Lattice Defects Research Articles

High thermoelectric performance in Ag-doped Bi0.5Sb1.5Te3 nanocomposites synthesized via low-temperature liquid phase sintering

In recent years, low-temperature liquid phase sintering (LPS) has emerged as a cost-effectiveness method for designing thermoelectric nanocomposites with reduced lattice thermal conductivity. However, their electrical conductivity often remains suboptimal, limiting the overall figure of merit (ZT). In this study, xwt% Ag/Bi0.5Sb1.5Te3 (x = 0,0.1,0.2,0.3,0.4) nanocomposites are prepared through low-temperature LPS method followed by subsequent annealing. Remarkably, a small amount of silver atoms was doped into the Bi0.5Sb1.5Te3 matrix post-annealing, significantly increasing carrier concentration and improving electrical conductivity. Additionally, residual Ag atoms formed Ag₂Te nanoprecipitates, and lattice defects (including grain boundaries, twin boundaries, dislocations, and lattice distortions) effectively reduced lattice thermal conductivity. The 0.3 wt% Ag/Bi0.5Sb1.5Te3 sample achieved a maximum ZT value of 1.36 at 400 K, double that of the pure Bi0.5Sb1.5Te3 sample, with an average ZT value of 1.17, among the highest reported. This work demonstrates significant potential for synthesizing high-performance thermoelectric materials via low-temperature LPS methods.

Studying the Defects in Spinel Compounds: Discovery, Formation Mechanisms, Classification, and Influence on Catalytic Properties.

Spinel ferrites demonstrate extensive applications in different areas, like electrodes for electrochemical devices, gas sensors, catalysts, and magnetic adsorbents for environmentally important processes. However, defects in the real spinel structure can change the many physical and chemical properties of spinel ferrites. Although the number of defects in a crystal spinel lattice is small, their influence on the vast majority of physical properties could be really decisive. This review provides an overview of the structural characteristics of spinel compounds (e.g., CoFe2O4, NiFe2O4, ZnFe2O4, Fe3O4, γ-Fe2O3, Co3O4, Mn3O4, NiCo2O4, ZnCo2O4, Co2MnO4, etc.) and examines the influence of defects on their properties. Attention was paid to the classification (0D, 1D, 2D, and 3D defects), nomenclature, and the formation of point and surface defects in ferrites. An in-depth description of the defects responsible for the physicochemical properties and the methodologies employed for their determination are presented. DFT as the most common simulation approach is described in relation to modeling the point defects in spinel compounds. The significant influence of defect distribution on the magnetic interactions between cations, enhancing magnetic properties, is highlighted. The main defect-engineering strategies (direct synthesis and post-treatment) are described. An antistructural notation of active centers in spinel cobalt ferrite is presented. It is shown that the introduction of cations with different charges (e.g., Cu(I), Mn(II), Ce(III), or Ce(IV)) into the cobalt ferrite spinel matrix results in the formation of various point defects. The ability to predict the type of defects and their impact on material properties is the basis of defect engineering, which is currently an extremely promising direction in modern materials science.

The key role of anti-solvent temperature in quantum dot/perovskite core-shell nanowire array solar cells

Combining perovskite with infrared quantum dots to construct a core-shell nanostructure nanowire array solar cell can increase the light absorption range and enhance the light absorption and carrier transport efficiency of the solar cell. However, the preparation of a perovskite absorber layer on a nanowire array with quantum dots often presents issues such as high roughness and a large number of lattice defects, which have a negative impact on the photovoltaic performance. The anti-solvent method is a commonly used technique to improve the quality of perovskite. The temperature variation of the anti-solvent can change solubility, and influence the reaction rate and crystal formation process of perovskite, thus affecting its photovoltaic performance. In this study, the quality of perovskite in the core-shell nanostructure nanowire array was improved by controlling the temperature of the anti-solvent (toluene). Experimental results show that as the temperature of toluene increases, the photovoltaic performance is gradually improved. When the toluene temperature was maintained at 75 °C, the device exhibited significantly improved photovoltaic performance with an efficiency of 12.64 %, surpassing the efficiency obtained without any anti-solvent modification. As the temperature of the anti-solvent increases, the absorption of visible and near-infrared light spectrum by the nanowire arrays is enhanced, which promotes the efficient generation of photo-generated carriers. Furthermore, defects in the nanowire arrays gradually decrease, leading to a reduction in carrier recombination. These findings provide valuable insights for advancing core-shell nanostructure nanowire array solar cells.

