Cubic Symmetry Research Articles

Defect-Induced Li-Ion Trapping and Hopping in a Grain Boundary-Engineered Li1.3Al0.3Ti1.7(PO4)3 Solid-State Electrolyte.

Understanding lithium-ion dynamics across defect-rich grain boundaries (GBs) is crucial for solid-state electrolytes. This study examines local electronic and structural changes in a Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid electrolyte via X-ray absorption spectroscopy (XAS) and their correlation with ion transport properties. GBs were tailored through conventional isothermal sintering (CIS) and spark plasma sintering (SPS). Ti L2,3-, Ti K-, O K-, and P L2,3-edges from XAS revealed octahedral symmetry in bulk regions of both LATP-CIS and LATP-SPS. However, Ti L2,3-edge spectra in total electron yield mode and Ti K-edge white line intensity shifts in LATP-SPS indicate lower oxidation states and structural distortions due to a significant amorphous GB fraction. Modulations in O K-edge and P L2,3-edge spectra further highlight local structural differences in GB regions of LATP-CIS and LATP-SPS. Electron energy loss spectroscopy (EELS) also reveals variations in Ti L2,3-edge splitting and pre-edge peak intensities, consistent with X-ray absorption near-edge spectroscopy analysis. LATP-SPS exhibits a higher Li content in the GB region than LATP-CIS. The GB ionic conductivity of LATP-SPS (σgb,300K ∼ 1.36 × 10-3 S/cm) is two orders higher than that of LATP-CIS (σgb,300K ∼ 3.84 × 10-5 S/cm), while grain conductivity remains similar. Trapping and hopping enthalpy estimations suggest that trapped Li ions contribute ∼27% of activation energy for LATP-SPS compared to ∼17% for LATP-CIS. Enhanced ion diffusion in polycrystalline LATP GBs is predicted from molecular dynamics simulations, where liquid-like ion pair correlations improve mobility. This work highlights the significant influence of GB-induced structural distortions, probed through XAS and EELS, on the ionic conductivity and charge transport in LATP electrolytes.

Structural and luminescent properties of a Cr3+/Sm3+ doped GdAlO3 orthorhombic perovskite for solid-state lighting applications.

The Cr3+ and Sm3+ doped GdAlO3 perovskite with formula Gd0.995Sm0.005Al0.995Cr0.005O3, was synthesized via a solid-state reaction method, and its structure, morphology, and photoluminescence properties were thoroughly investigated. The compound crystallizes in the orthorhombic Pbnm space group, with Cr3+ transition-metal ions substituting Al3+ in the octahedral symmetry site, and Sm3+ lanthanide (rare-earth) ions occupying the tetrahedral site. The material's morphology and chemical composition homogeneity were evaluated through Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analysis. Photoluminescence excitation (PLE) and emission spectra (PL) were used to shed light on the electronic structure of the Cr3+ cations, through crystal field analysis in the O h symmetry site. Theoretical studies enabled the precise assignment of the Cr3+ 3d-3d transitions. The intra-configurational 4f-4f transitions of Sm3+ resulted in a variety of excitation bands appearing in the high-wavelength range of the PLE spectrum. The photoluminescence studies supported the occurrence of energy transfer in the doped GdAlO3 perovskite between Gd3+, Sm3+ and Cr3+ ions. The obtained results suggest the high potential of the synthesized material for solid state lighting applications.

Four-component protein nanocages designed byprogrammed symmetry breaking.

Four, eight or twenty C3 symmetric protein trimers can be arranged with tetrahedral, octahedral or icosahedral point group symmetry to generate closed cage-like structures1,2. Virusesaccess more complex higher triangulation number icosahedral architecturesby breaking perfect point group symmetry3-9, but nature appears not to have explored similar symmetry breaking fortetrahedral or octahedral symmetries. Here we describe a general design strategy for building higher triangulation number architectures starting fromregular polyhedra through pseudosymmetrization of trimeric building blocks. Electron microscopy confirms the structures of T = 4 cages with 48 (tetrahedral), 96 (octahedral) and 240 (icosahedral) subunits, each with 4 distinct chains and 6 different protein-protein interfaces, and diameters of 33 nm, 43 nm and 75 nm, respectively. Higher triangulation number viruses possess very sophisticated functionalities; our general route to higher triangulation number nanocages should similarly enable a next generation of multiple antigen-displaying vaccine candidates10,11 and targeted delivery vehicles12,13.

