Distortion Of Lattice Structure Research Articles

Modulating perovskite crystallization and band alignment using coplanar molecules for high-performance indoor photovoltaics

The proper bandgap and exceptional photostability enable CsPbI3 as a potential candidate for indoor photovoltaics (IPVs), but indoor power conversion efficiency (PCE) is impeded by serious nonradiative recombination stemming from challenges in incomplete DMAPbI3 conversion and lattice structure distortion. Here, the coplanar symmetric structure of hexyl sulfide (HS) is employed to functionalize the CsPbI3 layer for fabricating highly efficient IPVs. The hydrogen bond between HS and DMAI promotes the conversion of DMAPbI3 to CsPbI3, while the coplanar symmetric structure enhances crystalline order. Simultaneously, surface sulfidation during HS-induced growth results in the in situ formation of PbS, spontaneously creating a CsPbI3 N-P homojunction to enhance band alignment and carrier mobility. As a result, the CsPbI3&HS devices achieve an impressive indoor PCE of 39.90% (Pin: 334.6 μW cm−2, Pout: 133.5 μW cm−2) under LED@2968 K, 1062 lux, and maintain over 90% initial PCE for 800 hours at ∼30% air ambient humidity.

Revealing the Structure-Luminescence Relationship in Robust Sn(IV)-Based Metal Halides by Sb3+ Doping.

Low-dimensional hybrid metal halides are an emerging class of materials with highly efficient photoluminescence (PL), but the problems of poor stability remain challenging. Sn(IV)-based metal halides show robust structure but exhibit poor PL properties, and the structure-luminescence relationship is elusive. Herein, two Sn(IV)-based metal halides (compounds 1 and 2) with the same constituent ((C6H16N2)SnCl6) but different crystal structures have been prepared, which however show poor PL properties at room temperature due to the absence of active ns2 electrons. To improve materials' PL properties, Sb3+ with active 5s2 electrons was embedded into the lattice of Sn4+-based hosts. As a result, efficient emissions were achieved for Sb3+-doped compounds 1 and 2 with a maximum PL efficiency of 14.28 and 62%, respectively. Experimental and calculation results reveal that the smaller distorted lattice structure of the host could result in the blueshift of the emission from Sb3+. Thus, a tunable color from red to orange was realized. Benefiting from the broadband efficient emission from Sb3+-doped compound 2, an efficient white light-emitting diode with a high color rendering index of up to 92.3 was fabricated to demonstrate its lighting application potential. This work promotes the understanding of the influence of robust Sn(IV)-based host lattice on the PL properties of Sb3+, advancing the development of environmentally friendly, low-cost, and high-efficiency Sn(IV)-based metal halides.

Lattice Strain Engineering of Ti3C2 Narrows Band Gap for Realizing Extraordinary Sonocatalytic Bacterial Killing.

The rapid development of sonodynamic therapy (SDT) provides a promising strategy for treating deep-seated multidrug-resistant (MDR) bacterial infection. However, the extreme scarcity of biologically functional and highly efficient sonosensitizers severely limits the further clinical practice of SDT. Herein, the lattice-strain-rich Ti3C2 (LS-Ti3C2) with greatly improved sonosensitizing effect is one-step synthesized using Ti3C2 and meso-tetra(4-carboxyphenyl)porphine (TCPP) by the solvothermal method for realizing extraordinary SDT. The intervention of TCPP causes all the Ti-O chemical bonds and most of the Ti-F chemical bonds on the surface layer of Ti3C2 to break down. The amino groups of TCPP are then recombined with these exposed Ti atoms to perturb the order of the Ti atoms, resulting in displacement of the Ti atoms and final lattice structural distortion of Ti3C2. The inherent lattice strain narrows the band gap of Ti3C2, which mainly facilitates the electron-hole pair separation and electron transfer under ultrasound irradiation, thereby resulting in US-mediated reactive oxygen species (ROS) production and the subsequent robust bactericidal capability (99.77 ± 0.16%) against methicillin-resistant Staphylococcus aureus (MRSA). Overall, this research offers a perspective into the development of Ti-familial sonosensitizers toward SDT practice.

