Defect Chemistry Research Articles

(Digital Presentation) Fabrication of Single-Crystal Layered Oxide Cathode through Variation on Heating Process

Since the announcement of a million-mile battery by Tesla, single-crystal processing of layered oxide cathode has received great attention recently. From single-crystal process, high Ni layered oxides with grain size in mm range tends to give better cycling performance due to better structural integrity against repeated charge/discharge cycles.However, during heating/calcination process of oxide/carbonates/nitrates powder compacts, it may involve decomposition, chemical reactions, diffusion, oxidation, sintering, grain-growth. For single-crystal process, the powder compacts need to be heated to higher temperatures (~950°C) for certain period of time. On the other hand, enough air/oxygen is need for Ni oxidation and better crystallization in Ni-rich layered structure. Therefore, it is important to investigate the processing of single-crystal Ni-rich layered oxide based on the sintering behavior, thermal gravimetric analysis, and phase transformation.Nevertheless, the lithiation/oxidation of Ni-containing oxides involves charge compensation resulted from defect reactions. As a result, the affected electrical, optical, structural, and electrochemical properties of layered oxides will be discussed based on defect chemistry consideration. The structural, microstructural and electrical properties of decomposed precursors and doped layered oxides will be examined using XRD, SEM and DC/AC impedance measurements. CV and charge/discharge tests from assembled coin cells will be used to evaluate electrochemical properties of single-crystal Ni-rich layered oxides.

Tuning Ionic Conductivity and Stability of Li10GeP2S12 Solid-State Electrolyte

All-solid-state Li-ion batteries gained a huge attention because they exhibit higher power density, wider electrochemical stability windows, and overall safety of solid-state electrolytes (SSE) compared to conventional liquid electrolyte-based batteries. Unfortunately, most of the SSE materials have not matched the ionic conductivity of their liquid counterpart. But, recent research and the synthesis of new materials have shown SSE can conduct ions at an equivalent or even higher rate. However, the electrochemical stability needs to be improved. There is a growing research effort in identifying a solid electrolyte that is both electrochemically stable and has a very high ionic conductivity. The Li10GeP2S12 (LGPS) is one of the superionic conductors, is known for its high ionic conductivity that can be deployed as a solid electrolyte in batteries. However, LGPS is not stable as exposed to air and moisture, posing challenges during its manufacturing, and designing process. Thus, in an attempt to optimize the stability and ionic conductivity, the effect of antimony (Sb), tin (Sn), and oxygen (O) substitution on conductivity and stability of LGPS is investigated using Density Functional Theory (DFT). The systematic study of compositional variation, phase stability, defects chemistry, and the impact on electronic properties and ionic conductivity is performed. Thus, this study will provide significant insights on ion conduction mechanisms and strategies that can tune the ionic conductivity and stability of LGPS based electrolytes. This project was supported in part by COE SJSU, DOE NERSC, and XSEDE.

Exploring Charged Defects and Dopability Limits of Solid Electrolytes, a Computational Study

All-Solid-State Lithium Batteries (ASSLBs) are a new generation of lithium batteries that is developed to meet high expectations in terms of safety, stability and high energy density. The liquid electrolyte of conventional Li-ion batteries is replaced in ASSLBs by a safer and more stable solid electrolyte (SE). These solid electrolytes must meet a number of requirements before they can be considered in ASSLBs, including a wide electrochemical stability window, a high ionic conductivity and a negligible electronic conductivity [1]. For a long time, researchers have focused on achieving the highest ionic conductivity possible on these materials, comparable to the one of liquid electrolytes. The ionic conductivity in SEs has been successfully increased by the introduction of defects (doping) and Li1.3Al0.3Ti1.7(PO4)3 and Li1.5Al0.5Ge1.5(PO4)3 solid electrolytes are both excellent examples of such achievement. However, the formation of defects can also have a significant effect on the SEs electronic conductivity [2],[ 3],[ 4]. Increasing the electronic conductivity in solid electrolytes is detrimental to the ASSLBs safety and integrity. Therefore, it is essential to understand the defect chemistry in SEs. Due to their negligible concentration, characterizing point defects is hardly possible using standard characterization techniques, justifying the need for first-principles calculations. In this work, we have investigated the defect chemistry of most common solid electrolytes (LixM2(PO4)3 (M = Zr, Ti, Ge, Al), Li7La3Zr2O12, LiLaTi2O6, Li10Ge(PS6)2, Li7P3S11, Li3PS4, Li3PO4 and LiPO3). For each SE, we computed the formation energies for intrinsic defects and assessed the dopability limits as a function of the synthesis conditions. We found that the position of the Fermi level and dopability limits depend strongly on lithium and oxygen/sulfur chemical potentials but also on the nature of the solid electrolyte. We advocate that it is imperative to better regulate the synthesis conditions if we want to gain control over the formation of defects in solid electrolytes. The outcoming properties of these materials, such as the ionic and electronic conductivities, depend on it. [1] N. Dudney. Springer. 2003, 624-642. [2] E. Zhao et al. J. Alloys Comp. 2019. 782, 384-391. [3] Y. Song et al. J. Mat. Chem. A. 2019, 7(40), 22898-22902. [4] Y. Shan et al. J. Power Sources. 1995, 54(2), 397-402.

