Non-stoichiometric Composition Research Articles

Spatial variation of the elemental components of thin films from BiSrCaCuO target deposited using low energy femtosecond pulsed laser deposition in high background gas pressure

In this work, we investigated the spatial variation of the elemental composition of the thin films produced by low-energy femtosecond pulsed laser deposition with BiSrCaCuO (BSCCO) as the target material. In addition, the effect of high background gas pressure and gas type on the thin film elemental composition was also investigated. The background gas pressure was varied between 4, 50, and 100 mTorr, using nitrogen (N2) and argon (Ar) as the gases. MgO substrates were positioned at the center and at different distances from the center to analyze the spatial variation of the deposited film. Despite the low energy from the fs laser pulse and the high background gas pressure, the constitutive elements of BSCCO, namely, bismuth (Bi), strontium (Sr), calcium (Ca), and copper (Cu), were detected on the substrate. However, their relative ratios were not preserved in the thin film. To explain the results, a collision-based model and peak-fitting method of the angular distribution were employed. The study highlights the importance of proper substrate positioning and how background gas type and pressure influence material deposition, with N2 resulting in lower deposition due to enhanced energy transfer during ablation processes. The non-stoichiometric composition of the films and their spatial variation emphasize the limitations of current deposition models, pointing to the need for refined approaches that better predict film quality and elemental distribution.

Non-Stoichiometric Amorphous Calcium Carbonate Forms in Macromolecular Condensates via Interphase Diffusion.

Transient amorphous phases are known as functional precursors in the formation of crystalline materials, both in vivo and in vitro. A common route to regulate amorphous calcium carbonate (ACC) crystallization is via direct interactions with negatively charged macromolecules. However, a less explored phenomenon that can influence such systems is the electrostatically driven formation of Ca-macromolecule dense phases. In this study, it is shown how Ca-macromolecule condensates that form via liquid-liquid phase separation (LLPS) can be used to control the formation of metastable ACC via diffusion-based mass transport. Contrary to the solid-like ACC particles that form in the dilute phase via rapid nucleation and growth, the condensate ACC gradually forms via carbonate diffusion into the dense droplets. This yields transient phases with non-stoichiometric compositions, similar to a solid solution. It is shown that the ability to control the concentration gradients across the phase boundary can be used to finely regulate the composition and stability of these amorphous precursors, offering new routes to control mineralization through transient phases.

Получение кермета в режиме горения инфильтрацией расплава Cu + Ti в пористый карбид титана

Results for the interaction of a hot porous titanium carbide frame obtained in the mode of self-propagating high-temperature synthesis with a copper-titanium melt, are presented. The studies were carried out using two types of samples: without and with preheating up to 300 ºC before synthesis in a furnace. The samples were flat compressed tabs of stock material consisting of two layers with different composition. The lower layer was Ti and C stock, and the upper layer was a mixture of Ti and Cu. The process of sample synthesis was carried out in air. After the reaction took place in the lower layer of the samples and the formation of a porous titanium carbide frame, in both samples the upper layer melted and was absorbed into the lower layer unreservedly. X-ray phase analysis of the central part of the sample showed the presence of three phases – Ti, Cu and Cu3Ti. It was found that the resulting composite was a porous TiC frame impregnated with an alloy of copper and titanium. Titanium carbide grains had a largely non-stoichiometric composition and were polyhedral particles of an average size of 20 microns, as well as particles of stoichiometric composition with a size of no more than 10 microns. An intermetallic compound was found in some areas on the surface of TiC particles in the form of a thin film. In addition, it was found that preheating the initial sample in a furnace to 300 ºC before synthesis increases the content of stoichiometric titanium carbide in the obtained cermet.