Ultraviolet–near infrared luminescence characteristics of Nd:La2Be2O5 single crystals for near-infrared emitting scintillators

The fabrication of 0.1, 0.5, 1.0, and 5.0 % Nd:La2Be2O5 single crystals was carried out by the floating zone method, and photoluminescence (PL) and scintillation properties were measured. The PL spectra showed some emission lines which was derived from the 4f-4f transitions of Nd3+ ions. The scintillation spectra showed a broad emission band originating from some lattice defect and the emission lines due to the 4f–4f transitions of Nd3+ ions. The afterglow levels of Nd:La2Be2O5 were 192.3 (0.1 % Nd), 205.9 (0.5 % Nd), 228.2 (1.0 % Nd), and 315.4 (5.0 % Nd) ppm. The 1.0 % Nd:La2Be2O5 showed the highest intensity in the dose-rate response functions among the samples, and a lower detection limit was 0.003 Gy/h.

Effects of Black Silicon Surface Morphology Induced by a Femtosecond Laser on Absorptance and Photoelectric Response Efficiency

In this study, the effects of variations in the height (h) and bottom radius (r) of black silicon microstructures on their absorptance and photoelectric response efficiency were analyzed. By using the relation cot⁡θ2=hr to combine the parameters, it was found that changes in morphology affected the absorptance of black silicon microstructures, with h being directly proportional to the absorptance, while r was inversely proportional. A positive correlation was observed between cot⁡θ2 and absorptance. However, the correlation between cot⁡θ2 and photoelectric response efficiency was not significant. Through Raman spectroscopy analysis of the samples, it was concluded that as the laser ablation energy density increased, more lattice defects were introduced, weakening the charge carrier transport efficiency. This study further elucidated the mechanism by which microstructural changes impacted the absorptance and energy density of black silicon, providing valuable insights for optimizing its energy density.

Advances in hybrid strategies for enhanced photocatalytic water splitting: Bridging conventional and emerging methods

Significant efforts have been dedicated to hydrogen production through photocatalytic water splitting (PWS) over the past five decades. However, achieving commercially viable solar-to-hydrogen conversion efficiency in PWS systems remains elusive. These systems face intrinsic and extrinsic challenges, such as inadequate light absorption, insufficient charge separation, limited redox active sites, low surface area, and scalability issues in practical designs. To address these issues, conventional strategies including heterojunction engineering, plasmonics, hybridization, lattice defects, sensitization, and upconversion processes have been extensively employed. More recently, innovative hybrid strategies like photonic crystal-assisted and polarization field-assisted PWS have emerged, which improve light absorption and charge separation by harnessing the slow photon effect, multiple light scattering, and the piezoelectric, pyroelectric, and ferroelectric properties of materials. This review article aims to provide a comprehensive examination and summary of these new synergistic hybrid approaches, integrating plasmonic effects, upconversion processes, and photonic crystal photocatalysis. It also explores the role of temperature in suppressing exciton recombination during photothermic photocatalysis. This article also highlights emerging strategies such as the effects of magnetic fields, periodic illumination, many-body large-hole polaron, and anapole excitations, which hold significant potential to advance PWS technology and facilitate renewable hydrogen generation.

Single-Atom Cobalt Catalyst with Boron and Nitrogen Codoped Graphene (Co-BN-G) Enables Adsorption and Catalytic Conversion of Polysulfides for High-Performance Lithium-Sulfur Batteries.

In lithium-sulfur batteries, the shuttling effect and sluggish redox conversion of soluble polysulfides lead to unsatisfactory sulfur utilization and capacity retention. In this research, we used a one-pot hydrothermal method to prepare graphene with single-atom Co and B, N codoped as a sulfur host in Li-S batteries, thereby suppressing the shuttling effect and facilitating the redox conversion of lithium polysulfides (LiPSs). A series of characterizations demonstrated that dual doping of B and N introduces more lattice defects and structural deformations in graphene oxide, thus enhancing its adsorption of polysulfides. Simultaneously, single-atom cobalt can also polarize adsorption and accelerate the conversion reaction of LiPSs. The Li-S cell with the as-prepared Co-BN-G sulfur host materials exhibited an excellent capacity of 1034 mAh g-1 at 0.5 C and satisfactory cycle performance (retention of 69% over 500 cycles). Even at a rate of 2 C, a discharge capacity of 851 mAh g-1 is achieved. The results show that the Co-BN-G configuration efficiently captures LiPSs and enhances their rate conversion kinetics in redox reactions, demonstrating significant practical potential.