(Invited) Electrocatalysts of Complex Oxides for Water Splitting

Low temperature electrolysis plays a critical role in our effort for energy generation with net zero or negative carbon impacts. This process produces green hydrogen through catalytic splitting of water and requires the development of highly active and, perhaps more importantly, highly stable electrocatalysts for oxygen evolution reaction (OER). This presentation will focus on examining the structure-property relationship of complex oxides that are made of AxByOz, where A and B can be a single metal cation or mixed cations, respectively. Depending the compositions, perovskite, pyrochlore, and Ruddlesden-Popper (RP) phase solids all have been found to be highly active for OER in either acid or base conditions. Noticeably, structurally defective solid catalysts such as those observed in defect perovskite (J. Am. Chem. Soc., 2014, 136, 14646-14649) often possess high activity. I will review some of the latest advancements in understanding the mechanisms of OER and discuss the new results on regulating the cation sites and oxygen defect chemistry for enhancing the bond-stability of key catalytic constituents and surface structures for OER performance.

(Invited, Digital Presentation) Synthesis and Atomic Scale Characterization of 2D Layered Heterostructures Atom by Atom: An Ultra-high Resolution Aberration-corrected Electron Microscopy Study

Defects can have a profound effect on the macroscale physical, chemical, and electronic properties of nanostructures. They can lead to structural distortions, introduce extra states in the band gap and give rise to excess potential locally at buried interfaces. While defects and interfaces have been a well-studied subject for decades, little is known about their local atomic and chemical structure, sub-Angstrom structural distortions within their vicinity.Using ultra-high-resolution aberration-corrected S/TEM imaging and spectroscopy, this talk will discuss our recent efforts on the determination of the defect chemistry and sub-Angstrom relaxation effects in nanostructures around at the interfaces in the family of 2D crystal heterostructures. In the family of 2D crystal transition metal dichalcogenides (TMDs) alloys, we report how on anisotropy of the building blocks in the 2D heterostructure, such as ReS2/MoS2 and WS2/Graphene, and their epitaxy and strain at the interface can affect their nucleation and growth. This work will further uncover the structural distortions that occur in these heterostructure across various length scales and reveals the underlying physics of the formation of such heterostructures and their strain state resulting from CVD synthesis.

Lanthanum Strontium Manganite Oxygen Electrode Reaction Mechanism in High-Temperature Solid Oxide Water Electrolysis

