Induced Structure Evolution Research Articles

Ce-doping induced structure evolution in FeNi-based (oxy)hydroxide for highly efficient oxygen evolution reaction

Structure evolution of the catalyst typically plays a key role in determining the catalytic activity in harsh reaction environment. Here we report a doping-reconstruction strategy to prepare catalyst for highly efficient oxygen evolution reaction (OER). Ce-doping has been induced in FeNi metal-organic frameworks (MOFs) to change the microstructure, which can further lead to the in-situ formation of active (oxy)hydroxides. As a result, the obtained Ce-FeNiOOH shows a low overpotential of 196 mV at 10 mA cm−2, with a small Tafel slope of 33.5 mV dec−1 and a good stability for 100 h. Moreover, by coupling with Pt/C, the two-electrode cell can achieve an excellent performance for overall water splitting with a low voltage of 1.44 V at 10 mA cm−2 (1.59 V at 100 mA cm−2). Synchrotron radiation spectroscopy reveals that Fe-O-Ce microstructure has been created with Ce-doping, which plays a key role for the further transition from MOFs to (oxy)hydroxide during OER.

Jahn‐Teller Effect Directed Bandgap Tuning of Birnessite for Pseudocapacitive Application

Birnessite MxMnO2 (M = Na+, K+, etc.) has emerged as a promising alternative to the classical MnO2 material owing to its improved pseudocapacitive performance for energy storage. Understanding their structure–property correlation is essential for the development and application of advanced supercapacitors. Herein, we adopt the crystal field theory and density functional simulation to reveal the structural dependence of the pseudocapacitive property of KxMnO2. Attributing to the Jahn–Teller effect of Mn3+, the bandgap of KxMnO2 can be tuned by changing the x value (i.e., the Mn(III)/Mn(IV) ratio). Then, we design a narrow‐bandgap K0.25MnO2 (0.84 eV), which affords a high capacitance of 415 F g−1 at 1 A g−1 and a desirable rate capability of 293 F g−1 at 20 A g−1. Operando Raman spectroscopy confirms that the Jahn–Teller induced structure evolution of [MnO6] octahedron accounts for the superior pseudocapacitive behavior of K0.25MnO2. This finding offers theoretical guidance to the design and application of birnessite materials for pseudocapacitors.

Structure evolution and mechanical properties of co-sputtered Zr-Al-B2 thin films

Zirconium diboride (ZrB2) represents a promising hard coating material for demanding high-temperature applications and could provide an excellent basis for fine-tuning mechanical properties via the concept of alloying. Here, combining density functional theory and experiments, we investigate the effect of aluminum alloying on thermally induced structure evolution and mechanical properties of α-structured Zr1 − xAlxB2 + Δ. Ab initio calculations predict a strong tendency for spinodal phase separation of hexagonal Zr1 − xAlxB2 solid solution into isostructural binaries. Experimental results confirm predictions of the insolubility of aluminum in the ZrB2 phase when the structure of magnetron co-sputtered Zr0.72Al0.28B2.64 films with an aluminum content of 8 at. % has a nanocomposite character consisting of hexagonal α-ZrB2 nanocolumns surrounded by an amorphous Al-rich tissue phase. The films are structurally stable up to 1100 °C but out-diffusion of Al atoms from boundary regions during annealing was observed. Al alloying causes a significant decrease in hardness when the hardness of the reference as-deposited ZrB2.2 and Zr0.72Al0.28B2.64 is 39 and 23 GPa, respectively. Low hardening effect in ternaries was observed after annealing at 1000 °C when the hardness increased from 23.5 to 26.5 GPa due to the locally increased concentration of point defects at the boundaries of the nanocolumns and Al-rich tissue phases. Young's modulus decrease from 445 (ZrB2.2) to 345 GPa (Zr0.72Al0.28B2.64) indicates a change in the mechanical response of the ternary film toward more ductile behavior.

Understanding the formation of antiphase boundaries in layered oxide cathode materials and their evolution upon electrochemical cycling

Understanding the formation of antiphase boundaries in layered oxide cathode materials and their evolution upon electrochemical cycling

Stepwise Li Substitution Induced Structure Evolution and Improved Nonlinear Optical Performance for Diamond-like Sulfides.

