Defect Concentration Research Articles

Variable Valence Ce-Based Cs2CeAgBr6 Perovskite Nanocrystals for Highly Selective Photoconversion of CO2 to CH4.

Lead halide perovskites demonstrate outstanding luminescent characteristics. However, the inclusion of lead components restricts their extensive utilization. Halide perovskite materials, formulated as A2M(III)M(I)X6 or A2M(IV)X6, possess the potential to serve as stable and eco-friendly substitutes for optoelectronic applications. Nevertheless, their wide bandgap (>3eV) hinders the practical implementation across various domains. Here, the variable valence Ce-based Cs₂CeAgBr₆ perovskite nanocrystals (NCs) are first synthesized with a bandgap of 2.65eV. Intriguingly, the coexistence of trivalent and tetravalent Ce can cause localized spin of the f-layer electrons of Ce, leading to Ce3+/4+ (the Ce valence state ranges between III and IV) defects. By manipulating trivalent and tetravalent Ce source proportions, a dual Ce-based perovskite achieves a minimal Ce3+/4+ defect content of 1.4%. The as-prepared Cs₂CeAgBr₆ NCs exhibit exceptional efficiency in CO2 reduction driven by sunlight, with a CH4 selectivity greater than 70% and a super high charge transfer rate of 802.5 µmol·g-1h-1, far surpassing previously reported findings. Additionally, theoretical calculations have elucidated the photocatalytic mechanism involved in CO₂ reduction. The outcomes of this investigation are expected to stimulate design and fabrication of novel lead-free perovskite nanocrystals.

The analysis of carrier transport mechanism at the interface of BZOPET-GR Schottky contact

Abstract Through the hydrothermal technique, we successfully deposited boron (B)-doped zinc oxide nanorods (ZnO NRs) onto a polyethylene terephthalate (PET)/graphene (GR) flexible substrate, creating a B-ZnO/PET/GR Schottky contact. The ZnO NRs exhibited a well-defined hexagonal structure with a lattice constant size of approximately 0.502 nm, as evidenced by characterization results. X-ray Photoelectron Spectroscopy (XPS) analysis revealed a reduction in defective oxygen content with increasing B ion doping.The current-voltage (I-V) characteristics of the Schottky contacts were systematically investigated over a temperature range of 160-300K. As the temperature increased, the barrier height exhibited an upward trend, while the ideality factor decreased. This behavior was ascribed to barrier inhomogeneity at the Schottky contact interface. Employing a single Gauss distribution function for barrier height, we verified and elucidated this phenomenon, contributing to a comprehensive understanding of the observed temperature-dependent electrical properties.

Entropy Manipulation of SrTiO3 Perovskite for Enhanced Thermoelectric and Mechanical Properties.

Reducing the thermal conductivity while maintaining excellent electrical transport properties is crucial for enhancing the thermoelectric performance of SrTiO3-based perovskites. Here, we successfully achieved this goal through precisely manipulating the configurational entropy. A series of Ca0.25Nd0.25Sr0.5-x BaxTiO3 (x = 0, 0.05, 0.15, 0.25) ceramics were successfully synthesized using the solid-state reaction combined with graphite burial sintering. It was discovered that structural defects from competing elements in the A-site not only slowed diffusion and hindered grain growth but also increased oxygen vacancies by creating additional gas transmission channels. The gradual decrease in carrier mobility with increasing entropy resulted in the degradation of electrical conductivity, while the Seebeck coefficient experienced a large enhancement due to band modification and increased carrier scattering. Meanwhile, multiscale defects, including point defects, local strain fields, dislocations, and grain boundaries, effectively scatter phonons, leading to a low lattice thermal conductivity of 1.73 W·m-1·K-1. Consequently, the sample with x = 0.15 exhibited a peak ZT of 0.15 at 900 K, reflecting a 148% enhancement compared to that of the matrix. In addition, the hardness increases with configurational entropy because of the chemical disorder, grain refinement, and increased defect concentration. The work emphasizes the importance of precise manipulation of configurational entropy, offering valuable insights for optimizing thermoelectric materials through entropy engineering strategy.

