Random Distribution Of Cations Research Articles

Effects of thermal, stress, and electric fields on microstructure and ion distribution of (Mg0.1Mn0.1Co0.1Ni0.2Ti0.1Cu0.1Zn0.2)Fe2.1O4 spinel ferrites

In this work, conventional sintering, hot-pressing sintering, and spark plasma sintering techniques were utilized to simulate the thermal field, thermal-stress field, and thermal-stress-electric field, respectively. The effects of these fields on the microstructure and cation distribution of the (Mg0.1Mn0.1Co0.1Ni0.2Ti0.1Cu0.1Zn0.2)Fe2.1O4 ferrite (HEF) material were comprehensively analyzed. The results indicate that in the temperature range of 1000–1100 °C, the thermal field provides the driving force for sintering, promotes grain growth (average particle size: 2→7 μm), and increases crystallinity degree. The stress field brings the particles into close contact with each other, facilitates diffusion, and delays grain growth (0.5→5 μm). The electric field reduces grain boundary energy, causes mass transfer, and makes the grains finer (0.5→0.7 μm) and more uniform. Mathematical model analysis reveals that the thermal field is beneficial to the random distribution of cations, which yields an inversion degree (γ) of about 2/3 and increases the configuration entropy of HEF. The stress field leads to lattice distortion, permits ions with larger radius to occupy tetrahedral positions, and changes the cell parameters and oxygen position parameter of HEF. Finally, the interaction between electric field and crystal charges increases the electrostatic field energy, which promotes the formation of positive spinel structure and maximizes the crystal field stability energy. X-ray photoelectron spectra, Raman spectra, and change in lattice constant confirm the rationality of the mathematical model, and can be used to establish the model of the crystal structure under field effects.

Local structure and ordering of Al atoms in AlxGa1−xN epilayers

In this study, we investigate the local structure of aluminum (Al) in a comprehensive series of AlxGa1−xN epilayers, where the Al concentration spans from the dilute limit to 100%. We analyze grazing incidence Al K-edge tender x-ray absorption spectroscopy data using both linear combination fitting based on reference limit spectra and full quantitative analysis. The results indicate deviations from random cation distribution with varying signs within the explored concentration range. Additionally, we observe a reduction in cationic interatomic distances over a wide concentration range, which contrasts with some previous studies conducted at hard x-ray absorption edges.

Compositional and Structural Disorder in Two-Dimensional AIIIBVI Materials

Two-dimensional (2D) van der Waals (vdW) AIIIBVI semiconductor materials, such as InSe and GaSe, are of considerable interest due to their potential use in various microelectronics applications. The range of properties of materials of this class can be extended further through the use of quasi-binary alloys of the InSe(Te)-GaSe(Te) type. In this work, we study the effect of compositional and structural disorder in 2D In(Ga)Se(Te) on the band structure and electronic properties using first principles modeling. The results for In(Ga)Se demonstrate a noticeable decrease in the band gap for structures with a random distribution of indium and gallium cations, while for In(Ga)Te with a random cation distribution, metallization occurs. Changes in the compositional arrangement of chalcogens (there can be either the same or different atoms on each side of the vdW gap) lead to pronounced changes in the band gap, but no significant changes in topology are observed. In addition, a significant effect of the distance between the layers on the band gap under compression along the c axis was found for both alloys under study. An important point of our study is that van der Waals gap engineering is a very powerful tool to control the properties of 2D materials and its alloys.

Enhanced Bacterial Growth by Polyelemental Glycerolate Particles.

