Linear magnetoresistance and structural distortion in layered SrCu_(4-x)P_(2) single crystals

We report a systematic study on layered metal SrCu_(4-x)P_(2) single crystals via transport, magnetization, thermodynamic measurements and structural characterization. We find that the crystals show large linear magnetoresistance without any sign of saturation with a magnetic field up to 30T. We also observe a phase transition with significant anomalies in resistivity and heat capacity at T_(p)~140 K. Thermal expansion measurement reveals a subtle lattice parameter variation near Tp, i.e.,?L_(c)/L_(c)~0.062%. The structural characterization confines that there is no structure transition below and above T_(p). All these results suggest that the nonmagnetic transition of SrCu_(4-x)P_(2) could be associated with structural distortion.

Structural distortions and magnetisms in Fe-doped LaMn_(1-x) Fe_x O_3(0

X-ray absorption spectra （XAS） at Mn K-edge and Fe K-edge in LaMnl-xFexO3 show that with the increase of Fe substitution the chemical valence of Mn4＋ decreases, while the chemical valence of Fe3＋ remains unchanged. Structural distortions, such as the rotating and tilting for oxygen octahedron in the unit cell vary with iron content. A phase transition occurs at the Fe content values of 0.2~0.3. The evolutions of rotation and tilting angle of FeO6/MnO6 octahedral may be the vital factors to the structure and magnetism. We believe that the spin configuration of Fe3＋ may vary from the intermediate spin t2g4eg1 （S = 3/2） to the higher spin t2g3eg2 （S = 5/2） near the phase transition.

Structural Distortion and Defects in Ti_3AlC_2 irradiated by Fe and He Ions

Ti_3AlC_2 samples are irradiated in advance by 3.5 MeV Fe-ion to the fluence of 1.0×10^（16） ion/cm^2,and then are implanted by 500 keV He-ion with the fluence of 1.0×10^（17） ion/cm^2 at room temperature.The irradiated samples are investigated by grazing incidence x-ray diffraction（GIXRD） and transmission electron microscopy（TEM）.GIXRD results show serious structural distortion,but without amorphization in the irradiated samples.Fe-ion irradiation and He-ion implantation create much more serious structural distortion than single Fe-ion irradiation.TEM results reveal that there are a large number of defect clusters in the damage region,and dense spherical He bubbles appear in the He depositional region.It seems that the pre-damage does not influence the growth of He bubbles,but He-ion implantation influences the pre-created defect configurations.

Colossal structural distortion and interlayer-coupling suppression in a van der Waals crystal induced by atomic vacancies

The interlayer coupling in van der Waals(vdW)crystals has substantial effects on the performance of materials.However,an indepth understanding of the microscopic mechanism on the defect-modulated interlayer coupling is often elusive,owing partly to the challenge of atomic-scale characterization.Here we report the native Se-vacancies in a charge-density-wave metal 2HNbSe2,as well as their influence on the local atomic configurations and interlayer coupling.Our low-temperature scanning tunneling microscopy(STM)measurements,complemented by density functional theory calculations,indicate that the Sevacancies in few-layer NbSe2 can generate obvious atomic distortions due to the Jahn-Teller effect,thus breaking the rotational symmetry on the nanoscale.Moreover,these vacancies can locally generate an in-gap state in single-layer NbSe2,and more importantly,lead to a colossal suppression of interlayer coupling in the bilayer system.Our results provide clear structural and electronic fingerprints around the vacancies in vdW crystals,paving the way for developing functional vdW devices.

Unsupervised machine learning to classify crystal structures according totheir structural distortion: A case study on Li-argyrodite solid-state electrolytes

High-throughput approaches in computational materials discovery often yield a combinatorial explosionthat makes the exhaustive rendering of complete structural and chemical spaces impractical. A commonbottleneck when screening new compounds with archetypal crystal structures is the lack of fast and reliabledecision-making schemes to quantitatively classify the computed candidates as inliers or outliers (too distortedstructures). Machine learning-aided workflows can solve this problem and make geometrical optimizationprocedures more efficient. However, for this to occur, there is still a lack of appropriate combinations ofsuitable geometrical descriptors and accurate unsupervised models which are capable of accurately differentiating between systems with subtle structural changes. Here, considering as a case study the compositionalscreening of cubic Li-argyrodites solid electrolytes, we tackle this problem head on. We find that Steinhardtorder parameters are very accurate descriptors of the cubic argyrodite structure to train a range of commonunsupervised outlier detection models. And, most importantly, the approach enables us to automatically classifycrystal structures with uncertainty control. The resulting models can then be used to screen computed structureswith respect to an user-defined error threshold and discard too distorted structures during geometricaloptimization procedures. Implemented as a decision node in computer-aided materials discovery workflows,this approach can be employed to perform autonomous high-throughput screening methods and make the useof computational and data storage resources more efficient.

