General Chemical Formula Research Articles

Hybrid electrocatalyst of CoFe2O4 decorating carbon spheres for alkaline oxygen evolution reaction

The exploration of highly effective, durable, and affordable electrocatalysts for the oxygen evolution reaction (OER) is vital in developing an alkaline electrolyzer for H 2 generation. Although binary transition metal oxides, particularly spinel ferrites with a general chemical formula MFe 2 O 4, are a promising class of candidates for OER, their intrinsically low electrical conductivity has a significant negative impact on their electrochemical performances. Herein, we report a simple one-step method for tailoring carbon spheres (CSs) with CoFe 2 O 4 (CFO) to form a CFO@CSs composite as a cost-effective electrocatalyst. The as-synthesized CFO@CSs features a high specific surface area of 56.94 m 2 /g and exhibits decently high OER catalytic activity with a relatively small overpotential of 390 mV at 10 mA/cm 2 , fast kinetics, and high durability in alkaline medium. Moreover, the pairing of the bare Ni mesh electrode as the cathode and the CFO@CSs on Ni mesh as the anode is set up to illustrate its feasibility for the overall alkaline water splitting. This study offers a cost-effective electrocatalyst for OER that can be used instead of precious metals in various renewable energy storage and conversion applications. CoFe 2 O 4 @carbon spheres nanohybrid (CFO@CSs) electrocatalyst was successfully prepared with a facile one-step solvothermal method, which shows excellent electrocatalytic OER performance with low overpotentials of 390 mV at 10 mA cm −2 OER. The assembled system CFO@CSs/NM||bare NM also shows good catalytic performance and excellent stability of the overall water splitting in alkaline media.

Structural and magnetic properties of DyCrTiO5 nanoparticles

The compounds with the general chemical formula RCrTiO5 (R = rare-earth ions) has an orthorhombic crystal structure having Pbam space group. However, there are limited work carried out on this group of materials, primarily in bulk to explore their structural and magnetic properties. The exploration of structural and magnetic properties of RCrTiO5 compounds in the nano dimension has not been reported to date. This report focuses on the synthesis of DyCrTiO5 nanoparticles using a simple, time saving and cost-effective sol–gel technique to investigate the role of size on structural as well as magnetic properties. The synthesized sample is calcined at 800 °C for three hours. The crystal structure is confirmed from the Le-Bail profile fitting of the x-ray diffraction (XRD) pattern. The DyCrTiO5 nanoparticles are crystallized in an orthorhombic structure with lattice parameters, a, b, c of 7.321 ± 0.001, 8.644 ± 0.002 and 5.840 ± 0.001 Å, respectively. The average particle size is found to be 53 ± 3 nm from transmission electron microscopy (TEM). From the temperature-dependent magnetization measurement, the obtained Néel temperature (TN) is 147 ± 2 K. In contrast to the bulk form, DyCrTiO5 nanoparticles do not show spin reorientation (SR) which is observed below 37 K or the magnetic compensation because of the dominating contribution of Dy3+ moment. In addition, the irreversibility in magnetization is suppressed when measured as a function of temperature in the heating and cooling cycle of the measurement with increasing the probing magnetic field. This indicates a feature similar to kinetic arrest. In isothermal magnetization measurements, exchange bias effect is observed because of interaction between the uncompensated spins on the surface of the nanoparticles.

Microwave-assisted synthesis of lanthanide coordination polymers with 2-bromobenzoic acid as ligand from hexa-lanthanide molecular precursors