N-Doped Porous Carbon Based on Anion and Cation Storage Chemistry for High-Energy and Power-Density Zinc Ion Capacitor.

Zinc ion hybrid capacitors (ZIHCs) show promise for large-scale energy storage because of their low cost, highly intrinsic safety, and eco-friendliness. However, their energy density has been limited by the lack of advanced cathodes. Herein, a high-capacity cathode material named N-doped porous carbon (CFeN-2) is introduced for ZIHCs. CFeN-2, synthesized through the annealing of coal pitch with FeCl3·6H2O as a catalytic activator and melamine as a nitrogen source, exhibits significant N content (10.95 wt%), a large surface area (1037.66 m2 g-1), abundant lattice defects and ultrahigh microporosity. These characteristics, validated through theoretical simulations and experimental tests, enable a dual-ion energy storage mechanism involving Zn2+ ions and CF3SO3 - anions for CFeN-2. When used as a cathode in ZIHCs, CFeN-2 achieves a high-energy density of 142.5W h kg-1 and a high-power density of 9500.1W kg-1. Furthermore, using CFeN-2 ZIHCs demonstrate exceptional performance with 77% capacity retention and nearly 100% coulombic efficiency after 10 000 cycles at 10 A g-1, showcasing substantially superior performance to current ZIHCs. This study offers a pathway for developing high-energy and high-power cathodes derived from coal pitch carbon for ZIHC applications.

Local Strain Effects on Lattice Defect Dynamics and Interstitial Dislocation Loop Formation in Irradiated Tungsten-Molybdenum Alloys: A Molecular Dynamics Study.

In this study, molecular dynamics (MD) simulations were used to investigate how alloying tungsten (W) with molybdenum (Mo) and local strain affect the primary defect formation and interstitial dislocation loops (IDLs) in W-Mo alloys. While the number of Frenkel pairs (FPs) in the W-Mo alloy is similar to pure W, it is half that of pure Mo. The W-20% Mo alloy, chosen for further analysis, showed minimal FP variance after collision cascades induced by primary knock-on atoms (PKAs) at 10 to 80 keV. The research examined hydrostatic strains from -1.4% to 1.6%, finding that higher strains correlated with increased FP counts and cluster formation, including IDLs. The following two types of IDLs were identified: majority ½ <111> loops as well as <100> IDLs that formed within the initial picoseconds of the simulations under higher tensile strain (1.6%) and larger PKA energies (80 keV). The strain effects also correlated with changes in threshold displacement energy (TDE), with higher FP formation under tensile strain. This study highlights the impact of strain and alloying on radiation damage, particularly in low-temperature, high-energy environments.

Synergistic modulation of SrTiO3-TiO2 colossal permittivity system by internal lattice defects and phase composition: Experimental and theoretical investigations

The SrTiO3–TiO2 composite ceramics with different contents of La doping were fabricated by traditional solid-state sintering methods. The performance of the colossal permittivity ceramics was enhanced by the synergistic design of the internal defect structure and phase composition. When the doping content is 2%, SrTiO3–TiO2 composite ceramics possessed a colossal permittivity (ԑr ∼ 1.1 × 105), low dielectric loss (tanδ ∼ 0.050) and favorable thermal stability (−70 °C-150 °C, ΔC/C25°C ≤ ±15%). Phase structure analysis suggested that a TiO2 secondary phase was induced at the grain boundaries of SrTiO3 phase with the addition of La3+ ions. XPS and dielectric behavior analyses revealed that oxygen vacancies and lattice defects formed by inhomogeneous ion-doping act to modulate the dielectric behavior in ceramics. The IBLC interfacial effects in relation to semiconductor grains and insulation grain boundaries are the main contributors to the colossal permittivity (CP) properties of ceramics, and the contribution of the IBLC effects becomes more prominent with increasing doping content. On the basis of first-principles analysis, the ceramic lattice undergoes severe deformation when the La content is increased, and the gathering of electrons at oxygen vacancies and defects is evident. As a result, it leads to enhanced grain semiconducting properties and interfacial effects, which facilitate colossal permittivity and low dielectric loss for ceramics. The results are prospective in the application of CP ceramics.