Beneficial Effects of La0.5Sr0.5CoO3 Coatings on Thin‐Film LiMn2O4 Cathodes for Lithium Ion Batteries

AbstractThe severe capacity loss of spinel LiMn2O4 (LMO) limits the utility of this otherwise promising lithium ion battery cathode material. One of the strategies to mitigate capacity fade is applying a coating on LMO particle surfaces. While this approach yields promising results, there is limited understanding of mechanisms whereby coatings improve LMO capacity retention. Herein, the effects of a new protective coating material, La0.5Sr0.5CoO3 (LSCO), in a thin‐film battery geometry that is amenable to fundamental studies of electrode processes, are reported. RF sputtering deposition is used to produce high quality 25–100 nm LMO cathodes on Al2O3 substrates with an intervening Pt/Ti back‐side contact layer. Cycling of the un‐coated cathodes results in capacity loss of 18% over 300 cycles. Adding a 2 nm LSCO layer reduces the capacity loss to 3%. While this may be due in part to reduced Mn dissolution, scanning transmission electron microscopy results indicate that the coating helps to preserve crystallinity and reduce lattice structure distortion due to inhibited formation of defect tetragonal spinel. Three‐electrode electrochemical impedance spectroscopy results reveal that the LSCO coating increases charge transfer and ohmic resistances, but the increases are generally too small to significantly impact cell performance even at high C‐rates.

Ultrafast Carrier Dynamics in 2D NbTe2 Films: Implications for Photonic and Optoelectronic Devices

As one of the representatives of emerging metallic transition-metal dichalcogenides, niobium ditelluride (NbTe2) has attracted intensive interest recently due to its distorted lattice structure and unique physical properties. Here, we report on the ultrafast carrier dynamics in NbTe2 measured using time-resolved pump–probe transient reflection spectroscopy. A thickness-dependent carrier relaxation time is observed, exhibiting a clear increase in the fast and slow carrier decay rates for thin NbTe2 flakes. In addition, pump-power-dependent measurements indicate that the carrier relaxation rates are power-independent and the peak amplitude of the transient reflectivity increases linearly with the pump power. The isotropic relaxation dynamics in NbTe2 is also verified by performing polarization-resolved pump–probe measurements. These results provide insight into the light–matter interactions and charge-carrier dynamics in NbTe2 and will pave the way for its applications to photonic and optoelectronic devices.

Distorted Lattice Structure of La and Nd Co-Doped Bismuth Titanate Bi3-XTi4O12 Nano-Grained Ceramics for High Quality Energy Storage Application

Capacitive energy storage technology becomes more popular due to the fast charging facilities. Bismuth titanate (BIT) is a lead-free ferroelectric material used as a dielectric medium in the capacitive energy storage system. La and Nd co-doped BIT has been synthesized through a solid-state reaction process to obtain improved dielectric properties. Various characterization technologies such as Fourier Transform Infrared (FTIR) and X ray diffraction (XRD) have been done to sure the reaction completion and absence of the impurity phase of BIT. Rietveld refinement of XRD has been carried out to investigate the crystal structural properties of La and Nd-doped BIT. Capacitive energy storage performances have been tested by measuring the parallel plate capacitance and quality factor of BIT ceramics. Co-doped BIT possesses the highest crystal density, which results in a high Q factor. The unit cell of the TiO6 octahedral of BIT becomes highly distorted as a consequence of La and Nd co-doping, which increases surface polarization, and the capacitance of BIT increases.

