Local Lattice Distortion Research Articles

Unconventional Non-Uniform Local Lattice Distortion in Dilute Ti-Mo Solid Solution

The substitutional solute atom induced local lattice distortion (LLD) in dilute metal solid solution was believed to be uniform because the solute atom was supposed to occupy the high symmetry lattice site without breaking the point group symmetry of the crystal lattice. Contrary to this conventional picture, we report in this paper that substitutional Mo atom in Ti-Mo solid solution occupies an off-center position instead of the high symmetry lattice site and leads to highly non-uniform LLD, as evidenced by our first principles calculations. The physics underlying the off-center occupation and non-uniform LLD are shown to be the Jahn-Teller splitting of the degenerated d states of Mo atom. With which, the solid-solutions suffering from non-uniform LLD are predicted. The non-uniform LLD challenges the application of classical solid solution hardening model based on uniform LLD and spherical stress tensor assumption to this kind of solid solutions. This work also questions the traditional view that elementary substitutional solute atoms in metal solid solutions should not induce anelastic relaxation and internal friction.

Local Lattice Distortion and Chemical Short Range Order in High Entropy Alloys

Local Lattice Distortion and Chemical Short Range Order in High Entropy Alloys

Influence of NiFe<sub>2</sub>O<sub>4</sub> nanoparticle doping on properties of single-domain YBCO bulk superconductors

NiFe<sub>2</sub>O<sub>4</sub> (NFO) nanoparticle doped YBCO bulk superconductors are fabricated by using a novel top-seed infiltration growth (TSIG) technique. The growth morphology, microstructure and superconducting properties are investigated. The results show that at low doping levels, the normal growth of YBCO single domain is not affected by the NFO doping, but at high doping levels, obvious random nucleation appears at the edge of the sample. The measurement of levitation force indicates that the maximum levitation force on the sample first increases and then decreases with the increase of the NFO doping amount, and the largest levitation force is obtained to be 33.93 N for the sample with a doping level of 0.2% (weight percent). Low-temperature magnetization measurement shows that the YBCO sample exhibits that <i>T</i><sub>c</sub> value decreases with NFO amount increasing, and the superconducting transition width (Δ<i>T</i><sub>c</sub>) also broadens gradually. The sample with the optimal doping (0.2% weight percent) presents an enhanced zero-field <i>J</i><sub>c</sub> value of 8.68 × 10<sup>4</sup> A/cm<sup>2</sup>, which is 31% higher than the sample without dopant. In addition, a more obvious secondary peak of 4.37 × 10<sup>4</sup> A/cm<sup>2</sup> at a field of 1 T is observed for the 0.2 wt.% NFO doped sample, which indicates the existence of enhanced <italic/>δ<i>T</i><sub>c</sub> pinning in the bulk. The SEM measurement shows that two types of particles are trapped in the Y-123 matrix for YBCO sample doped with 0.2% weight percent NFO: one is the large particle with a size mainly ranging from 0.5 μm to 2.0 μm, and the other is small nano-inclusion mainly ranging from dozens of nanometers to about several hundreds of nanometers. Such a microstructure is very similar to the microstructure of the undoped sample we reported earlier. So whether the NFO nanoparticles exist in the microstructure cannot be judged just from the morphology of the nano-inclusions. The electron probe microarea analysis (EPMA) result shows that different concentration distributions of Ni and Fe elements are observed in the sample doped with 0.2% weight percent NFO, which indicates the separation of NFO nanoparticles in the heat treatment process, and the dissolved Ni and Fe ions finally exist in the form of element substitutions in the YBCO bulk. Such element substitutions can introduce local lattice distortions and weak-superconducting regions into the superconducting matrix, which can act as effective flux pinning centers, and hence improving the properties of the samples.

