Isovalent Substitution Research Articles

The influence of isovalent substitutions of Pb2+ by Cd2+ and heterovalent substitutions of Pb2+ by Sc3+ on a superionic Faraday transition in Pb1 – xCdxF2 (x = 0.33) and Pb1 – x ScxF2+x (x = 0.1) solid solutions based on the fluorite-type modification β-PbF2 with sp. gr. Fm¯3m has been studied. The Faraday phase transition can be characterized by the temperature Tλ corresponding to maximum on the heat capacity curve and temperature Tα corresponding to the beginning of the structural disorder anion sublattice. Both of these temperatures are found on the temperature conductivity dependence σdc(T ) of β-PbF2, Pb0.67Cd0.33F2 and Pb0.9Sc0.1F2.1 crystals. The values of Tλ and Tα in solid solutions compared with β-PbF2 matrix (Tλ = 715 ± 10K, Tα = 597 ± 12 K) decrease by 100–110 and 30–45 K for Pb0.67Cd0.33F2 and Pb0.9Sc0.1F2.1, respectively. Decreasing of temperature Tλ leads to an increase in temperature interval of existence of the superionic state. For T > Tλ the anionic conductivity of fluorite-type Pb0.67Cd0.33F2, Pb0.9Sc0.1F2.1, and β-PbF2 crystals reaches anomalously high values of σdc = 1–2 S/cm (873 K) at an ion transfer activation enthalpy equals to Hσ = 0.3 eV.

To date, there is still a lack of definite knowledge regarding the toxicity of Cu(OH)2 nanoparticles towards bacteria. This study was aimed at shedding light on the role played by released cupric ions in the toxicity of nanoparticles. To address this issue, the bactericidal activity of Cu(OH)2 was at first evaluated in sterile water, a medium in which particles are not soluble. In parallel, an isovalent substitution of cupric ions by Mg2+ was attempted in the crystal structure of Cu(OH)2 nanoparticles to increase their solubility and determine the impact on the bactericidal activity. For the first time, mixed Cu1-xMgx(OH)2 nanorods (x ≤ 0.1) of about 15 nm in diameter and a few hundred nanometers in length were successfully prepared by a simple co-precipitation at room temperature in mixed alkaline (NaOH/Na2CO3) medium. For E. coli, 100% reduction of one million CFU per mL (6 log10) occurs after only 180 min on contact with both Cu(OH)2 and Cu0.9Mg0.1(OH)2 nanorods. The entire initial inoculum of S. aureus is also killed by Cu(OH)2 after 180 min (100% or 6 log10 reduction), while 0.01% of these bacteria stay alive on contact with Cu0.9Mg0.1(OH)2 (99.99% or 4 log10 reduction). The bactericidal performances of Cu(OH)2 and the magnesium-substituted counterparts (i.e. Cu1-xMgx(OH)2) are not linked to cupric ions they release in water since their mass concentrations after 180 min are much lower than minimal concentrations inhibiting the growth of E. coli and S. aureus. Finally, an EPR spin trapping study reveals how these nanorods kill bacteria in water: only the presence of hydrogen peroxide, a by-product of the normal metabolism of oxygen in aerobic bacteria, allows the Cu(OH)2 and its magnesium-substituted counterparts to produce a lethal amount of free radicals, the majority of which are the highly toxic HO˙.

In this work, we study thermoelectric properties of GeTei-based alloys, doped with bismuth, with partial substitution of lead for germanium: Ge0.86Pb0.1Bi0.04Te. The aim of the study is to explore the possibility of increasing the thermoelectric efficiency of a compound by combining optimal doping and isovalent substitution to improve the electronic properties with a simultaneous decrease of the lattice thermal conductivity. We studied alloy samples prepared in two different research laboratories using similar, but not completely identical procedures. It is shown that the electronic (thermoelectric power and electrical conductivity) properties of the samples of the two groups are in good agreement with each other. The properties of alloys depend on the thermal history of the samples due to the presence at temperatures of 600-800 K of a phase transition from a low-temperature rhombohedral to a high-temperature cubic structural modification and missibility gap in GeTe-PbTe quasibinary system below 870 K. The thermoelectric figure of merit of alloys reaches a maximum value of 1.5 at a temperature of about 750 K. Keywords: thermoelectric alloys, thermoelectric power, electrical conductivity, thermal conductivity