Microwave-assisted reactions, between 2-bromobenzoic acid (2-bbH) and hexa-lanthanide molecular precursors of general chemical formula Ln6(µ6-O)(µ3-OH)8(NO3)6(H2O)12·2NO3·2H2O [Ln6], lead to iso-structural 1D coordination polymers of general chemical formula [Ln(2-bb)3]∞ with Ln = Eu, Tb or Dy. These compounds crystallize in the monoclinic system, space group P21/c (n°14), with the following cell parameters (for the Dy-derivative): a = 12.3809(10) Å, b = 21.8653(16) Å, c = 7.9119(7) Å, β = 98.709(3)°, V = 2117.2(3) Å3 and Z = 4. The influence of the hexa-nuclear precursors over the final coordination polymer is demonstrated. Indeed, while the hexa-nuclear complexes collapse during the synthetic process their progressive destruction affords a unique 1D coordination polymer that cannot be readily obtained otherwise. Additionally, some iso-structural hetero-lanthanide derivatives with general chemical formulas [EuxTb1-x(2-bb)3]∞ and [YxTb1-x(2-bb)3]∞ with 0 ≤ x ≤ 1 have been prepared from the corresponding hexa-nuclear complexes [Eu6xTb6-6x] and [Y6xTb6-6x], respectively. Luminescent properties have been recorded and colorimetric coordinates have been calculated for all the compounds. These measurements indicate that the molecular chains host strong intermetallic energy transfers.

High-entropy structure design in layered transition metal dichalcogenides

Layered high-entropy compounds have been attracting a lot of attention in recent times due to their potential applications in energy storage and conversion. Generally, an intra-layer scheme is widely used to realize the high-entropy structure by introducing multi-principal elements into the metal-atom layers. Here, we propose an intercalation high-entropy scheme to realize the high-entropy structure in a series of layered transition metal dichalcogenides with a general chemical formula of MX2. Multi-principal metal elements are intercalated into the van-der-Waals gaps between MX2 slabs resulting in a series of (HEM)xMX2 compounds, in which HEM is high-entropy metals mainly composed of 3d transition metal elements such as Fe0.2Co0.2Cr0.2Ni0.2Mn0.2. Moreover, three kinds of 2D high-entropy magnetic lattices (a0×a0, 3a0×a0, 3a0×3a0) in the intercalated layers are found by tuning the intercalant content x. Significant differences in the effective moment and spin frustration among them are revealed. Furthermore, a multi-layered high-entropy structure is realized by a combination of intra-layer and intercalation schemes. The new intercalation high-entropy scheme and versatile 2D high-entropy structures reported in this work will reinforce the spirit on the exploration of new low-dimensional high-entropy systems for future applications.

Hexanuclear Molecular Precursors as Tools to Design Luminescent Coordination Polymers with Lanthanide Segregation.

Solvothermal reactions between hexanuclear complexes with the general chemical formula [Ln6(μ6-O)(μ3-OH)8(NO3)6(H2O)12]·2NO3·2H2O and 2-bromobenzoic acid (2-bbH) lead to a series of isostructural one-dimensional coordination polymers with the general chemical formula [Ln2(2-bb)6]∞ with Ln = Sm, Eu, Tb, Dy, and Y. These coordination polymers crystallize in the orthorhombic space group Fdd2 (No. 43) with the following cell parameters: a = 29.810(3) Å, b = 51.185(6) Å, c = 11.7913(14) Å, V = 17992(4) Å3, and Z = 16. The europium- and terbium-based derivatives show sizable luminescence intensities under UV excitation. Isostructural heterolanthanide coordination polymers have also been prepared. Their luminescent properties suggest that during the synthetic process the starting hexanuclear complexes are destroyed but strongly influence the distribution of the different lanthanide ions over the metallic sites of the crystal structure. Indeed, it is possible to prepare heterolanthanide coordination polymers in which lanthanide-ion segregation is controlled.

