Isovalent Substitution Research Articles

ZnSe and ZnSe:Mn nanocrystals were obtained by combustion synthesis (self-propagating high-temperature synthesis) using current pulses to initiate a reaction with amplitudes of ∼35 A and ∼40 A. The magnitude of the amplitude of the current pulse affects the size of the nanocrystals, their phase composition, the ratio of the cubic and hexagonal phases, the degree of microstresses and the density of dislocations. The inclusion of Mn dopants into ZnSe has little effect on the nanocrystal morphology and strongly influences the morphology of polycrystals. An EPR spectrum of Mn2+ ions with a hyperfine structure constant A = 6.55 mТ and a g-factor g = 2.0055, which is due to Mn2+ ions in a cubic environment, was found in self-activated and doped ZnSe and ZnSe: Mn nanocrystals. It was found that increasing the amplitude of the current pulse, which initiates the combustion synthesis reaction, increases the intensity of the diffusion processes and more effective isovalent substitution of Zn2+ ions by Mn2+ ions in the crystal lattice of ZnSe nanocrystals. The photoluminescence spectra of ZnSe and ZnSe:Mn nanocrystals were investigated, and individual emission bands were detected in the integral spectra. There were three such individual bands in the photoluminescence spectrum of ZnSe nanocrystals. Their maxima were characterized using the following parameters: λ max = 592 nm (E = 2.095 eV), λ max = 543 nm (E = 2.282 eV), and λ max = 505 nm (E = 2.455 eV). Six individual emission bands were detected in the photoluminescence spectra of ZnSe:Mn nanocrystals with the parameters: λ max = 675. 5 nm (E = 1.835 eV), λ max = 642.5 nm (E = 1.929 eV), λ max = 613 nm (E = 2.022 eV), λ max = 583.5 nm (E = 2.124 eV), λ max = 550 nm (E = 2.255 eV), λ max = 528.5 nm (E = 2.345 eV). This paper discusses the nature of the centers of radiative recombination of individual bands.

Solid state reaction used to prepared the high temperature superconductor of YBa2Cu3-xAgxO6.5+δ compounds, Ag was isovalent substitution Cu for (x=0.0, 0.15, 0.25, 0.35, 0.45). Iodometric titration used to determine the oxygen content in the samples. The value of O2 was varies from sample to another .The result of titration exhibited value of δ is increasing when increasing of concentration of Ag. The samples was analyzed by x-ray diffraction(XRD) patterns has been used to determine the purity of the used materials ,calculation of the lattice constants and determination of its phase .The study shows a high purity samples with an orthorhombic single phase ,resistivity measurement by four probe technique and morphological analysis by Scanning Electron Microscopy (SEM).These parameters are the forming pressure of the pellets , the sintering temperature was 950oC for sintering time (30hours) with the flow of oxygen gas of about (1.25)L/min. The maximum Tc value was 94.2K for YBa2Cu5.5Ag0.45O6.5+δ, it is found Tc value increasing when increased x in the YBa2Cu3-xAgxO6.5+δ supercomputers.

Correction for ‘Investigation of factors affecting the stability of compounds formed by isovalent substitution in layered oxychalcogenides, leading to identification of Ba3Sc2O5Cu2Se2, Ba3Y2O5Cu2Se2, Ba3Sc2O5Ag2Se2 and Ba3In2O5Ag2Se2’ by Gregory J. Limburn et al., J. Mater. Chem. C, 2022, 10, 3784–3795; https://doi.org/10.1039/D1TC05051F.

Since the huge breakthrough in 2018, research on halide solid-state electrolytes (SSEs) has set off a new craze. In comparison with oxide and sulfide SSEs, halide SSEs have more balanced properties in various aspects, including ionic conductivity, electrochemical stability window, and moisture resistance. Herein, the overall knowledge and deep understanding of halide SSEs and their practical applications in all-solid-state batteries (ASSBs) are introduced. Firstly, the principle of screening halide SSE components is proposed. Among F, Cl, Br and I anions, the Cl anion is excellent owing to its suitable ionic conductivity and electrochemical stability window. The Sc, Y, and lanthanide elements are also more compatible with Cl anions in terms of electronegativity. Secondly, the structural design theory of halide SSEs with high ionic conductivity and the mechanism of Li ion migration are described. A monoclinic structure is more conducive to Li ion migration, compared with trigonal and orthorhombic structures. Additionally, substitution strategies for halide SSEs are discussed, mainly including dual-halogen, isovalent cation substitution, and aliovalent cation substitution. Furthermore, the mechanism of moisture resistance and synthesis method of halide SSEs are analyzed. Compared with the solid-state reaction and mechanochemistry method, wet chemical synthesis is more likely to achieve scale-up production of halide SSEs. Finally, the application prospects and challenges of halide SSEs in ASSBs are outlined.