Valley transport in Kekulé structures of graphene

Valleytronics is an emergent discipline in condensed matter physics and offers a new way to encode and manipulate information based on the valley degree of freedom in materials. Among the various materials being studied, Kekulé distorted graphene has emerged as a promising material for valleytronics applications. Graphene can be artificially distorted to form the Kekulé structures rendering the valley-related interaction. In this work, we review the recent progress of research on Kekulé structures of graphene and focus on the modified electronic bands due to different Kekulé distortions as well as their effects on the transport properties of electrons. We systematically discuss how the valley-related interaction in the Kekulé structures was used to control and affect the valley transport including the valley generation, manipulation, and detection. This article summarizes the current challenges and prospects for further research on Kekulé distorted graphene and its potential applications in valleytronics.

Enhanced stability and rate performance of zinc-doped cobalt hexacyanoferrate (CoZnHCF) by the limited crystal growth and reduced distortion

Cobalt hexacyanoferrate (CoHCF) is a potential cathode for aqueous Na-ion batteries due to its high theoretical specific capacity (170 m Ah g^(-1));however,its lower rate capability and cyclability limit its applications.Structural distortion at a weak N-coordinated crystal field during cycling disintegrates Co,yielding an irreversible reaction.Different Zn amounts ranging 0–1 were added to the Co site to suppress the structural irreversibility of CoHCF,yielding Co_(1-x)Zn_(x)HCF powder;this Zn (x≤0.09) addition reduced the powder’s dimension because the lower four coordination of Zn–N,not the six coordination of Co–N,limits the powder growth.Simultaneously,a small lattice parameter and interaxial angle (~90°) are obtained,implying that a narrower Co_(1-x)Zn_(x)HCF inner structure is formed to accommodate Na ions.Moreover,the electronic conductivity of Co_(1-x)Zn_(x)HCF gradually increased within 0–0.09 range.A smaller particle size with a high surface area leads to a near-surface-limited redox process,similar to a capacitive reaction.Both the surface-limited reaction and electronic conductivity enhances the reversibility due to the smaller charge transfer resistance at the electrode/electrolyte interface caused by Zn addition.Replacing redox-active Co with non-active Zn amount of 0.07 (Co_(1-x)Zn_(x)HCF) slightly reduces the specific capacity from 127 to 119 mAh g^(-1)at 0.1 A g^(-1)due to the shrunken Co charging sites.Rate performance is enhanced by compromising the capacity and reduced distortion,resulting in 81%retention at a 20-times-faster charging rate.Notably,the Co_(1-x)Zn_(x)HCF sample exhibited the good stability while preserving 74%of the initial capacity at 0.5 A g^(-1)after 200 cycles.

Local structure distortion and spin Hamiltonian parameters for Cr^(3+)-V_(Zn) tetragonal defect centre in Cr^(3+) doped KZnF_3 crystal

The quantitative relationship between the spin Hamiltonian parameters （D, g｜｜ Ag） and the crystal structure parameters for the Cr3＋-Vzη tetragonal defect centre in a Cr3＋ ：KZnF3 crystal is established by using the superposition model. On the above basis, the local structure distortion and the spin Hamiltonian parameter for the Cr3＋-Vzn tetragonal defect centre in the KZnF3 crystal are systematically investigated using the complete diagonalization method. It is found that the Vzn vacancy and the differences in mass, radius and charge between the Cr3＋ and the Zn2＋ ions induce the local lattice distortion of the Cr3＋ centre ions in the KZnF3 crystal. The local lattice distortion is shown to give rise to the tetragonal crystal field, which in turn results in the tetragonal zero-field splitting parameter D and the anisotropic g factor Ag. We find that the ligand F- ion along I001] and the other five F- ions move towards the central Cr3＋ by distances of A1 = 0.0121 nm and A2 = 0.0026 nm, respectively. Our approach takes into account the spin-rbit interaction as well as the spin-spin, spin other-orbit, and orbit-rbit interactions omitted in the previous studies. It is found that for the Cr3＋ ions in the Cr3＋：KZnF3 crystal, although the spin-rbit mechanism is the most important one, the contribution to the spin Hamiltonian parameters from the other three mechanisms, including spin- spin, spin-other-orbit, and orbit-orbit magnetic interactions, is appreciable and should not be omitted, especially for the zero-field splitting （ZFS） parameter D.