High-temperature solid oxide water electrolysis cells have become the center of attention of the research community owing to several advantages over traditional water electrolysis technologies. Among others, solid oxide water electrolysis represents highly efficient technology with the possibility to operate in a reversible regime (fuel cell/steam electrolysis). Despite the fast reaction kinetics due to the high operating temperature (600-900 °C). A more detailed understanding of the reaction mechanism is of critical importance to further develop this technology.Lanthanum-strontium-manganite La1-xSrxMnO3-δ is still considered a viable material for an oxygen electrode due to its high electrical conductivity, good chemical stability, and thermomechanical compatibility with various solid electrolytes. However, its negligible ionic conductivity is frequently reported in the literature. Although, La1-xSrxMnO3-δ is utilized as an oxygen electrode for several decades and its properties are reported in the literature, the reaction mechanism occurring on this oxygen electrode is insufficiently described, with multiple discrepancies occurring between the individual authors. The open literature almost exclusively considers the oxygen reduction reaction. Here La1-xSrxMnO3-δ is described exclusively as a pure electron conductor. In the case of the oxygen evolution reaction, only the mechanism reversed to the oxygen reduction is considered, which is clearly an oversimplification.Recent articles tend to connect the defect chemistry of La1-xSrxMnO3-δ and electrochemistry to disapprove the generally accepted description of reaction mechanisms, owing to the rather low agreement between theory and experimental data. In the framework of this study, a series of experiments was conducted, both under current-less as well as current-load conditions using laboratory button cells. Oxygen electrodes based on various mixtures of La0.8Sr0.2MnO3-δ-ZrO2:Y2O3 were tested to prove that La1-xSrxMnO3-δ may become a mixed ionic-electron conductor under specific conditions.The obtained data showed that conditions, such as oxygen partial pressure, temperature and, in particular, the polarization history, could result in a partial reduction of Mn4+ to Mn2+ in the crystal lattice of La1-xSrxMnO3-δ. The change of valence is of a great importance because it creates oxygen vacancies through which oxide ions can be transported. Therefore, under such conditions La1-xSrxMnO3-δ becomes a partial mixed ionic-electron conductor, significantly increasing the number of active reaction sites in the three-dimensional structure of the electrode. The most recent articles reported this behavior; however, only during the oxygen reduction reaction owing to the most suitable conditions for the Mn oxidation state transition. Within the framework of this study, the aim is to expand this concept also to the conditions of the oxygen evolution reaction, which has been completely omitted in the literature. The presented results significantly contribute to the understanding of solid oxide cells and represent a solid base for further modelling of the electrolysis cell, and optimization of its construction as well as operational conditions.This work was supported by the Technology Agency of the Czech Republic under project no. TK04030143.

Ultra-high piezoelectric performance by rational tuning of heterovalent-ion doping in lead-free piezoelectric ceramics

The vision of “lead-free” instead of “lead” is growing as people pay more attention to environmental problems, especially since performance improvement of lead-free piezoelectric materials is imminent. The introduction of local heterogeneity, relaxor behavior, and nanodomain engineering based on heterovalent-ions has been proved to be highly effective for further increasing of performance of piezoelectric materials. However, how the doping level will work towards improving the piezoelectric performance, especially the lead-free piezoelectrics is an open question. In this work, we have assembled (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics based on the traditional phase-structure construction strategy and used microscale heterovalent-ion Al element doping to regulate its piezoelectric properties. The optimization of piezoelectric properties, on the one hand, comes from large lattice distortion caused by appropriate Al doping, leading to high asymmetry and enhancement of the displacement of B−site ions. On the other hand, the behavior of a ceramic with a low defect concentration and an N-type conductivity mechanism is guided by its defect chemistry. The defect configuration analysis explains in detail the process of Al3+ ions entering A-sites and B-sites in turn with change in the doping concentration, that is, from donor doping to acceptor doping, and the influence of the change in defect concentration caused by this process on piezoelectric properties. When the doping level of Al3+ ions is 0.25 mol%, it is exciting to find that the piezoelectric performance is significantly high (piezoelectric coefficient d33 = 638 pC/N, electromechanical coupling factor kp = 54%). The interpretation of heterovalent-ion doping in this work is different from the strategy for traditional high-performance piezoelectric materials. This discovery facilitates a new mechanism of doping for improving piezoelectricity, which will help to further improve the piezoelectric performance of different piezoelectric materials.