An in-depth multi-technique characterization of rare earth carbonates – RE2(CO3)3·2H2O – owning tengerite-type structure

The present study has been conducted to contribute, once and for all, filling the lack of structural information for the whole class of rare earth (RE) carbonates owning the tengerite-(Y) structure. A complete structural characterization, carried out by Rietveld refinement of X-ray powder diffraction (XRD) data, was comparatively performed for the first time on several hydrated RE carbonates, having the general chemical formula RE2(CO3)3·xH2O, RE = Y, Gd, Tb, Dy, Ho and Er. All samples share the same space group and lattice parameters similar to tengerite-(Y); the structures are also closely related, consisting in all cases of a three-dimensional framework of nine-fold coordinated RE atom polyhedral, linked together by carbonate ions. In addition to relatively minor changes in fractional coordinates of atom sites and corresponding interatomic distances, the only perceivable difference lies in the lattice parameters affected by the ionic radius of RE3+. However, in the case of Er, which has the lowest cationic radius among the analyzed RE, the stabilization of tengerite structure is at its limit condition, because the carbonate groups are heavily distorted. Furthermore, FT-IR and Raman spectra confirm the main structural features obtained by Rietveld refinements. The observed morphology of the various samples is almost the same, being characterized by the presence of bidimensional rod-like particles grouped in agglomerates, typical of tengerite crystals, thus indicating that the crystallization mechanism occurring during the hydrothermal synthesis is the same, irrespective of the involved RE cation.

Recent advances in carbon nitride-based nanomaterials for hydrogen production and storage

There are different types of materials comprising of carbon and nitrogen elements. Typical materials are the cyanogen family, beta carbon nitride, graphitic carbon nitride, azafullerenes, and heterofullerenes, N-containing heterocycles. Except cyanogen (C2N2) is a gas, most others are solid. Among these solids, the graphitic carbon nitride, with the general chemical formula of C3N4, is widely studied in heterogeneous catalysis and energy storage. Such applications exploit the resiliency of the material in different environments due to its labile protons and Lewis acid functionalities, as well as its layered structure. The structure of graphitic C3N4 allows it to store a significant amount of hydrogen. Furthermore, it offers the space for dopants, which are used purposely for tuning the band gap and the electronic properties of C3N4 to make it suitable for water splitting using sun light, or many other applications in waste water treatment under radiation. We think that the material is important and it is not being exploited at its highest capability, especially in hydrogen production via water splitting technique. This review aims to summarize recent outcomes using the carbon nitride material in hydrogen production, and a brief about hydrogen storage. We also highlight future research directions which might worth being persuaded.

Dopants for Enhanced Performance of Tin-Based Perovskite Solar Cells—A Short Review

Lead-based perovskite solar cells had reached a bottleneck and demonstrated significant power conversion efficiency (PCE) growth matching the performance of traditional polycrystalline silicon solar cells. Lead-containing perovskite solar cell technology is on the verge of commercialization and has huge potential to replace silicon solar cells, but despite the very promising future of these perovskite solar cells, the presence of water-soluble toxic lead content is a growing concern in the scientific community and a major bottleneck for their commercialization. The less toxic, tin-based perovskite solar cells are promising alternatives for lead-free perovskite solar cells. Like lead-based perovskite, the general chemical formula composition of tin-based perovskite is ASnX3, where A is a cation and X is an anion (halogen). It is evident that tin-based perovskites, being less-toxic with excellent photoelectric properties, show respectable performance. Recently, numerous studies reported on the fabrication of Sn-based perovskite solar cells. However, the stability of this novel lead-free alternative material remains a big concern. One of the many ways to stabilize these solar cells includes addition of dopants. In this context, this article summarizes the most important fabrication routes employing dopants that have shown excellent stability for tin-based perovskite photovoltaics and elaborates the prospects of lead-free, tin based stable perovskite photovoltaics.

