe platelet nanocrystals is examined using molecular dynamics (MD) simulations. Asymmetry of the environment of atoms at the end surface layers leads to anisotropic deformation of the cubic lattice and to a relative shift of Cd and Se sub-lattices. Interference of distortions of the crystal lattice originating at the terminal surfaces leads to changes of symmetry of the CdSe lattice in the whole sample volume. In the models, 2-3 nm thick, for all types of surfaces under examination, the initial cubic lattice symmetry gets lost in the whole sample volume. Graphical abstractᅟ.

A critical issue of atomic-size effects in the new class of metallic materials, high entropy alloys (HEAs), containing multi-principal alloying elements is addressed by considering the intrinsic lattice distortion. Although the development effort on these new HEAs has revealed the potential of HEAs for elevated temperature applications, a clear physical description of lattice distortions in these advanced alloys containing different atomic sizes is still lacking at the present time. In this study, we proposed a new model to address the lattice distortion of crystalline lattices in these alloys, and a series of physical parameters to address the atomic-size difference can then be defined. The optimal parameter, α 2 , is found to be effective in explaining the lattice distortion, intrinsic strain energy and excess entropy in HEAs, as well in other multicomponent alloy systems.

The metamagnetic transition and magnetic-field-induced strain are investigated in the Gd66Sm34 and Gd63Sm37 alloys. The thermal- or magnetic-field-induced magnetoelastic transitions are observed in these alloys at room temperature, which are accompanied by large lattice distortion and minimal hysteresis. Large reversible magnetostriction of 900 and 350 ppm can be obtained in the Gd63Sm37 alloy at 290 K with the magnetic fields of 1 T and 0.5 T, respectively. This excellent magnetostrictive performance is attributed to the lattice change during the magnetic-field-induced magnetoelastic transition.

The development of a model to extend the range of the embedded atom method (EAM) is presented. The model is founded on the premise that the dislocation core generates a distortion field within the lattice that extends well beyond the range of operation of the embedded atom method. The resulting misfit potential is based on a characteristic function that accounts for long range lattice distortion. The characteristic function was established by the fitting the coefficients to the distortion at given distances from the dislocation core. The misfit potential enabled the determination of long range dislocation interactions and was applied in the simulation of dislocation core stress fields in the body centered cubic Fe lattice. These stress profiles are reported.

This work examines the anisotropic microstructure and the lattice distortions of nonpolar a-plane \((11\bar 20)\) GaN (a-GaN) films by using the grazing-incidence X-ray diffraction technique. Faulted a-GaN films typically exhibit an in-plane anisotropy of the structural properties along the X-ray in-beam directions. For this reason, the anisotropic peak broadenings of the X-ray rocking curves (XRCs) were observed for various angle (phi) rotations for a-GaN films with and without SiNx interlayers. Analysis revealed the peak widths of the XRCs displayed an isotropic behavior for a nonpolar a-GaN bulk crystal. Thus, the in-plane anisotropy of the XRC peak widths for nonpolar a-GaN films apparently originates from the heteroepitaxial growth of the a-GaN layer on a foreign substrate. The lattice distortion analysis identified the presence of compressive strains in both the two in-plane directions (the c- and the m-axis), as well as a tensile strain along the normal growth direction. In addition, the observed frequency shifts in the Raman E2 (high) mode for the a-GaN films showed the existence of considerable in-plane compressive strain on both a-GaN films, as confirmed by the lattice distortion analysis performed using the grazing-incidence XRD method.

Calcium-for-strontium cation substitution of the a(-)b(0)c(0)/b(0)a(-)c(0)-distorted, cation-ordered, n = 2 Ruddlesden-Popper phase, YSr2Mn2O7, leads to separation into two phases, which both retain an a(-)b(0)c(0)/b(0)a(-)c(0)-distorted framework and have the same stoichiometry but exhibit different degrees of Y/Sr/Ca cation order. Increasing the calcium concentration to form YSr0.5Ca1.5Mn2O7 leads to a change in the cooperative tilting on the MnO6 units to a novel a(-)b(-)c(-)/b(-)a(-)c(-) arrangement described in space group P21/n11. Low-temperature, topochemical fluorination of YSr2Mn2O7 yields YSr2Mn2O5.5F3.5. In contrast to many other fluorinated n = 2 Ruddlesden-Popper oxide phases, YSr2Mn2O5.5F3.5 retains the a(-)b(0)c(0)/b(0)a(-)c(0) lattice distortion and P42/mnm space group symmetry of the parent oxide phase. The resilience of the a(-)b(0)c(0)/b(0)a(-)c(0)-distorted framework of YSr2Mn2O7 to resist symmetry-changing deformations upon both cation substitution and anion insertion/exchange is discussed on the basis the A-site cation order of the lattice and the large change in the ionic radius of manganese upon oxidation from Mn(3+) to Mn(4+). The structure property relations observed in the Y-Sr-Ca-Mn-O-F system provide insight into assisting in the synthesis of n = 2 Ruddlesden-Popper phases, which adopt cooperative structural distortions that break the inversion symmetry of the extended lattice and therefore act as a route for the preparation of ferroelectric and multiferroic materials.