A series of Li3MI6 compounds with M = Lu–Sm were produced by ball milling and solid state synthesis. Cation disorder within the layers largely influences the ionic transport properties, which can be tuned by isovalent and aliovalent substitution.

Background. Exploring the effect of isomorphic substitution of atoms on structure and features of oxide compounds is one of the main tasks of modern materials science. Of particular interest are representatives of compounds An+1BnO3n+1 family (in particular, AIILn2Sc2O7 scandates) with slab perovskite-like snrucnure, which possess a number of practically important properties..This work is devoted to study the possibility of La atoms by smaller Dy atoms substitution in two-slab perovskite-like structure of BaLa2Sc2O7 and its effect on the crystallographic features of the BaLa2-xDyxSc2O7 scandates synthesized. Methods. The method of synthesis of new phases by heat treatment of co-crystallized salts, powder X-ray diffraction methods and the method of second optical harmonic generation by the obtained phases are used in the work. Results. The boundaries of isovalent substitution of La atoms (0 £ х £ 1,0) and the crystallographic parameters of the synthesized BaLa2-xDyxSc2O7 phases with a two-slab structure are determined. The indexing of the X-ray powder diffraction pattern of the BaLa2-xDyxSc2O7 (0 £ х £ 1,0) has revealed the tetragonal symmetry of the heat treated samples. The observed systematic extinctions and test results for the generation of a signal of the second optical harmonic of laser radiation indicate that their crystal structure belongs to centrosymmetrical P42/mnm space group. The character of the phase relations in the BaLa2-xDyxSc2O7 system and the type of concentration dependences the parameters of the tetragonal unit cells of BaLa2-xDyxSc2O7 phases with a two-slab structure indicate that by their nature these phases are limited row of solid solutions. The most probable mechanism of destruction of slab perovskite-like structure in samples BaLa2-xDyxSc2O7 with x > 1 was determined and a comparative comparison the stability of the slab structure of scandates AIILa2-xDyxSc2O7 (AII = Ba, Sr) was performed. Сonclusions. The obtained results indicate the possibility of a sufficiently significant isomorphic substitution of REE atoms in slab perovskite-like structure of BaLn2Sc2O7 scandates, can be further used to regulate their properties and are of undoubted interest for solving the problem of a targeted search new compounds of the type MeLnnBIIInO3n+1 with this type of structure.

Owing to their magnificent chemical and physical properties, transition metal-based heterostructures are potential materials for applications ranging from point-of-care diagnostics to sustainable energy technologies. The cryptomelane-type octahedral molecular sieves (K-OMS-2) are extensively studied porous materials with a hollandite (2 × 2 tunnel of dimensions 4.6 × 4.6 Å2) structure susceptible to the isovalent substitution of metal cations at the framework of MnO6 octahedral chains. Here we report a facile in situ synthesis of framework-level zirconium (Zr)-doped K-OMS-2 nanoribbons in poly(3,4-ethylenedioxythiophene) (PEDOT) nanoflakes at a water/chloroform interface at ambient conditions. An oxidant system of KMnO4 and ZrOCl2·8H2O initiated the polymerisation at temperatures ranging from 5° to 50 °C. The lattice distortions arising from the framework-level substitution of Mn4+ by Zr4+ in the K-OMS-2 structure were evidenced with powder X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and N2 adsorption-desorption studies. Transmission electron microscopic and mapping images confirmed that PEDOT/Zr-K-OMS-2 comprises a highly crystalline random network of two-dimensional PEDOT flakes and Zr-doped K-OMS-2 nanoribbons. In this regard, the proposed interfacial strategy affirms an in situ method for the morphological tuning of heterostructures on polymer supports at low temperatures.