Anionic defects engineering of Co3O4 catalyst for toluene oxidation

Development of advanced metal oxide catalysts for volatile organic compounds (VOCs) abatement is of great environmental and economic importance. Herein, a defective Co3O4 catalyst is delineated via N doping. The anionic defects engineering significantly facilitated the oxygen vacancies formation, leading to a distorted lattice structure, increased active surface oxygen and enhanced oxygen mobility of Co3O4 catalyst. These features promise an excellent toluene oxidation performance with 50% toluene conversion temperature (T50) of 208 °C and 90 % toluene conversion temperature (T90) of 218 °C at a space velocity of 60,000 mL g−1h−1, about 33 °C and 53 °C lower than that of the pristine Co3O4, respectively. Meanwhile, the N doped Co3O4 catalyst maintains a high hydrothermal stability at 210 °C. This work exemplifies the significance of anionic defects for the intrinsic catalytic oxidation ability improvement, providing a guidance for the upgradation of the metal oxide for the application of VOCs catalytic degradation and beyond.

Multifunctional two-dimensional glassy graphene devices for vis-NIR photodetection and volatile organic compound sensing

Multifunctional devices are of great interest for integration and miniaturization on the same platform, but simple addition of functionalities would lead to excessively large devices. Here, the photodetection and chemical sensing device is developed based on two-dimensional (2D) glassy-graphene that meets similar property requirements for the two functionalities. An appropriate bandgap arising from the distorted lattice structure enables glassy graphene to exhibit comparable or even improved photodetection and chemical sensing capability, compared with pristine graphene. Due to strong interactions between glassy graphene and the ambient atmosphere, the devices are less sensitive to photoinduced desorption than the ones based on graphene. Consequently, the few-layer glassy graphene device delivers positive photoresponse, with a responsivity of 0.22 A W−1 and specific detectivity reaching ~1010 Jones under 405 nm illumination. Moreover, the intrinsic defects and strain in glassy graphene can enhance the adsorption of analytes, leading to high chemical sensing performance. Specifically, the extracted signal-to-noise-ratio of the glassy graphene device for detecting acetone is 48, representing more than 50% improvement over the device based on graphene. Additionally, bias-voltage- and thickness-dependent volatile organic compound (VOC) sensing features are identified, indicating the few-layer glassy graphene is more sensitive. This study successfully demonstrates the potential of glassy graphene for integrated photodetection and chemical sensing, providing a promising solution for multifunctional applications further beyond.

Investigation of room temperature multi-functional properties of Nd doped mullite Bi2Fe4O9

Mullite type Bi2Fe4O9 (BFO) and Nd doped Bi2Fe4O9 (BNFO) systems were developed using conventional solid state route under normal atmospheric pressure. The structural phase compositions were analyzed using x-ray diffraction (XRD). The analysis revealed BFO orthorhombic primary phase with traces of secondary phase and compressive lattice structural distortion, the same being evident from theoretically calculated (LSDA + U and PBE + U)correlated systems, where LSDA is Local spin density approximation, Hubbard U = 4.5eV and PBE is Perdew, Burke and Ernzerh of exchange correlation functional. Raman spectral analysis showed changes in the frequency and line width with respect to Nd doping, which correlates the lattice distortion observed in XRD analysis. Henceforth, the Bi2-xNd2xFe4O9with x = 0, 0.01, 0.03, will be referred as BFO, BNFO1 and BNFO3. From the dielectric and optical studies, a significant increase in the dielectric constant and narrower band gap was observed in the BNFO samples, compared to BFO. The room temperature vibrating sample magnetometer (VSM) analysis of the BNFO samples showed weak ferromagnetic hysteresis behavior. Also, a significant enhancement of magnetic moment was observed with increased concentration of Nd in BNFO samples. This could be due to suppression of oxygen vacancies by the Nd dopant, that reduces the super-exchange interaction of Fe3+-O-Fe3+ and introduce Dzyaloshinskii-Moriya (D-M) interactions. The BNFO3 with control over its dielectric constant, optical band gap and magnetization by doping, makes it a viable material for magneto-electric and other multifunctional applications.