The Khangalas orogenic Au deposit, Yana-Kolyma metallogenic belt (Northeast Russia): structure, ore mineral and isotopic (O, S, Re, Os, Pb, Ar, He) composition, fluid regime and formation conditions

The Khangalas orogenic gold deposit is located in the central part of the Yana-Kolyma metallogenic belt. The structure of the deposit is determined by several mineralized crush zones with a thickness of up to 70 m and a length of up to 1400 m in the arch and on the southwest wing of the anticline of the northwest strike. Host rocks – Upper Permian terrigenous deposits. Ore bodies are characterized by massive, banded, veined, disseminated and breccia structures. The main vein minerals are quartz, carbonates, sericite is less common. The main ore minerals are pyrite, arsenopyrite; minor – galena, sphalerite, chalcopyrite, native Au; rare – Fe-gersdorffite, tetrahedrite, argentotennantite. Hypergenic minerals – sulfates, phosphates, arsenates and hydroxides – are widely manifested in the linear oxidation zone. Mineral formation occurred in two stages – gold-sulfide-quartz and silver-quartz ones. Quartz veins with visible Au were formed with the involvement of low-concentrated (about 5.0 wt.% eq. NaCl) of hydrocarbonate hydrotherms with CO2 in the gas component, at a temperature of 330–280 °C and a pressure of about 0.8 kbar. Disseminated gold-bearing pyrite-3 (up to 39.3 g/t Au) and arsenopyrite-1 (up to 23.8 g/t Au) from sericite-carbonate-quartz metasomatites have a non-stoichiometric composition, Fe excess and S lack (and As in Ару), Fe/(S+As)=0.47–0.52 (Py3) and 0.47–0.50 (Ару1). The predominant form of “invisible” gold in Py3 and Apy1 is structurally related Au+. Isotopic composition of oxygen δ18O quartz (from +15.2 to +16.1‰), oxygen in the fluid δ18OH2O (from +8.4 tо +9.2‰)‰), sulfur δ34S in sulfides (from –2.1 to –0.6‰); isotopic ratio 187Os/188Os (from 0.2212 to 0.2338) in native gold and Pb in galena (206Pb/204Pb=18.0214, 207Pb/204Pb=15.5356, 208Pb/204Pb=38.2216), as well as the geochemical features of Py3 and Apy1 suggest the participation in ore formation mainly of sources from the subcontinental lithospheric mantle and, to a lesser extent, crustal reservoirs. The formation of the gold ore bodies of the deposit is related to the completion of reverse and thrust fault progressive deformation of the stage D1, which occurred in the Valanginian of the Early Cretaceous (about 137 million years ago) during late-orogenic processes in the Yana-Kolyma belt with regional south-western transport of rocks. The results obtained are important for predictive metallogenic and prospecting work aimed at identifying large-volume gold mineralization of orogenic belts.

Single Crystalline, Non-Stoichiometric Hydrogen-Bonded Organic Frameworks Showing Versatile Fluorescence Depending on Composition Ratios and Distributions.

Hydrogen-bonded organic frameworks (HOFs) composed of multicomponent molecules in a non-stoichiometric composition have drawn great interest due to their tunable properties. However, the photobehavior of the single crystals of such mixed HOFs has not been explored. Here, we report on the synthesis, characterization and photobehavior of single crystalline non-stoichiometric HOFs (NS-HOFs). NS-HOFs (BTNT-1) with various composition ratios were successfully obtained as single crystals from two analogue tetratopic carboxylic acids, possessing naphthalene and benzothiadiazole cores (NTTA and BTTA, respectively). The heterogeneous distribution of the components was thoroughly confirmed by time-resolved fluorescence microscopy and local crystallographic analysis using focused synchrotron X-ray radiation. The versatile fluorescence of BTNT-1 behavior depends on the composition ratio and distribution of the component in the single crystals. We observed not only fluorescence bands with various colors such as purple, blue, green and white, depending on the composition ratios, but also different emission bands from a single crystal. We provide details on their emission lifetimes following the composition, emission color and targeted region on the crystal. This work is the first example of single crystal studies applied to organic porous co-crystals and demonstrates unique and versatile optical properties of carboxylic acid-based NS-HOFs. The results provide a concept of creating functional mixed porous materials capable of different and tunable optical properties.

