Influence Of Cation Substitution Research Articles

The Magnetic and Color Reflectance Properties of Hematite: From Earth to Mars

AbstractHematite is a canted antiferromagnet with reddish color that occurs widely on Earth and Mars. Identification and quantification of hematite is conveniently achieved through its magnetic and color properties. Hematite characteristics and content are indispensable ingredients in studies of the iron cycle, paleoenvironmental evolution, paleogeographic reconstructions, and comparative planetology (e.g., Mars). However, the existing magnetic and color reflectance property framework for hematite is based largely on stoichiometric hematite and tends to neglect the effects of cation substitution, which occurs widely in natural hematite and influences the physical properties of hematite. Thus, magnetic parameters for stoichiometric hematite are insufficient for complete analysis of many natural hematite occurrences and can lead to ambiguous geological interpretations. Remagnetization, which occurs pervasively in red beds, is another ticklish problem involving hematite. Understanding red bed remagnetization requires investigation of hematite's formation and remanence recording mechanisms. We elaborate on the influence of cation substitution on the magnetic and color spectral properties of hematite, and on identifying hematite and quantifying its content in soils and sediments. Studies of remagnetization mechanisms are discussed, and we summarize methods to discriminate between primary and secondary remanences carried by hematite in natural samples to aid primary remanence extraction in partially remagnetized red beds. Although there remain unknown properties and unresolved issues that require future work, recognition of the properties of cation‐substituted hematite and remagnetization mechanisms for hematite will aid identification and interpretation of the magnetic signals that it carries, which is environmentally important and responsible for magnetic signals on Earth and Mars.

Ecotoxicity of cationic cellulose polymers to aquatic biota: The influence of charge density

Better performances of cellulose-based polymers can be achieved by adjust their architecture including the density of cationic modifications. In this study, the influence of cationic substitution on the ecotoxicity of four quaternized hydroxyethyl cellulose polymers (SK-H, SK-L, SK-M, SK-MH) was studied, using an aquatic biota acute ecotoxicity classification, and rheological and physicochemical characterization. The ecotoxicity characterization was achieved by performing standard ecotoxicity assays with seven key trophic level species: Vibrio fischeri, Raphidocelis subcapitata, Chlorella vulgaris, Daphnia magna, Brachionus calyciflorus, Heterocypris incongruens, and Danio rerio. Median effective concentrations were used to compute hazard concentrations, through the species sensitive distribution curves method. The microalga C. vulgaris and rotifer B. calyciflorus were the most sensitive species to the studied polymers. The SK-H variant was highly toxic to the rotifer. Overall, variants with intermediate levels of cationic charge (SK-M, SK-MH) presented the lowest toxicity. The SK-M variant showed the lowest value of maximum acceptable concentration (0.00354 mg/L), thus being indicated as the least toxic variant. Therefore, the obtained results suggest that industry could direct the development of this type of polymers by tailoring its cationic substitution to moderate levels, in such a way that both functionality and environmental toxicity could be maximized.

Influence of cation substitution on electrical conductivity of microcrystalline ceramics based on (Cu1-xAgx)7GeSe5I solid solutions

Ceramic samples based on the microcrystalline powders (Cu1–хAgx)7GeSe5I (x = 0, 0.25, 0.5, 0.75, 1) were prepared by pressing them at the pressure close to 400 MPa and subsequent annealing at 873 K for 36 hours. Using the microstructural analysis, the average size of microcrystallites of these samples was determined. Investigation of electrical conductivity of ceramics based on (Cu1 хAgx)7GeSe5I solid solutions was carried out using the method of impedance spectroscopy in the frequency range from 10 Hz to 3×105 Hz and within the temperature range 293...383 K. Analysis of the Nyquist plots allowed determining the contributions of ionic and electronic components to the total electrical conductivity. The temperature dependence of ionic and electronic conductivity in Arrhenius coordinates is linear, which indicates their thermoactivation character. The compositional behaviour of ionic and electronic conductivity, as well as their activation energies have been studied. Their nonlinear character can be explained by the complex process of recrystallization and Cu+ ↔ Ag+ cation substitution within the cationic sublattice.