Atomistic simulations of spin-lattice coupling effects on magnetomechanics in skyrmion materials

Skyrmion-based spintronic devices are considered one of the prime candidates for the next generation of functional devices. The mechanistic understanding of magnetomechanics arising from the intrinsic spin-lattice coupling in skyrmion materials becomes an attractive issue. In this paper, by taking MnSi as an example, we proposed an atomistic simulation model based on the developed spin-lattice dynamics scheme for skyrmion materials. The calculated magnetomechanical properties are examined to be qualitatively consistent with the experimental measurement, which suggests that our model is appropriate for the study of thermodynamics, magnetics, and mechanics of skyrmion materials. In addition, the microscopic understanding of the thermodynamic and kinetic aspects of magnetomechanics in skyrmion materials are presented. Through the intrinsic spin-lattice coupling, the transformation of magnetic ordering by external magnetic field results in the change of mechanical properties, for instance, the global mechanical anisotropy and local distortion of lattice structure. The calculation results indicate the magnetomechanics are the result of spin nonalignment induced by the synergistic effects of Dzyaloshinsky-Moriya interaction, Heisenberg exchange interaction, and Zeeman interaction of interspins and elastic interactions of interlattices. Further, the relaxation time of the lattice structure is calculated to characterize the speed of mechanical response against the magnetic ordering changes, which might provide hints of low-energy consumption and low applied electric current in driving skyrmions. The microscopic understanding provided by current study could help the research and design of skyrmion-based spintronic devices.

Role of disorder and correlations in the metal-insulator transition in ultrathin SrVO3 films

Metallic oxide SrVO3 represents a prototype system for the study of the mechanism behind thickness-induced metal-to-insulator transition (MIT) or crossover in thin films due to its simple cubic symmetry with one electron in the 3d state in the bulk. Here we report a deviation of chemical composition and distortion of lattice structure existing in the initial 3 unit cells of SrVO3 films grown on SrTiO3 (001) from its bulk form, which shows a direct correlation to the thickness-dependent MIT. In-situ photoemission and scanning tunneling spectroscopy indicate a MIT at the critical thickness of ~3 unit cell (u.c.), which coincides with the formation of a (root2Xroot2)R45 surface reconstruction. However, atomically resolved scanning transmission electron microscopy and electron energy loss spectroscopy show depletion of Sr, change of V valence, thus implying the existence of a significant amount of oxygen vacancies in the 3 u.c. of SrVO3 near the interface. Transport and magneto-transport measurements further reveal that disorder, rather than electron correlations, is likely to be the main cause for the MIT in the SrVO3 ultrathin films.

Hybrid catalyst with monoclinic MoTe2 and platinum for efficient hydrogen evolution

Transition metal dichalcogenides (TMDs) are considered as promising catalysts for the hydrogen evolution reaction (HER) owing to their abundant active sites such as atomic vacancies and step edges. Moreover, TMDs have polymorphism, which has stimulated extensive studies on tuning of surface electronic structures for an active HER. The polymorphism in TMDs provides an opportunity for new hybrid catalysts with TMDs and other catalytic metals via surface engineering that can create a novel functional surface of the catalytic electrode for the active HER. Here, we report a hybrid catalyst with monoclinic MoTe2 and platinum (Pt) for the HER. Pt atoms were chemically bound to the surface of monoclinic MoTe2 that has an atomically distorted lattice structure, which produces a distinct Pt-Te alloy layer. The Pt/MoTe2 hybrid catalyst exhibits an active HER with a Tafel slope of 22 mV per decade and an exchange current density of 1.0 mA/cm2, which are the best values among those reported for TMD-based catalysts. The use of minimum amount of Pt on atomically distorted metallic TMDs realizes rich catalytic active sites on large basal planes for efficient hydrogen production.