Ultrafast Lithium-Ion Diffusion in Oxyhalides

All solid-state batteries are a promising technology due to their employment of inorganic solid electrolytes (SEs), which are safer compared to their flammable, liquid counterparts. Recently, halide SEs have gained significant attention due to their relatively high ionic conductivity (> 1 mS/cm), wide electrochemical stability window, and compatibility with various electrode materials. However, prior to 2023, no known halide materials could reach the conductivities of the state-of-the-art sulfide SEs (> 10 mS/cm). This can be attributed to the close-packed anion arrangement of existing halide conductors, which confines lithium ions to narrow and high-energy conduction pathways. Recently, a new Li oxyhalide superionic conductor LiMOCl4 (M=Nb/Ta) was reported with extremely high ionic conductivities greater than 10 mS/cm [1]. Unlike previously found halide conductors, LiMOCl4 has a non-close-packed anion framework that provides a large conduction pathway. We present a first-principles investigation of the phase stability, electrochemical stability, and Li-ion conductivity in the LiMXCl4 (M = Ta, Nb, Sb, Ti, Zr, Hf, Sn, and X = O, F, Cl) family of superionic conductors. We identify a mixed-anion framework as key to stabilizing the oxyhalide structure and demonstrate the impact of aliovalent anion and cation substitutions on material properties. Long ab-initio molecular dynamics simulations spanning 10’s of ns confirm room temperature superionic conductivity in all systems. Probabilistic analysis of the rotational dynamics at the picosecond timescale contributes direct, quantitative evidence correlating the high Li-ion conductivity in oxyhalide systems with the soft tilting motion of MO2Cl4 octahedral groups present in the material. Our findings supply the theoretical underpinnings for the effectiveness of LiMXCl4 family of superionic conductors as catholytes compatible with 4-V-class layered cathodes and provide essential design criteria for constructing new Li halide superionic conductors with conductivity greater than 10 mS/cm.[1] Y. Tanaka, K. Ueno, K. Mizuno, K. Takeuchi, T. Asano, A. Sakai, Angew. Chem. Int. Ed. 2023, 62, e202217581; Angew. Chem. 2023, 135, e202217581.

Strain Programming of Oxygen Octahedral Symmetry in Perovskite Oxide Thin Films

AbstractThe collective rotations of oxygen octahedra play an important role in determining the physical properties of functional perovskite oxides. The epitaxial strain can serve as an effective means to modify the oxygen octahedral symmetry (OOS), i.e., oxygen octahedral rotation or tilt (OOR/OOT). However, the strain‐OOS coupling that may alter the details of the OOS, thereby the physical properties, has not been fully understood. In this work, it is demonstrated that epitaxial strain can not only induce a structural phase transition but also precisely tune the degree of OOR. The correlated metal CaNbO3, which is orthorhombic, is studied by growing as epitaxial thin films. By imposing epitaxial strain, it is found that the film undergoes a structural phase transition from orthorhombic to tetragonal upon fully straining (i.e., from a+b−b− to a0a0c−). In unstrained films, the octahedral rotation along the c‐axis is as large as 15.7° that can be tuned to 6.6° by strain. This finding offers a general approach to manipulating OOR/OOT via strain engineering in complex oxide heterostructures.

