Tetrahedral Distortion Research Articles

Crystal structure and microwave dielectric properties of BaZn(1-x)CoxP2O7 ceramics

BaZn(1-x)CoxP2O7 (0 ≤x≤ 0.125) ceramics were synthesized using the solid-state reaction method, with sintering temperatures ranging from 875 °C to 975 °C. The study systematically investigated the phase composition, crystal structure, and microstructure of the ceramics, and correlated these characteristics with their dielectric properties. Additionally, density functional theory (DFT) was employed to examine the energy band structure, electron density, and density of states of the materials. The dielectric constant εr values were primarily influenced by polarizability, while the Q × f values of BaZn(1-x)CoxP2O7 ceramics were predominantly affected by the packing fraction and full width at half maximum (FWHM). The temperature coefficient of resonant frequency was influenced by a decrease in bond valence and an increase in PO4 tetrahedral distortion. Notably, the BaZn0.975Co0.025P2O7 ceramic demonstrated promising microwave dielectric properties, with εr = 8.15, Q × f = 42,431 GHz, and τf = −27.5 ppm/°C, when sintered at 950 °C for 4 h.

Polymeric dichlorido-bridged copper(II) offset stacked dimer coordination compounds and molecular spin stairs

A family of oxygen coordinated dichlorido-bridged n-X-2-pyridone (1, n = 3, X = Cl; 2, n = 3, X = Br; 3, n = 4, X = Cl; 4, n = 4, X = Br; 5, n = 5, X = Cl; 6, n = 5, X = Br) Cu(II) offset stacked dimer compounds, denoted molecular spin stairs, have been prepared and analyzed by single-crystal X-ray diffraction (1–4), powder X-ray diffraction (1–6), and variable temperature magnetic susceptibility measurements (1–6). Ferromagnetism is dominant in all compounds with a weaker antiferromagnetic exchange present in 1–4. The ferromagnetic exchange correlates to increased twist angles which are defined by the extent of the tetrahedral distortion of the copper coordination sphere and the identity of the halogen on the ring. The compounds were qualitatively fit to a ferromagnetic Heisenberg chain model with a Curie-Weiss interchain correction. The general Hamiltonian used is of the form H = − J ∑ S 1 S 2 . The ratio of exchange energies denoted α ( α = J FM | J AFM | ) ranges between 2.6 and 4.7. This family of compounds constitutes possible S = ½ Haldane-like materials.

Manipulating Chiroptical Activities in 0D Chiral Hybrid Manganese Bromides by Solvent Molecular Engineering.

0D hybrid metal halides (0D HMHs) with fully isolated inorganic units provide an ideal platform for studying the correlations between chiroptical activities and crystal structures at atomic levels. Here, through the incorporation of different solvent molecules, a series of 0D chiral manganese bromides (RR/SS-C20H28N2)3MnBr8·2X (X = C2H5OH, CH3OH, or H2O) are synthesized to elucidate their chiroptical properties. They show negligible circular dichroism signals of Mn absorptions due to C2v-symmetric [MnBr4]2- tetrahedra. However, they display distinct circularly polarized luminescence (CPL) signals with continuously increased luminescence asymmetry factors (glum) from 10-4 (X = C2H5OH) to 10-3 (X = H2O). The increased glum value is structurally revealed to originate from the enhancement of [MnBr4]2- tetrahedral bond-angle distortions, due to the presence of different solvent molecules. Furthermore, (RR/SS-C20H28N2)MnBr4·H2O enantiomers with larger bond-angle distortions of [MnBr4]2- tetrahedra are synthesized based on hydrobromic acid-induced structural transformation of (RR/SS-C20H28N2)3MnBr8·2H2O enantiomers. Therefore, such (RR/SS-C20H28N2)MnBr4·H2O enantiomers exhibit enhanced CPL signals with |glum| up to 1.23×10-2. This work provides unique insight into enhancing chiroptical activities in 0D HMH systems.

Antimony doping in A2ZnCl4 (A= Rb, Cs) metal halides enabling tunable near-infrared emission

Lead-free metal halides with stable and tunable emission have shown great promise for broad application prospects in the visible light range. However, it remains a fundamental challenge to realize tunable near-infrared (NIR) luminescence in these metal halide materials. Herein, a cation regulation strategy in zero-dimension organic metal halides A2ZnCl4:Sb3+ (A = Rb, Cs) to achieve tunable NIR luminescence is reported. The prepared A2ZnCl4:Sb3+ (A = Rb, Cs) halides exhibited efficient broadband NIR emission, which originates from self-trapped excitons of the [SbCl4]− polyhedron. Based on the regulation of cation, the [SbCl4]− tetrahedral distortion capacity changes, exciton–phonon coupling is enhanced, leading to a red shift of the emission wavelength. The results provide inspiration for the regulation of the self-trapped excitons luminescence of halides and demonstrate potential as a non-visible light source for night vision.