While polyelemental alloys are shown to be promising for healthcare applications, their effectiveness in promoting bacterial growth remains unexplored. In the present work, we evaluated the interaction of polyelemental glycerolate particles (PGPs) with Escherichia coli (E. coli) bacteria. PGPs were synthesized using the solvothermal route, and nanoscale random distribution of metal cations in the glycerol matrix of PGPs was confirmed. We observed 7-fold growth of E. coli bacteria upon 4 h of interaction with quinary glycerolate (NiZnMnMgSr-Gly) particles in comparison to control E. coli bacteria. Nanoscale microscopic studies on bacteria interactions with PGPs showed the release of metal cations in the bacterium cytoplasm from PGPs. The electron microscopy imaging and chemical mapping indicated bacterial biofilm formation on PGPs without causing significant cell membrane damage. The data showed that the presence of glycerol in PGPs is effective in controlling the release of metal cations, thus preventing bacterial toxicity. The presence of multiple metal cations is expected to provide synergistic effects of nutrients needed for bacterial growth. The present work provides key microscopic insights of mechanisms by which PGPs enhance biofilm growth. This study opens the door for future applications of PGPs in areas where bacterial growth is essential including healthcare, clean energy, and the food industry.

Design and optical properties of a new binary Bi1/2Na1/2TiO3-Eu1/2Na1/2TiO3 solid solution system

A new binary (1-x)Bi1/2Na1/2TiO3+xEu1/2Na1/2TiO3 system was synthesized by a simple chemical method. X-ray diffraction and Raman scattering studies on the crystal structure of Eu1/2Na1/2TiO3-modified Bi1/2Na1/2TiO3 materials proved that Eu1/2Na1/2TiO3 was well dissolved into the host Bi1/2Na1/2TiO3 materials. The random incorporation of impurity cations of Eu1/2Na1/2TiO3 materials during solute into host Bi1/2Na1/2TiO3 crystal resulted in compressing the rhombohedral structure of the host material. The random distribution of impurity cations of Eu1/2Na1/2TiO3 into the host Bi1/2Na1/2TiO3 lattices exhibited a complex change in the optical bandgap of pure Bi1/2Na1/2TiO3 materials with the value ranging from 3.04 eV to 2.89 eV. Strong photoemission of Eu1/2Na1/2TiO3-modified Bi1/2Na1/2TiO3 materials obtained at room temperature was related to electron transition from 4f-4f levels of Eu3+ cations incorporated with the host lattice. We expected our work to provide a simple method to integrate the photoluminescence properties in lead-free ferroelectric materials for innovative electronic applications.

Thermoelectric properties of high-entropy rare-earth cobaltates

High-entropy concept introduced with a promising paradigm to obtain exotic physical properties has motivated us to explore the thermoelectric properties of Sr-substituted high-entropy rare-earth cobaltates i.e., (LaNdPrSmEu)1-xSrxCoO3 (0 ≤ x ≤ 0.10). The structural analysis of the samples, synthesized using the standard solid-state route, confirms the orthorhombic structure with the Pbnm space group. The Seebeck coefficient and electrical resistivity decrease with rising Sr concentration as well as with an increase in temperature. The multiple A-site ions in high-entropy rare-earth cobaltates result in an improved Seebeck coefficient (α) compared to La0.95Sr0.05CoO3, associated with a decrease in the CoOCo bond angle, which further enhances the power factor. The random distribution of cations at the rare-earth site results in a significant lowering of phonon thermal conductivity. As a result, a maximum figure of merit (zT) of 0.23 is obtained at 350K for (LaNdPrSmEu)0.95Sr0.05CoO3, which is one of the highest values of zT reported at this temperature for oxide materials. This study shows promise to decouple thermoelectric parameters using the high-entropy concept in several materials.