One of the key scientific issues for exploration of novel infrared nonlinear optical (NLO) crystals is to obtain ones with good hybrid NLO behaviors. Herein, we report four diamond-like Ag-based sulfides via stepwise Li substitution of Ag in Ag2ZnSnS4, including Ag2ZnSnS4 (1), (Li1.22Ag0.78)ZnSnS4 (2), (Li1.58Ag0.42)ZnSnS4 (3), and Li2ZnSnS4 (4). With the increase of Li content, the sulfide's noncentrosymmetric crystal structure changes from tetragonal I42m for 1, to orthorhombic Pmn21 for 2 and 3, and to monoclinic Pn for 4. Accordingly, their NLO responses are improved along with the increase of Li content, viz. from non-NLO-active for 1, to non-phase-matchable for 2 and 3, and to phase-matchable for 4. Their optical band gaps also increase regularly. The relationship between their chemical compositions, crystal structures, and NLO activities is investigated by means of chemical structural analysis and theoretical calculation. This work offers a new systematic case for designing promising NLO-active compounds via rarely adopted cation's stepwise partial substitution and understanding the chemical composition-structure-NLO property relationship.

HCl induced structure evolution and dual-frequency broadband microwave absorption of PANI hierarchical microtubes

High-performance absorbers are in urgent demand for dealing with the increasing electromagnetic wave (EMW) pollution caused by the rapid development of information technology. Herein, we developed a simple SDS/HCl-assisted oxidative polymerization method for the controllable synthesis of nanorod-coated PANI hierarchical microtubes as an efficient EMW absorber. The morphological evolution can be expediently achieved from hierarchical microtubes and solid nanofibers to nanorods by adjusting the HCl concentration. The formation of PANI hierarchical microtubes is caused by the cooperation of SDS and the minimum surface energy. What is more, morphology-dependent conductivity and EMW absorption properties were systematically investigated. Owing to the hierarchical 1D hollow structure and carrier concentration, the ultimate conductivity reached 0.08 S/cm at [HCl] = 7.5 mM. The corresponding HCl-doped PANI hierarchical microtubes exhibited superior EMW absorption properties (EMWAPs) with a large absorption of −43.6 dB and a wide absorption band of 5.84 GHz in relation to a 1.55 mm thick sample. The excellent EMWAPs are the consequence of the high conductivity and distinctive 1D, hierarchical, and hollow structure, which generate enhanced permittivity, multiple resonances, strong attenuation capability, multiple scattering, and EM radiation. Owing to their tunable morphology, tunable conductivity, and excellent EMWAPs, the PANI hierarchical microtubes offer great promise for fields such as sensors, electronics, optics, catalysis, energy storage, and EMW absorption and shielding.

Si/Al ratio induced structure evolution during desilication-recrystallization of silicalite-1 to synthesize nano-ZSM-5 catalyst for MTH reaction

Introducing mesopores into nano-ZSM-5 zeolite could further shorten its micropore length and significantly enhance its catalytic stability in methanol to hydrocarbons (MTH) reaction. In this work, a series of hierarchical nano-ZSM-5 were synthesized by desilication-recrystallization of silicalite-1. Through adjusting the NaAlO2 additive amount, SiO2/Al2O3 feed ratio was controlled to induce the structure evolution of ZSM-5. Hollow structured nano-ZSM-5 was synthesized at high SiO2/Al2O3 feed ratio, while mesopores were further created in the shell of hollow nano-ZSM-5 with low SiO2/Al2O3 ratio. The acid amount of ZSM-5 gradually increased from 0.13 to 0.91 mmol g−1 and the acid strength also enhanced with decreasing the SiO2/Al2O3 ratio from 400 to 25. The strong acidity promoted aromatization reaction and the sample prepared with a SiO2/Al2O3 ratio of 25 showed the highest aromatics selectivity of 56.45%. Under suitable SiO2/Al2O3 ratio of 50, synthesized nano-ZSM-5 possessed large external surface area of 133 m2 g−1 and proper acidity of 0.66 mmol g−1, endowing it long lifetime of 132 h. The adjustable pore structure and acidity achieved by controlling the Si/Al ratio during the desilication-recrystallization of silicalite-1 provides possibility for the directional preparation of ZSM-5 with long lifetime and high selectivity for other MTH reaction.