Oxidative Dissolution Behavior of Synthetic Chalcopyrite with Non-Stoichiometric Compositions

Chalcopyrite (CuFeS2) is the most important Cu mineral, accounting for 70% of copper reserves in the world. Cu metal is primarily produced from chalcopyrite-containing ores by an extraction process involving flotation, pyrometallurgy, and electrorefining. Owing to the ongoing depletion of high-grade ores, hydrometallurgical processes involving copper leaching from chalcopyrite-containing ores using acidic ferric sulfate solutions have been intensively studied. However, efficient copper leaching remains a challenge, and the details of the dissolution mechanism of chalcopyrite in natural resources remain unclear.Investigation using synthetic minerals with controlled compositions and morphologies is an effective approach for understanding the dissolution mechanism. In this study, we prepared dense pellets of synthetic chalcopyrite with stoichiometric and non-stoichiometric compositions and compared their oxidative dissolution behaviors in an acidic ferric sulfate solution.The nominal compositions of the prepared samples are Cu0.250Fe0.250S0.500 (stoichiometric composition), Cu0.240Fe0.260S0.500, Cu0.245Fe0.260S0.495, and Cu0.265Fe0.245S0.490. The powder samples were synthesized via a high-temperature reaction using Cu wire, Fe wire, and S powder as raw materials. The dense pellets (diameter 10 mm and thickness of approximately 3 mm) were obtained by pulse current pressure sintering and subsequent annealing at 500 ℃. Density measurements and scanning electron microscopy observations revealed that the morphologies such as grain size and density of the obtained pellets were almost constant, regardless of the nominal composition. In X-ray diffraction analyses, the diffraction peaks of the obtained pellets were consistent with the chalcopyrite phase (CuFeS2, PDF #00-037-0471). The scanning electron microscopy with energy dispersive spectrometry analysis confirmed that no other phase was detected in the Cu0.250Fe0.250S0.500, Cu0.240Fe0.260S0.500, and Cu0.265Fe0.245S0.490 pellets.To enable electrochemical measurements, dense pellets were cut and embedded in resin after connecting the copper leads. Obtained electrode samples were immersed in 0.1 M Fe(SO4)1.5 – 10−4 M FeSO4 – 0.18 M H2SO4 at 70 ℃ for 24 h. The concentration of Cu ions in the solution was determined by inductivity coupled plasma atomic emission spectrometry and the dissolution rates of the samples were evaluated. The corrosion potentials of the synthesized chalcopyrite samples were also measured. shows the measured dissolution rates and corrosion potentials. The Cu dissolution rates for the chalcopyrite samples with non-stoichiometric compositions (Cu0.240Fe0.260S0.500, Cu0.245Fe0.260S0.495, and Cu0.265Fe0.245S0.490) were over one order of magnitude than those for the samples with stoichiometric composition (Cu0.250Fe0.250S0.500). This result demonstrates that a small difference in composition significantly affects the dissolution rate in the ferric sulfate solution. The corrosion potentials of the electrodes with non-stoichiometric compositions were less noble than those of the stoichiometric composition sample. At the corrosion potential, the rate of anodic dissolution of the chalcopyrite phase was equal to that of the cathodic reaction of the oxidant in the solution (mainly the reduction rate of the Fe(III) species). Considering the shift in the corrosion potential, increasing the dissolution rate is attributed to the enhancement of the anodic dissolution reaction of the chalcopyrite phase by the change in its composition from stoichiometry. Figure 1

Operando Raman Microscopy Studies on Next Generation Positive Electrode and Electrolyte Materials