Re‐entrant dipole glass‐like behavior and lattice dynamics of 0.65Bi(Mg1/2Ti1/2)O3‐0.35PbTiO3

AbstractThe 0.65Bi(Mg1/2Ti1/2)O3‐0.35PbTiO3 (0.65BMT‐0.35PT) ceramic, nearby morphotropic phase boundary (MPB), between tetragonal and rhombohedral was prepared. Dielectric permittivity dependence of temperature exhibits a re‐entrance dipole glass‐like behavior near room temperature. The behavior was described by the Vogel‐Fulcher law and the new glass model. Furthermore, a phenomenological statistical model was employed to determine the distribution of clusters dependence of temperature. The lattice dynamics of the 0.65BMT‐0.35PT ceramic was estimated by Raman spectroscopy from 298‐723 K. A disruption of ferroelectric long‐range order and an occurrence of local lattice distortion were revealed. The relaxor‐ferroelectric (r‐FE) nature of the 0.65BMT‐0.35PT was characterized by polarization‐electric field P(E). A close relation between the distribution of clusters and ferroelectric properties was established.

Possible Charge Density Wave and Enhancement of Thermoelectric Properties at Mild-Temperature Range in n-Type CuI-Doped Bi2Te2.1Se0.9 Compounds.

Bi2Te3-based compounds have long been studied as thermoelectric materials in cooling applications near room temperature. Here, we investigated the thermoelectric properties of CuI-doped Bi2Te2.1Se0.9 compounds. The Cu/I codoping induces the lattice distortion partially in the matrix. We report that the charge density wave caused by the local lattice distortion affects the electrical and thermal transport properties. From the high-temperature specific heat, we found a first-order phase transitions near 490 and 575 K for CuI-doped compounds (CuI)xBi2Te2.1Se0.9 (x = 0.3 and 0.6%), respectively. It is not a structural phase transition, confirming from the high-temperature X-ray diffraction. The temperature-dependent electrical resistivity shows a typical behavior of charge density wave transition, which is consistent with the temperature-dependent Seebeck coefficient and thermal conductivity. The transmission electron microscopy and electron diffraction show a local lattice distortion, driven by the charge density wave transition. The charge density wave formation in the Bi2Te3-based compounds are exceptional because of the possibility of coexistence of charge density wave and topological surface states. From the Kubo formula and Boltzmann transport calculations, the formation of charge density wave enhances the power factor. The lattice modulation and charge density wave decrease lattice thermal conductivity, resulting in the enhancement of thermoelectric performance simultaneously in CuI-doped samples. Consequently, an enhancement of thermoelectric performance ZT over 1.0 is achieved at 448 K in the (CuI)0.003Bi2Te2.1Se0.9 sample. The enhancement of ZT at high temperature gives rise to a superior average ZTavg (1.0) value than those of previously reported ones.

Alloying effects on low‒energy recoil events in concentrated solid‒solution alloys

Alloying elements at low-concentrations into pure metals is usually adopted to improve their mechanical properties and irradiation performance. Recently developed single-phase concentrated solid-solution alloys (CSAs) comprised of two or more elements, all at high concentrations, have demonstrated good radiation resistance. CSAs are characterized by their extreme disordered states that arise from the random arrangement of different elements and accompanied random local lattice distortions. In this work, we investigate low-energy recoil events in Ni0.5X0.5 (X = Fe and Co) CSAs and Ni0.8X0.2 (X = Fe, Co, Cr, and Pd) CSAs using ab initio molecular dynamics simulations to understand the effects of different disorder on defect production in CSAs. The threshold displacement energies are determined along three high-symmetric directions by randomly choosing independent primary knock-on atoms in each direction. As expected, the threshold energies in Ni and its CSAs are anisotropic, with the highest values found in the [111] direction. The calculated threshold energies of Fe in NiFe are smaller than those in NiCo and Ni, especially along the [111] direction. An inspection of the atomic trajectories inside the collision cascade reveals that the effect of chemical disorder outweighs the site-to-site lattice distortions in determining the threshold energies. Especially, different interaction properties between elements due to their different electronic structures are responsible for the observed different threshold energies. The local environment dependence of threshold energies suggests that local elemental arrangement can be used to understand and predict threshold energies in disordered alloys.