P2 Receptor Antagonists Rescue Defective Heme Content in an In Vitro SLC25A38-Associated Congenital Sideroblastic Anemia Cell Model

P2 Receptor Antagonists Rescue Defective Heme Content in an In Vitro SLC25A38-Associated Congenital Sideroblastic Anemia Cell Model

Design and Characterization of Se/Nb2O5 Interfaces as High Infrared‐ Absorbers and High Frequency Band Filters

AbstractHerein a new class of optoelectronic devices beneficial for infrared light absorption and high‐frequency application in the terahertz frequency domain are designed and fabricated. The devices are formed by coating a highly transparent thin layer of Nb2O5 onto a selenium‐thin film to form Se/Nb2O5 (SNO) optical interfaces. Although coating of Nb2O5 nanosheets decreased the crystallite sizes and increased the strain and defect concentration in the hexagonal structured Se films, they successfully increased the light absorption by ≈148% in the infrared range of light. A blueshift in the energy band gap of Se from 2.02 to 2.30 eV is observed. The coating of the Nb2O5 onto Se suppressed the free carrier absorption in Se and Nb2O5. As dielectric active layers, SNO interfaces showed a major resonance dielectric peak centered at 1.67 eV. The optical conductivity and terahertz cutoff frequency analyses which are handled using the Drude‐Lorentz approach revealed the highest drift mobility and free carrier concentration of 17.17 cm2 Vs−1 and 5.0 cm−3 when an oscillator of energy of 1.75 eV is activated. In addition, the terahertz cutoff frequency spectra which varied in the range of 4.0–131 THz showed the suitability of the SNO devices for terahertz technology and other optoelectronics.

Trap‐Engineering the Persistent Luminescence of Ca3Ga4O9:Tb3+ via Al3+ Substitution for Optical Data Storage

AbstractOptically stimulated luminescence (OSL) materials hold great potential for optical data storage (ODS) and anticounterfeiting applications. Nevertheless, the scarcity of suitable luminescent materials with deep‐level traps remains a significant obstacle. Herein, a host substation strategy have been employed to tune the persistent luminescence (PersL) and OSL properties of Ca3Ga4O9:Tb3+ by Al3+ substitution through trap engineering and demonstrated their potential. Specifically, the photoluminescence of the Ca2.985(Ga1‐y%Aly%)4O9:0.5%Tb3+ of Tb3+ is first investigated due to its different occupancies of Ca2+. The influence of host substitution on the crystal structure, trap depth, trap density, PersL, and OSL properties have further investigated. A series of strong PersL and OSL peaks from the Ca2.985(Ga1‐y%Aly%)4O9:0.5%Tb3+ with bluish‐green emissions have been observed. The Ca2.985(Ga1‐y%Aly%)4O9:0.5%Tb3+ have shown controllable photon release upon thermal and optical stimuli, enhancing their performance for ODS. Thermally stimulated luminescence suggests that vacancy and defect concentrations inside the Ca3‐x%(Ga1‐y%Aly%)4O9:x%Tb3+ can be manipulated by Tb3+ doping and Al3+ substitution, which ultimately leads to the formation of deep traps and a broad distribution of traps with increased deep trap concentration. The work demonstrates that trap engineering through Al3⁺ substitution is an effective method for tuning PersL and OSL properties of Ca2.985(Ga1‐y%Aly%)4O9:0.5%Tb3+ for ODS.