Structure distortion, optical and electrical properties of ZnO thin films co-doped with Al and Sb by sol-gel spin coating

ZnO thin films co-doped with A1 and Sb with different concentrations and a fixed molar ratio of AlCl3 to SbCl3 at 1：2, are prepared by a sol-gel spin-coating method on glass annealed at 550 ℃ for 2 h in air. The x-ray diffraction results confirm that the ZnO thin films co-doped with Al distortion, and the biaxial stresses are 1.03× 10^8. 3.26× 10^8 and Sb are of wurtzite hexagonal ZnO with a very small 5.23 × 10^8, and 6.97× 10^8 Pa, corresponding to those of the ZnO thin films co-doped with Al and Sb in concentrations of 1.5, 3.0, 4.5, 6.0 at% respectively. The optical properties reveal that the ZnO thin films co-doped with Al and Sb have obviously enhanced transmittance in the visible region. The electrical properties show that ZnO thin film co-doped with Al and Sb in a concentration of 1.5 at% has a lowest resistivity of 2.5 Ω·cm.

Grain size and structure distortion characterization of α-MgAgSb thermoelectric material by powder diffraction

Nanostructuring, structure distortion, and/or disorder are the main manipulation techniques to reduce the lattice thermal conductivity and improve the figure of merit of thermoelectric materials. A single-phase α-MgAgSb sample, MgAg0.97Sb0.99, with high thermoelectric performance in near room temperature region was synthesized through a high-energy ball milling with a hot-pressing method. Here, we report the average grain size of 24–28 nm and the accurate structure distortion, which are characterized by high-resolution neutron diffraction and synchrotron x-ray diffraction with Rietveld refinement data analysis. Both the small grain size and the structure distortion have a contribution to the low lattice thermal conductivity in MgAg0.97Sb0.99.

Local structure distortion and spin Hamiltonian parameters of oxide-diluted magnetic semiconductor Mn-doped ZnO

The local structure distortion, the spin Hamiltonian （SH） parameters, and the electric fine structure of the ground state for Mn^2＋ （3d^5） ion in ZnO crystals are systematically investigated, where spin-spin （SS）, spin-other-orbit （SOO） and orbit-orbit （OO） magnetic interactions, besides the well-known spin-orbit （SO） coupling, are taken into account for the first time, by using the complete diagonalization method. The theoretical results of the second-order zerofield splitting （ZFS） parameter D, the fourth-order ZFS parameter （a-F）, the Zeeman g-factors： g// and g⊥, and the energy differences of the ground state： δ1 and δ2 for Mn^2＋ in Mn^2＋： ZnO are in good agreement with experimental measurements when the three O^2- ions below the Mn^2＋ ion rotate by 1.085° away from the [111]-axis. Hence, the local structure distortion effect plays an important role in explaining the spectroscopic properties of Mn^2＋ ions in Mn^2＋： ZnO crystals. It is found for Mn^2＋ ions in Mn^2＋： ZnO crystals that although the SO mechanism is the most important one, the contributions to the SH parameters, made by other four mechanisms, i.e. SS, SOO, OO, and SO-SS-SOO-OO mechanisms, are significant and should not be omitted, especially for calculating ZFS parameter D.

Theoretical Study of Electron Paramagnetic Resonance Spectra and Local Lattice Distortion for Mn^(2+) in Zn(ClO_4)_2·6(H_2O)Mg(ClO_4)_2·6(H_2O)

The electron paramagnetic resonance（EPR） spectra of trigonal Mn^（2＋） centers in Zn（ClO4）2·6（H2O） and Mg（ClO4）2·6（H2O） crystals were studied on the basis of the complete energy matrices for a d^5 configuration ion in a trigonal ligand field. It was demonstrated that the local lattice structure around a trigonal Mn^（2＋） center has an compressed distortion along the crystalline c3 axis, and when Mn^（2＋） is doped in the Zn（ClO4）2·6（H2O） and Mg（ClO4）2·6（H2O） crystals, there is a similar local distortion. From the EPR calculation, the local lattice structure parameters R=2.183 2 ？, for Zn（ClO4）2·6（H2O）, R=2.130 2 ？, for Mg（ClO4）2·6（H2O） have been determined.