Thermally induced structure evolution on the corrosion behavior of Al-Ni-Y amorphous alloys

The effect of thermally induced structural evolution on the corrosion behavior of Al-Ni-Y amorphous alloys was investigated. Structural relaxation annealing significantly enhanced the corrosion resistance of Al-Ni-Y alloys, and the main reason was attributed to the decreased free volume promoting the formation of a highly protective passive film. The corrosion behavior of Al-Ni-Y alloys was closely associated with nanocrystal size after partially devitrified annealing. The larger nanocrystals caused more obvious composition heterogeneity around the nanoscale precipitates, deteriorating the corrosion resistance. In addition, the component and energy band of the passive film on Al-Ni-Y alloys with structure evolution were also discussed.

Structural Correlation to Piezoelectric and Ferroelectric Mechanisms in Rhombohedral Pb(Zr,Ti)O3 Ceramics by in-Situ Synchrotron Diffraction.

The evidence of fundamental lattice strain and domain switching contribution to the piezoelectric and ferroelectric responses of ceramics has been well studied, while the contribution from crystal structure variation has been rarely reported in terms of the existence of intergranular stress/strain and crystallographic texture. In the present study, the detailed electric field induced structure evolution in rhombohedral PbZr0.55Ti0.45O3 (PZT55) has been investigated by in-situ high-energy synchrotron diffraction. The phase of PZT55 is stable in the rhombohedral one against bipolar electrical loading. It is interesting to find that both spontaneous polarization and unit cell volume exhibit a butterfly shape in response to electric field. Direct evidence has revealed that the lattice strain and volume expansion show similar variation tendency to the piezoelectric response in the rhombohedral PZT55. The macro-polarization of PZT55 derives from the combination of domain switching and spontaneous polarization change.

In Situ Atomic-Scale Observation of Electrochemical Delithiation Induced Structure Evolution of LiCoO2 Cathode in a Working All-Solid-State Battery.

We report a method for in situ atomic-scale observation of electrochemical delithiation in a working all-solid-state battery using a state-of-the-art chip based in situ transmission electron microscopy (TEM) holder and focused ion beam milling to prepare an all-solid-state lithium-ion battery sample. A battery consisting of LiCoO2 cathode, LLZO solid state electrolyte and gold anode was constructed, delithiated and observed in an aberration corrected scanning transmission electron microscope at atomic scale. We found that the pristine single crystal LiCoO2 became nanosized polycrystal connected by coherent twin boundaries and antiphase domain boundaries after high voltage delithiation. This is different from liquid electrolyte batteries, where a series of phase transitions take place at LiCoO2 cathode during delithiation. Both grain boundaries become more energy favorable along with extraction of lithium ions through theoretical calculation. We also proposed a lithium migration pathway before and after polycrystallization. This new methodology could stimulate atomic scale in situ scanning/TEM studies of battery materials and provide important mechanistic insight for designing better all-solid-state battery.

Cancrinite-group minerals: Crystal-chemical description and properties under non-ambient conditions—A review

![Figure][1] This is a review of the thermal and compressional behavior of cancrinite-group minerals with a description of the mechanisms, at the atomic scale, that govern their P - T -induced structure evolution. The open-framework structure of this group of feldspathoids is characterized by the [CAN] topology, which contains large parallel channels (confined by 12-membered rings of tetrahedra), surrounded by columns of cages. At least two structural “subgroups” can be identified according to the nature of the constituents filling the cages, irrespective of the channel population. The minerals of the “cancrinite subgroup” show [NaH2O]+ clusters into the cages and those of the “davyne subgroup” contains [CaCl]+ clusters. Beside a similar bulk compressibility and expansivity at room conditions for all the minerals of the group, a different elastic anisotropy, coupled with different deformation mechanisms of the tetrahedral framework, were found to be mainly controlled by the nature of the population filling the cages. The role played by the channel populations appears to be secondary. These experimental findings allow us to provide a model of the structure evolution in response to the different cage content, i.e., NaH2O+ and CaCl+. The high-temperature studies of the hydrous members of the cancrinite subgroup reveal a slow dehydration process, often irreversible at the timescale of the experiments and leading to quasi-anhydrous high-temperature forms that keep their crystallinity even up to 800–900 K (at room P ). The experiments at high pressure on the cancrinite-group minerals show a high- P stability, at least up to 7–8 GPa (at room- T ), which is quite surprising if we consider their microporous nature. The P -induced stability is the effect of a pronounced structural flexibility, which in turn is based mainly on tilting of rigid tetrahedra around O atoms that behave as hinges. The character and the mechanisms that govern the P-T -induced P 63-to- P 63/ m phase transition in the compounds of davyne subgroup are also discussed. [1]: pending:yes