Synthesis and luminescence characterizations of Ag and Na doped LiAlO2 for OSL dosimetry

Optically Stimulated Luminescence (OSL) materials are advanced technology materials widely used in critical applications from radiation dosimetry, biomedicine, and optical data storage to archaeometry. These materials store energy by trapping charge carriers and convert this energy back into light by optical stimulation. However, there are significant challenges such as control of trap distribution and complete understanding of luminescence mechanisms. This study aims to overcome these challenges by comprehensively investigating the luminescence characteristics of lithium aluminate (LiAlO2) pellet materials produced by the sol-gel method and enabling the development of a new OSL dosimetric material. The crystal structures of the synthesized materials were confirmed by X-Ray Diffraction (XRD) method and their morphologies were investigated by Scanning Electron Microscope (SEM). Detailed discussions on defect concentrations and lattice parameters of LiAlO2 are presented. To obtain promising luminescence signals for passive dosimetry, LiAlO2 were doped with various lanthanides (Ce and Gd) and metals (Cu, Ag, Na, Mg and Ca). Especially, the co-doping of Ag and Na ions provided a significant increase in Thermoluminescence (TL) and OSL signals. The effects of dopant elements on TL and OSL signals were investigated comprehensively, and the OSL components and lifetimes were analyzed in detail. As a result, it was determined that TL traps of the developed LiAlO2:Ag,Na pellets at 100 °C were the main source of OSL signals. The reusable OSL signals and almost linear dose-response ratio up to 2 Gy of this material make it a candidate for radiation dosimetry applications. While the developed LiAlO2:Ag,Na material exhibits promising OSL sensitivity and low fading over 2 weeks, the signal stability is dependent on an initial preheat treatment at 100 °C, which reduces around 80 % of the initial OSL signal associated with shallow traps. This characteristic supports the material’s application in dosimetry but may limit sensitivity in low-dose contexts.

Synergistic Effect of Ag, Sb Dual‐Cation Substitution on Cu2ZnSn (S, Se)4 High‐Efficiency Solar Cells

ABSTRACTThe poor crystal quality inside an absorber layer and the presence of various harmful defects are the main obstacles restricting the properties of Cu2ZnSn (S, Se)4 (CZTSSe) thin‐film solar cells. Cation doping has attracted considerable research attention as a viable strategy to overcome this challenge. In this paper, based on Sb‐substituted CZTSSe system, we prove that Ag partially substituting Cu may be a feasible strategy. After a series of characterization of the films, it was discovered that the crystal quality and crystallinity of the films were further improved by introducing Ag into Cu2Zn(Sb, Sn) (S, Se)4 (CZTSSSe), and the concentrations of CuZn accepter defects and 2[CuZn + SnZn] defect clusters were effectively inhibited. At the same time, the carrier concentration is increased. The results show that when the Ag doping ratio is 15%, the photovoltaic conversion efficiency (PCE) reaches 8.34%, compared with the single‐doped Sb element, the efficiency is increased by 24%. For the first time, this study investigates the collaborative effect of Sb, Ag dual‐cation substitution in CZTSSe. The solar cell performance enhancement mechanism offers new potential for the advancement of CZTSSe thin‐film solar cell technology in the future.

Accumulation of oxygen interstitial-vacancy pairs under irradiation of corundum single crystals with energetic xenon ions

Single crystals of α-Al2O3 with broad sides oriented perpendicular to the c crystal axis have been irradiated by 231-MeV xenon ions with fluence varying from 5×1011 to 1014 ions/cm2. The spectra of radiation-induced optical absorption (absorption of a pristine crystal is subtracted) have been decomposed into Gaussians serving as a measure of oxygen-related Frenkel defects (vacancy-interstitial pairs). The concentration of all structural defects considered – vacancy-type F and F+ centers as well as oxygen interstitials – continuously increases with ion fluence. Therefore, radiation-induced origin of elementary absorption bands at 5.6 and 6.6 eV tentatively ascribed earlier to charged and neutral oxygen interstitials has been proved for the first time. The concentrations of charged interstitials (in the form of superoxide ions) have been directly determined by the EPR method. The evolution of cathodoluminescence bands typical of self-trapped excitons (VUV band at 7.6 eV) and F-type defects (bands peaked around 3.0 and 3.8 eV) with the rise of Xe-ion-irradiation fluence has been measured and analyzed.