The integration of multi-luminescence in Sr2SnO4:xEr3+/Sm3+

Er 3+ and Sm 3+ ions were co-doped in Sr 2 SnO 4 : x Er 3+ /Sm 3+ ceramics to achieve the integration of photo-stimulated luminescence (PSL), thermal-stimulated luminescence (TSL) and photochromism (PC) in one single material. The effect of doped Er 3+ content on the microstructure, PC, PSL and TSL of the ceramcis has been investigated. It is found that moderate Er 3+ content ( x ≤ 0.003) could enhance PC, photoluminescence and TSL performance of the ceramics. The PSL and TSL are greatly depressed when x ≥ 0.005. This variation is caused by the change of kinds of formed defects. In addition, we have proposed a new method for optical information storage using the PSL as the optical signal, in which up-conversion luminescence from Er 3+ is the reference signal. This strategy could prevent the occurring of error signal. A simple mechanism on the luminescence modulation, PC, PSL and TSL is proposed basing on the defect chemistry. The application demonstration shows the ceramics’ potential in optical devices due to their multi-functional optical properties. • PC, PSL and TSL properties of Er 3+ /Sm 3+ co-doped Sr 2 SnO 4 ceramic were investigated. • PSL occurs when 980 nm stimulated, with three peaks located at 582 nm, 622 nm and 672 nm. • The method using PSL signal can avoid the influence of original signal. • Moderate Er 3+ concentration ( x ≤ 0.003) could enhance PC, PL and TSL performance. • A new method for optical information storage based on PSL signal and UC signal has been proposed.

The role of sulfur valency on thermoelectric properties of sulfur ion implanted copper iodide

Copper iodide (CuI) is a promising semiconductor with many potential applications in the fields of opto-electronics, solar cells, photodetectors and thermoelectric for energy harvesting. 30 keV 32S+ ions were implanted with fluences between 5.0 × 1014 and 1.1 × 1016 ions cm−2 which results in 0.3–5.5 at% peak sulfur concentration at an average depth of ~ 30 nm. Sulfur implantation increased electrical conductivity by up to 100 % (42.3 Ω−1 cm−1) for film implanted with the highest fluence (1.1 × 1016 ions cm−2), which was due to an increase in hole density of one order of magnitude. The thermoelectric power factor increased by over 300 % for low-fluence (≤1.0 × 1015 ions cm−2) implanted CuI films which is attributed to a simultaneous 22 % increase in electrical conductivity (25.9 Ω−1 cm−1) and a 95 % increase in the Seebeck coefficient (498.6 µVK−1), which overcomes the typical trade-off. XPS results showed that doped sulfur ions are in S2- states for low-concentration doped films, whereas for high-fluence (≥ 2.5 × 1015 ions cm−2) implanted films, a fraction of the sulfur ions are also present in an elemental state. Sulfur solubility impacts its valency which alters the defect chemistry and thermoelectric properties of the sulfur implanted CuI films. Sulfur doping by ion implantation is a promising strategy to improve the electrical conductivity and power factor in wide bandgap thermoelectric materials.

Studies of structure, dielectric and conduction mechanism of Bi3+/Yb3+ modified BaTiO3

The present communication aims at the study of the structural, dielectric, electrical and conduction properties of Bi3+/Yb3+ substituted BaTiO3 with a chemical composition of Ba0.5Bi0.5Yb0.5Ti0.5O3. The modified BaTiO3, could be synthesized by a solid state reaction technique. The X-ray diffraction data and pattern revealed the formation of the above compound with tetragonal crystal system. The material's molecular structure (Ba–Ti–O bond, O–Ti–O stretching-mode, metal-oxygen bond, optical band gap, and so on) was determined using room temperature Fourier transform infrared (FTIR) and UV–visible spectroscopic spectra. Detailed investigations of the material's electrical (dielectric/leakage current and impedance) behavior over a wide temperature (250C–5000C) and frequency (1 kHz–1000 kHz) range revealed the presence of capacitive, resistive, and conductive mechanisms. On the investigation of the polarization-electric field (P-E) hysteresis loop on multiple substitution, the change of ferroelectric polarization (spontaneous and residual) and storage density of BaTiO3 was observed. Defect chemistry of the modified barium compound has been discussed in the details.