Influence of Tb on easy magnetization direction and magnetostriction of ferromagnetic Laves phase GdFe_2 compounds

The crystal structure,magnetization,and spontaneous magnetostriction of ferromagnetic Laves phase Gd Fe2 compound have been investigated.High resolution synchrotron x-ray diffraction（XRD） analysis shows that Gd Fe2 has a lower cubic symmetry with easy magnetization direction（EMD） along [100] below Curie temperature TC.The replacement of Gd with a small amount of Tb changes the EMD to [111].The Curie temperature decreases while the field dependence of the saturation magnetization（Ms） measured in temperature range 5–300 K varies with increasing Tb concentration.Coercivity Hc increases with increasing Tb concentration and decays exponentially as temperature increases.The anisotropy in Gd Fe2 is so weak that some of the rare-earth substitution plays an important role in determining the easy direction of magnetization in GdFe_2.The calculated magnetostrictive constant λ100 shows a small value of 37×10^（-6）.This value agrees well with experimental data 30×10^（-6）.Under a relatively small magnetic field,GdFe_2 exhibits a V-shaped positive magnetostriction curve.When the field is further increased,the crystal exhibits a negative magnetostriction curve.This phenomenon has been discussed in term of magnetic domain switching.Furthermore,magnetostriction increases with increasing Tb concentration.Our work leads to a simple and unified mesoscopic explanation for magnetostriction in ferromagnets.It may also provide insight for developing novel functional materials.

Complex alloying effect on thermoelectric transport properties of Cu2Ge(Se(1-x)Tex)3

To enhance the thermoelectric performance of Cu2GeSe3, a series of Te-alloyed samples Cu2Ge（Se（1-x）Tex）3 are synthesized and investigated in this work. It is found that the lattice thermal conductivity is reduced drastically for x = 0.1 sample, which may be attributed to the point defects introduced by alloying. However, for samples with x ≥ 0.2, the lattice thermal conductivity increases with increasing x, which is related to a less distorted structure. The structure evolution,together with the change in carrier concentration, also leads to a systemically change in electrical properties. Finally, a z T of 0.55@750 K is obtained for the sample with x = 0.3, about 62% higher than that for the pristine sample.

Determination of charge-compensated C3v (Ⅱ) centers for Er3+ ions in CdF2 and CaF2 crystals

A unified theoretical method is established to determine the charge-compensated C3v(Ⅱ)centers of Er3+ions in CdF2 and CaF2 crystals by simulating the electron paramagnetic resonance(EPR)parameters and Stark energy levels.The potential(Er^(3+)–F^(−)–O_(4)^(2−))and(Er^(3+)-F_(7)^(−)-O_(4)^(2−))structures for theC3v(Ⅱ)centers of Er3+ions in CdF2 and CaF2 crystals are checked by diagonalizing 364×364 complete energy matrices in the scheme of superposition model.Our studies indicate that the C3v(Ⅱ)centers of Er3+ions in CdF2 and CaF2 may be ascribed to the local(Er^(3+)-F^(−)-O_(4)^(2−))structure,where the upper ligand ion F−undergoes an off-center displacement by∆Z≈0.3˚A for CdF2 and∆Z≈0.29˚A for the CaF2 along the C3 axis.Meanwhile,a local compressed distortion of the(ErFO4)6−cluster is expected to be∆R≈0.07˚A for CdF2:Er3+and∆R≈0.079˚A for CaF2:Er3+.The considerable g-factor anisotropy for Er3+ions in each of both crystals is explained reasonably by the obtained local parameters.Furthermore,our studies show that a stronger covalent effect exists in the C3v(Ⅱ)center for Er3+in CaF2 or CaF2,which may be due to the stronger electrostatic interaction and closer distance between the central Er3+ion and ligand O2−with the(Er^(3+)-F^(−)-O_(4)^(2−))structure.

Conductivity of CeO_2 Modified SrTiO_3 Ceramics

The CeO2 modified SrTiO3 ceramics were prepared by conventional ceramic process. The SrTiO3 matrix and CeO2 additive were combined in following system:SrTiO3 +x(CeO2·TiO2), where x is the weight percent , of which x (wt%)=2,5, 10, 15, 20,25, and 30. The samples were sintered at 1400℃ for an hour in air. The Ce element in SrTiO3 ceramics is used as an impurity donor. The scanning electron microscopic (SEM) analysis and X-ray diffractive examination of SrTiO3 ceramics containing CeO2 indicated that there exists a Ce2O3 secondary phase (viz. glass phase) and it had solid solution solubility for impurities which decrease the semiconductive property of SrTiO3 ceramics , and weaken the oxidation of the surface of grain and thus increase the conductivity of the grains. The semiconducting ceramics process lightly distorted cubic structure at room temperature. This paper mainly gives a study of the conductivity of CeO2 modified SrTiO3 ceramics.