Fabrication and optical properties of new (1-x)Bi1/2Na1/2TiO3+xHo1/2Na1/2TiO3 solid solution materials

A new binary (1-x)Bi1/2Na1/2TiO3+xHo1/2Na1/2TiO3 solid solution system was synthesized by a simple chemical method. The crystal structure of (1-x)Bi1/2Na1/2TiO3+xHo1/2Na1/2TiO3 system was characterized by X-ray diffraction, showing that the crystal structure of the system followed the rhombohedral structure with symmetry of Bi1/2Na1/2TiO3 materials. The distortion lattice parameters of Bi1/2Na1/2TiO3 resulted from the random distribution of Ho impurity cations into the host lattice of Bi1/2Na1/2TiO3 materials to form the solution. The direct optical bandgap energy of Bi1/2Na1/2TiO3 materials was slightly changed in the range of 3.04–2.99 eV after the addition of Ho1/2Na1/2TiO3. The strong enhancement in photoemission properties of Bi1/2Na1/2TiO3 materials was related to electron transition from 5S2 to 5I8 level of Ho3+ cations randomly incorporated with the host Bi1/2Na1/2TiO3 lattice. We expected our work to open a new simple way to integrate the photoluminescence properties in lead-free ferroelectric materials for further smart optoelectronic devices application.

Al-Doped SrMoO3 Perovskites as Promising Anode Materials in Solid Oxide Fuel Cells.

Two perovskite materials with SrMo1−xAlxO3−δ (x = 0.1, 0.2) compositions have been synthesized by reduction from the corresponding scheelite phases, with SrMo1−xAlxO4−δ stoichiometry; the pertinent characterization shows that the defective perovskites can be used as anode materials in solid oxide fuel cells, providing maximum output power densities of 633 mW/cm2 for x = 0.2. To correlate structure and properties, a neutron powder diffraction investigation was carried out for both perovskite and scheelite phases. Both perovskites are cubic, defined in the Pm-3m space group, displaying a random distribution of Mo and Al cations over the 1a sites of the structure. The introduction of Al at Mo positions produced conspicuous amounts of oxygen vacancies in the perovskite, detected by neutrons. This is essential to induce ionic diffusion, providing a mixed ionic and electronic conduction (MIEC), since in MIEC electrodes, charge carriers are combined in one single phase and the ionic conductivity can be one order of magnitude higher than in a conventional material. The thermal expansion coefficients of the reduced and oxidized samples demonstrated that these materials perfectly match with the La0.8Sr0.2Ga0.83Mg0.17O3−δ electrolyte, La0.4Ce0.6O2−δ buffer layer and other components of the cell. Scanning electron microscopy after the test in a real solid oxide fuel cell showed a very dense electrolyte and porous electrodes, essential requirements for this type of fuel. SrMo1−xAlxO3−δ perovskites are, thus, a good replacement of conventional biphasic cermet anodes in solid oxide fuel cells.

Magnetic and optical properties of new (1 − x)Bi0.5Na0.5TiO3 + x CaMnO3−δ solid solution materials

CaMnO3-δ-modified Bi0.5Na0.5TiO3 was fabricated by using a sol–gel method. In the modified Bi0.5Na0.5TiO3, a single perovskite with distorted structure was obtained due to the random distribution of Ca and Mn cations in the host lattice. The co-modification in A- and B-sites of Bi0.5Na0.5TiO3 via Ca and Mn resulted in the reduction of optical band gap and induction of room-temperature ferromagnetism. Co-modification of A- and B-sites in lead-free ferroelectric Bi0.5Na0.5TiO3 is suitable for fabricating smart materials in electronic devices.

The evolution of saponite: An experimental study based on crystal chemistry and crystal growth