A synergetic approach of band gap engineering and reduced lattice thermal conductivity for the enhanced thermoelectric property in Dy ion doped ZnO

Donor cation substituted ZnO demonstrate a promising performance for the green energy harvesting and conservation. In this work we report the marked improvement in the thermoelectric transport properties of rare earth Dy ion substituted ZnO to achieve a maximum figure of merit ZT as 0.11 at 923 K for the 0.1 atomic% of Dysprosium doping. The enhancement in the TE properties were mainly through the increase in carrier concentration and by the energy filtering of carriers at the potential barrier formed in the lattice by Dy doping, which has a large atomic size and localized magnetic moment due to the presence of unpaired electrons. With the substitution of Dy3+ ion, excess electrons were generated in the conduction band of ZnO lattice and they were free to move hence to contribute for the upliftment of Fermi level towards the conduction band with an increment in the effective electron mass. Introduction of donor ion causes distortion of lattice structure and the induced strain responsible for the reduction of lattice thermal conductivity.

Extraordinary Second Harmonic Generation in ReS2 Atomic Crystals

We report the observations of unexpected layer-dependent, strong, and anisotropic second harmonic generations (SHGs) in atomically thin ReS2. Appreciable (negligible) SHGs are obtained from even (odd) numbers of ReS2 layers, which is opposite to the layer-dependence of SHGs in group VI transition metal dichalcogenides, such as MoS2 and WS2. The results are analyzed from ReS2's crystal structure, implying second harmonic polarizations generated from the interlayer coupling. Pumped by a telecomband laser, SHG from the bilayer ReS2 is almost one order of magnitude larger than that from the monolayer WS2. The estimated second-order nonlinear susceptibility of 900 pm/V is remarkably high among those reported in two-dimensional materials. The laser polarization dependence of ReS2's SHG is strongly anisotropic and indicates its distorted lattice structure with more unequal and non-zero second-order susceptibility elements.

Structural and electrical properties of ZnO/Zn0.85Mg0.15O thin film prepared by pulsed laser deposition

The electrical transport properties are the key factors to determine the performance of ZnO-based quantum effect device. ZnMgO is a typical material to regulate the band of ZnO. In order to investigate the electrical properties of the interface of ZnO/Zn[Formula: see text]Mg[Formula: see text]O films, three kinds of ZnO/Zn[Formula: see text]Mg[Formula: see text]O films have been fabricated with different thickness. After comparing the structural and electrical properties of the samples, we found that the independent Zn[Formula: see text]Mg[Formula: see text]O hexagonal wurtzite structure (002) peak can be detected in XRD spectra. Hall-effect test data confirmed that the two-dimensional electron gas (2DEG) became lower because of the decrease of thickness of Zn[Formula: see text]Mg[Formula: see text]O films, increase of impurity scattering and lattice structure distortion caused by the increase of Mg content.

Influence of Na doping on the magnetic properties of LaFeO3 powders and dielectric properties of LaFeO3 ceramics prepared by citric sol-gel method

The emergence of ferromagnetism in perovskite oxide LaFeO3 nanoparticles and colossal dielectric response in ceramics has inspired researchers to study the effect of various dopants on the magnetic and dielectric properties of LaFeO3 powders and ceramics. However, the influence of alkali element Na doping has not been studied yet, and the origin of such ferromagnetic behavior is still ambiguous. The primary objective of the present work is to elucidate the effect of Na doping on the magnetic properties of La1−xNaxFeO3 (x=0, 0.1 and 0.2) powders and dielectric properties of corresponding ceramics prepared by citric sol-gel method. FE-SEM results showed that the introduction of Na dopant actually resulted in the formation of nonstoichiometric La1−xFeO3 and x/2 Na2O. Compared to the canted AFM behavior for the pure powder, ferromagnetic behavior with enhanced magnetization of 2.11emu/g at 10kOe could be obviously observed at room temperature for the powder with x=0.2. XPS measurement suggested nonstoichiometric Fe/La ratio which leads to the distortion of lattice structure and enlarged canting angle between the two AFM coupled Fe sublattice should be responsible for the enhancement of magnetization in the Na-doped samples. Meanwhile, the introduction of Na dopant lowered the growth temperature of grains of the parent LFO and resulted in larger average grain size, which in turn leaded to great enhancement of ε′ into the order of 105 at 100Hz at the cost of high tanδ for the Na-doped ceramics.