Dielectric and local piezoelectric properties of lead-free KNN-based perovskite ceramics

Influence of cation substitutions in (K0.5Na0.5)NbO3–Ba(Li2/5W3/5)O3 ceramics on structure parameters, microstructure, dielectric, ferroelectric and local piezoelectric properties have been studied. Depending on solid solutions compositions, changes in structure parameters and effective d33 piezoelectric coefficient and other properties were observed.

Influence of cation substitution on mechanical properties of (Cu1-xAgx)7GeSe5I mixed crystals and composites on their base

Influence of cation substitution on mechanical properties of (Cu1-xAgx)7GeSe5I mixed crystals and composites on their base

Ferroelectric and local piezoelectric properties of modified KNN ceramics

Influence of cation substitution on structure parameters, microstructure, dielectric, ferroelectric and local piezoelectric properties of (K0.5Na0.5)NbO3 ceramics additionally modified by Li+ and Mn3+ cations (up to 10 at. %) have been studied. Changes in dielectric properties and effective d33 piezoelectric coefficients were observed depending on compositions of solid solutions.

Crystal growth, structural and electrical properties of (Cu1-хAgx)7GeS5I superionic solid solutions

Single crystals of (Cu1-хAgx)7GeS5I solid solutions were grown by vertical zone crystallization method. XRD studies have shown that they crystallize in face-centered cubic lattice of the argyrodite structure (space group F4¯3m, Z = 4). Structural studies were performed on the basis of original structure model by means of Rietveld refinement method. Electrical measurements were carried out in the temperature interval 300–360 K and in the range of frequencies 10 Hz–10 GHz. Temperature and frequency dependences of electrical conductivity were analyzed. Influence of cation substitution on the electrical conductivity as well as relationship between structural and electrical properties of (Cu1-хAgx)7GeS5I solid solutions were studied.

Temperature-Induced structural phase transformations in Cu1.50Zn0.30Te and Cu1.75Cd0.05Te single crystals

The results of studying the temperature-induced polymorphic phase transformations in Cu1.50Zn0.30Te and Cu1.75Cd0.05Te single crystals are presented. The single crystals have been investigated in the range of 290–1100 K using X-ray diffraction analysis. The temperature dependences of the unit-cell parameters, X-ray density, and coefficients of thermal expansion for each polymorphic modification of Cu1.50Zn0.30Te and Cu1.75Cd0.05Te single crystals are presented. The influence of cationic substitution (replacement of Cu2+ with Zn2+ and Cd2+ cations) on the phase-formation processes, number of polymorphic modifications, and temperature of structural phase transition in single crystals of these solid solutions is demonstrated.

Influence of cation substitution on the polymorphic transformation in Ag2–х Cu х S (х = 0.45, 0.8, and 1.07) crystals

The influence of the concentration substitution of Ag ions for Cu ions in the structure of Ag2–хCuхS (х = 0.45, 0.8, and 1.07) solid solutions on the temperature of polymorphic phase transitions is demonstrated. The phase composition of Ag2–хCuхS (х = 0.45, 0.8, and 1.07) solid solutions has been investigated by X-ray diffraction at different temperatures. It is shown that the structure of the polymorphic modification of Ag0.93Cu1.07S composition and the phase transition temperature correspond to the structure and parameters of AgCuS single crystal. The structures of the modifications of compositions with a high silver concentration (Ag1.55Cu0.45S and Ag1.2Cu0.8S) and the phase transitions temperatures differ from the structure and corresponding parameters of AgCuS single crystal.