Stealth dark matter spectrum using Laplacian Heaviside smearing and irreducible representations

We present nonperturbative lattice calculations in the quenched approximation of the low-lying meson and baryon spectrum of the SU(4) gauge theory with fundamental fermion constituents. This theory is one instance of stealth dark matter, a class of strongly coupled theories, where the lowest mass stable baryon is the dark matter candidate. This work constitutes the first milestone in the program to study stealth dark matter self-interactions. Here, we focus on reducing excited state contamination in the single-baryon channel by applying the Laplacian Heaviside method, as well as projecting our baryon operators onto the irreducible representations of the octahedral group. We compare our resulting spectrum to previous work involving Gaussian smeared nonprojected operators and find good agreement with reduced statistical uncertainties. We also present the spectrum of the low-lying odd-parity baryons for the first time. Published by the American Physical Society 2024

Antimicrobial, anticancer and photocatalytic dye degradation activities of silver nanoparticles phytosynthesized from Secamone emetica aqueous leaf extract

Secamone emetica (Family: Apocynaceae) is traditionally used for several ailments among indigenous people due to the bioactive components present in it. Nanomedicine has undergone impressive modifications and the development of new drugs with significant healthcare outcomes. The purpose of the present study was to green synthesize and characterize silver nanoparticles (Ag-NPs) using aqueous leaf extract of S. emetica, and to study their in vitro antimicrobial, anticancer and photocatalytic dye degradation activities. Various spectroscopic and microscopic analytical tools were used to characterize the Ag-NPs. Selective G+ve, G−ve bacteria and fungal species were used to test the Ag-NPs antibacterial and antifungal activity. Anticancer efficacy of the Ag-NPs was appraised by MTT test using MDA-MB 231 human breast cancer cells. Degradation of Rhodamine B dye by the Ag-NPs under visible light was assessed. The characterization studies confirmed the formation of Ag-NPs which were crystalline cubical symmetry with an average size of 26.69 nm. Dose dependent antimicrobial activity displayed a maximum zone of inhibition of 22.39 mm against E. coli followed by 21.28 mm against S. aureus at 100 µL/mL concentration of Ag-NPs. The IC50 value of synthesized Ag-NPs on MDA-MB 231 cell lines was 0.5 μg/mL. The Ag-NPs catalyst degraded 96 % of Rhodamine B dye in 150 min under visible light. Phytosynthesized Ag-NPs showed strong antimicrobial and anticancer properties and also revealed excellent dye degradation capacity. It is possible to further utilize the biosynthesized Ag-NPs as a possible source of antimicrobial, anticancer, and dye-degradation activities.

Characters are quantum numbers

Abstract Character tables represent an invaluable tool for applications of group theory in physics and chemistry. They are useful, among other applications, to carry out the projection of functions which later on constitute the basis to simplify the calculations and establish the selection rules. However, the physical interpretation of the character tables as quantum numbers is not visible. In this contribution we prove that the characters are indeed conserved quantities associated with the discrete symmetry of a molecule. In the process, the eigenfunction method of symmetry projection emerges in natural form, an approach not discussed in traditional textbooks. A non trivial example involving the octahedral group ${\cal O}_h$ is presented.

Antimony stable isotope fractionation during adsorption onto birnessite: A molecular perspective from X-ray absorption spectroscopy and density functional theory

Sorption of antimony (Sb) onto birnessite significantly influences the fate of Sb in oceanic and terrestrial environments and fractionates Sb isotopes. Nevertheless, little is known about Sb isotopic fractionation during its adsorption on birnessite. Here, we show the value of Δ123Sbadsorbed-aqueous increases from −0.398 to −0.332 ‰ in 1 h and then decreases and stabilizes at −0.384 ‰ in 72 h. The enrichment of the light Sb isotope is predominantly due to the distortion of the octahedral symmetry. X-ray absorption spectroscopy results indicate Sb first forms a double-corner-sharing complex on birnessite and then transforms to a double-edge-sharing complex during adsorption. The optimized bond distances for double-corner-sharing (3.37 Å) and double-edge-sharing (2.90 Å) complexes calculated using density functional theory (DFT) fits well with the structure (3.41 and 3.00 Å) revealed by X-ray absorption spectroscopy, respectively. The fractionation derived from reduced partition function ratios calculated using DFT aligns well with the experimental results. Therefore, the variation in Sb isotopic fractionation during adsorption is attributed to the evolving structure of Sb complexes on birnessite. Our results demonstrate the isotopic fractionation of Sb during adsorption on birnessite and provide a molecular-scale understanding of Sb behavior, contributing to the correct reconstruction of the Sb isotope composition of ancient seawater using ferromanganese crusts and nodules, and efforts to trace Sb migration in epigenetic mining environments.