The growing demand for high-performance Li-ion cells nowadays has encouraged researchers to deeply understand the evolution of the various battery’s components over time. Ageing mechanisms have a great impact on the battery life performance; therefore, a better understanding of these complex processes may allow the prolongation of their useful cycle life. Monitoring the cathode material during battery operation is crucial since it represents the performance-limiting component in most of the LIBs [1]. Particularly, cobalt free lithium transition metal oxides are currently gaining interest as active materials for enabling higher energy density cells. Among them, LiNiO2 presents relatively high capacity and long durability. However, this material suffers from capacity loss and thermal instability at highly de-intercalated states due to its non-stoichiometric composition [2]. The mechanisms involved in the capacity fade remain still unclear making it crucial to understand these processes throughout cycling.Among the methods available to perform operando measurements for Li-ion electrodes, Raman spectroscopy is well stablished to track structural evolution and chemical composition during charge and discharge [3,4]. With this work, an optimised electrode configuration [5] is presented which enables the monitoring of the different electrode phase transitions over several cycles. The developed methodology is applied for the investigation of LiNiO2 active material as a benchmark to understand the evolution of lithium metal oxides among time. The spectra collection obtained was rapidly analysed via the analysis tool PRISMA [6]. Overall, the ability of operando Raman as a pertinent diagnostic tool to follow electrodes behaviour during commercially relevant cycling conditions is demonstrated.[1] Matteo Bianchini et al. Angew. Chem. Int. Ed. (2019), 10434-10458, 58 (31).[2] Edgar Bautista Quisbert et al. Small. (2023) 2300616 19 (30).[3] Hui et al. J. Am. Chem. Soc.(2022) 9434-9442, 144 (21).[4] Sole et al. Faraday discussions (2016) 223-231, 72.[5] Timothy E. Rosser et al, J. Electrochem. Soc. (2021), 070541 (168).[6] Flores E et al. Chemistry-methods (2022) 2 (10).

Non-Stoichiometric Effects on Viscoelasticity in DGEBA-EDA Systems: Insights from Brillouin Light Scattering.

The initial and final stages of the isothermal curing reaction between diglycidyl ether of bisphenol A and ethylenediamine were investigated by using Brillouin light scattering spectroscopy. High-frequency acoustic parameters were measured for these stages as a function of the diamine molar fraction, ranging from the pure prepolymer to the pure cross-linker. Significant differences in the concentration dependencies of the mechanical parameters are interpreted in relation to changes in the system's viscoelastic properties. At the final stage of the reaction, the concentration dependencies exhibit notable changes at two characteristic nonstoichiometric compositions─one corresponding to amine excess and the other to epoxy excess. While these concentrations align well with Flory's critical gel points, experimental evidence suggests they should instead be interpreted as vitrification points.

Fine structural analysis of calcium–niobium–gallium garnet (CNGG) by single-crystal anomalous X-ray scattering

Fine structural analysis of calcium–niobium–gallium garnet (CNGG) by single-crystal anomalous X-ray scattering

The ore mineralization of the gold-bearing Murunsky node located within the Aldan Shield

Mineralogical and geochemical investigations of the underexplored gold ore deposits within the Murunsky node, specifically the Seredinskoye and Andreevskoye ore fields, were conducted utilizing mineralogical and microprobe analytical techniques. The study identified several minerals, including bismuth minerals such as wittichenite and aikinite; cadmium mineral greenockite; cobalt minerals cobaltite and carrollite; arsenic minerals arsenosulvanite and tennantite; antimony minerals antimonite and tetrahedrite; tellurium minerals hessite and Te-canfieldite; mercury mineral cinnabar; thallium minerals raguinite and copper-rich talcusite; and tin minerals kesterite and jeanbandyite. Additionally, potassium sulfide djerfisherite with an unusual silver admixture was discovered. The findings underscore the remarkable and largely untapped potential of the Murunsky massif, particularly concerning its ore mineralization. A notable characteristic of the identified minerals is their non-stoichiometric composition, which includes the presence of impurities and isomorphic substitution of elements, attributed to the disequilibrium conditions under which they formed. The discoveries of raguinite and jeanbandyite represent the first occurrences of these minerals in Russia.