Ce-doped tetracationic garnets (Gd, M)3Al2Ga3O12(M = Y, Lu) form a family of new multipurpose promising scintillation materials. The aim of this work was to evaluate the scintillation yield in the materials of quaternary garnets activated by cerium ions with partial isovalent substitution of the matrix-forming gadolinium ions by yttrium or lutetium ions.Materials were obtained in the form of polycrystalline ceramic samples, and the best results were shown by samples obtained from the raw materials produced by the coprecipitation method. It was found that ceramics obtained from coprecipitated raw materials ensure a uniform distribution of activator ions in the multi-cationic matrices, which enables the high light yield and fast scintillation kinetics of the scintillation. It was demonstrated that the superstoichiometric content of lutetium/gadolinium in the material is an effective method to suppress phosphorescence accompanied scintillation. For ceramics with the composition (Gd, Lu)3Al2Ga3O12 , a scintillation yield of more than 50.000 ph/MeV was achieved. The scintillation kinetics was measured to be close to the kinetics with a decay constant of 50 ns.In terms of the set of the parameters, the developed scintillation materials are close to the recently developed alkali halide materials LaBr3:Ce, GdBr3:Ce. Moreover, they have high mechanical hardness, are characterized by the absence of hygroscopicity, and are better adapted to the manufacture of pixel detectors used in modern devices for medical diagnostics.

Synergistic effect of grain boundaries and phonon engineering in Sb substituted Bi2Se3 nanostructures for thermoelectric applications

Suppression of thermal conductivity in LaCoO3 ceramic by lattice disorder and mass fluctuation scattering for thermoelectric application

Atomic layer deposition (ALD) offers a viable route for the growth of thin and conformal films over 3-D topographies and is becoming attractive as a method to grow films thin enough, and with sufficient dielectric constants (k), for the fabrication of next-generation dynamic random memories (DRAMs). Through isovalent A-site substitution of Sr for Ba in the ABO3 perovskite the dielectric constant can be tuned to be orders of magnitude greater than either SrTiO3 or BaTiO3 near ambient temperatures. We used ALD to grow thin (≤ 15 nm) Ba x Sr1-x TiO3 (BST) films that are epitaxially integrated to SrTiO3 (001) (STO) and Zintl-templated Ge (001). Films of three compositions, which are x ~ 0.7, 0.5 and 0.3, and thicknesses of 7.8 to 14.9 nm were grown at 1.05 Torr and 225 °C using barium bis(triisopropylcyclopentadienyl), strontium bis(triisopropylcyclopentadienyl), titanium tetraisopropoxide and H2O. Film compositions were controlled by changing cycle ratios (Ba:Sr, Ba:Ti and Sr:Ti) and confirmed by in situ X-ray photoelectron spectroscopy (XPS). Films were amorphous as deposited and required post-deposition vacuum annealing at 650-710 °C to crystallize. Epitaxy was confirmed with X-ray diffraction and transmission electron microscopy. Only BST (00l) out-of-plane diffraction signals were detected. Capacitance-voltage (C-V) measurements revealed that BST thin films grown by ALD on STO (001) have dielectric constant values ranging from 210 for Ba0.71Sr0.26TiO3 to 368 for Ba0.48Sr0.43TiO3. The dielectric constant k increased with thickness with x in the range of 0.27 ≤ x ≤ 0.31. Interfacial effects inherent to the ~ 10 nm Ba x Sr1-x TiO3 films on Ge (001) affect the capacitance measurements leading to k of 87 and 140 for 10.9 and 14.6 nm films, respectively. The epitaxial films have high k in the bulk. Using capacitance measurements for Ba x Sr1-x TiO3 films (x~0.5) 13 to 18.4 nm thick, a bulk k of 3200 at RT and a low interfacial capacitance density (C/A) of 100 fF/mm2 were extracted from thickness dependent relationships.