Optical and Structural Properties of Cuprous Oxide Shell Coated Gold Nanoprisms

AbstractCuprous oxide nanoparticles can be prepared with a great morphological control, and their composites with gold nanostructures are intensively studied owing to their catalytic performance. In this study, cuprous oxide shell growth on nanosized prism‐shaped gold nanoparticles is investigated, where the core‐particle morphology does not match the prototypical cubic or octahedral symmetry of the embedding cuprous oxide particle. It is shown that different shell morphology is obtained depending on the reducing agent used for the shell deposition. Strong reducing agent (hydrazine) leads to a multi‐slab‐like coating with smooth facets, while under milder conditions (hydroxylamine) a multi‐grain coating is obtained. Successful realization of time‐dependent spectroscopic and structural investigations indicate that in this latter case cuprous oxide shell growth is initiated site‐selectively, namely in the highly curved regions of the particle, with a higher growth rate around the tips of the nanoprisms. This is supported by correlative single‐nanoparticle spectroscopy/scanning electron microscopy measurements, that allow to establish the connection between the optical properties and the structure of these plasmonic/semiconductor core/shell nanoparticles.

La3+-adjusted optical and ligand field parameters in low CoO impurities Na2O–ZnO borate glass matrix

The effect of La2O3 on the ligand field and optical properties of the current glass system was investigated. In detail, the absorption band at (493–499 nm) is ascribed to 4T1g (F) → 2T1g (H) transition of Co2+ in octahedral symmetry. The absorption band at (574–580 nm) is ascribed to 4A2 (4F)→4T1(4P) transitions of Co2+ in tetrahedral symmetry. On the other hand, the electronic transition at (639–644 nm) is attributed to 5T2g→ 5Eg transition of Co3+ in octahedral symmetry. Moreover, the redshift of the absorption edges reduces the optical bandgaps from 3.42 eV to 3.24 eV. Additionally, the La2O3-free glass sample exhibited a transition at ∼230 nm in the UVC region. However, this glass sample showed an displayed transparency in the UVA and UVB regions. Furthermore, the redshift of the absorption edges resulted in the glass sample with the highest La2O3 content (i.e., 8 mol%) becoming UVA transparent while blocking UVC and UVB regions. The obtained data regarding the ligand field parameters indicate an increase in the ligand field splitting (10Dq), reflecting the increased interplay strength between Co2+ in tetrahedral symmetry and its ligands. Also, the values of the nonlinear refractive index and nonlinear optical parameters increased due to the enhancement of basicity within the glass network. These findings suggest that the glass with the greatest concentration has the potential to be utilized as an optical filter that allows UVA while blocking UVC and UVB electromagnetic waves.

Structural, Optical, and Morphological Study of Manganese Substituted Cobalt Ferrite and Its Effect on the Magnetic and Dielectric Properties of PVA Composites

Nanopowders of Mn-substituted CoFe2O4 were prepared in different proportions using the sol-gel auto-combustion method and were structurally and morphologically studied. In another step, composites based on polyvinyl alcohol (PVA) with Mn-substituted CoFe2O4 fillers were prepared, and the effect of the Mn-substituted CoFe2O4 on the optical, magnetic, and dielectric properties was studied. X-ray analysis revealed the formation of polycrystalline Mn-substituted CoFe2O4. The results showed a decrease in the lattice constant with Mn2+ substituted and incorporated into the crystal structure of CoFe2O4. The Fourier confirmed the spinel structure of the Mn-substituted CoFe2O4 transform infrared spectrum where absorption bands appeared at 569–561 and 446–407 cm-1, which are attributed to tetrahedral and octahedral groups. The magnetic properties were affected when Mn ions were substituted with CoFe2O4, as shown by the results of VSM. It was observed that the saturation magnetization, remnant magnetization, and coercivity decreased with increasing Mn content. The dielectric constant and loss tangent of PVA/MnxCo1−xFe2O4 were also studied. The difference in the diameters of the substituted and host ions causes the dielectric constant to increase following the substitution of Mn ions.