AbstractElement incorporation and partitioning during the evolution of clay minerals have significant implications for element cycling in geochemical processes. The main aim of this experimental study is to further our understanding of element redistribution and crystal growth during smectite evolution under different physicochemical conditions. The precursors (i.e., pure Mg- and Ni-saponite) were separately prepared by hydrothermal syntheses at the same set of temperatures (i.e., RT, 50, 150, 180, 200, and 220 °C) for one day. Then the starting materials were obtained from the mechanical mixtures of the identical molar weight of Mg- and Ni-smectite precursors prepared at the same temperature. Subsequently, Series I samples were obtained by hydrothermally treating different starting materials at 220 °C for two weeks while Series II samples were hydrothermally synthesized under various temperatures (220, 300, 400, and 500 °C) for one week using the starting materials prepared at 220 °C. Both the precursors and resultant saponites were characterized by XRD, FTIR, TEM, and STEM. The FTIR spectra of the precursors only exhibit the vMg3OH and vNi3OH bands, corresponding to Mg-saponite and Ni-saponite, respectively. However, the occurrence of vMg2NiOH and vNi2MgOH bands in the resultant saponite indicates the dissolution of the corresponding Mg- and Ni-saponite precursors and recrystallization of Mg-Ni mixed saponite. The dissolution extents of Mg- and Ni-saponite precursors, which affect the degrees of random distribution of octahedral Ni and Mg in resultant Mg, Nisaponite, are significantly controlled by the temperature gap (ΔT) between the precursors prepared and the resultant Mg, Ni-saponite obtained. In general, a larger ΔT leads to a higher dissolution extent of saponite precursors and a higher degree of random distribution of octahedral Ni and Mg cations in the resultant Mg, Ni-saponite structures. Thus, the distribution mode of octahedral cations in saponite, which is not only relevant to a given hydrothermal temperature but also dependent on ΔT for final products, cannot be used as a geothermometer. TEM and STEM observations provide visual evidence that the particles of saponite coarsen when ΔT is higher than zero. Both the crystal-chemical and morphological features during saponite evolution suggest that saponite particles coarsen mainly via partial/complete dissolution of precursors followed by recrystallization and growth of Mg, Ni-saponite in which crystal growth by layer attachment cannot be excluded. This study presents an experimental approach to evaluate the evolution of clay minerals in terms of crystal chemistry and crystal growth and offers a better understanding of the contributions of clay mineral evolution to element cycling.

Short‐range ordering in the Li‐rich disordered rock salt cathode material Li2VO2F revealed by Raman spectroscopy

AbstractLi‐rich disordered rock salt (DRS) materials are new promising high‐capacity cathode candidates for Li‐ion batteries. DRS structures were initially assumed to have a completely random cation and anion distribution, but recent reports suggest that some of these structures can exhibit local atomic arrangements, or short‐range ordering (SRO). Here, we prove the existence of SRO in the Li‐rich DRS material Li2VO2F by employing Raman spectroscopy supported by density functional theory (DFT) calculations. Our results suggest that this combination of Raman spectroscopy with computational tools is useful for SRO estimation in this new class of Li‐rich DRS cathode materials.

Intrinsic and tunable ferromagnetism in Bi0.5Na0.5TiO3 through CaFeO3-\u03b4 modification

New (1-x)Bi0.5Na0.5TiO3 + xCaFeO3-δ solid solution compounds were fabricated using a sol–gel method. The CaFeO3-δ materials were mixed into host Bi0.5Na0.5TiO3 materials to form a solid solution that exhibited similar crystal symmetry to those of Bi0.5Na0.5TiO3 phases. The random distribution of Ca and Fe cations in the Bi0.5Na0.5TiO3 crystals resulted in a distorted structure. The optical band gaps decreased from 3.11 eV for the pure Bi0.5Na0.5TiO3 samples to 2.34 eV for the 9 mol% CaFeO3-δ-modified Bi0.5Na0.5TiO3 samples. Moreover, the Bi0.5Na0.5TiO3 samples exhibited weak photoluminescence because of the intrinsic defects and suppressed photoluminescence with increasing CaFeO3-δ concentration. Experimental and theoretical studies via density functional theory calculations showed that pure Bi0.5Na0.5TiO3 exhibited intrinsic ferromagnetism, which is associated with the possible presence of Bi, Na, and Ti vacancies and Ti3+-defect states. Further studies showed that such an induced magnetism by intrinsic defects can also be enhanced effectively with CaFeO3-δ addition. This study provides a basis for understanding the role of secondary phase as a solid solution in Bi0.5Na0.5TiO3 to facilitate the development of lead-free ferroelectric materials.