Complex Processing of Saponite Waste from a Diamond-Mining Enterprise

The solution of the sludge utilization problem and yield increase at processing plants have great importance today all over the world. Disasters associated with the tailings dams failures have madeus develop technologies of tailings sludge utilization as a commercial product, reducing the environmental damage on the regions of mineral extraction. This research aimed to provide new data, methods and an analytical approach to solve the saponite sludge accumulation problem on mining enterprises with silicate coagulant to increase the rate of cycle water clarification for the enrichment process and the recycling of sludge to reduce its hazardous effect. Samples were taken in the deposit located in the north of the European part of Russia, where diamond bearing ore contain montmorillonite minerals, mostly saponite, which is considered to be a perspective secondary product. The content of this mineral in the sludge is above 20 wt.%. Saponite is a clay mineral with the general chemical formula (Ca,Na)0.3(Mg, Fe2+)3(Si, Al)4O10(OH)2·4H2O. The mineral has high adsorption, ion exchange, and catalytic and filtration properties; due to the developed diffuse layer, saponite particles are highly stable in an aqueous medium—the resulting suspension is highly stable and has slow sedimentation. During the research, a positive effect on the sedimentation process of clay saponite particles was established, due to the introduction of a coagulant containing 70% tricalcium silicate, at a dosage of 2 g/dm3 coagulant; the degree of purification of water containing the saponite clay suspension is 99%. The condensed sediment after the thermal drying and with the limestone addition can be used again as a coagulant or secondary product with enhanced properties;therefore, the sludge will be processed, and not stored.

Liudongshengite, Zn4Cr2(OH)12(CO3)·3H2O, a new mineral of the hydrotalcite supergroup, from the 79 mine, Gila County, Arizona, USA

ABSTRACTA new mineral species, liudongshengite, ideally Zn4Cr2(OH)12(CO3)·3H2O, has been found in the 79 mine, Gila County, Arizona, USA. It occurs as micaceous aggregates or hexagonal platy crystals (up to 0.10 × 0.10 × 0.01 mm). The mineral is pinkish and transparent with white streak and vitreous luster. It is brittle and has a Mohs hardness of ∼1.5, with perfect cleavage on (001). No twinning or parting is observed macroscopically. The measured and calculated densities are 2.95 (3) and 3.00 g/cm3, respectively. Optically, liudongshengite is uniaxial (−), with ω = 1.720 (8), ε = 1.660 (7) (white light). An electron microprobe analysis, combined with the carbon content measured using an elemental combustion system equipped with mass spectrometry, yielded the empirical formula (Zn3.25Mg0.17Cr2.58)Σ6.00(OH)12(CO3)1.29·3H2O, based on (M2+ + M3+) = 6 apfu, where M2+ and M3+ are divalent and trivalent cations, respectively.Liudongshengite belongs to the quintinite group within the hydrotalcite supergroup and is the Cr-analogue of zaccagnaite-3R, Zn4Al2(OH)12(CO3)·3H2O. It is trigonal, with space group Rm and unit-cell parameters a = 3.1111(4), c = 22.682(3) Å, and V = 190.12(4) Å3. The crystal structure of liudongshengite is composed of positively charged brucite-like layers, [M2+1–xM3+x(OH)2]x+, alternating with negatively charged layers of (CO3)2–·3H2O. Compared to other minerals in the quintinite group, liudongshengite is remarkably enriched in M3+, with an M2+:M3+ ratio of 1.33:1. Like zaccagnaite-3R and many other hydrotalcite-type minerals, liudongshengite may also possess polytypes, as a series of synthetic hydrotalcite-type compounds with a general chemical formula [Zn4Cr2(OH)12]X2·4H2O, where X = Cl–, NO3–, or ½ SO42–, but with unit-cell parameters different from those for liudongshengite, have been reported previously.

Application of stoichiometric hydrogen atoms for balancing organic combustion reactions

Abstract Combustion is a common redox reaction, and organic combustion is one of the basic contents in chemistry curriculum. The transferred H-atom is commonly used as a redox indicator in organic chemistry and biochemistry. Nevertheless, the relationship between the number of transferred H-atoms and the number of transferred electrons has not been fully revealed. Oxidation number (ON) is an electron-counting concept. Without knowing the ONs, the number of transferred electrons cannot be counted and therefore, the redox reactions cannot be classified, defined, and balanced. This paper explores the new H-atom method for counting the number of transferred H-atoms. It provides a half-reaction approach to balance the overall organic combustion reactions. Only simple arithmetic procedures are needed to determine the number of transferred H-atoms and consequently the number of transferred electrons. According to this method, the mathematical formulas for assigning the number of transferred H-atoms can be deducted by balancing the general chemical formulas of organic compounds in half and overall organic combustions. Furthermore, the number of transferred electrons and their stoichiometric categories can be determined conveniently by any given organic chemical formula in organic combustion reactions.