Phase transition, structural and magnetic parameters of vanadium-substituted Bi0.9Sm0.1FeO3 multiferroic ceramics

ABSTRACT The inorganic multiferroic compounds Bi0.9Sm0.1Fe1 − x V x O3 (x = 0.0, 0.015, 0.03, and 0.045) were prepared by the solid-state reaction method. X-ray diffraction analysis confirmed the rhombohedral perovskite-like structure with minor traces of the impurity phases Bi2Fe4O9 and Bi25FeO40. The lattice parameters a and c, and the volume of the hexagonal unit cell were extracted from the X-ray diffraction data and found to increase as the V5+ content is increased. The average crystallite size was estimated to be in the range 380–415 Å. Fourier transform infrared spectroscopy confirmed the rhombohedral perovskite-like structure via the vibration bands of the octahedral FeO6 group observed between 410 and 570 cm−1. A differential scanning calorimeter was used to record the thermal scans which revealed that the compounds have undergone crystalline phase transitions at temperatures in the range 300–320°C. A 4.5% V + 5 substitution has shifted the transition peak by 20°C. The magnetic hysteresis loops taken at room temperature with a vibrating sample magnetometer revealed the ordinary ferromagnetic behavior. The V5+ substitution enhanced the remanent magnetization, but the magnetic coercivity was found to fluctuate around an average value of about 1000 Oe. The compound Bi0.9Sm0.1Fe0.955V0.045O3 exhibited the maximum remanent magnetization.

Effect of Coordination Structure of Iron Ions on Iron Oxide Activity Coefficients in the CaO‐SiO2‐FeO‐Fe2O3 Slags at 1573 K Under Oxygen Partial Pressures Between 10−9 and 10−4 atm

Activity coefficients of FeO and FeO1.5 in CaO‐SiO2‐FeO‐Fe2O3 melts have been investigated from the perspective of the coordination structures of iron ions. The percentages of Fe2+ and Fe3+ in octahedral symmetry (Fe3+(oct)) and Fe3+ in tetrahedral symmetry (Fe3+(tetr)) were measured by Mössbauer spectroscopy. It has been found that both values of γFeO and monotonically increase with increasing and that the γFeO values are higher than the values suggesting that FeO is more readily released from the silicate network to precipitate FeOx‐bearing compound from the slag than FeO1.5. It has also been found that the value increases with increasing the ratio of Fe3+(oct) pct./Fe3+(tetr) pct., which indicates that the values of (oct) are higher than those of (tetr). Accordingly, the hierarchy of the activity coefficients, i.e., γFeO > (oct) > (tetr) holds in the present system. The magnitude of effective ionic radii is in the hierarchy of Fe2+ > Fe3+(oct) > Fe3+(tetr), and thereby the bond strength between iron ion and oxide ion is in the hierarchy of Fe3+(tetr) > Fe3+(oct) > Fe2+. This suggests that Fe2+ are more loosely and Fe3+(tetr) are more rigidly bound to the silicate skeleton.

Crystal structures and photoluminescence properties of undoped and Fe3+ doped Li2Ba3(P2O7)2 pyrophosphate nanopowders