Hierarchical van der Waals Assemblies to Boost Deep‐Ultraviolet Nonlinear‐Optical Capabilities in Boron Phosphate

AbstractCristobalite‐type boron phosphate BPO4, an important nonlinear‐optical (NLO) crystal, exhibits nearly the largest bandgap (Eg ≈ 9.3 eV) and a significant second‐harmonic‐generation (SHG) effect (d36 ≈ 0.7 pm V−1) in the deep‐ultraviolet (DUV, < 200 nm) spectral region. However, its conventional tetrahedral framework structure tends to have low structural anisotropy, resulting in a severe deficiency of birefringence (Δn < 0.01), which fails to achieve DUV birefringent phase matching. In this work, the local anisotropy of tetrahedral structures are proposed to enlarge by constructing van der Waals (vdW) anisotropic motifs under synthetic chemical conditions, which can effectively convert unattainable extreme external forces into internal stresses in chemical bond structures. Depending on unique hierarchical vdW assemblies, enormous tetrahedral distortions can be achieved by stable in‐plane or in‐line bond matching between rigid tetrahedral primitives. First‐principles calculations demonstrate that the birefringence of 2D layered and 1D chained BPO4 achieved by vdW engineering are scaled from Δn < 0.01 to 0.07–0.13, with the shortest birefringent phase‐matched wavelengths down to DUV 189–154 nm. The finding is of seminal importance for the design of vdW NLO crystals in structural chemistry and would provide opportunities to explore unique vdW DUV NLO materials under extreme synthetic conditions.

Ab initio study of stability and quadrupole coupling constants in borophosphates.

The DFT method was used to predict the formation energies and quadrupole coupling constants CQ in a series of borophosphates: Li3BP2O8, Li2NaBP2O8, Na3BP2O8, Li2B3PO8, Na5B2P3O13, LiNa2B5P2O14 and Na3B6PO13 composed of different networks and different amounts of borate and phosphate units. The change in formation energies with increasing number of B atoms in this series is attributed to the multiplicity of boron sites and is explained by density of states calculations. The calculated CQ values of 7Li, 23Na and 11B are correlated with the coordination and distortion of polyhedra to elucidate the influence of local and more distant environments. As for the CQ of 11B, it should be in the ranges of 0.26-0.36, 0.48-0.84 and ∼1 MHz for boron tetrahedral distortion indices of 0.004-0.013, 0.015-0.019 and 0.033, respectively, whereas CQ ∼3.0 MHz corresponds to boron in a triangular site. The obtained numerical relationships make it possible to predict the quadrupole frequencies for these nuclei based only on their local environment, and vice versa, to propose structural models from NMR data. These results provide guidance for studying similar characteristics of other borophosphates, the structure of which varies depending on the initial reaction, composition and temperature.

Insight into the low-temperature electrical polarization behavior of multiferroic Bi2Fe4O9

Structure, dielectric and pyroelectric properties are investigated for polycrystalline Bi2Fe4O9 ceramics. Antiferromagnetic transition is observed at ∼249 K during the dielectric measurement. Various pyroelectric characterization verifies the current peak at ∼144 K dominantly related to intrinsic ferroelectric transition and the other one because of intrinsic relaxation in the vicinity of ∼280 K, respectively. As confirmed by in-situ Raman measurement under varying temperature and electric field, the ferroelectric polarization at lower temperature is mainly ascribed to structural distortion in Fe1O4 tetrahedron reflected by Fe1–O vibrations at mode of 206 cm−1. The relaxation at higher temperature is originated from the off-center motion of Fe ions due to dipole reorientation shown as the stretching of O atom along c-axis at mode of 554 cm−1. Our study definitely presents the existence of intrinsic ferroelectric order below room temperature, which provides the supplementary reference for subsequent research on Bi2Fe4O9.