Study of the Processes of Non-Stoichiometric Compositions Based on CsSiB3O7

Study of the Processes of Non-Stoichiometric Compositions Based on CsSiB3O7

Development of pyrargyrite Ag3SbS3 absorber films through sulfurization of Ag–Sb stacks for thin-film photovoltaics

Development of pyrargyrite Ag3SbS3 absorber films through sulfurization of Ag–Sb stacks for thin-film photovoltaics

Electrochemical properties of B-site non-stoichiometric layered perovskite SmBa0.5Sr0.5CoxO5+d (x=1.9–2.1) cathodes for IT-SOFC

Electrochemical properties of B-site non-stoichiometric layered perovskite SmBa0.5Sr0.5CoxO5+d (x=1.9–2.1) cathodes for IT-SOFC

Signatures of nearly compensated magnetism and spin glass behavior in highly frustrated β-Mn-type Mn50Fe25+xAl25-x Heusler alloys.

The present study examines the effect of Fe/Al concentration on the structural and magnetic properties of Mn-rich Mn50Fe25+xAl25-x (x = 5, 10, 15) Heusler alloys through x-ray diffraction, temperature- and field-dependent DC magnetization, thermoremanent magnetization, magnetic memory effect, AC susceptibility measurements, and DFT calculations. The samples crystallize in a cubic β-Mn structure. The trend shows a reduction in lattice parameters (unit cell volume) with the increasing Fe proportion. These alloys exhibit strong antiferromagnetic interactions with large frustration parameters, indicating the presence of competing magnetic interactions. The DC magnetization data reveal spin glass-like features with a peak at spin glass freezing temperature (Tf). The observation of bifurcation in temperature-dependent zero-field-cooled and field-cooled magnetization curves, exponential dependence of the temperature variation of remanence and coercivity, magnetic relaxation, and magnetic memory effect below Tf support the spin-glass character of these alloys. The frequency dependence of Tf is also examined in the context of dynamic scaling laws, such as the Vogel-Fulcher law and critical slowing down model, which further supports the presence of spin glass behavior. In the theoretical DFT calculations, the electronic structure is found to be metallic and similar for both spin projections. Moreover, the antiferromagnetic arrangement of the magnetic moments, in line with the experimental observations, is stabilized by exchange interactions, resulting in an almost compensated total magnetic moment of 0.02-0.38µB/f.u. This is probably caused by the frustrated structure and non-stoichiometric compositions of Mn50Fe25+xAl25-x.

Unlocking the potential of Cu3SbSe3: Ultralow thermal conductivity and enhanced thermoelectric performance

Unlocking the potential of Cu3SbSe3: Ultralow thermal conductivity and enhanced thermoelectric performance

A review on ultra‐small undoped MoS2 as advanced catalysts for renewable fuel production

AbstractMolybdenum disulfide (MoS2) has garnered significant attention in the field of catalysis due to the high density of active sites in its unique two‐dimensional (2D) structure, which could be developed into numerous high‐performance catalysts. The synthesis of ultra‐small MoS2 particles (<10 nm) is highly desired in various experimental studies. The ultra‐small structure could often lead to a distinct S–Mo coordination state and nonstoichiometric composition in MoSx, minimizing in‐plane active sites of the 2D structure and making it probable to regulate the atomic and electronic structure of its intrinsic active sites on a large extent, especially in MoSx clusters. This article summarizes the recent progress of catalysis over ultra‐small undoped MoS2 particles for renewable fuel production. Through a systematic review of their synthesis, structural, and spectral characteristics, as well as the relationship between their catalytic performance and inherent defects, we aim to provide insights into catalysis over this matrix that may potentially enable advancement in the development of high‐performance MoS2‐based catalysts for sustainable energy generation in the future.