Iron telluride (FeTe) is known to display bicollinear magnetic order at low temperatures together with a monoclinic lattice distortion. Because the bicollinear order can involve two different wave vectors $(\ensuremath{\pi}/2,\ensuremath{\pi}/2)$ and $(\ensuremath{\pi}/2,\ensuremath{-}\ensuremath{\pi}/2)$, symmetry considerations allow for the possible stabilization of a nematic state with short-range bicollinear order coupled to monoclinic lattice distortions at a ${T}_{S}$ higher than the temperature ${T}_{N}$ where long-range bicollinear order fully develops. As a concrete example, the three-orbital spin-fermion model for iron telluride is studied with an additional coupling ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\lambda}}}_{12}$ between the monoclinic lattice strain and an orbital-nematic order parameter with ${B}_{2g}$ symmetry. Monte Carlo simulations show that with increasing ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\lambda}}}_{12}$ the first-order transition characteristic of FeTe splits and bicollinear nematicity is stabilized in a (narrow) temperature range. In this new regime, the lattice is monoclinically distorted and short-range spin and orbital order breaks rotational invariance. A discussion of possible realizations of this exotic state is provided.

We performed reverse Monte Carlo (RMC) modeling on neutron total scattering data and obtained an atomic structure consistent with the local and the average structures of the relaxor ferroelectric Pb(Zn1/3Nb2/3)O3. By analyzing the model structure from the RMC analysis, we found evidence for a significant off-centering of the lead ion that varied in magnitude and direction, leading to a partial ordering of polarizations over a few unit cells. We also estimated the static lattice distortion of the oxygen lattice from the bond-length distributions of atomic pairs.

The kinetics of lattice distortion introduction and lattice relaxation at the surface of thermally-oxidized 4H-SiC (0001) were investigated. Our results suggested that lattice distortion introduction and lattice relaxation seem to follow zeroth and second order rate laws, respectively. The obtained activation energy of ~3.9 eV for lattice distortion introduction and ~1 eV for its relaxation indicate that the lattice distortion is determined by a bond rearrangement or movement process with a relatively low activation energy. Furthermore, the formation of byproducts which remain at the surface region of 4H-SiC was predicted to be a possible origin of the significant lattice distortion.

We have carried out a series of calculations to investigate the electronic band structure of bulk HgTe strained along c-direction with the constant-volume by means of the full potential linearized augmented plane-wave method. Our results show that there is a topological insulating phase induced by the lattice distortions, which is in agreement with previous theoretical and experimental results. Importantly, the distortion-induced band gap is large up to 0.19 eV in either expansion or compression along c-direction. It is indicated that the bulk HgTe under proper lattice distortions would be possibly made the room temperature application for material engineering with low energy consumption.

A series of calculations are carried out to investigate the electronic band structure of bulk HgTe strained in ab-plane with the assumption of the relaxed-volume and the constant-volume by means of the full potential linearized augmented plane-wave method. Our results show that there is a topological insulating phase induced by the lattice distortions, which is in agreement with previous theoretical and experimental results. Importantly, the distortion-induced band gap is larger than 0.3 eV in either expansion or compression in ab-plane. It is indicated that the bulk HgTe under proper lattice distortions would be possibly made the room temperature application for spintronic devices with low energy consumption.

Bi1.85Mn0.15Te3 hexagonal nanoplates with a width of similar to 200 nm and a thickness of similar to 20 nm were synthesized using a solvothermal method. According to the structural characterization and compositional analysis, the Mn2+ and Mn3+ ions were found to substitute Bi3+ ions in the lattice. High-level Mn doping induces significant lattice distortion and decreases the crystal lattice by 1.07% in the a axis and 3.18% in the c axis. A high ferromagnetic state with a Curie temperature of similar to 45 K is observed in these nanoplates due to Mn2+ and Mn3+ ion doping, which is a significant progress in the field of electronics and spintronics.