Intramolecular charge transfer in bulky “diazabutadiene-M(II)-catecholate” chromophores (M = Ni, Co): A role of a molecular geometry

Two monomeric heteroleptic charge transfer (CT) complexes NiII(3,6-Cat)(DADdipp) (1) and CoII(3,6-Cat)(DADdipp) (2) of “α-diimine-MII-catecholate” general type were prepared in the course of two-step synthetic procedures, based on 3,6-di-tert-butyl-o-benzoquinone (3,6-DTBQ) and 1,4-bis(2,6-di-isopropylphenyl)-1,4-diaza-1,3-butadiene (DADdipp). Square-planar coordination environment in complex 1 enables an implementation of a low energy ligand-to-ligand charge transfer (LL’CT), thus making NIR NiII chromophore (λmax = 1107 nm, in toluene) with high absorptivity of light and a fine sensitivity of CT energy towards solvent polarity (red solvatochromic shift from CH3CN to toluene at 192 nm). Energy of frontiers orbitals and HOMO-LUMO gap of 1 is evaluated in synergy of UV-vis-NIR spectroscopy, cyclic voltammetry, and DFT calculations, with a good accordance of data sets. A significant ligands’ bulkiness provided a tetrahedral distortion of square-planar N2O2 polyhedron of 2 in solutions (CH3CN, CH2Cl2, THF, toluene), that changed CT nature drastically with a concomitant decrease of absorptivity and an elimination of solvatochromism. Electrochemical behavior of studied complexes is defined by the differences in geometry of a coordination environment and corresponding mutual arrangement of metal and ligand orbitals (in solution): one-electron redox processes of square-planar NiII derivative 1 are predominantly ligand-centered, while redox transitions in tetrahedral CoII complex 2 proceed with the substantial participation of cobalt center.

A 0D lead-free Nickel halide-based perovskite exhibiting greenish light emission and high color rendering index

In this paper, a novel low-dimensional Ni(II)-based hybrid perovskite compound [(C3H7)4N]Ni2Cl6 endowed with interesting solid-state light-emission properties has been investigated using thermal (TGA-DSC), Hirshfeld surfaces, FT-Infrared spectroscopy, optical and photoluminescence measurements. The structure packing consists of 0D framework ascribed as a layered arrangement of organic and dimeric [Ni2Cl6]1− groups perpendicular to the crystallographic c axis and stabilized by means of weak intermolecular bonds yielding a 3D framework. The UV-visible investigation reveals a direct optical gap energy of value 3.72 eV, confirming the semi-conducting nature of the elaborated material. The photoluminescence properties reveals a greenish broad-band emission caused by self-trapped excitonic states (STESs) as well as the remarquable the inorganic tetrahedron distortion in the 0D crystal dimensionality. Such bright light emission yields to good luminescence properties with a very high CRI value of 96, CIE color coordinates of (0.32; 0.35), and a CCT value of 5722 K and. The Stokes shift between excitation wavelengths (325, 345, 375, 395 nm) and their corresponding emission bands (450, 460, 472, 480 nm) are discussed. The current findings could be used for the development of environment-friendly hybrid perovskites for UV and solar cell applications.

Generalized relationships between the ionic radii of octahedral cations and the b crystallographic parameter of clays and related minerals

AbstractOver several decades, a wealth of literature has been devoted to correlations between the chemistries of phyllosilicates and their crystallographic unit-cell parameter values. The c parameter is currently used because of its relation to the layer-to-layer distance, characteristic of the various families of phyllosilicates. The b parameter is also of interest because it allows measurement of the layer lateral dimensions and inherent structural adjustments. This unit-cell distance can be extracted from X-ray diffraction traces from the (06ℓ;33ℓ) diffraction region and by attributing the main diffraction peak observed to a 060 reflection, leading to the relationship b = 6.d(060). The aim of this paper is to revisit the relationships between the b value (or equivalent) of the phyllosilicate (i.e. TO, TOT and TOTO) or hydroxide (i.e. hydroxide, oxyhydroxide and layered double hydroxide) families and the layer chemistry based on a mean ionic radius R of octahedral cations, calculated as $R = \mathop \sum \nolimits_{i = 1}^n ( {r_i.x_i} )$, where ri is the ionic radius of the octahedral cation i and xi is its molar fraction over n types of octahedral cations ($\mathop \sum \nolimits_{i = 1}^n ( {x_i} ) = 1$). The data were collected from the literature and involved both natural and synthetic samples with both dioctahedral and trioctahedral structures of the octahedral sheet. The results showed that b values can be linked strongly to R, leading to suitable linear regressions for all of the studied structures. All correlations were found to be applicable irrespective of the di- or trioctahedral nature of the octahedral sheet, and these are discussed in light of (1) the lateral dimension of the octahedral sheet and (2) the dimensional misfit between the tetrahedral and octahedral sheets. For hydroxide families, all data can be gathered on a single b vs R correlation line, and the dimensional properties of the octahedral sheet can be interpreted simply based on an oxygen–cation–oxygen mean distance. For TO structures, two general b vs R correlation trends were reported, and these were assigned to two adjustment mechanisms corresponding to distinct types of tetrahedral and octahedral distortions. For the mica TOT family, two main trends were also reported, whereas the use of the synthetic mica series allowed us to demonstrate that the obtained scattering of data was mainly driven by the presence of multiple limited solid solutions. Such chemical complexity was also noted for smectites, especially regarding the tetrahedral composition and associated variability in layer charge. This variability made it difficult to propose a general regression correlating b to R values for smectites, although the regression obtained for neutral TOT layers can apply as a first-order relation. Finally, a single general b vs R correlation was obtained for chlorites, and the observed slope of the regression was interpreted according to the role played by the isolated hydroxide sheet on the evolution of the lateral dimension of the structures.