Preparation of CeO2@AC and CeO2@NF nanocomposites for waste water treatment

This research focuses on the elimination of Rose bengal dye using nanoparticles consisting of cerium oxide (CeO2) loaded onto activated carbon (CeO2@AC) and carbon nanofibers (CeO2@NF). These nanoparticles were developed through co-precipitation techniques. X-ray diffraction and transmission electron microscopy (TEM) were employed to verify the structural properties and crystalline dimensions of these nanocomposites. The average particle sizes for CeO2, CeO2@AC, and CeO2@NF nanocomposites are determined to be 7.5 nm, 10.5 nm, and 10.0 nm, respectively from XRD. The TEM images shows regularly shaped spherical particles falling within the size range of 7 to 15 nm. Raman spectroscopy and X-ray photoelectron spectroscopy were utilized to investigate their electronic characteristics and the presence of lattice defects, specifically oxygen vacancies, was quantified. The distinctive structure and lattice defects contribute to the photocatalytic degradation of RB dye, with CeO2, AC, and NF exhibiting photocatalytic efficiencies of 75 %, 88 %, and 89.8 %, respectively, when exposed to UV light. Additionally, the magnetic properties of the synthesized samples were examined using a vibrating sample magnetometer. Consequently, cerium oxide nanocomposites combined with activated carbon and nanofibers have demonstrated their utility as multifunctional materials, suitable for photocatalysis.

Lattice defects and surface adsorption properties of gold-bearing chalcopyrite: A theoretical study based on DFT

Chalcopyrite (CuFeS2), as one of the carrier minerals of gold, undergoes significant alterations in lattice and surface properties upon doping with gold impurities. These changes markedly influence its separation and purification techniques, especially flotation. Using Density Functional Theory (DFT) based on first-principles, we analyze the influence of gold impurities on the lattice defects and surface properties of chalcopyrite. We developed an adsorption model using prop-2-yn-1-yl diethylcarbamodithioate (PDEC), a sulfur ester collector with an ethynyl group, on gold-infused chalcopyrite to elucidate the adsorption mechanism. Our findings indicate that the Au atom primarily occupies interstitial sites within the chalcopyrite lattice, resulting in an expanded lattice structure. Despite the doping, the lattice remains a p-type semiconductor with increased conductivity, facilitated by Au 6 s orbitals contributing to impurity levels within the conduction band from 2 to 4 eV. Additionally, there is a marked rise in spin-up electrons, with Integrated |Spin Density| results showing greater electron localization in Cu15Fe16S32Au and Cu16Fe16S32Au compared to ideal chalcopyrite crystal (Cu16Fe16S32). The Au atom exhibits maximum stability when adsorbed onto the S-Fe bonds on chalcopyrite surfaces, primarily forming covalent bonds through electron acceptance from Fe 3d orbitals. The presence of gold impurities decreases the collector's adsorption energy on the chalcopyrite (112) surface. However, PDEC exhibits enhanced adsorption performance relative to Al-DECDT and Z-200, primarily due to the chelation between thiocarbonyl and ethynyl groups of PDEC and the gold-bearing chalcopyrite (112) surface. Electron donation from Fe 4p orbitals of surface to the S 3 s and 3p orbitals of collector forms a sigma bond, while the ethynyl group undergoes hybridization with the Au 5d orbitals from −5 to −2.5 eV, fostering stable electron transfer.

Influence of morphological variations in cobalt bismuth oxide on supercapacitor performance

In this study, we successfully synthesized novel cobalt bismuth oxide (CBO) using various solvothermal methods. These materials were then utilized as active electrode materials for supercapacitors and photocatalysts. A variety of techniques was employed to analyse the crystal structure, morphology, and surface of the prepared samples. The morphological analysis revealed that S1 (nanosheet) and S3 (nanoneedles) are in nanostructure form. The S3 electrode demonstrated a specific capacitance of 270.9 F g-1 at a current density of 1 Ag-1, compared to the S1 electrode, which exhibited a specific capacitance of 181.7 F g-1 under the same conditions. Furthermore, when subjected to a current density of 3 A g-1, the S1 and S3 retained 79 % and 62 % of their capacitance, respectively after 2000 cycles. The morphological variations in the samples play a crucial role in capacitive performance and mechanism, characterised by a significant presence of lattice defects and oxygen vacancies.