Analysis of Ground-state Zero-field Splitting for Mn^(2+) Ions in[Co(H_(2)O)]XY_(6) (X=Si,Sn,Pt;Y=F,Cl)

The electron paramagnetic spectra of trigonal Mn^(2+) centers in[Co(H_(2)O)_(6)]SiF6,[Co(H_(2)O)_(6)]SnF6,and[Co(H_(2)O)_(6)]PtCl6 crystals were studied on the basis of the complete energy matrices for a d5 configuration ion in a trigonal ligand field.When Mn^(2+) is doped in the[Co(H_(2)O)_(6)]SiF6,[Co(H_(2)O)_(6)]SnF6,and[Co(H_(2)O)_(6)]PtCl6 crystals crystals,there is a similar local distortion.The experimental results show that the local lattice structure around a trigonal Mn^(2+) center has an elongation distortion along the crystalline C3 axis.From the EPR calculation,the local lattice structure parameters R=2.278A,θ=52.6406? for[Co(H_(2)O)_(6)]SiF6,R=2.280,θ=52.4936° for[Co(H_(2)O)_(6)]SnF6 and R=2.244A,θ=53.0616? for[Co(H_(2)O)_(6)]PtCl6 were determined.

Regulating Electron-Hole Separation to Promote the Photocatalytic Property of BiOBr_1−xI_x/BiOBr Local Distorted Hierarchical Microspheres

In this work, hierarchical BiOBr1−xIx/BiOBr heterojunction photocatalyst with a microsphere morphology was synthesized by a facile solvothermal process. It demonstrated that the local structure of the photocatalysts was highly distorted due to the substitution of bromide ions by iodine ions. The photocatalytic properties were evaluated by the photodecomposition of aqueous phenol solution under visible-light irradiation. The results indicated that all the composite photocatalysts exhibited high photocatalytic activity. In particularly, the BiOBr1−xIx/BiOBr (x = 0.25) sample exhibited over 92% degradation efficiency of phenol within 150 min, which is 24.6 and 3.08 fold enhancement in the photocatalytic activity over the pure phased BiOBr and BiOI, respectively. Moreover, this excellent photocatalytic property can be expanded to other colorless organic contaminants, verifying the common applicability of BiOBr1−xIx/BiOBr (x = 0.25) as an excellent visible-light photocatalyst for organics decomposition. The significant improvement in the photocatalytic activity can be explained by the high efficiency of charge separation due to the enhancement in the internal electric fields and band match that comes from the local structure distortion. This work provides valuable information for the design of highly active photocatalysts toward the environmental remediation.

Investigation of structural,magnetic and optical properties of rare earth substituted bismuth ferrite

Polycrystalline BiFeO3 and rare earth substituted Bio.gRo.lFeO3 （BRFO, R=Y, Ho and Er） compounds were prepared by rapid solid state sintering technique. Structural phase analysis indicated that all the compounds stabilized in rhombohedral structure （R3c space group） and a small orthorhombic phase fraction was observed in BRFO compounds. From the Raman spectra results, the changes in the phonon frequencies （A1） and line widths suggested lattice distortion in the BRFO compounds as was evidenced in the XRD analysis. Compared to the linear variation of magnetization with magnetic field （M-H） shown by BFO, an obvious M-H loop was observed in BRFO compounds which could be due to the suppression of space modulated spin structure and was explained on the basis of weak ferromagnetism and field induced spin reorientation. UV-Vis spectroscopy evidenced a change in local FeO6 envi- ronment due to shift in the 6Alg→4T2g energy transition band. BRFO compounds with improved remnant magnetization and coercive field are applicable for magnetoelectric devices.

Impact of Technological Progress and Industrial Structure Distortion on Energy Intensity in China

The paper measures the industrial structure distortion(ISD)index by region in China from 1978 to 2016 using data on employment and output shares of the three industries.It also analyzes the impact of ISDs by region on energy intensity using a spatial panel model.The results show that since the reform and opening up,the ISD index by region has declined significantly,with the lowest index in the eastern region,the medium one in the central region and the highest in the western region.The estimated results of the spatial econometric model indicate that there is a significant inter-regional dependence of energy intensity in China;there is a significant indirect effect of ISD,despite no significant direct effect on energy intensity;in terms of total effect,ISD is an important factor inhibiting the decline of energy intensity.The results also unveil that higher energy prices and foreign trade are positive factors declining energy intensity,while FDI worsens energy intensity and R&D spending has no significant positive impact on curbing energy intensity.In order to reduce energy intensity,China should work to eliminate the micro cause of ISDs,promote the transfer of agricultural labor,establish a market-oriented mechanism for energy price formation,and enhance the efficiency of R&D spending.