SnS-induced element diffusion Simultaneous optimization of interface and bulk defects in High-Efficiency CZTSSe solar cells

High-quality interfacial contact and absorber are significant for high-efficiency Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells. With this in mind, the paper puts forward the idea of using a sputtering SnS interlayer at the CZTSSe/Mo interface. The high-temperature decomposition of SnS allowed for the compensation of S and Sn elements in the absorber, as well as induced the redistribution of Na and Cu elements. The diffusion of Na element to the absorber optimizes the crystal quality and improves the interface contact, and the Cu-poor absorber reduces the concentration of CuZn defects. Introducing the SnS-10 interlayer significantly reduces the charge loss, bulk and interface recombination of the device, leading to further improvements in the open-circuit voltage (VOC), short-circuit current density (JSC), and filling factor (FF). Finally, the power conversion efficiency (PCE) of CZTSSe thin film solar cells increased from 8.92 % to 10.49 %, in which the contribution rates of VOC, JSC, and FF to PCE were 27.12 %, 32.33 %, and 40.55 %, respectively. The most significant contribution of the electrical parameters to the PCE was the reverse saturation current density (J0). This finding provides an effective solution to obtain a high-quality interface and absorber, effectively restraining carrier recombination.

A novel combining Raman-photoluminescence method to characterize the brittle and plastic states of fused silica based on nanoscale ring structures and atomic point defects

Fused silica has been widely used in many key technical domains. However, the inevitably induced micron-sized brittle fractures during manufacturing processes seriously affect its service performance. Scanning electron and atomic force microscopes are mainly employed to estimate the brittle and plastic states (BPS) of the precise fused silica components, which would put strict demands on the dimensions of detected components and damage the detected surfaces. Herein, the evolution rules of the D2 characteristic peak intensities in Raman spectra corresponding to three-fold rings with the BPS were explored. Interestingly, it is found that the D2 peak intensity first greatly increases in brittle-plastic mixing zones and then sharply decreases in brittle zones. The evolution mechanisms of the nanoscale rings with respect to the BPS were further revealed using the molecular dynamics modeling. The enveloping-space compression of rings and the ring conversion from large- to small rings are found to be the leading factors of the significant increase of the three-fold rings in brittle-plastic mixing zones. And the abrupt destruction of ring structures due to amounts of damaged Si-O bonds in brittle zones contributes to the sharp decrease of the three-fold rings. Based on the evolution rules of the nanoscale rings with the BPS, the brittle-plastic mixing zones could be distinguished from the brittle and plastic zones. It also implies that the rings, especially three-fold rings may dominate the BPS. Moreover, the change laws of the photoluminescence properties with BPS were also studied. It has been found that the photoluminescence envelope area sharply increases with the BPS. It indicates that the concentrations of the atomic point defects would sharply increase with the BPS. Based on the evolution rules of the atomic point defects with the BPS, the brittle and plastic zones could be distinguished. Therefore, a novel Raman-photoluminescence combined method was proposed to characterize the BPS. Finally, its wide applicability was also verified in various specific cases. To sum up, the investigation develops a novel spectral method to effectively characterize the BPS. It is significant for the early warning of the material brittle fractures and the nondestructive characterization of fused silica during the manufacturing processes, which could vigorously promote the further application of fused silica components in various fields.

Effects of defect concentration on ferromagnetism in Xe-irradiated GaN films

Effects of defect concentration on ferromagnetism in Xe-irradiated GaN films

Effect of fiber breakage defect and waviness defect on compressive fatigue behavior and damage evolution of 3D multiaxial braided composites

This paper reports the effects of fiber breakage defects and waviness defects on the compressive fatigue behavior and the progressive damage evolution process of 3D Multiaxial Braided Composites (3DMBCs). Combined with finite element compression simulation and ultra-depth microscope, the internal defect content of composites with different braiding angles was determined. The results demonstrate that the weakening effect of waviness and fiber breakage defects is greater than the strengthening effect of the braiding angle. This causes the fatigue resistance of 3DMBCs with the 31° braiding angle being better in both directions of 0° and 90°. The increase of 4° waviness and 10% fiber breakage defect results in the average fatigue life of composites being shortened by 48% and the energy consumption rate increased by 10% at 85% stress level in the 90° compression direction. The alteration in loading direction modifies the included angle corresponding to the stress component. The stress component parallel to the fiber direction under compressive fatigue load leads to interfacial debonding in the composites, whereas the stress component perpendicular to the fiber direction results in pronounced shear failure.