Mn2+ induced structure evolution and dual-frequency microwave absorption of MnxFe3−xO4 hollow/porous spherical chains made by a one-pot solvothermal approach

Mn2+ induced structure evolution and dual-frequency microwave absorption were found in MnxFe3−xO4 (0 ≤ x ≤ 1.09) hollow/porous spherical chains.

Influence of the composition-induced structure evolution on the electrocaloric effect in Bi0.5Na0.5TiO3-based solid solution

The present work investigated the influence of the composition induced structure evolution on the electrocaloric effect in lead-free (0.935−x)Bi0.5Na0.5TiO3–0.065BaTiO3–xSrTiO3 (BNBST, BNBSTx) ceramics. It was found that broad ∆T peak could be observed for all compositions and the electrocaloric strength α (α=ΔTmax/ΔE) in BNBST0.02 could reach as high as 0.27Kmm/kV. The increase of the SrTiO3 concentration led to a shift of ∆Tmax to a lower temperature, resulting in a large near room-temperature electrocaloric strength α of 0.17Kmm/kV in BNBST0.22.

Fluorous 'ponytails' lead to strong gelators showing thermally induced structure evolution.

Appending perfluoroalkyl substituents to bis(urea) gelators results in significantly decreased inter-chain interactions with markedly thinner fibres and hence more cross-linked and more transparent gels with potential applications in the crystallisation of fluorinated pharmaceuticals. Gel structure has been probed by detailed SANS measurements which indicate a surprising structure evolution on thermal cycling, not seen for hydrocarbon analogues. The SANS data are complemented by the single crystal X-ray structure of one fluorinated gelator.

Composition induced structure evolution and large strain response in ternary Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3-SrTiO3 solid solution

A ternary perovskite lead-free solid solution Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3-SrTiO3 was designed and fabricated using a conventional fabrication process. The temperature and composition dependence of the ferroelectric, dielectric, piezoelectric, and electromechanical properties were systematically investigated, and a schematic phase diagram was established. The introduction of the SrTiO3 was found to induce a structure evolution from the ferroelectric rhombohedra to ergodic relaxor pseudocubic phases. At a critical composition with SrTiO3 of 0.15, large strain level of ∼0.25% was obtained under a moderate field of 4.4 kV/mm at 0.1 Hz and the normalized strain reached up to 585 pm/V. Through the combination of the X-ray diffraction results with the piezoresponse force microscopy analysis, the composition induced structure evolution process and intrinsic mechanism responsible for the large strain response were discussed. The large strain level also makes the system quite promising for application to “on-off” actuators.

High-pressure study of a natural cancrinite

The high-pressure elastic behavior and the P -induced structure evolution of a natural cancrinite from Cameroun {Na 6.59 Ca 0.93 [Si 6 Al 6 O 24 ](CO 3 ) 1.04 F 0.41 ·2H 2 O, a = 12.5976(6) A, c = 5 .1168(2) A, space group: P 6 3 } were investigated by in situ single-crystal X-ray diffraction under hydrostatic conditions up to 6.63(2) GPa with a diamond-anvil cell. The P - V data were fitted with an isothermal Birch-Murnaghan type equation of state (BM EoS) truncated to the third order. Weighted fit (by the uncertainty in P and V ) gave the following elastic parameters: V 0 = 702.0(7) A 3 , K V 0 = 51(2) GPa, and K V ′ = 2.9(4). A linearized BM EoS was used to fit the a - P and c - P data, giving the following refined parameters: a 0 = 12.593(5) A, K a 0 = 64(4) GPa, K a ′ = 4.5(9), for the a -axis, and c 0 = 5.112(3) A, K c 0 = 36(1) GPa, K c ′ = 1.9(3) for the c -axis (elastic anisotropy: K a 0 : K c 0 = 1.78:1). A subtle change of the elastic behavior appears to occur at P > 4.62 GPa, and so the elastic behavior was also described on the basis of BM EOS valid between 0.0001–4.62 and 5.00–6.63 GPa, respectively. The high-pressure structure refinements allowed the description of the main deformation mechanisms responsible for the anisotropic compression of cancrinite on (0001) and along [0001]. A comparative analysis of the structure evolution in response of the applied pressure and temperature of isotypic materials with cancrinite-like topology is carried out.