Utilisation of pyrochlore-typeoxideas catalyst in bioanode of coffee mac microbial fuel cell: Boost of electric voltage and reduction of wastes

ABSTRACT This study is a contribution to development of material based on transition metal oxides with application in electrochemical devices. A pyrochlore-like solid solution with general chemical formula Bi1.2Ce0.3Sb1.5CuO7 was synthesised. The pyrochlore structure was determined by X-ray powder diffraction. The pressed pyrochlore powder sample was analysed by scanning electron microscopy to show effect of substitution fraction of cerium and to determine its grain size and morphology. Energy dispersive of X-rays was performed to confirm effective substitution of bismuth for cerium. The EDX analysis was supported by X-ray photoelectron spectroscopy which also gave information on respective oxidation states of cations. Several modes of vibration due to metal-oxygen bonds of pyrochlore-like material were studied by Fourier-transform infrared spectroscopy. The results suggested that this compound contained major component of pyrochlore and minor component of CeO2. The dielectric measurements carried out at frequency 1 MHz in temperature range –40°C–90°C proved that pyrochlore compound possessed dielectric constants ranging between 12 and 28. Furthermore, owing to its high electrical conductivity, synthesised material has been utilised as bioanode in a microbial fuel cell. This bio-electrochemical device converted organic wastes into electricity using microorganisms as biocatalysts. It displayed greater electron transfer from electroactive biofilm towards the bioanode by improving its electrical energy output. The presence of pyrochlore in electrode allowed a power density of 25 mW/m2. It was almost the same as that obtained with a graphite carbon modified by the conducting polymer polypyrrole. The MFC with pyrochlore solid oxide was advantageously more stable having longer lifetime and indicating its suitability to substitute the polypyrrole at the bioanode. Besides, the colour of the coffee mac leachate in the anolyte (anode compartment) became less dark, which means that the maximum chemical oxygen demand (COD) was removed and converted into electric energy.

Rare-earth doped Ni–Co ferrites synthesized by Pechini method: Cation distribution and high temperature magnetic studies

The present work was focused on the effect of rare earth doping on the structural and magnetic properties of Ni–Co ferrite materials with general chemical formula Ni0.5Co0.5Fe1.98R0.02O4 (R = La, Nd, Sm, Gd, Dy). All the ferrites, synthesized by the Pechini method, possess cubic symmetry with Fd3_m space group. A very small change in lattice parameter has been observed with rare earth (R3+) doping. The cation distribution between the tetrahedral (A-site) and octahedral sites (B-site), as estimated by X-ray diffraction analysis (XRD) revealed that the R3+, Co2+ and Ni2+ ions have migrated to the octahedral site. Room temperature magnetization results, obtained from Vibrating Sample Magnetometer (VSM) measurements, showed that saturation magnetization of rare-earth doped ferrites is strongly dependent on magnetic moment of rare earth ion. The coercivity increases with increase in the atomic number of rare-earth ion, which could be justified on the grounds of the stability of spin-orbital coupling that controls the magnetic anisotropy in ferrites. The results further suggest that the Curie temperature is dependent on lattice parameter and hence inter-atomic distance between magnetic ions.

Size effect of the guest cation on the AlO4 framework in aluminate sodalite-type oxides M8[Al12O24](SO4)2 (M= Sr2+ and Ca2+) in the I43m phase.