Dynamical Mechanism of Polarons and Bipolarons in Poly(p-Phenylene Vinylene)

Studies on Poly(p-Phenylene Vinylene) (PPV) and derivatives have experienced enormous growth since they were successfully used to fabricate the first efficient prototypes of Polymer Light-Emitting Diodes in the 90s. Despite this rapid progress, understanding the relationship between charge transport and the morphology in these materials remains a challenge. Here, we shed light on the understanding of the transport mechanism of polarons and bipolarons in PPVs by developing a two-dimensional tight-binding approach that includes lattice relaxation effects. Remarkably, the results show that the PPV lattice loses the energy related to its conjugation during time by transferring this amount of energy to electrons. Such a process for energy transfer permits the quasiparticles to overcome the potential barrier imposed by the local lattice deformations, that are formed in the presence of an additional charge and, consequently, their electric field assisted transport takes place. Within the framework of this transport mechanism, a better insight into the origin of the carrier mobility in PPV and derivatives can be achieved and would be a useful guide for improving their chemical structures and morphologies.

Parametrically constrained geometry relaxations for high-throughput materials science

Reducing parameter spaces via exploiting symmetries has greatly accelerated and increased the quality of electronic-structure calculations. Unfortunately, many of the traditional methods fail when the global crystal symmetry is broken, even when the distortion is only a slight perturbation (e.g., Jahn-Teller like distortions). Here we introduce a flexible and generalizable parametric relaxation scheme and implement it in the all-electron code FHI-aims. This approach utilizes parametric constraints to maintain symmetry at any level. After demonstrating the method’s ability to relax metastable structures, we highlight its adaptability and performance over a test set of 359 materials, across 13 lattice prototypes. Finally we show how these constraints can reduce the number of steps needed to relax local lattice distortions by an order of magnitude. The flexibility of these constraints enables a significant acceleration of high-throughput searches for novel materials for numerous applications.

Local structure of Ni80X20 (X: Cr, Mn, Pd) solid-solution alloys and its response to ion irradiation

The local structure of Ni80X20 (X: Cr, Mn, Pd) solid-solution alloys was investigated with x-ray absorption and total scattering x-ray diffraction methods. Atomic pair distribution function (PDF) analysis indicated that the local lattice distortion is strongly relevant to the atomic size mismatch, and the local lattice distortion in Ni80Pd20 alloy is obviously larger than that in other solid-solution alloys. The bond length of different atomic pairs was derived from the fitting of extended x-ray absorption fine structure spectra. Quantitative analysis of the local bonding environment in Ni80Cr20 during Ni ion irradiation suggested that Cr atoms tend to form clusters in Ni80Cr20 with the increase of ion dose.

Severe local lattice distortion in Zr- and/or Hf-containing refractory multi-principal element alloys

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.

Probing Phase Separation and Local Lattice Distortions in Cuprates by Raman Spectroscopy

It is generally accepted that high temperature superconductors emerge when extra carriers are introduced in the parent state, which looks like a Mott insulator. Competition of the order parameters drives the system into a poorly defined pseudogap state before acquiring the normal Fermi liquid behavior with further doping. Within the low doping level, the system has the tendency for mesoscopic phase separation, which seems to be a general characteristic in all high Tc compounds, but also in the materials of colossal magnetoresistance or the relaxor ferroelectrics. In all these systems, metastable phases can be created by tuning physical variables, such as doping or pressure, and the competing order parameters can drive the compound to various states. Structural instabilities are expected at critical points and Raman spectroscopy is ideal for detecting them, since it is a very sensitive technique for detecting small lattice modifications and instabilities. In this article, phase separation and lattice distortions are examined on the most characteristic family of high temperature superconductors, the cuprates. The effect of doping or atomic substitutions on cuprates is examined concerning the induced phase separation and hydrostatic pressure for activating small local lattice distortions at the edge of lattice instability.

Spatial confinement tuning of quenched disorder effects and enhanced magnetoresistance in manganite nanowires

Complex oxides have rich functionalities and advantages for future technologies. In many systems, quenched disorder often holds the key to determine their physical properties, and these properties can be further tuned by chemical doping. However, understanding the role of quenched disorder is complicated because chemical doping simultaneously alters other physical variables such as local lattice distortions and electronic and magnetic environments. Here, we show that spatial confinement is an effective approach to tuning the level of quenched disorder in a complex-oxide system while leaving other physical variables largely undisturbed. Through the confinement of a manganite system down to quasi-one-dimensional nanowires, we observed that the nature of its metal-insulator phase transition exhibits a crossover from a discontinuous to a continuous characteristic, in close accordance with quenched disorder theories. We argue that the quenched disorder, finite size, and surface effects all contribute to our experimental observations. Noticeably, with reduced nanowire width, the magnetoresistance shows substantial enhancement at low temperatures. Our findings offer new insight into experimentally tuning the quenched disorder effect to achieve novel functionalities at reduced dimensions.