Phase transition and electrical properties in the Li-modified Bi0.5Na0.5TiO3-based lead-free ceramics

Phase transition and electrical properties were demonstrated for a Li-modified Bi0.5Na0.5TiO3-based solid solution. (0.935 − x)Bi0.5Na0.5TiO3 − xBi0.5Li0.5TiO3 − 0.065BaTiO3 with 0.5 mol% Mn doping was prepared by a conventional solid state reaction method. Close inspection of X-ray diffraction patterns indicated that no characteristic peaks splitting happened, indicating the pseudocubic structure for all the compositions. At a critical composition x of 0.06, optimized performance was obtained with piezoelectric constant d 33 of 176 pC/N, electromechanical coupling factors k P of 0.33, and k t of 0.52, respectively. In addition, it was found that the Li substitution could lead to a disruption of long-range ferroelectric order and obtain enhanced frequency dispersion behavior accompanied with the decreasing of the depolarization temperature T d, which was responsible for the observed weaker ferroelectric polarization and electromechanical response. The composition induced structure evolution was also discussed combined with the Raman spectroscopy.

Temperature Induced Structure Evolution of Regioregular Poly(3-hexylthiophene) in Dilute Solution and its Influence on Thin Film Morphology

The structure evolution of regioregular poly(3-hexylthiophene) (P3HT) in THF dilute solution and its influence on thin film morphology were studied by a combination of static and dynamic laser light scattering (SLS and DLS) and transmission electron microscopy (TEM). Most P3HT is not directly soluble in THF at room temperature. A thermal treatment at high temperature effectively redisperses P3HT microsized aggregates, and introduces two modes in DLS measurement. The fast mode with ⟨Rh⟩f ∼ 4 nm is P3HT unimer coil, while the slow mode with ⟨Rh⟩s∼ 90 nm is P3HT associate. The linear relationship between ⟨Γ⟩ and q2 passing through origin indicated both modes are diffusive. DLS showed the percentage of large associates is increasing, and that of the unimer coils is decreasing with temperature. The ratio, ⟨Rg⟩s/⟨Rh⟩s ∼ 0.8, indicates the associates are closely packed spherical in shape. The structure of P3HT in dilute solution greatly influences its morphology on thin films. We found that the memory of chain conformation and association in solution are carried into drop casted film, TEM examination of drop casted thin film morphology clearly indicated that the densely packed spherical associates are elastic with its morphology unchanged during evaporation process because of its visco-elastic nature; while the P3HT unimer coils assemble and crystallize into nanofibrils. The nanofibrils' percentage decreases with temperature because the coexistence equilibrium between P3HT unimer and spherical associates shifts greatly to the associates side. However, this apparent equilibrium of unimer−associate is in a metastable state. Over a long time, the system will gradually form larger and more stable aggregates which are in equilibrium with unimers at room temperature. Overall, after a proper thermal treatment in solution, it suppresses aggregates formation and increases electronic and opto-physics properties when drop casting is conducted at room temperature.

Measuring the transmittivity of light: A tool for testing the quality of magnetic liquids

The purpose of our work is to demonstrate that the time dependence measuring of optical transmittivity of magnetic liquids provide a way for testing the magnetic field induced structure evolution. We report on some time evolution of transmittivity of polarized rays in two different obtained kerosene base ferrofluids and in a transformer oil ferrofluid forming an emulsion in water.