Sr8[Al12O24](SO4)2 (SAS) and Ca8[Al12O24](SO4)2 (CAS) are members of the aluminate sodalite-type oxides with the general chemical formula M8[Al12O24](XO4)2 (M2+ is the guest cation and XO42- is the guest anion). To discuss the role of the guest cations (M2+ = Sr2+ and Ca2+) on the rotation of AlO4 in the oxygen tetrahedral framework in the I43m phase, the crystal structure parameters and the probability density function of the guest ions in SAS and CAS have been investigated via synchrotron radiation X-ray powder diffraction by considering Gram-Charlier expansions. The interatomic distances between the M2+ and O2- ions evaluated from the maximum positions in the probability density distribution are almost equal to the sum of the ideal ionic radii of the M2+ and O2- ions. This result suggests that the geometry of the AlO4 tetrahedral framework and the fluctuation of the guest ions are mainly caused by steric effects between the M2+ and O2- ions.

Highly Luminescent Europium-Based Heteroleptic Coordination Polymers with Phenantroline and Glutarate Ligands.

Isostructural lanthanide-based coordination polymers with general chemical formula [Ln(phen)(glu)(NO3)]∞ with Ln = La-Tm (except Ce and Pm) have been synthesized by hydrothermal methods (H2glu stands for glutaric acid and phen stands for 1,10-phenantroline). They crystallize in the monoclinic system with the P21/c (no. 14) space group. The crystal structure has been solved on the basis of the La derivative. It can be described as the superimposition of molecular chains of dimeric La(phen)(NO3)-La(phen)(NO3) units bridged by glutarate ligands. Luminescent properties have been explored and show that the Eu derivative exhibits the highest luminance observed for Eu-based coordination polymers (85 to 105 cd·m-2). Effects of the dilution of the Eu3+ and Tb3+ luminescent ions by Gd3+ optically inactive ions are unexpected and to the best of our knowledge unprecedented. This could be related to the different intermetallic energy-transfer mechanisms in competition and to the nonisotropic distribution of the lanthanide ions in these molecular alloys. The investigation of molecular alloys with general chemical formula [Eu1-xTbx(phen)(glu)(NO3)]∞ with 0 ≤ x ≤ 1 highlights a very sizable and constant Eu3+ luminescence whatever the x value, which further confirms the existence of very strong intermetallic energy transfers in this family of compounds. It is also noticeable that some coordination polymers based on weakly emissive lanthanide ions exhibit very well defined emission spectra.

Meteoritic amino acids as chemical tracers of parent-body chemistries

ABSTRACT The analysis of the organic matter of meteorites made it possible to identify over 70 amino acids (AA), including 8 of those found in living organisms. However, their relative abundances vary drastically with the type of the carbonaceous chondrite, even for isomers of same chemical formula. In this report, we address the question whether this difference may have its origin in the relative stability of these isomers according to the conditions they experienced when they were formed and after. To this end, we rely on the fact that for most of the species observed so far in the interstellar medium (ISM), the most abundant isomer of a given generic chemical formula is the most stable one (minimum energy principle, MEP). Using quantum density functional theory (DFT) simulations, we investigate the relative stability of the lowest energy isomers of alanine (Ala) and amino butyric acid (ABA) in the neutral, protonated, and zwitterionic structures together with corresponding nitrile precursors. It is shown that β-alanine and γ-ABA are the most stable in a protonated form, whereas α-AA are the most stable in the zwitterionic and nitrile structures. The different composition of the carbonaceous chondrites CIs and CMs could be linked to the chemical context of the aqueous alterations of the parent bodies.

Effect of sintering conditions and doping type on the functional properties of ZnO semiconductors

Electrical properties and microstructure of ZnO ceramic bodies doped with a constant ratio of different dopants were studied under several of sintering conditions. The selected general chemical formula was (99Zn–M) where M=CuO, V2 O5 , MnO2 and GeO2 . The different compositions were processed by the conventional solid state reaction and fired at various temperatures between 1000 and 1300 °C for 1–3 h. The degree of sintering of the ZnO bodies was identified from the determination of the physical properties. The obtained results showed that, the optimum sintering conditions of ZnO varistors are either 1200 °C/3 h or 1300 °C/2 h. Both the electric modulus and dielectric loss tangent were studied as a function of frequency. The addition of CuO gave the maximum breakdown voltage, highest dielectric constant and the best electrical conductivity in the studied compositions. Also, the addition of V2 O5 gave the minimum dielectric loss, and therefore, the two samples could be used in different useful technological applications.