Wurtzite CuNi2InS4 Nanocrystals: A Quaternary Chalcogenide Magnetic Semiconductor.

For the first time, quaternary chalcogenide CuNi2InS4 nanocrystals with a wurtzite structure have been designed and fabricated as a new magnetic semiconductor. The phase structure analysis suggests that the synthesized wurtzite CuNi2InS4 phase has a disordered structure in which Cu+, Ni2+, and In3+ ions share the same lattice site of the unit cell with a random cation distribution. The prepared CuNi2InS4 nanocrystals have uniform bullet-like morphology, small size distribution, good monodispersity, and high crystallinity. The magnetic properties investigation reveals that the wurtzite CuNi2InS4 nanocrystals can exhibit a weak ferromagnetic moment with the blocking temperature at around 13 K thanks to the disordered wurtzite structure and the high content of magnetic Ni2+ ions. As for the semiconducting properties, the as-obtained wurtzite CuNi2InS4 nanocrystals show a strong and broad visible light absorption and have a direct bandgap of 1.45 eV. Due to their favorable optical properties, the fabricated thin film of CuNi2InS4 nanocrystals exhibits a good photoelectric response to the solar spectrum, which makes the obtained new phase potential candidate for applications in the photovoltaics. This work demonstrates a new metastable I-II2-III-VI4 chalcogenide that can be used to render multiple functionalities and applications.

Magnetic and optical properties of new (1 − x) Bi0.5Na0.5TiO3 + x BaMnO3−δ solid solution materials

A solid solution of BaMnO3−δ and Bi0.5Na0.5TiO3 was prepared using a sol–gel method. X-ray diffraction analysis of Bi0.5Na0.5TiO3 − x BaMnO3−δ samples indicated a rhombohedral structure of Bi0.5Na0.5TiO3 materials during distortion due to the random distribution of Ba and Mn cations in the host lattice. The substitution of Ba and Mn at A- and B-sites in the perovskite structure of Bi0.5Na0.5TiO3 changed the optical band gap due to local defect and/or promotion of oxygen vacancies. The samples exhibited strong room temperature ferromagnetism, which overcame the weak ferromagnetism and diamagnetism of Bi0.5Na0.5TiO3 materials. Our study provided a flexible approach to integrate the ferromagnetism properties of ferroelectric materials.

The structural evolution and optical properties of Mg1-xZnxAl1.8Cr0.2O4 pink ceramic pigments

Abstract In this work, pink ceramic pigments based on the composition of Mg1-xZnxAl1.8Cr0.2O4(x = 0.0,0.3,0.5,0.7,1.0) were synthesized by using a gel polymerization method. We focused on studying the effect of A-site ion doping on the random cation distribution, microstructure and optical absorption performance. Field Scanning electron microscopy (FESEM), X-ray diffraction (XRD) and the Rietveld refinement method with a GSAS program were applied for micromorphology and cation distribution analyses. The optical performance of the pigments was studied by UV–vis and CIE L*a*b* spectrophotometry. All samples had a single spinel phase within the calcination temperature range of 800 °C–1400 °C and the primary grain size of the synthesized pigments were approximately 0.5–1 μm. The ion distribution in the tetrahedron and octahedron was largely dependent upon the calcining temperature and composition. The oxygen parameter, cell parameter, and T-O and M-O band lengths also varied with the cation distribution, leading to a change in the spinel structure and octahedron crystal field parameter and ultimately changing the optical absorption properties of the synthetic pigments. This study lays the foundation for subsequent studies of colour modification in ceramics.