The role of A-site ion on proton diffusion in perovskite oxides (ABO3)

By performing detailed density functional theory (DFT) calculations, we investigate the effect of A ion vacancy on both hydroxide ion rotation and proton transfer in Y-doped BaZrO3. We find that A ions reduce the barrier for proton diffusion in a perovskite oxide, demonstrating the significance of perovskite structures as proton conductors. Proton diffusion is understood as a two-step mechanism consisting of hydroxide ion rotation and proton transfer. In both steps, lattice deformations play an important role – specifically, the outward O-B-O bending and A ion motions are important for hydroxide ion rotation, and inward O-B-O bending facilitates proton transfer. By comparing the bond strength, we reveal that an A ion can reduce the bond strength of O and B ion, thereby reducing the energy barrier for local lattice deformation such as O-B-O bending motion, which facilitates both hydroxide ion rotation and proton transfer. Our analysis provides a detailed atomistic understanding of the role of A-site ion on proton diffusion in perovskite oxides. The study presented here not only indicates the advantage of perovskite oxides as proton conductors but also elucidates the origin of proton diffusion barrier which can pave the way for design of novel proton conductors.

Tailoring the local lattice distortion of Nd3+ by codoping of Y3+ through first principles calculation for tuning the spectroscopic properties

Trivalent rare earth ions have rich and unique energy levels arising from 4f inner shell configurations, which can be widely used in lasers, display, and bioimaging, etc. As the f-f transition of the rare earth ions is parity-forbidden, it is necessary to dope the active ions in the host with an appropriate coordination structure to relax the forbidden. In this work, a first principles calculation based on the density functional theory was applied to investigate the local structure symmetries of Nd3+ ions in Nd3+,Y3+:SrF2 crystal. The computational results show that the clusters of [mNd3+-nY3+] (m + n = 2, 3, 4, 5 and 6) would be formed when Y3+ is codoped in Nd3+:SrF2 crystal. The formation energy of the [mNd3+-nY3+] cluster decreases when the value of m + n increases, or the value of n increases with m + n fixed, then the lattice structure becomes more stable. Furthermore, the first coordination shell of Nd3+ was cubic when the n ≤ 1, and it would transform to be the lower symmetric square antiprism structure with n ≥ 2. The forbidden of the electric dipole transition was thus relaxed due to breaking of the symmetry. The experimental results show the absorption cross section of Nd3+ was increased from 0.45 ×10−20 cm2 to 5.2×10−20 cm2, and the emission intensity was also enhanced by about 20 times through codoping Y3+ ions, which agreed well with the calculated results. It suggests that the tailoring of the local lattice distortion of the active ions may open interesting possibilities in the design of rare earth doped materials.

Perovskite Sr1-x(Na0.5Bi0.5)xTi0.99Mn0.01O3 Thin Films with Defect Dipoles for High Energy-Storage and Electrocaloric Performance.

Dielectric capacitors have received more and more attention because of fast charge/discharge capability. However, the energy-storage performance still cannot meet the demand. In this work, lead-free perovskite Sr1-x(Na0.5Bi0.5)xTi0.99Mn0.01O3 (x = 0, 0.005, 0.01, and 0.02) thin films prepared by the sol-gel method were carefully studied. Defect dipoles and local lattice distortion were created by doping Mn at the B-site, enabling ferroelectric polarization behavior. To further enhance polarization, co-substitution at the A-site was adopted. Na+ and Bi3+ can make up Na+-Bi3+ ion pairs. Meanwhile, off-center NaSr+ and BiSr3+ ions with a small radius can lead to the distortion of the octahedral [TiO6] in the lattice to induce local polarization regions. Under the combined action of A-site and B-site doping, polarization and breakdown strength were greatly improved. Finally, a high energy density (53 J cm-3) and good thermal stability were achieved. Furthermore, the negative electrocaloric effect was also achieved. The adiabatic temperature change is about -8.5 at 300 K. This work demonstrates that the Sr0.99(Na0.5Bi0.5)0.01(Ti0.99Mn0.01)O3 thin film with excellent energy-storage performance and the negative electrocaloric effect is a promising multifunctional material.