The comprehensive study of the electronic density distribution of CuCr0.99Ln0.01S2 (Ln = La, Ce) solid solutions was carried out using both X-ray photoelectron and emission spectroscopy. It was found that cationic substitution of chromium with lanthanum or cerium atoms does not significantly affect the atomic charges of the matrix elements (Cu, Cr, S) in the lanthanide-doped solid solutions. The copper atoms in the composition of CuCrS2-matrix and the lanthanide-doped solid solutions were found to be in the monovalent state. The chromium and lanthanide atoms were found to be in the trivalent state. This fact indicates the isovalent cationic substitution character. The sulfur atoms were found to be in the divalent state. The near-surface layers contain the additional oxidation forms of sulfur (S0, S4+, S6+) and copper (Cu2+) atoms. The detailed analysis of the valence band structure using DFT calculations has shown that partial DOS distribution character of the matrix elements is preserved after the cationic substitution. The experimental valence band spectra structure of CuCrS2-matrix and CuCr0.99Ln0.01S2 is determined by the occupied copper d-states contribution. The contribution of the lanthanide states in the valence band structure is lower in comparison with those for the matrix elements. The major contribution of the lanthanide states was found to be mainly localized near the conduction band bottom.

Antibacterial and cell-friendly copper-substituted tricalcium phosphate ceramics for biomedical implant applications

Trace element geochemistry of sphalerite and chalcopyrite in arc-hosted VMS deposits

For the first time, the synthesis was carried out and the physicochemical properties of solid solutions based on the multiferroic BiFeO3 were studied. It was found that the samples were characterized by a rhombohedrally distorted perovskite structure. It was shown that a slight isovalent substitution of Bi3+ ions by La3+ ions and Fe3+ ions by Co3+ ions in BiFeO3 (x ≤ 0.10) leads to an increase in the specific magnetization. This can be attributed to structural distortions and causes weak ferromagnetism to occur. The studied samples are p-type semiconductors and have good sensory properties even without catalysts. It was found that the maximum values of the S response were obtained at temperatures close to the ferromagnetic Curie temperature, the value of which is consistent with the studies of electrical properties.

Argyrodites are a wide class of tetrahedrally close–packed ternary and quaternary compounds that have a large number of representatives. Argyrodite family compounds always include two types of cations: univalent (type A) and multivalent (type B). B type multivalent cations (3–5) are tetrahedrally coordinated by anions and form a rigid anionic framework, and the univalent A type cations are located in the cavities between them and have different occupancy of crystallographic positions (disordered sublattice). The most common are argyrodites based on four and five valence p–elements. Type A and B cations are subject to isomorphic substitution, which in combination with the proximity of the crystal lattice parameters causes a significant number of solid solutions between the compounds with the structure of argyrodite. These solid solutions are formed by both isovalent and heterovalent substitution, which is used to optimize the functional parameters of the studied materials. Argyrodite structure compounds can be used as optical, superionic, and thermoelectric materials. This work aims to study the physico–chemical interaction at isovalent Si4+↔Ge4+and heterovalent substitution of P5+↔Ge4+ within the Ag7SiS5I–Ag7GeS5I and Ag6PS5I–Ag7GeS5I systems. Several alloys in the Ag6PS5I–Ag7GeS5I and Ag7SiS5I – Ag7GeS5I systems were synthesized by a direct single–temperature method using the pre–synthesized quaternary argyrodites. The obtained samples were investigated by the methods of differential thermal (DTA), X–ray diffraction (XRD), and microstructural (MSA) analyses. Based on the obtained results, it was found that the Ag6PS5I–Ag7GeS5I section is partly quasi–binary due to the incongruent melting of Ag6PS5I. The liquidus of the system is formed by lines of primary crystallization of Ag2S and Ag7GeS5I crystals, which intersect at the point with coordinates: 6 mol. % Ag7GeS5I, 1009 K. The subsolidus part of the Ag6PS5I–Ag7GeS5I system is characterized by the formation of a continuous series of solid solutions. The phase diagram of the Ag7SiS5I–Ag7GeS5I system is characterized by unlimited solubility of components in liquid and solid phases. In the Ag6PS5I–Ag7GeS5I system a positive deviation from Vegard's law is observed.