Enhanced point defect phonons scattering through huge isovalent substitution substantially reduces the lattice thermal conductivity of half-Heusler alloys.

The conditions of isovalent substitution of Nd atoms for Sm atoms in A-positions of the BaNd2In2O7 two-slab perovskite-like structure of the BaNd2-xSmxIn2O7 type (0 £ x £ 1.8) have determined by X-ray powder diffraction methods. Tetragonal crystal structure (space group P42/mnm) of the BaNd2-xSmxIn2O7 phases with substitution degree of Nd atoms equal to 0.5, 1.0, 1.5 and 1.8 was determined by the Rietveld method. Crystal structure of BaNd2-xSmxIn2O7 is based on the two-dimensional (infinite in the XY plane) perovskite-like blocks, consisting of two slabs of the deformed InO6 octahedra connected by vertices. Ba atoms are localized only at 4f position inside the perovskite block, while REE atoms are placed only at 8j position at the boundary of the perovskite block. The adjacent perovskite-like blocks are separated by a slab of LnO9 polyhedra and held together by - O - Ln - O - interblock bonds. It is established that the isovalent substitution of Nd atoms by smaller Sm atoms leads to a decrease in the length of the Ln - O2 distance (from 0.230(2) nm to 0.206(2) nm) and to an increase in the degree of deformation of the interblocks of LnO9 polyhedra, the inner block polyhedra BaO12, and the InO6 octahedra as well. Such structural changes destabilize the interblock "stitching" and are one of the main destruction factors of the slab perovskite-like structure of the BaNd2-xSmxIn2O7 phases at x > 1.8. Data obtained could be used for directed regulation of structure-sensitive properties of materials based on the BaNd2In2O7 indate.

Abstract This article reports on the exploration of the chemical versatility of entropy‐stabilized pyrochlores (A2B2O7) with large chemical disorder introduced on the B site, as well as the study of isovalent and aliovalent substitution on the B site and of Ca2+‐doping on the A site. Among all the 20 new compounds obtained in this study, 8 are entropy‐stabilized: RE2(TiZrHfGeSn)2 (with RE = Gd–Ho and Y), Pr2(TiZrHfScNb)2O7, and RE2(TiGeSnAlNb)2O7 (with RE = Er and Y). Moreover, some physical properties (magnetic, electrical, thermal, and optical properties) of these high‐entropy pyrochlores have been screened, and some of them could be potentially interesting for applications. For example, we observed low thermal diffusivity values (between 0.4 and 0.7 m2 s−1) making them interesting for thermal barrier coating or tunable optical bandgaps in the visible region that could make them appealing as photocatalysts or in optical applications. Furthermore, single‐phased compounds were obtained for almost all the rare earths (REs) on the A site. Therefore, when five nonmagnetic cations are used for the B site, it enables to study the magnetic properties and, more specifically, the influence of the local chemical and structural disorder on the exotic ground states observed in monocationic RE pyrochlores.

The structural characterization and electrical transport measurements at ambient and applied pressures of the compounds of the LaAg1−xAuxSb2 family are presented. Up to two charge density wave (CDW) transitions could be detected upon cooling from room temperature and an equivalence of the effects of chemical and physical pressure on the CDW ordering temperatures was observed with the unit cell volume being a salient structural parameter. As such LaAg1−xAuxSb2 is a rare example of a non-cubic system that exhibits good agreement between the effects of applied, physical, pressure and changes in unit cell volume from steric changes induced by isovalent substitution. Additionally, for LaAg0.54Au0.46Sb2 anomalies in low temperature electrical transport were observed in the pressure range where the lower charge density wave is completely suppressed.