Soft X-ray absorption spectroscopy investigations of Bi6FeCoTi3O18 and LaBi5FeCoTi3O18 epitaxial thin films

High-quality single-crystalline Bi6FeCoTi3O18 and LaBi5FeCoTi3O18 thin films were prepared by pulsed laser deposition. X-ray diffraction characterizations indicate a more disordered lattice structure of the LaBi5FeCoTi3O18 film. The magnetic measurement results demonstrated significantly enhanced ferromagnetism in the LaBi5FeCoTi3O18 film. The modulation of oxidation and hybridization states caused by substituting Bi with La was studied using the soft X-ray absorption spectroscopy. The spectroscopic results revealed the reduced concentration of oxygen vacancies and the more distorted lattice structure in the LaBi5FeCoTi3O18 film, which explained the enhanced ferromagnetism.

Strain rate sensitivity of nanoindentation creep in an AlCoCrFeNi high-entropy alloy

Creep behaviors of an AlCoCrFeNi high-entropy alloy with the body-centered cubic structure were investigated by nanoindentation. The enhanced strain gradient induced by higher strain rate leads to decreased strain rate sensitivity during creep process. The present alloy exhibits excellent creep resistance, mainly due to its large entropy of mixing and highly distorted lattice structure.

Effect of Fe substitution on microstructure and properties of bismuth titanate thin films

Bi4Ti3O12 and Fe doped Bi4Ti3O12 (Bi4Ti2.94Fe0.03O12, BTFO) thin films were prepared on FTO/glass (SnO2:F) substrates by the sol–gel method. The effects of Fe doping on the microstructures, dielectric and ferroelectric properties of the films were investigated. X-ray diffraction analyses reveal a lattice distortion for the BTFO thin film. At an applied field of 500kV/cm, the leakage current density of the BTFO thin film is 1.15×10−5A/cm2, which is about 2 orders of magnitude lower than that of the pure BTO thin film (2.73×10−3A/cm2). The electrical conduction mechanisms of the BTO and BTFO thin films are dominated by Ohmic conduction at the low electric field region and gradually transite to space-charge-limited conduction at the higher electric field region. The dielectric constant and dielectric loss of BTFO thin film at 100kHz are 313 and 0.05, respectively. The BTFO thin film shows an enhanced ferroelectric property (Pr=30.88μC/cm2), which is mainly attributed to the lower leakage current density, the distorted lattice structure and the improved surface microstructure.

Lattice Distortion in In3SbTe2 Phase Change Material with Substitutional Bi.

Sb atoms in In3SbTe2 (IST) are partially substituted by 3.2–5.5 at.% of Bi atoms. As a result, the NaCl crystal structure of IST is slightly distorted. The distorted inter-planar angles observed with fast Fourier transformation of the lattice images are within the maximum range of interplanar angles calculated by density functional theory. When the Bi content is increased, the crystallization temperature becomes relatively lower than that of IST, the activation energy decreases from 5.29 to 2.61 eV, and the specific heat and melting point are obviously reduced. Consequently, phase change random access memory (PRAM) fabricated with Bi-doped IST (Bi-IST) can operate with lower power consumption than pure IST PRAM. The set and reset speeds of PRAM cells fabricated with Bi-IST are both 100 ns with 5.5 at.% Bi, which are obviously faster than the switching speeds of PRAM cells fabricated with IST and Ge2Sb2Te5 (GST). These experimental results reveal that the switching speed is closely related with the thermal properties of the distorted lattice structure.