The successful realization of sustainable energy technologies is nested into the incorporation of resilient storage technologies in grid due to their intermittent nature of energy production. Among these technologies, rechargeable batteries are ubiquitous due to their low cost, easy maintenance, high round trip efficiency and durability. Recently, Na-ion batteries have garnered significant interest for their potential grid application due to inexpensive and earth abundant raw materials. However, their successful commercialization faces several hurdles at both material and cell levels. In particular, the development of high voltage and capacity Na-ion cathodes is one of the key challenges for the successful realization of high energy density sodium ion batteries.1 Whilst layered Na-ion transition metal oxides are the frontrunners for practical application, their poor air stability and cycling stability are still required to be addressed.2 On other hand, phosphate cathodes offer high structural stability and insertion voltages as well rich structural diversity.3 Among them, NASICON-Na3V2(PO4)3 cathode is attractive because of its high intercalation voltage (3.45 V vs. Na+/Na0), moderate capacity (~120 mAh g-1) and excellent rate capability.4 The sodium (de)intercalation process in the NVP cathode proceeds via a two-phase mechanism and the corresponding redox activity is ascribed to the operation of V4+/V3+ couple. Further, other cations are substituted in the place of vanadium of the NVP lattice to seek the participation multiple redox centers, thereby enhancing intercalation capacities. Particularly, the NASICON end member Na4VMn(PO4)3 has garnered significant attention due to its reduced cost, improved insertion voltage and the participation of V5+/V4+, V4+/V3+ and Mn3+/Mn2+ redox couples.5,6 Herein, we will present a comprehensive study on the structural and electrochemical properties of Na3+xV2-xMnx(PO4)3 series. We will show how it is important to modulate electronic and crystal structures of the NASICON framework to attain high capacity and high-rate performances.7 Further, we will also discuss about the impact of alio-/iso-valent cationic substitutions into the NVP framework, which enhances their rate performances and cycle life.8 References Yabuuchi, K. Kubota, M. Dahbi and S. Komaba, Chem. Rev. 2014, 114, 11636.F. Wang, Y. You, Y. X. Yin, Y. G. Guo, Adv. Energy Mater. 2017, 8, 1701912.Masquelier, L. Croguennec, Chem. Rev. 2013, 113, 6552.Chen, C. Wu, L. Shen, C. Zhu, Y. Huang, K. Xi, J. Maier, Y. Yu, Adv. Mater. 2017, 29, 1700431.Zhou, L. Xue, X. Lü, H. Gao, Y. Li, S. Xin, G. Fu, Z. Cui, Y. Zhu, J. B. Goodenough, Nano Lett. 2016, 16, 7836.Chen, V. M. Kovrugin, R. David, O. Mentré, F. Fauth, J. Chotard, C. Masquelier, Small Methods 2019, 3, 1800218.Ghosh N. Barman, M. Mazumder, S. K. Pati, G. Rousse, P. Senguttuvan, Adv. Energy Mater. 2020, 10, 1902918.Ghosh, N. Barman, P. Senguttuvan, Small 2020, 16, 2003973.

The electronic structures and anisotropic transport properties of doped-GeSe monolayers are systematically explored by performing the density functional theory combined with non-equilibrium Green’s function method. Numerical results of the cohesive energy and formation energy show that it is possible to substitute Ge/Se with isovalent atoms and group-V atoms at room temperature. Isovalent substitutions of Ge/Se atoms can maintain the semiconducting features of monolayer GeSe. While the doping of group-V atoms modifies drastically the electronic structures of doped-GeSe and makes metallic properties appear. In addition, the anisotropy of electronic transport of monolayer GeSe also can be effectively manipulated by substitutional doping. In particular, the isotropic electronic transport properties are shown in the devices based on GeSe with P substituting Ge atom. An obvious negative differential resistance behavior with a large current peak-to-valley ratio up to the radio of 103 is gained in N-dope device. These results are useful for the future potential applications of GeSe materials in next-generation high-efficiency electronic devices.