Framework and Channel Modifications in Mayenite (12CaO·7Al2O3) Nanocages By Cationic Doping

Mayenite (Ca12Al14O33, C12A7), and its electride variant (C12A7:2e–) have attracted attention as functional materials with high ionic conductivity, and for potential uses in oxidation catalysis, fuel cells, and hydrogen storage. In contrast to anionic substitutions into C12A7, less is known about the influence of cationic substitutions on this material. This study applies DFT methods to rigorously understand the influences of Mg2+, Cu2+, Sr2+, Fe3+, Ir4+, P5+ and V5+ (2+ ≤ ZV ≤ 5+, where ZV is the cation valence, unitless) substitutions on the structural and electronic features of C12A7 and its electride variant. Substitutions alter the lattice parameters, in relation to their size, and alter charge localization. Substitutions also affect mayenite’s cage framework, resulting in the formation of a “window” that connects two adjacent cages. While Mg2+, Sr2+, P5+, and V5+ substitutions maintain their F+-like attractive nature, Cu2+, Fe3+, and Ir4+ neutralize such a tendency in the cages of their correspondin...

Enhanced Red Emission in LiY1-xMo2O8: xEu3+ Phosphors for White Light Emitting Diodes

Red emission in LiY1-xMo2O8: xEu3+ is enhanced by substituting Sr2+ in the crystal lattice of LiYMo2O8 and. Influence of cation substitution on the photoluminescence properties of these phosphors are elucidated using powder X-ray diffraction, Raman spectrum and photoluminescence excitation and emission spectra. Long range ordering in the crystal lattice with progressive europium doping and distortion induced by bigger ion substitution are confirmed from Raman spectra.

A novel efficient Mn4+ activated Ca14Al10Zn6O35 phosphor: application in red-emitting and white LEDs.

A new, highly efficient deep red-emitting phosphor Ca14Al10Zn6O35:Mn(4+) was developed as a component of solid-state white light-emitting diodes (LEDs). The structural and optical characterization of the phosphor is described. The phosphor exhibits strong emission in the range of 650-700 nm when excited by 460 nm excitation, with a quantum efficiency approaching 50%. Concentration dependence of Mn(4+) luminescence in Ca14Al10Zn6O35:Mn(4+) is investigated. Attempts to understand the thermal stability on the basis of the thermal quenching characteristics of Ca14Al10Zn6O35:Mn(4+) is presented. The results suggest that phosphors deriving from Ca14Al10Zn6O35:Mn(4+) have potential application for white LEDs. In addition, influence of cation substitution on the luminescence intensity of these phosphors is elucidated.

Structural, spectroscopic, and thermophysical investigations of the oxyfluorides CsZnMoO3F3 and CsMnMoO3F3 with the pyrochlore structure

The structure, infrared and Raman spectra, heat capacity, and thermal expansion have been investigated. It has been shown that, down to liquid-helium temperatures, the cubic pyrochlore structure of the CsMnMoO3F3 and CsZnMoO3F3 oxyfluorides remains stable. The influence of cation substitution on individual features of the properties of the oxyfluorides has been analyzed.

Influence of Cation Substitution and Activator Site Exchange on the Photoluminescence Properties of Eu3+-Doped Quaternary Pyrochlore Oxides