Harnessing the Defects at Hetero‐Interface of Transition Metal Compounds for Advanced Charge Storage: A Review

The ability of transition metal compounds (TMCs; e.g., transition metal oxides, transition metal dichalcogenides) to achieve maximum energy and power density is undermined by their marginal electrical and ionic conductivity. There has been rapidly growing interest in a paradigm enabled by the construction of heterostructured TMCs over the past decades because it can increase the charge transport and storage capabilities of TMC‐based electrodes. The introduction of defects is a critical tool that allows the manipulation of heterostructures by altering the electronic structure and stress field. In this way, the electrochemical performance of the material can be optimized. Herein, recent progress in the development of heterostructured TMCs from the perspective of defects is comprehensively discussed. It is emphasized the mechanisms by which defects influence the electrochemical performance of heterostructures and effective strategies to incorporate the 0D to 2D defects (vacancies, elemental doping, lateral hetero‐interface, lattice mismatch, etc.) around the hetero‐interface, which is a focus that differs from previous reviews of heterostructured TMCs. Related problems and future directions in the defect chemistry of heterostructured TMCs are also discussed. This review highlights the significance of defects for guiding the rational design of TMC electrodes for use in advanced energy storage devices.

Effects of Li–B–Si–Ca–Mn glass addition on the densification, microstructure, and dielectric properties of (Ca,Sr)(Zr,Ti)O3 ceramics

Finding a suitable sintering aid to lower the sintering temperature of the dielectric material is important for making multilayer ceramic capacitors (MLCCs) with copper electrodes. In this study, Li–B–Si–Ca–Mn (LBSCM) glasses were prepared by melt quenching with the addition of an anti-reduction agent as a sintering aid for (Ca0.7Sr0.3)(Zr0.97Ti0.03)O3 dielectric ceramics (CSZT). Based on the defect chemistry and interaction between CSZT and LBSCM glass, the effects of the Li–B–Si glass addition on the sintering, microstructure, and dielectric properties of CSZT were investigated. It was found that the addition of 5 wt% LBSCM glass resulted in a dense microstructure after sintering at a temperature range of 975 °C–1100 °C in 99%N2–1%H2. The capacitance at 1 MHz between 140 and 150 pF, loss of about 0.19%, the breakdown voltage of about 1050 V, insulation resistance around 1011 Ω were obtained for the MLCCs with the size of 0805 using the CSZT added with 5 wt% LBSCM glass as the raw material and copper as the inner electrode sintered at 1000 °C for 1 h and 3 h under a reduction atmosphere of 1% H2/99% N2 mixture gas. This suggests that the CSZT added with 5 wt% LBSCM can be a good candidate as a dielectric material for MLCCs with copper electrodes.

Vacancy-Rich MoSSe with Sulfiphilicity-Lithiophilicity Dual Function for Kinetics-Enhanced and Dendrite-Free Li-S Batteries.

The sluggish redox kinetics of sulfur and the uncontrollable growth of lithium dendrites are two main challenges that impede the practical applications of lithium-sulfur (Li-S) batteries. In this study, a multifunctional host with vacancy-rich MoSSe vertically grown on reduced graphene oxide aerogels (MoSSe/rGO) is designed as the host material for both sulfur and lithium. The embedding of Se into a MoS2 lattice is introduced to improve the inherent conductivity and generate abundant anion vacancies to endow the 3D conductive graphene based aerogels with specific sulfiphilicity-lithiophilicity. As a result, the assembled Li-S batteries based on MoSSe/rGO exhibit greatly improved capacity and cycling stability and can be operated under a lean electrolyte (4.8 μL mg-1) and a high sulfur loading (6.5 mg cm-2), achieving a high energy density. This study presents a unique method to unlock the catalysis capability and improve the inherent lithiophilicity by heteroatom doping and defect chemistry for kinetics-enhanced and dendrite-free Li-S batteries.

Advances in Engineered Metal Oxide Thin Films by Low-Cost, Solution-Based Techniques for Green Hydrogen Production.

Functional oxide materials have become crucial in the continuous development of various fields, including those for energy applications. In this aspect, the synthesis of nanomaterials for low-cost green hydrogen production represents a huge challenge that needs to be overcome to move toward the next generation of efficient systems and devices. This perspective presents a critical assessment of hydrothermal and polymeric precursor methods as potential approaches to designing photoelectrodes for future industrial implementation. The main conditions that can affect the photoanode’s physical and chemical characteristics, such as morphology, particle size, defects chemistry, dimensionality, and crystal orientation, and how they influence the photoelectrochemical performance are highlighted in this report. Strategies to tune and engineer photoelectrode and an outlook for developing efficient solar-to-hydrogen conversion using an inexpensive and stable material will also be addressed.