Structural regulation and sodium storage mechanism of high-performance non-graphitic carbon derived from semi coke

Non-graphitic carbon (NGC) is considered as one of the most promising anodes for sodium-ion batteries (SIBs) because of its low cost and abundant reserves. Nevertheless, there is significant debate regarding the contribution mechanism of sloping and plateau capacity. Herein, a series of NGC with adjustable defect concentration, carbon phases and pore structure are synthesized with semi-coke as precursor to explore the sodium storage mechanism and an “adsorption-insertion-filling” model is proposed based on the in-depth analysis of microstructure and electrochemical behaviors. The very attraction about this work is that the entire discharge curve is divided into three regions for analysis, and the corresponding cause for each region is traced. To be specific, the defects and disordered structure contribute to the surface-controlled absorption behavior in the sloping region >0.1 V, the pseudo-graphitic structure shows diffusion-controlled insertion behavior in the plateau region between 0.1 and 0.05 V, and the closed pores formed by curved graphite-like structure provide plateau capacity (<0.05 V) through the filling of quasi-metallic sodium. This study provides theoretical education for the optimization of NGC anode structure and a novel approach for the excessive value-added utilization of semi coke.

Influence of Bi2O3 on structural and optical characteristics of PbO⋅B2O3⋅Bi2O3⋅SiO2 glasses

In this study, the influence of Bi2O3 on the structural and optical characteristics of the glass samples with the molar composition of 17PbO⋅23B2O3⋅xBi2O3⋅(60-x)SiO2, prepared using the conventional melt quenching approach, is described. X-ray diffraction spectra reveal the amorphous nature of the prepared series. Density (D), molar volume (Vm), glass transition temperature (Tg), and other physical parameters have been evaluated. FTIR spectra show the presence of bismuth as [BiO3] and [BiO6] structural units and of borate as [BO3] and [BO4] structural units. It is found that the increase in non-bridging oxygens can be attributed to the increase in cut-off wavelength and decrease in bandgap energy with the rise in bismuth concentration. Urbach's energy values demonstrate that the presence of Bi2O3 in the existing glass system might affect the defect concentration. All glass samples possess a high refractive index suggesting that the current glasses may be useful for developing non-linear optical systems.

Enhanced Piezoelectric Response Attained by Defect Dipoles in BiFeO3-based Lead-Free Ceramics.

The impact of defects on the performance of piezoelectric materials has been a topic of considerable debate, due to the competing actions of the deteriorating effect of the defects themselves on the ceramic resistance and the positive effect on the piezoelectric performance resulting from the defect polarization. In order to probe its combined influence on piezoelectric properties, here, we designed BiFeO3 (BF)-based ceramics with different defect concentrations. It has been demonstrated that the incorporation of an appropriate concentration of defects into ceramics can effectively enhance their piezoelectric properties while maintaining their insulating properties. During the polarization process, both the intrinsic polarization and defect dipoles are oriented along the direction of the electric field. This occurs in the presence of a high temperature environment as well as an applied electric field, which results in a complementary enhancement of the macroscopic ferro- and piezoelectric properties. Consequently, the piezoelectric performance of BF-BT-BKT ceramics is achieved (d33 = 203 ± 5 pC/N, TC = 502 °C, kp = 33.05%). This work provides a framework for understanding the intrinsic structural mechanism of bismuth ferrate.

How Do the Morphology and Crystal Facet of CeO2 Determine the Catalytic Activity toward NO Removal?