Stannate-based pyrochlore-type red phosphors CaGd(1-x)SnNbO7:xEu(3+), Ca(1-y)Sr(y)Gd(1-x)SnNbO7:xEu(3+), and Ca(0.8-x)Sr0.2GdSnNbO(7+δ): xEu(3+) were prepared via conventional solid-state method. Influence of cation substitution and activator site control on the photoluminescence properties of these phosphors are elucidated using powder X-ray diffraction, Rietveld analysis, Raman spectrum analysis, and photoluminescence excitation and emission spectra. The Eu(3+) luminescence in quaternary pyrochlore lattice exemplifies as a very good structural probe for the detection of short-range disorder in the lattice, which otherwise is not detected by normal powder X-ray diffraction technique. The Eu(3+) emission due to magnetic dipole transition ((5)D0-(7)F1 MD) is modified with the increase in europium concentration in the quaternary pyrochlore red phosphors. (5)D0-(7)F1 MD transition splitting is not observable for low Eu(3+) doping because of the short-range disorder in the pyrochlore lattice. Appearance of narrow peaks in Raman spectra confirms that short-range disorder in the crystal lattice disappears with progressive europium doping. By using Sr as a network modifier ion in place of Ca we were able to increase the f-f transition intensities and europium quenching concentration. The influence of effective positive charge of the central Eu(3+) ions when it replaces a metal ion having lower oxidation state such as Ca(2+) was also investigated. The relative intensities of A1g (∼500 cm(-1)) and F2g (∼330 cm(-1)) Raman vibrational modes get inverted when Eu(3+) ions replaces Ca(2+) ions instead of Gd(3+) as trivalent europium ions can attract the electron cloud of oxygen ions strongly in comparison with divalent calcium ions. The influence of positive charge effect of Eu(3+) in Ca0.7Sr0.2GdSnNbO7+δ:0.1Eu(3+) phosphor is greatly strengthened the charge transfer band and (7)F0-(5)L6 transition intensities than that of the Ca0.8Sr0.2Gd0.9SnNbO7:0.1Eu(3+) phosphor. Our results suggest that the photoluminescence properties can be enhanced by simple compositional adjustments in the quaternary pyrochlore-type red phosphors.

Influence of cationic substitutions on the first charge and reversible capacities of lithium-rich layered oxide cathodes

The reversible capacity values of lithium-rich layered oxide cathodes depend on the length (capacity) of the plateau region during the first charge. With an aim to understand the factors that control the length of the plateau region and thereby enhance the reversible capacity, the effects of various cationic substitutions in Li1.2Mn0.6Ni0.2O2 have been investigated systematically. Specifically, substitutions of (i) M3+ = Al3+, Cr3+, Fe3+, Co3+, and Ga3+ for equal amounts of Mn4+ and Ni2+ in Li1.2Mn0.6−0.5xNi0.2−0.5xMxO2 with x = 0.06, 0.13, and 0.2, (ii) Ti4+ for Mn4+ in Li1.2Mn0.6−xTixNi0.2O2 with x = 0.025, 0.05, and 0.1, and (iii) Mg2+ for Ni2+ in Li1.2Mn0.6Ni0.2−xMgxO2 with x = 0.025, 0.05, and 0.1 have been investigated. The cationic substitutions affect the first charge capacity values both in the sloping region corresponding to the oxidation of the transition-metal ions to the 4+ state and in the plateau region corresponding to the oxidation of O2− ions to O2 and/or transition-metal ions beyond 4+, which control the reversible capacity values in subsequent cycles. While the changes in the sloping-region capacity could be readily understood by considering the redox activities of the transition-metal ions, the plateau-region capacity is found to depend sensitively on the metal–oxygen covalence, which is dictated by the relative positions of the metal:3d band with respect to the top of the O2−:2p band, and electron delocalization. For instance, an overlap of the Co3+/4+:t2g band with the top of the O2−:2p band along with a partially filled t2g band across the shared octahedral edges makes the oxygen loss from the lattice and/or oxidation beyond 4+ much more facile.

Oxygen permeation and oxidation states of transition metals in (Fe, Nb)-doped BaCoO 3 − δ perovskites

The influence of cation substitution on the transition metal oxidation states, oxygen nonstoichiometry and oxygen transport properties of Ba(Co, Fe, Nb)O 3 − δ perovskites was investigated with room temperature XRD, X-ray absorption near edge structure and high temperature oxygen permeation measurements. Results show that substitution of Fe for Co is accompanied by a decrease in the lattice constant, whereas Nb substitution leads to the opposite trend. With increasing Fe and/or Nb content, the oxygen permeation flux decreases, whereas the apparent activation energy of the oxygen permeation increases. The oxidation state of Co is smaller than +3 and susceptible to the variation of cation composition. In contrast, the oxidation states of Fe and Nb are larger than +3 and close to +5, respectively, and almost independent of the composition. The influence of Fe and Nb contents on the oxygen transport properties is discussed in terms of the oxygen stoichiometry and metal–oxygen bonding.