On native point defects in ZnSe

Aiming at a fundamental understanding of the defect chemistry of pure ZnSe for optical and quantum applications, systematic density functional theory calculations with hybrid exchange-correlation functionals were performed to build an accurate database of native defects in ZnSe, including isolated defects and first nearest-neighbor defect–defect complexes. From the defect formation energies, zinc vacancy is found to be the most prevalent defect as the Fermi level approaches the conduction band edge, while zinc interstitial in the selenium tetrahedron and selenium vacancy become the most prevalent defects as the Fermi level approaches the valence band maximum. The divacancy complex, consisting of first nearest-neighboring zinc and selenium vacancies, is also found to have a favorable binding energy across the entire bandgap. Its formation energy is, however, always higher than either the isolated zinc or selenium vacancy, meaning it will never be the predominant defect in equilibrium. Finally, a point defect with extended spin coherence in Fluorine-implanted ZnSe was recently discovered, and it was found to exhibit a broad emission peak centered at 2.28 eV. The identity of this defect was determined to be either zinc vacancy or its associated complex according to the electron paramagnetic resonance measurements. Explicit simulations of the optical signatures of all zinc vacancy-related native defects were conducted here, showing that both zinc vacancy and divacancy are the most likely native defect contributors to that peak.

Characterization of cation disorder and oxygen vacancies in Li‐rich Li2TiO3

AbstractLi2TiO3 has a broad stoichiometric range and wide application prospects such as cathode, tritium breeder, and microwave dielectric materials. Particularly, Li2TiO3 shows a faster tritium release performance and exceptional chemical and radiation stabilities, making it one of the most promising solid breeder materials. Li‐rich Li2TiO3 has been developed for years as an advanced breeder material due to its enhanced tritium production and better stability in hydrogen atmosphere. However, the defect chemistry responsible for accommodating excess Li and how the non‐stoichiometry improves the material's performance is still unclear. In this work, the crystal structure and non‐stoichiometry‐induced defects in Li‐rich Li2TiO3 were investigated by means of X‐ray diffraction, electron spin resonance, and X‐ray photoelectron spectroscopy. Results show that oxygen vacancies and cation disorder both play a major role in the incorporation of excess Li. The sintering atmosphere (air/vacuum) has a negligible effect on the formation of the non‐stoichiometry‐induced defects but will influence the concentration of the oxygen vacancies. The better stability in the reduction atmosphere may be ascribed to the oxygen vacancies inside the Li‐rich Li2TiO3 crystals.

Iron and aluminum substitution mechanism in the perovskite phase in the system MgSiO3-FeAlO3-MgO

AbstractFe,Al-bearing MgSiO3 perovskite (bridgmanite) is considered to be the most abundant mineral in Earth’s lower mantle, hosting ferric iron in its structure as charge-coupled (Fe2O3 and FeAlO3) and vacancy components (MgFeO2.5 and Fe2/3SiO3). We examined concentrations of ferric iron and aluminum in the perovskite phase as a function of temperature (1700–2300 K) in the MgSiO3-FeAlO3-MgO system at 27 GPa using a multi-anvil high-pressure apparatus. We found a LiNbO3-structured phase in the quenched run product, which was the perovskite phase under high pressures and high temperatures. The perovskite phase coexists with corundum and a phase with (Mg,Fe3+,☐)(Al,Fe3+)2O4 composition (☐ = vacancy). The FeAlO3 component in the perovskite phase decreases from 69 to 65 mol% with increasing temperature. The Fe2O3 component in the perovskite phase remains unchanged at ~1 mol% with temperature. The A-site vacancy component of Fe2/3SiO3 in the perovskite phase exists as 1–2 mol% at 1700–2000 K, whereas 1 mol% of the oxygen vacancy component of MgFeO2.5 appears at higher temperatures, although the analytical errors prevent definite conclusions. The A-site vacancy component might be more important than the oxygen vacancy component for the defect chemistry of bridgmanite in slabs and for average mantle conditions when the FeAlO3 charge-coupled component is dominant.