In-depth approach and establishment from a structural perspective of LiFePO4 cathodes for lithium-ion batteries by a two-step sintering

Most synthesis of olivine LiFePO4 (LFP) studies have emphasized the importance of a two-step sintering process for the formation of a uniform carbon coating. However, in this study, it is found that, as an advantage of the two-step sintering process, stable carbonization not only improves lithium-ion conductivity by forming a coating layer but also increases the uniformity of the internal crystal structure. In addition to basic crystallinity and structure analysis using X-ray diffraction (XRD), in-depth calculations are performed to explain the formation mechanism of crystal structure according to the two-step sintering process and the temperature of the first sintering step. In particular, lattice defects and structural uniformity are closely investigated from the crystal structure perspective by comparing lattice micro-strain and dislocation density. Improvement in lithium-ion conductivity from structural uniformity is also demonstrated through cyclic voltammetry (CV) analysis. As a result, it is confirmed that LFP, which undergoes a high-temperature two-step sintering, has high capacity and excellent cycle retention at high rates. Furthermore, ex-situ XRD analysis demonstrates the performance difference according to lithium-ion mobility by comparing the LiFePO4/FePO4 two-phase transformation reaction of two-step sintered LFP and the plateau stability during charging.

Efficient photoreforming of plastic waste using a high-entropy oxide catalyst

Simultaneous catalytic hydrogen (H2) production and plastic waste degradation under light, known as photoreforming, is a novel approach to green fuel production and efficient waste management. Here, we use a high-entropy oxide (HEO), a new family of catalysts with five or more principal cations in their structure, for plastic degradation and H2 production. The HEO shows higher activity than that of P25 TiO2, a benchmark photocatalyst, for the degradation of polyethylene terephthalate (PET) plastics in water. Several valuable products are produced by photoreforming of PET bottles and microplastics including H2, terephthalate, ethylene glycol and formic acid. The high activity is attributed to the diverse existence of several cations in the HEO lattice, lattice defects, and appropriate charge carrier lifetime. These findings suggest that HEOs possess high potential as new catalysts for concurrent plastic waste conversion and clean H2 production.

Charge-induced high-valence zirconium-doped CuCo2S4/Co(OH)2 nanowires promote bifunctional water splitting

Spinel-type materials are attracting great attention as potential electrocatalysts for the hydrogen- and oxygen-evolution reactions. However, their inherent catalytic activities are not on par with those of precious-metal catalysts, and their poor stabilities continue to constrain their rapid development. In this study, we fabricated Zr-CuCo2S4 nanowires and Co(OH)2 nanosheet–nanowires using electrochemical methods, resulting in lattice defects, sulfur vacancies, and more exposed active sites that catalyze the hydrogen- and oxygen-evolution reactions. DFT calculations revealed that sulfur vacancies enhance intrinsic activity, while Zr doping reduces the energy barrier for H*–OH* adsorption, promotes the formation of additional sulfur vacancies, and modulates active-site Cu/Co valence states, which greatly enhances water-dissociation and H*-adsorption kinetics. Consequently, Zr-CuCo2S4/Co(OH)2 requires low overpotentials of 88 and 208 mV, respectively, to support highly stable alkaline hydrogen- and oxygen-evolution reactions at 10 mA cm−2. This study provides a rational strategy for designing low-cost spinels for green and clean energy.