Cerium oxide (CeO2) exhibits application potential for the selective catalytic reduction of nitrogen oxides (NOx) with NH3 (NH3-SCR). The crystal facets and morphology of CeO2 have a vital impact on the catalytic performance of NH3-SCR. However, the precise influence mechanisms on SCR activity remain elusive. In this work, CeO2 is successfully synthesized with three distinct crystal facets and nine diverse morphologies. This investigation involves a comprehensive blend of theoretical analysis and experiments, to gain profound insights into the underlying mechanisms governing the SCR catalytic activity concerning morphology and crystal facets. By closely integrating density functional theory (DFT) calculations, Ab initio thermodynamic analysis, SCR catalytic activity experiments, and X-ray photoelectron spectroscopy experiments, it is discovered that the concentration of surface-active oxygen (O*) plays a pivotal role in determining the catalytic activity of CeO2 in SCR reactions, as opposed to factors like specific surface area or oxygen defect concentration. This experimental-theoretical joint study provides design principles of CeO2 catalysts for NO removal.

Unveiling the synergistic deformation mechanism in three-dimensional continuous network graphene-reinforced copper matrix composites

Three-dimensional continuous graphene-reinforced copper matrix composites (3D-Gr/Cu) have excellent mechanical properties due to their special configuration and strengthening mechanisms. To figure out the deformation mechanism of 3D-Gr/Cu, atomic models of 3D-Gr/Cu with different configuration of graphene network (GN) and concentration of defects are constructed and studied by molecular dynamic simulations in this work. Atomic structure evolution during stretching process is investigated, and the mechanical properties of 3D-Gr/Cu, GN and Cu models are studied. Thereby, synergistic deformation between GN and Cu in 3D-Gr/Cu is revealed, and the deformation coordination between GN and Cu is regulated by GN structure and Gr/Cu interface. Furthermore, intrinsic defects in graphene with a suitable concentration help to construct the three-dimensional GN, improve the Gr/Cu interface bonding, and thus enhance the deformation coordination between GN and Cu. These results provide a profound explanation of the deformation mechanism and a new basis for defect engineering in 3D-Gr/Cu.

Pore defect and corrosion behavior of HVAF-sprayed Co21Fe14Ni8Cr16Mo16C15B10 high entropy metallic glass coatings

Pore defect is a primary bottleneck limiting corrosion resistance of the coatings. The relationship between porosity and corrosion behaviors of HVAF-sprayed Co21Fe14Ni8Cr16Mo16C15B10 high entropy metallic glass (HE-MG) coatings was investigated by 3D XRT, XPS, SKPFM and SVET techniques. The potential difference between pores and surrounding regions expedites corrosion tendency. The corrosion current density of the coating and concentration of defects in passivation film increase as a function of porosity, thereby degrading corrosion resistance. The lowest porosity coating displays exceptional anti-corrosion due to compact films enriched with Cr2O3 and Mo4+ oxides. These findings provide valuable insights for designing corrosion-resistance coatings.

Oxygen 1s X-ray Photoelectron Spectra of Iridium Oxides as a Descriptor of the Amorphous-Rutile Character of the Surface.

Characterization of the surface of iridium oxide (IrOx) materials is of crucial importance to understand catalysts for the oxygen evolution reaction (OER) in low-temperature water electrolysis. While much of our current knowledge is based on well-defined single-crystal surfaces, surface-sensitive techniques like X-ray photoelectronic spectroscopy (XPS) are relevant to characterize the nanostructures considered. In this work, we describe a simple approach to use oxygen 1s spectra as an identifier of the amorphous/crystalline characteristics of iridium oxide structures from purely amorphous to purely crystalline. This conceptual approach was validated on seven commercially available materials. The presence of oxygen-associated defects in the surface moieties/species is shown even for purely crystalline materials with defect concentration increasing with greater amorphous character. This methodology provides us with an accessible ex situ descriptor of the catalyst surface as a baseline for further studies of the impact on catalytic properties.