Influence of Cationic Substitutions on the Oxygen Loss and Reversible Capacity of Lithium-Rich Layered Oxide Cathodes

The influence of cationic substitutions on the ease with which oxygen loss occurs from lithium-rich layered oxide cathodes during first charge has been studied with three series of samples: Li[Li0.33Mn0.67−xTix]O2 (0 ≤ x ≤ 0.67), Li[Li0.2Mn0.54−xTixNi0.13Co0.13]O2 (0 ≤ x ≤ 0.27), and Li[Li0.2Mn0.60−xTixNi0.20]O2 (0 ≤ x ≤ 0.40). The lattice parameters and cell volume increase monotonically with the substitution of a larger Ti4+ for Mn4+, indicating the formation of solid solutions. It is found that substitution of Ti4+ for Mn4+ decreases the degree of oxygen loss and consequently the charge and discharge capacity values, while substitution of Co3+ for (Mn0.54+Ni0.52+) increases the oxygen loss and consequently the charge and discharge capacity values. While the former is attributed to a stronger binding of oxygen to Ti and a decrease in the metal−oxygen covalence due to a larger charge transfer gap between the Ti3+/4+ 3d and O2− 2p bands, the latter is attributed to a weaker binding of oxygen to Co and an ...

Magnetic and Static Nonlinear Dielectric Response in Doped CdCr2S4

The influence of cation substitution on the magnetic and static nonlinear dielectric response in the doped magnetic relaxor ferroelectrics CdCr2S4 is investigated within the framework of the spherical random-bond-random-field model (SRBRF) and the site-dilution Heisenberg model by adding an appropriate coupling term between the magnetic and ferroelectric subsystems. A-site substitution of the Cd by Fe in Cd1-xFexCr2S4 is found to reduce significantly the magnetization, which well agrees with the experimental results. Furthermore, the doping Fe ions play a crucial role in the spin-pair correlation and the nonlinear dielectric properties.

Doping effect on the magnetocapacitance in Cd1−xFexCr2S4

The influence of cation substitution on the Curie temperature and the magnetocapacitance in the doped magnetic relaxor ferroelectrics CdCr2S4 is investigated within the framework of the spherical random-bond-random-field model for the relaxor ferroelectric sublattice and the Heisenberg model for the magnetic sublattice. The site-dilution model is also introduced to describe the doping effect. A-site substitution of the Cd by Fe in Cd1−xFexCr2S4 is found to increase significantly the value of the Curie temperature, which well agrees with the experimental results. Additionally, the doping Fe ions play a crucial role in the fluctuation of spin-pair correlation and magnetocapacitive response.

Influence of cation substitution on electrical conductivity of the n-type Cu xIn yCr zSe 4 spinels

The single-crystal X-ray diffraction studies have shown that indium ions admixed with CuCr 2Se 4 may locate both in tetra- and octahedral sites of the spinel structure. This property has strong impact on electrical conductivity of the compounds under study. It appeared that octahedral coordination of In 3+ ions leads to metallic conduction, while tetrahedral coordination of In causes semiconducting properties. The thermopower measurement revealed that all samples show n-type conduction in the temperature range 290–480 K. In Cu[Cr 1.38In 0.62]Se 4 a collective electron behaviour in the unfilled of the lowest Cr 3+ Mott-Hubbard sub-band of 3d 3 t 2g band is observed, while in (Cu 0.46In 0.54)Cr 2.08Se 4 a hopping process involving a transfer of electrons from Cr 2+ to Cr 3+ takes place.