Undoped and Fe3+ doped Li2Ba3(P2O7)2 pyrophosphate nanopowders were produced by a solid-state reaction process. The prepared samples underwent characterizations using XRD, SEM with EDS, HR-TEM with SAED, FTIR, Raman, UV-Vis, EPR and PL techniques. The XRD analysis confirms the orthorhombic crystal structure of the prepared samples and unit cell parameters were evaluated. The samples exhibited stone-like structures with low aggregation based on the micrographs obtained from SEM and HR-TEM images. Additionally, the grain and particle sizes of the powder samples were evaluated. The elements Li, O, P, Ba and Fe were confirmed to be present in the produced samples by EDS spectra. FT-IR and Raman spectral investigation revealed the fundamental vibrational and bending modes of various phosphate groups. The energy bands, identified as characteristic bands of Fe3+ ions, were produced in the UV–visible region of the optical absorption spectrum for the doped sample. The crystal field and inter-electronic parameters (Dq = 915, B = 700 and C = 2715 cm−1) were also evaluated. Furthermore, the refractive index and metallization criteria properties were calculated using energy bandgap values of 4.46 and 4.38 eV of the produced samples. The doping of Fe3+ ions led to a reduction in the bandgap energy, resulting in a red-shift. A resonance signal was observed in the EPR spectrum at g = 2.05, which can be ascribed to iron ions entering the host lattice at a distorted octahedral symmetry sites and this was also supported by optical absorption studies. The produced sample showed emission peaks at 354, 440 and 530 nm in the ultraviolet, blue and green regions of its photoluminescence spectrum. Photometric parameters, such as CCT, CRI and CIE chromatic coordinates, reveal that the prepared samples could bee used in LEDs applications. This work offers novel visions into diphosphate compounds doped with transition metal ions.

Ferromagnetic Insulating Ground-State Resolved in Mixed Protons and Oxygen Vacancies-Doped La0.67Sr0.33CoO3 Thin Films via Ionic Liquid Gating.

The realization of ferromagnetic insulating ground state is a critical prerequisite for spintronic applications. By applying electric field-controlled ionic liquid gating (ILG) to stoichiometry La0.67Sr0.33CoO3 thin films, the doping of protons (H+) has been achieved for the first time. Furthermore, a hitherto-unreported ferromagnetic insulating phase with a remarkably high Tc up to 180 K has been observed which can be attributed to the doping of H+ and the formation of oxygen vacancies (VO). The chemical formula of the dual-ion migrated film has been identified as La2/3Sr1/3CoO8/3H2/3 based on combined Co L23-edge absorption spectra and configuration interaction cluster calculations, from which we are able to explain the ferromagnetic ground state in terms of the distinct magnetic moment contributions from Co ions with octahedral (Oh) and tetrahedral (Td) symmetries following antiparallel spin alignments. Further density functional theory calculations have been performed to verify the functionality of H+ as the transfer ion and the origin of the novel ferromagnetic insulating ground state. Our results provide a fundamental understanding of the ILG regulation mechanism and shed light on the manipulating of more functionalities in other correlated compounds through dual-ion manipulation.

Calcination temperature dependence of tri-magnetic nanoferrite Ni0.33Cu0.33Zn0.33Fe2O4: Structural, morphological, and magnetic properties

The calcination temperature plays a pivotal role in determining the physical and magnetic properties of ferrite nanoparticles, influencing their performance and applicability in various applications. In this study, Ni0.33Cu0.33Zn0.33Fe2O4 nano ferrites were produced using the coprecipitation method and subsequently calcined at different temperatures, specifically 500 °C, 550 °C, 600 °C, 650 °C, and 700 °C. The X-ray diffraction analysis confirmed the presence of cubic spinel ferrite phase (Fd-3m) and revealed an increase in crystallite size from 12.84 to 20.19 nm as the calcination temperature increased from 500 °C to 700 °C. X-ray photoelectron spectroscopy analysis provided insights into chemical oxidation states. Scanning electron microscopy and transmission electron microscopy images revealed that at higher calcination temperatures, nanoparticles tend to aggregate. This aggregation is associated with an observable rise in particle size, increasing from 18.16 to 29.11 nm for nanoparticles calcined at 500 °C and 700 °C, respectively. Energy-dispersive X-ray confirmed pure elemental compositions. Fourier transform infrared spectroscopy identified red and blue shifts in wavenumbers corresponding to tetrahedral and octahedral group complexes, respectively. Nanoparticles calcined at 700 °C exhibited the highest saturation magnetization (62.642 emu/g) and coercivity (75.27 G), as revealed from the vibrating sample magnetometry analysis. Upon increasing the calcination temperature from 500 °C to 700 °C, the ferromagnetic contribution was improved from 24.26% to 98.64% along with a reduction in superparamagnetic contribution from 75.74% to 1.34%, respectively. The electron paramagnetic resonance (EPR) study showed an increase in the values of g and ΔHpp with the rise in calcination temperature. This observation suggests an enhancement in dipole–dipole interactions. Furthermore, a linear relationship was discovered between the g factor and crystallite size, inducting the formation of single domain. Finally, altering the calcination temperature adjusted the physical and magnetic properties of Ni0.33Cu0.33Zn0.33Fe2O4 nanoparticles. This adjustment indicates their potential for versatile applications, particularly in hyperthermia treatment and as T2 contrast agents in magnetic resonance imaging.