Dependence of the crystal structure on the d-units amount in semi-crystalline poly(lactic acid)

The study investigates the impact of the d-lactic acid units content on the crystallinity and crystal structure of commercial poly(lactic acid) (PLA) grades, which are copolymers of poly(l-lactic acid) (PLLA) containing a minor amount of d-units. As the d-units content increases, a detectable decrease in crystallinity was observed along with a simultaneous rise in mobile amorphous fraction (MAF) and a reduction in rigid amorphous fraction (RAF). The percentage of d-units was found not to significantly affect RAF thickness, suggesting that the d-units are not completely excluded from the crystals. The inclusion of d-units as defects in the PLA crystal lattice was confirmed by XRD analysis, which disclosed that the crystal phase gets gradually richer of d-units as the crystallization time evolves. FT-IR analysis proved that the incorporation of d-units in the crystal phase is promoted by the formation of local CH3···O=C interactions, similar to those massively active between PLLA and poly(d-lactic acid) (PDLA) in the stereocomplex. The establishment of these interactions leads to a contraction of the interplanar distances and a decrease in the crystal cell volume with increasing the crystallization time and the d-units percentage. In summary, the study proves that for PLA copolymers containing a d-units percentage at least up to about 8 %, d-units are included in the crystal lattice.

Hematite Defect Development for Gallic Acid Sensing

AbstractNanostructured iron (III) oxide was prepared by a facile hydrothermal method using poly(triazine imide) (PTI) as a sacrificial template. The physicochemical properties of pristine iron oxide and its analogue obtained in the presence of PTI confirmed strong effect of the latter as the morphology improving agent. Moreover, application of nitrogen rich semiconducting polymer during hydrothermal synthesis increased number of defects. The obtained sample was used as an electroactive additive for carbon‐paste electrode. PTI‐modified sample demonstrated 1.52 times higher oxidation current, and 1.39 lower charge transfer resistance compared to hematite obtained without PTI, as was confirmed by CV and EIS data. Therefore, it was proposed to use the as a sensor for the detection of gallic acid. The developed method showed excellent linearity within a concentration range of 67 nM to 17.7 µM with a detection limit equal to 44 nM and limit of quantification of 132 nM. Stablitity and reproducibility tests, as well as real sample analysis confirmed applicability of the proposed sensor for practical application. Excellent electrochemical properties of the submicron hematite particles are attributed to the developed lattice defects, which served as reaction centers and charge transducing points.

Enhanced flux pinning properties of Ga2O3: YBCO nanocomposite superconductor

The effect of adding various concentrations (0.1 to 0.5 wt%) of Ga2O3 nanorods (NRs) on structural, electrical, magnetic, and flux pinning properties of the YBa2Cu O7-δ (YBCO) superconductor is studied. The critical current density (Jc) and flux pinning force (Fp) values are found enhance significantly, and the nanocomposite sample with x = 0.2 wt% shows the maximum enhancement among the samples under study. At 4 K, the maximum value of Jc (Jcmax) and Fp (Fpmax) for the 0.2 wt% sample are ∼ 2.87 and 3 times higher and at 65 K, these increments are ∼ 3.54 and 3.4 times, as compared to pure YBCO respectively. Moreover, the Jc value for the composite samples has a lower decay with increasing temperature than the pure YBCO samples. The enhanced superconducting properties of the xGa2O3: YBCO can be attributed to the lattice defects induced by Ga2O3 NRs, which act as effective pinning centers.

Hierarchical Nb@NbN core-shell-like nanocolumns for asymmetric supercapacitors

Transition metal nitrides (TMNs) are promising electrode materials for supercapacitors because of their high electrical conductivity and chemical stability. The rational design and facile synthesis of TMNs electrode materials with a unique nanostructure are the key to develop high-performance supercapacitors. Herein, we propose a two-step, binder-free, and eco-friendly approach utilizing magnetron sputtering at an oblique angle deposition configuration to fabricate hierarchical Nb@NbN core–shell-like nanocolumns for supercapacitors. This distinctive heterostructure not only creates lattice defects, increases active surface area, facilitates ion diffusion and charge transfer, but also optimizes the electronic structure and enhances the conductivity. As a result, the hierarchical Nb@NbN core–shell-like nanocolumn electrodes exhibit a high areal capacitance of 53.3 mF cm−2 at 1 mA cm−2 and an excellent capacitance retention of 93.5 % after 20,000 cycles, outperforming pristine NbN and the majority of previously reported TMNs electrodes. Moreover, the assembled Nb@NbN nanocolumns//VN thin films asymmetric supercapacitor device can deliver a maximum energy density of 49.8 mWh cm−3 and power density of 82 W cm−3. This work presents a facile and environmentally friendly strategy for the synthesis of TMNs core–shell-like nanocolumns, and further demonstrates their promising potential for use in supercapacitors.