First-principles study to probe the effect of substitution at X and Z sites on the electronic, magnetic and transport properties of Co2X(V, Nb, Ta)Z(Al, Ga, In, Si, Ge, Sn) Heusler alloys

Kagome metals AV_{3}Sb_{5} (A=K, Rb, and Cs) exhibit a characteristic superconducting ground state coexisting with a charge density wave (CDW), whereas the mechanisms of the superconductivity and CDW have yet to be clarified. Here we report a systematic angle-resolved photoemission spectroscopy (ARPES) study of Cs(V_{1-x}Nb_{x})_{3}Sb_{5} as a function of Nb content x, where isovalent Nb substitution causes an enhancement of superconducting transition temperature (T_{c}) and the reduction of CDW temperature (T_{CDW}). We found that the Nb substitution shifts the Sb-derived electron band at the Γ point downward and simultaneously moves the V-derived band around the M point upward to lift up the saddle point (SP) away from the Fermi level, leading to the reduction of the CDW-gap magnitude and T_{CDW}. This indicates a primary role of the SP density of states to stabilize the CDW. The present result also suggests that the enhancement of superconductivity by Nb substitution is caused by the cooperation between the expansion of the Sb-derived electron pocket and the recovery of the V-derived density of states at the Fermi level.

State-of-the-art synthesis for layered oxide cathodes for Li and Na-ion battery involves prolonged high temperature (>700°C) multistep processing for long reaction times (~24 hours) under high oxygen pressure, followed by slurry casting after mixing with binders and additives. Here, we demonstrate an intermediate temperature (250-350°C) molten hydroxide-based electrodeposition process to grow alkali ion (Li+, Na+) intercalated transition metal oxides across multiple transition metal chemistries of the Li system (from layered LiCoO2 to cobalt-less orthorhombic LiMnO2, layered Li2MnO3, spinel LiNixMn1-xO4, LiMn2O4,) and Na system (O3 and P2 NaxCoO2, O’3 NaxMnO2) in thick film form factors. The highly textured ([110]||ND), dense (>95%) electroplated LiCoO2 cathodes can perform at ultrahigh thickness of ~200 µm (areal capacity ~13.6 mAh/cm2) in comparison to 40-60 µm for state-of-the-art slurry cast cathodes (areal capacity ~3-4 mAh/cm2 with a porosity of ~20%), a fivefold increase in areal capacity and volumetric energy density. We discuss the interplay of bulk crystallographic orientation of the electro-active material (LiCoO2), surface terminating planes interacting with the electrolyte, and electrochemically grown conformal surface protective layers on the electrochemical-chemo-mechanical degradation mechanisms during intercalation and deintercalation for high voltage operation (>4.2 V vs. Li). We also demonstrate electrochemically controllable isovalent transition metal doping and substitution in ceramic oxides (LiCoxMn1-xO2) by electrodeposition. Our findings highlight the influence of the unique molten hydroxide-based solution chemistry platform and electrochemical processing parameters, on regulating the phase assemblage, designing the microstructure, and controlling crystallographic orientation during electrocrystallization.

The semiconductor Cu2ZnSnSe4 (CZTSe) is a promising candidate for both thermoelectric and photovoltaic energy harvesting applications due to a combination of features such as direct band gap, high absorption coefficient, and low thermal conductivity. We report the solid-state synthesis and characterization of Mn-doped Cu2Zn1-xMnxSnSe4 (x = 0, 0.05, 0.10, and 0.15) in an attempt to explore the effect of isovalent substitution at the Zn site. X-ray diffraction and Raman spectroscopy of all specimens confirmed the formation of a single-phase tetragonal kesterite structure (space group I4̅). The band gap obtained by UV-visible diffuse reflectance measurements was 1.42 eV for all compositions. Thermoelectric properties were measured in the range 300-785 K. Electrical resistivity was metallic and reduced on Mn doping, while the Seebeck coefficient exhibited a p-type semiconducting behavior that enhanced on Mn doping, with associated enhancement of the power factor. Lattice thermal conductivity showed a 1/T behavior, falling from about 1.9-2.7 W m-1 K-1 at 300 K to 0.51-0.9 W m-1 K-1 above 750 K. The combined effect of enhanced power factor and reduced lattice thermal conductivity resulted in a figure of merit ZT in the range of 0.19-0.42 above 750 K. Thin-film photovoltaic devices with a CZTSe absorber and an SnSe electron transport layer gave 3.2% efficiency.