Electronic structure and atomic level complexity in Al0.5TiZrPdCuNi high-entropy alloy in glass phase

High entropy alloys (HEAs), or concentrated solid solution alloys, are chemically complex metallic solid solutions in which five or more elements occupy the same crystallographic lattice sites with nearly equal compositions. The high degree of chemical disorder gives rise to considerable local lattice distortions, atomic-level stresses, and complex electronic structure, resulting in interesting properties. We calculated the electronic structure and the atomic-level stresses of AlxTiyZryPdyCuyNiy, x = 0.5, y = 1 (Al0.5TiZrPdCuNi) HEA in the glassy phase using the density functional theory (DFT) approach. We also briefly discuss the electronic structure in its crystalline phase. Whereas it has been reported recently that the crystalline phase of this HEA is obtained as a metastable phase during the crystallization of a glassy phase, the crystalline phase was found to be unstable at T = 0 in the DFT calculation. For this reason, we focus mainly on the glassy phase in this work. The importance of charge transfer among elements on the atomic-level pressure and the role for atomic-level stresses to characterize the electronic and structural heterogeneity are discussed.

Influence of Gelatin–Agarose Composites and Mg on Hydrogel-Carbonate Aggregate Formation and Architecture

Hydrogels are adequate systems for investigating biological structural material formation as they mimic a wide range of biomineralization conditions. Previous studies focused on the influence of single-component gel systems in the growth of calcite aggregates and their microstructure characteristics. In this work, we investigate the effects of hydrogel mixtures (gelatin/agarose), in the presence and absence of Mg in the growth medium, on calcite aggregate formation, hydrogel incorporation in the calcite, mode of crystallite assembly, and hierarchical mineral organization. We find marked differences between aggregates developed in gel mixtures with increased content of either gelatin or agarose. The presence of Mg, in addition to the gel incorporation, strongly influences the local lattice deformation within the aggregates. The mode of local deformation (homogeneous or localized) is closely related to the size, distribution, and crystallographic co-orientation of subunits within the aggregate. An increase in agarose induces homogeneous distribution of local deformation within the aggregates and formation of a graded mineral arrangement (archetypical spherulites), while an increase in gelatin leads to differentiation of the center and rim portions within the same aggregate. On a higher hierarchical level, when all subunits of an aggregate are considered, both agarose and gelatin evoke the formation of polycrystals.

Direct Visualization of Spatial Inhomogeneity of Spin Stripes Order in La1.72Sr0.28NiO4

In several strongly correlated electron systems, the short range ordering of defects, charge and local lattice distortions are found to show complex inhomogeneous spatial distributions. There is growing evidence that such inhomogeneity plays a fundamental role in unique functionality of quantum complex materials. La1.72Sr0.28NiO4 is a prototypical strongly correlated perovskite showing spin stripes order. In this work we present the spatial distribution of the spin order inhomogeneity by applying micro X-ray diffraction to La1.72Sr0.28NiO4, mapping the spin-density-wave order below the 120 K onset temperature. We find that the spin-density-wave order shows the formation of nanoscale puddles with large spatial fluctuations. The nano-puddle density changes on the microscopic scale forming a multiscale phase separation extending from nanoscale to micron scale with scale-free distribution. Indeed spin-density-wave striped puddles are disconnected by spatial regions with negligible spin-density-wave order. The present work highlights the complex spatial nanoscale phase separation of spin stripes in nickelate perovskites and opens new perspectives of local spin order control by strain.

Probing the Local Lattice Distortions in Doped SrTiO3 Using Quantitative STEM

Probing the Local Lattice Distortions in Doped SrTiO₃ Using Quantitative STEM

Critical Review of Chemical Complexity Effect on Local Structure of Multi-principal-Element Alloys

The multi-principal-element alloy (MPEA) strategy has radically changed the pathway of alloy development by shifting the search for useful alloys from the corners to the center region of the phase diagram. Distinct from conventional one-principal-element alloys, chemically complex MPEAs exhibit extreme diversity in terms of atomic size and chemistry, potentially distorting their local structure. The present review summarizes recent experimental and theoretical progress on study of the local structure of such materials, with emphases on local lattice distortion and the charge transfer effect.