Intrinsic defects and the influences on electrical transport properties in quaternary diamond-like compounds: Cd2Cu3In3Te8 as an example

Over the years, the fact that the quaternary diamond-like thermoelectric materials show much lower carrier mobilities than ternary compounds remains mysterious. In this work, by adopting first-principles defect chemistry and electrical transport calculations, the fundamental origin of the difference on carrier mobility between quaternary and ternary diamond-like compounds is addressed, exemplified by Cd2Cu3In3Te8. The results of defect chemistry show that the main intrinsic defects in quaternary compound Cd2Cu3In3Te8 are substitutional defects, i.e., CdIn and CdCu, differing from the copper vacancy defect in ternary Cu-based compound such as CuInTe2. The low defect formation energies in Cd2Cu3In3Te8 result in high defect concentrations, which is caused by the similar atomic radii and electronegativities between CdIn and CdCu. Further calculations show that the low-energy defects are mainly located around the valence band maximum in Cd2Cu3In3Te8. The electrical transport calculations, considering both the acoustic phonon scattering and ionized impurity scattering, demonstrate that mainly due to the higher concentration of the ionized defects, the mobility of the quaternary Cd2Cu3In3Te8 is much lower than that of ternary CuInTe2. Our work sheds light on the intrinsic defects in quaternary diamond-like compounds and their influence on charge transport.

Hydrated ammonium manganese phosphates by electrochemically induced manganese-defect as cathode material for aqueous zinc ion batteries

Aqueous zinc ion batteries (AZIBs) with the merits of low cost, low toxicity, high safety, environmental benignity as well as multi-valence properties as the large-scale energy storage devices demonstrate tremendous application prospect. However, the explorations for the most competitive manganese-based cathode materials of AZIBs have been mainly limited to some known manganese oxides. Herein, we report a new type of cathode material NH4MnPO4·H2O (abbreviated as AMPH) for rechargeable AZIBs synthesized through a simple hydrothermal method. An in-situ electrochemical strategy inducing Mn-defect has been used to unlock the electrochemical activity of AMPH through the initial charge process, which can convert poor electrochemical characteristic of AMPH towards Zn2+ and NH4+ into great electrochemically active cathode for AZIBs. It still delivers a reversible discharge capacity up to 90.0 mAh/g at 0.5 A/g even after 1000th cycles, which indicates a considerable capacity and an impressive cycle stability. Furthermore, this cathode reveals an (de)insertion mechanism of Zn2+ and NH4+ without structural collapse during the charge/discharge process. The work not only supplements a new member for the family of manganese-based compound for AZIBs, but also provides a potential direction for developing novel cathode material for AZIBs by introducing defect chemistry.

Engineering oxygen vacancy of MoOx nanoenzyme by Mn doping for dual-route cascaded catalysis mediated high tumor eradication

There is an urgent need to develop photosensitive nanoenzymes with better phototherapeutic efficiency through simple processes. By exploiting semiconductor catalysis and defect chemistry principles, herein, a MnMoOx composite semiconductor nanoenzyme was developed to achieve a fully integrated theranostic nanoenzyme for highly efficient photo/chemo-enzyme-dynamic eradication of deep tumors. Relative to iron oxides, manganese oxides offer ideal catalytic performance under near-neutral conditions, which helps to broaden the suitable pH range of the MnMoOx nanoenzyme for antitumor therapy. Furthermore, with the assistance of glutathione depletion, Mn4+/Mo6+ was successfully converted to Mn2+/Mo5+, inhibiting the scavenging of reactive oxygen species (ROS) and promoting cycling. Therefore, MnMoOx has favorable catalase (CAT)-like activity and oxidase (OXD)-like activity in the tumor microenvironment (TME) for promoting the “H2O2O2O2−” and “H2O2OH” cascade reactions. The abundant oxygen vacancy defects also promote the surface plasmon resonance (SPR) effect in the second near-infrared (NIR-II) window of MnMoOx, which significantly enhanced its photothermal therapy (PTT) effect and catalytic activity. In detail, ROS production was significantly enhanced due to the adsorption of water and oxygen molecules by the rich oxygen vacancies of MnMoOx. MnMoOx also exhibited excellent multi-modal imaging activity (including computed tomography (CT), magnetic resonance imaging (MRI), and photoacoustic (PA)), which can be exploited to better guide the administration of medication.