Magnetic and optical properties of MgMnO3−-modified Bi0.5Na0.5TiO3 materials

Abstract The phase structural, optical and magnetic properties of a new (1 − x)Bi0.5Na0.5TiO3 + xMgMnO3−δ compound were investigated. The MgMnO3−δ -modified Bi0.5Na0.5TiO3 materials were fabricated using sol–gel method. Results of X-ray diffraction and Raman scattering indicated that the MgMnO3−δ materials were good solid solutions in the Bi0.5Na0.5TiO3 compound. The random distribution of Mg and Mn cations in the host lattice of Bi0.5Na0.5TiO3 materials reduced the optical band gap from 3.11 eV to 1.99 eV for 9 mol% MgMnO3−δ-modified Bi0.5Na0.5TiO3 materials. The complex magnetic behaviour in MgMnO3−δ-modified Bi0.5Na0.5TiO3 materials was obtained. The weak ferromagnetism vs. diamagnetism transformed to ferromagnetism vs. para/antiferromagnetic property depending on the concentration of MgMnO3−δ solid solution in Bi0.5Na0.5TiO3 samples. Our work can further contribute to the study of current injection ferromagnetic material in host lead-free ferroelectric materials for smart electronic device application.

Optically Active Defects Induced by 10 MeV Electron Beam in Transparent MgAl2O4 Ceramics

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Tunable magnetic properties of Bi0.5Na0.5TiO3 materials via solid solution of NiTiO3

A solid solution of NiTiO3 in Bi0.5Na0.5TiO3 materials was fabricated by sol–gel technique. According to the X-ray diffraction analysis, (1 − x)Bi0.5Na0.5TiO3 + xNiTiO3 materials exhibited a rhombohedral structure following the Bi0.5Na0.5TiO3 crystal symmetry. The random distribution of Ni cations into the host lattice of Bi0.5Na0.5TiO3 materials decreased the optical band gaps from 3.06 to 2.74 eV for 9 mol.% NiTiO3 solid solution. The magnetic properties of Bi0.5Na0.5TiO3 materials were tuned from weak ferromagnetism to ferromagnetism and of compensation of ferromagnetism with diamagnetic and/or antiferromagnetic property. This work provides understanding of the role of exchange interaction of cation transition metals to integrate magnetic properties in lead-free ferroelectric materials for smart multifunctional electronic devices.

Rare earth and transition metal based entropy stabilised perovskite type oxides

Multicomponent oxides with perovskite type of structure containing up to 10 different cations in equiatomic amounts have been synthesised for the first time. Out of eleven systems synthesised, only six systems crystallised as single phase perovskite type compounds with random and homogenous cation distribution on the respective sites. The formation of phase pure 10-cationic system, (Gd0.2La0.2Nd0.2Sm0.2Y0.2)(Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)O3, in contrast to the multiphase mixtures observed in five of the lower entropy systems (containing 6 cations) indicates a possible role of entropy in the stabilisation of a single phase crystal structure. The entropy driven structural stabilisation effect is further supported by the reversible phase transformation, from single phase to multiple phase upon cyclic heat treatment, observed in the (Gd0.2La0.2Nd0.2Sm0.2Y0.2)MnO3 system. This type of entropic signature has been observed in rocksalt based high entropy oxide systems. However, it has not been reported before for perovskite based compounds, as shown in this study.

Structural, optical, and magnetic properties of SrFeO 3-δ -modified Bi 0.5 Na 0.5 TiO 3 materials

Abstract SrFeO3-δ-modified Bi0.5Na0.5TiO3 materials were fabricated by a sol–gel method. SrFeO3-δ materials existed as a well solid solution in Bi0.5Na0.5TiO3 materials, resulting in the random distribution of Sr and Fe cations into the lattice of the host. The impurities of Sr and Fe cations preferred to substitute at the A-site and B-site in Bi0.5Na0.5TiO3 materials, respectively. These cations distorted the structure of the host materials due to differences in the radius of the cations of impurity and the host. The modified materials showed reduced optical band gap and strongly induced ferromagnetism at room temperature. This work presents a new method for integrating room-temperature ferromagnetism in lead-free ferroelectric materials to overcome the limitations of single transition metals as dopants.