The adverse effect of fossil fuels on the environment is driving research to explore alternative energy sources. Research studies have demonstrated that renewables can offer a promising strategy to curb the problem, among which thermoelectric technology stands tall. However, the challenge with thermoelectric materials comes from the conflicting property of the Seebeck coefficient and the electrical conductivity resulting in a low power factor and hence a lower figure of merit. Researchers have reported various techniques to enhance the figure of merit, particularly in metal chalcogenide thermoelectric materials. Here we present a review on isovalent substitution as a tool to decouple the interdependency of the electrical conductivity and Seebeck coefficient to facilitate simultaneous enhancement in these two parameters. This is proven true in both cationic and anionic side substitutions in metal chalcogenide thermoelectric materials. Numerous publications relating to isovalent substitution in metal chalcogenide thermoelectric are reviewed. This will serve as a direction for current and future research to enhance thermoelectric performance and device application. This review substantiates the role of isovalent substitution in enhancing metal chalcogenide thermoelectric properties compared with conventional systems.

This paper is aimed to the determination of the optical pseudogap values in phases with argyrodite structure by a simple method of diffuse reflectance spectroscopy. Samples of (Cu1-xAgx)7PSe6 (x = 0, 0.2, 0.3, 0.4, 0.6, 0.7, 0.9, 1.0) solid solutions were obtained in the form of microcrystalline powders by grinding in agate mortar. The diffuse reflectance spectra of the obtained (Cu1-xAgx)7PSe6 samples were studied in the spectral range 220–1400 nm (293 K) and analyzed using the Kubelka-Munk function. It was found that for (Cu1-xAgx)7PSe6 solid solutions the increase in the copper amount causes a shift of the beginning of the absorption edge to the region of higher energies. The optical pseudogap of (Cu1-xAgx)7PSe6 solid solutions was estimated by combining the Kubelka-Munch theory and the Tauc equation. It is established that the isovalent cationic substitution of Ag+ → Cu+ leads to a monotonic decrease in the values of the optical pseudogap, as a result, the compositional dependence of which is close to linear. This behavior of the optical pseudogap can only be associated with a decrease in the lattice parameters and characterizes the formation of solid solutions.

The strategy of using aliovalent substitution in A2B2O6 double perovskites remained the popular choice to enhance the charge carrier concentration in order to increase their electrical conductivity. In the present investigation, we have shown that the isovalent substitution in A-site can facilitate in manipulating the oxidation states of B-site transition metal cations in double perovskites, which in turn helps in increasing the carrier concentration. Further, using the strategy of manipulating valence states of B-site cations, we could enhance the thermoelectric (TE) power factor of double perovskites. Ceramic samples of Ba x Sr2−x CrMoO6 (x = 0.0, 0.1, 0.2, and 0.3) double perovskites have been synthesized via solid-state reaction route. The phase constitution and morphological study have been carried out via x-ray diffraction (XRD) and field scanning electron microscope (FESEM). Rietveld refinement of XRD data confirms the polycrystalline cubic structure with Pmm space group. Negative values of Seebeck coefficient have been observed for these oxides in the temperature range from room temperature to 1100 K, confirming electrons as the majority charge carriers. The electrical conductivity of Sr2CrMoO6 double perovskite is found to be increased by more than an order of magnitude due to isovalent Ba2+ doping in place of Sr2+. As a result, 5 times enhancement of TE power factor has been attained in Ba x Sr2−x CrMoO6. Charge transport mechanism of these double perovskites is found to be governed by the small polaron hopping conduction model. x-ray photoelectron spectroscopy spectra validate the presence of multivalent cations of Mo5+, Mo6+, Cr3+, and Cr6+ in these double perovskites. Furthermore, the detailed defect chemistry analysis suggests that owing to Ba substitution, Cr is oxidized from Cr3+ to Cr6+ oxidation states, which enhances the electron concentration and reduces the low mobility oxygen vacancies leading to dramatically improved electrical conductivity.

Influence of rare-earth doping on the structural and magnetic properties of orthoferrite La0.50R0.50FeO3 ceramics obtained under high pressure

Late Triassic granitic magmatism and tungsten mineralization in NE China: Geochronological and geochemical constraints from the Tantoushan quartz-wolframite vein-type deposit