Primitive quantum gates for an SU(2) discrete subgroup: Binary octahedral

We construct a primitive gate set for the digital quantum simulation of the 48-element binary octahedral (BO) group. This non-Abelian discrete group better approximates SU(2) lattice gauge theory than previous work on the binary tetrahedral group at the cost of one additional qubit—for a total of six—per gauge link. The necessary primitives are the inversion gate, the group multiplication gate, the trace gate, and the BO Fourier transform. Published by the American Physical Society 2024

Local electronic structures of annealing induced phases in cobalt doped TiO2 nanoparticles: a combined study of transmission electron microscopy and x-ray absorption fine structure spectroscopy

The evolution of the nanostructures and electronic properties of 5% cobalt-doped TiO2 nanoparticles (NPs) annealed at 400 °C, 600 °C, and 800 °C have been investigated to understand the structural phase transformations through chemical co-precipitation synthesis. A detailed analysis of the X-ray Diffractogram confirms that the sample annealed at 400 °C is anatase, at 600 °C, the mixed phase of anatase and rutile evolves, and at 800 °C, the sample is of rutile structure. A detailed morphological study by scanning transmission electron microscope provides the particle size, lattice spacing, and variation in polycrystalline grain growth at different phases. Electron Energy Loss Spectroscopy analysis indicates from the O K, Co, and Ti L 2,3-edges that Ti4+ ions are primarily in an octahedral symmetry with the oxygen ligands changing their structural phases from anatase to mixed phase and then stable rutile phase with increasing temperature of annealing. X-ray Absorption Near Edge Spectroscopy (XANES) extracts information about the varying oxidation states and 3-dimensional geometry of Ti-ions. The unresolved issues of the structural details at the atomic-scale picture with the local environment of the cation with a few nearest neighbour shells are derived from Extended X-ray Absorption Fine Structure (EXAFS) and pre-edge parts of the absorption spectra. The limits of EXAFS in this situation of asymmetric bond length disorder, which is typical for mixed-valence oxides, are generated to reconcile the two data and highlight the value of pre-edge XANES analysis for identifying local heterogeneities in structural and compositional motifs. TiO2 possesses unique properties depending upon its structural phase. The Ti L 2,3-edge spectrum indicates that there is an octahedron connectivity of the Oxygen atoms at the anatase state which transforms to a higher energetic tetrahedral correspondence as it proceeds towards the rutile phase. The driving force behind such interest is to modulate the properties of TiO2 NPs to better photocatalytic material and to integrate its application as a versatile energy storage device.

Behavior analyses of chromium into LiZnNbO4 host through optical spectroscopy and X-ray diffraction

A LiZnNbO4 sample was produced through the solid-state reaction method, according to which, chromium was introduced in the sample as impurity. X-ray diffraction (XRD), luminescence, excitation, emission decay time and emission quantum efficiency analyses were carried out. Structural analysis based on the sample's XRD data showed LiZnNbO4 compound belonging to the P4122 space group. Luminescence measurements evidenced broad emission band centered at 800 nm, which was associated with spin-allowed electronic transition from the excited state 4T2(4F) to the fundamental state 4A2(4F). Emission decay time reached 7.8 μs under 460 nm excitation and 0.43 quantum efficiency. Excitation spectrum showed bands associated with of Cr3+ ions transitions4A2(4F)→ 4T1(4F) and 4A2(4F)→ 4T2(4F), at 460 nm and 644 nm, respectively in octahedral symmetry. Crystal field parameter Dq = 1553 cm−1 and Racah B = 621 cm−1 were found by using transition energies from both the excitation spectrum and Tanabe-Sugano matrices.