Inversion, chemical complexity, and interstitial transport in spinels

AbstractSpinels with the generic chemical formula AB2O4 have potential applications in nuclear energy and batteries. In both cases, their functionality is related to mass transport through the crystal. Here, using long‐time atomistic simulations, we examine the impact of the cation structure on interstitial transport in two spinel chemistries, inverse MgGa2O4 and double MgAlGaO4. We emphasize two aspects of the transport properties: the unit mechanisms that are described by individual barriers, for which we introduce pole‐figure‐like plots, and the aggregate behavior of those unit mechanisms. Compared to previous work on normal spinels, we find that inversion significantly reduces the rate of interstitial transport in these structures and has an impact on the stability of defects as they move through the lattice. In particular, B cation interstitials are found to be kinetically stable only in the inverse MgGa2O4. These results provide new insight into relationship between structure, chemistry, and transport in spinels.

High-Entropy Structure Design in Layered Transition Metal Dichalcogenides

Layered high-entropy compounds have been attracting a lot of attention in recent times due to their potential application in energy storage and conversion. Generally, an intra-layer scheme is widely used to realize the high-entropy structure by introducing multi-principal elements into the metal-atomic layers. Here, we propose an intercalation high-entropy scheme to realize the high-entropy structure in a series of layered transition metal dichalcogenides with a general chemical formula of MX2. Multi-principal metal elements are intercalated into the van-der-Waals gaps between MX2 slabs resulting in a series of (HEM)xMX2 compounds, in which HEM is high-entropy metals mainly composed of 3d transition metal elements such as Fe0.2Co0.2Cr0.2Ni0.2Mn0.2. Moreover, three kinds of 2D high-entropy magnetic lattices (a0 × a0, √3a0 × a0, √3a0 × √3a0) in the intercalated layers are found by tuning the intercalation content x. Significant differences in the effective moment and spin frustration among them are revealed. Furthermore, a multi-layered high-entropy structure is realized by a combination of intra-layer and intercalation schemes. The new intercalation high-entropy scheme and versatile 2D high-entropy structures reported in this work will reinforce the spirit on the exploration of new low-dimensional high-entropy systems for future applications.

Matching conflicting oxidation conditions and strain accommodation in perovskite epitaxial thin-film ferroelectric varactors

Perovskite oxide materials of the general chemical formula ABO3 are a rich playground for epitaxial stacks of different functional layers for novel device applications. In the example of a tunable metal–insulator–metal ferroelectric varactor (tunable capacitor) made from the highest conducting perovskite SrMoO3 as an electrode and the tunable dielectric Ba0.5Sr0.5TiO3 (BST), we show how the extremely conflicting oxidation potentials can be conciliated in a fully functional heterostructure. Controlling the growth kinetics by the substrate temperature, oxygen pressure, and oxidation time, the formation of the non-conducting Mo6+ states can be effectively suppressed and the BST cation stoichiometry can be tuned. The cumulative impact of the cation nonstoichiometry, epitaxial strain, and oxygen deficiency in the BST films leads to the expansion of their c-axis lattice parameter via the formation of point defects. The dielectric permittivity of 440, the high tunability of 3.5, and the quality factor of 50 are achieved for the varactors at the frequency of 1 GHz. It turns out that the varactor performance is anti-correlated to the tetragonal lattice distortion of BST, which itself is interrelated to the oxidation conditions. The mechanism of the leakage current through oxygen deficient BST layers of the varactors is analyzed within the combined scenarios of the space-charge limited current and Poole–Frenkel field-assisted emission from traps. The achieved high capacitance per unit area of 0.04 pF/μm2 and moderate leakage currents of 0.025 μA/pF make these varactors suitable for applications in microwave microelectronic devices.