Neodymium (Nd3+)-doped yttrium iron Garnet (YIG) nanoparticles, with compositional variation of NdxY3−xFe5O12 (0.0 ≤ x ≤ 3.0), were prepared by co-precipitation method. The prepared nanoparticles were characterized using TGA, XRD, TEM, SEM, EDX, and FTIR. The calcination temperature was chosen according to the maximum decomposition temperature (˃ 810 °C) achieved in TGA. XRD confirmed the successful phase formation, at the chosen sintering temperature (1100 °C), of Garnet for x < 3.0 (cubic Ia3d symmetry), after which the orthoferrite phase NdFeO3 at x = 3.0 (orthorhombic Pnma symmetry) was formed. The incorporation of Nd3+ increased the lattice parameters (12.3833–12.5020 A), porosity (34.127–39.549%) and crystallite size (82.66–129.99 nm). Agglomerated, distorted, and irregularly shaped nanoparticles were observed in TEM and SEM with the elemental composition confirmed by EDX, inconsistency with the proposed NdxY3−xFe5O12. The FTIR analysis revealed the characteristic bands at 657, 600, and 565 cm−1 with Nd3+ doping concentration between 0.0 and 1.5. These bands disappeared at x = 3.0, where the orthoferrite phase of NdFeO3 dominated. UV–Vis spectroscopy revealed the semiconducting behavior of the prepared samples with energy gaps ranging between 2.89 and 3.02 eV. A broad emission band was observed, in the range 500–550 nm, in the PL spectra of all the prepared samples in agreement with the calculated band energies. The transport properties were studied by DC conductivity measurements and analyzed by the Arrhenius plots, from which two activation energies were determined for each sample. The magnetic properties, investigated by VSM, showed that isovalent substitution of Y3+ by Nd3+ dramatically influenced room temperature parameters, such as saturation magnetization, coercivity, and remanence magnetization.

The substitution of alkali metal cation or halogen anion based on nonlinear crystals is an effective strategy to exploit new optical materials. The strategy has been successfully expanded to discover two new lead halides, Rb3Pb2(CH3COO)2X5 (X = Br, Cl). The substitution of the Cs+ cation with a Rb+ cation can not only increase the local dipole moment of the distorted [PbBr4O2] polyhedron but also reduce the cell unit, resulting in a large net macroscopic polarization. Therefore, Rb3Pb2(CH3COO)2Br5 possesses a strong second-harmonic generation (SHG) response (6 × KDP) and a large birefringence (0.18@1064 nm). Furthermore, by the substitution of the Br- anion with a Cl- anion, Rb3Pb2(CH3COO)2Cl5 exhibits a high laser damage threshold (LDT, 84 × AgGaS2) and a short UV cutoff edge of 287 nm, as well as moderate SHG response (3 × KDP) and birefringence (0.11@1064 nm). Detailed theory calculations elucidate the origin of the linear and nonlinear optical properties of these compounds.

Genesis of the Jigongcun Re-rich quartz vein-type Mo deposit, southern Tibet: Constraints from mineralogy, fluid inclusions, geochronology, H–O–S isotopes, and in situ trace element compositions of molybdenite

Low-angle grain boundaries (GBs) constitute the most important current-limiting mechanism in the operation of biaxially textured YBa2Cu3O7−d (YBCO)-coated conductors. Ca doping of YBCO is known to improve the critical current density J c across the GB because of carrier doping by anisovalent Ca2+ substitution for Y3+ and the strain relief induced by Ca segregation at the GB cores; however, the reduction of the superconducting critical temperature T c accompanying such doping is a marked drawback. Here we study the substitution of isovalent Nd3+ for Y3+ again using strain-driven segregation, in this case Nd3+, to improve J c without incurring significant T c reduction. Transport characteristics of low-angle GBs of 10% Nd-doped YBCO, Y0.9Nd0.1Ba2Cu3O7−d, grown on single crystal and 6° and 9° [001] tilt symmetric bicrystal SrTiO3 substrates are reported. It was found that J c across the 6° GB recovers to the intra-grain J c value in the 10% Nd-doped YBCO, while the 9° GB shows a modest J c enhancement compared to the pure YBCO 9° GB without a significant T c reduction. It is shown that the transparency of the GB could be enhanced without a large T c reduction by the isovalent substitution of rare-earth ions, suggesting new opportunities for cation segregation engineering in YBCO by isovalent rare-earth substitution.

Isovalent sulfur substitution to induce a simultaneous increase in the effective mass and weighted mobility of a p-type Bi-Sb-Te alloy: an approach to enhance the thermoelectric performance over a wide temperature range

Superconductivity from buckled-honeycomb-vacancy ordering