SurfFlow: High-throughput surface energy calculations for arbitrary crystals

SurfFlow: High-throughput surface energy calculations for arbitrary crystals

Pd-Bi-Based Catalysts for Selective Oxidation of Glucose into Gluconic Acid: The Role of Local Environment of Nanoparticles in Dependence of Their Composition

Palladium–bismuth nanomaterials are used in various chemical applications such detectors, electrodes, and catalysts. Pd-Bi catalysts are attracting widespread interest because these catalysts enable the production of valuable products quickly and efficiently, and are environmentally friendly. However, the composition of the catalyst can have a significant impact on its catalytic performance. In this work, we identified a correlation between the composition of the catalyst and its efficiency in converting glucose into sodium gluconate. It was found that the conversion decreases with increasing bismuth content. The most active catalyst was the 0.35Bi:Pd sample with a lower bismuth content (glucose conversion of 57%). TEM, SEM, EXAFS, and XANES methods were used to describe, in detail, the surface properties of the xBi:Pd/Al2O3 catalyst samples. The increase in particle size with increasing bismuth content, observed in the TEM micrographs, was associated with the low melting point of bismuth (271 °C). The SEM method showed that palladium and bismuth particles were uniformly distributed over the surface of the support in close proximity to each other, which allowed us to conclude that an alloy of non-stoichiometric composition was formed. The EXAFS and XANES methods established that bismuth was located on the surface of the nanoparticle predominantly in an oxidized state.

Large Electromechanical Response in a Polycrystalline Alkali-Deficient (K,Na)NbO3 Thin Film on Silicon.

The demand for large electromechanical performance in lead-free polycrystalline piezoelectric thin films is driven by the need for compact, high-performance microelectromechanical systems (MEMS) based devices operating at low voltages. Here we significantly enhance the electromechanical response in a polycrystalline lead-free oxide thin film by utilizing lattice-defect-induced structural inhomogeneities. Unlike prior observations in mismatched epitaxial films with limited low-frequency enhancements, we achieve large electromechanical strain in a polycrystalline (K,Na)NbO3 film integrated on silicon. This is achieved by inducing self-assembled Nb-rich planar faults with a nonstoichiometric composition. The film exhibits an effective piezoelectric coefficient of 565 pm V-1 at 1 kHz, surpassing those of lead-based counterparts. Notably, lattice defect growth is substrate-independent, and the large electromechanical response is extended to even higher frequencies in a polycrystalline film. Improved properties arise from unique lattice defect morphology and frequency-dependent relaxation behavior, offering a new route to remarkable electromechanical response in polycrystalline thin films.

Unraveling the Effect of Compositional Ratios on the Kesterite Thin-Film Solar Cells Using Machine Learning Techniques

In the Kesterite family, the Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells (TFSCs) have demonstrated the highest device efficiency with non-stoichiometric cation composition ratios. These composition ratios have a strong influence on the structural, optical, and electrical properties of the CZTSSe absorber layer. So, in this work, a machine learning (ML) approach is employed to evaluate effect composition ratio on the device parameters of CZTSSe TFSCs. In particular, the bi-metallic ratios like Cu/Sn, Zn/Sn, Cu/Zn, and overall Cu/(Zn+Sn) cation composition ratio are investigated. To achieve this, different machine learning algorithms, such as decision trees (DTs) and classification and regression trees (CARTs), are used. In addition, the output performance parameters of CZTSSe TFSCs are predicted by both continuous and categorical approaches. Artificial neural networks (ANN) and XGBoost (XGB) algorithms are employed for the continuous approach. On the other hand, support vector machine and k-nearest neighbor’s algorithms are also used for the categorical approach. Through the analysis, it is observed that the DT and CART algorithms provided a critical composition range well suited for the fabrication of highly efficient CZTSSe TFSCs, while the XGB and ANN showed better prediction accuracy among the tested algorithms. The present work offers valuable guidance towards the integration of the ML approach with experimental studies in the field of TFSCs.