Direct spectroscopic observation of the reversible redox mechanism in A3V2(PO4)3(A=Li,Na) cathode materials for Li-ion batteries

Alkali Vanadium (III) phosphates are a promising class of positive electrode materials for Li-, Na- and K-ion battery applications. Herein, the reversible redox mechanism of Li3V2(PO4)3 and Na3V2(PO4)3 cathodes during charge/discharge vs. Li+/Li0 is directly observed by Soft X-ray Absorption Spectroscopy. For both Li3V2(PO4)3 and Na3V2(PO4)3 spontaneous surface Li + insertion is observed after exposure to Li + electrolyte. Furthermore, for Li3V2(PO4)3 a reversible charge-discharge process is observed from 3.0 V–4.8 V with only slight increase in O contributions to O 2p - V 3d unoccupied hybridised states after charge/discharge vs. Li+/Li0. For Na3V2(PO4)3, persistent VO6 tetrahedral distortion and an accompanying V5+ state is observed, particularly at the surface, after discharge vs. Li+/Li. These observations further elucidate the particular atomic and electronic structure changes and charge-discharge mechanisms of high voltage NASICON and anti-NASICON cathode materials for Li-ion battery applications.

Polyhedral Distortions and Unusual Magnetic Order in Spinel FeMn2O4.

Spinel compounds AB2X4 consist of both tetrahedral (AX4) and octahedral (BX6) environments with the former forming a diamond lattice and the latter a geometrically frustrated pyrochlore lattice. Exploring the fascinating physical properties and their correlations with structural features is critical in understanding these materials. FeMn2O4 has been reported to exhibit one structural transition and two successive magnetic transitions. Here, we report the polyhedral distortions and their correlations to the structural and two magnetic transitions in FeMn2O4 by employing the high-resolution neutron powder diffraction. The cation distribution is found to be (Mn0.92+Fe0.13+)A(Mn3+Fe0.93+Mn0.12+)BO4. While large trigonal distortion is found even in the high-temperature cubic phase, the first-order cubic-tetragonal structural transition associated with the elongation of both tetrahedra and octahedra with shared oxygen atoms along the c axis occurs at TS ≈ 750 K, driven by the Jahn-Teller effect of the orbital active B-site Mn3+ cation. Strong magnetoelastic coupling is unveiled at TN1 ≈ 400 K as manifested by the appearance of Néel-type collinear ferrimagnetic order, an anomaly in both tetrahedral and octahedral distortions, as well as an anomalous decrease of the lattice constants c and a weak anomaly of a. Upon cooling to TN2 ≈ 65 K, it evolves to a noncollinear ferrimagnetic order accompanied by the different moments at the split magnetic sites B1 and B2. Only one-half of the B-site Mn3+/Fe3+ spins, i.e., the B2-site spins in the pyrochlore lattice, are canted, which is a unique magnetic order among spinels. The canting angle between A-site and B2-site moments is ∼25°, but the B1-site moment stays antiparallel to the A-site moment even at 10 K. This noncollinear order is accompanied by a modification of the O-B-O bond angles in the octahedra without significant change in lattice constants or tetrahedral/octahedral distortion parameters, indicating a distinct magnetoelastic coupling. We demonstrate distinct roles of the A-site and B-site magnetic cations in the structural and magnetic properties of FeMn2O4. Our study indicates that FeMn2O4 is a wonderful platform to unveil interesting magnetic order and to investigate their correlations with polyhedral distortions and lattice.

A one-dimensional organic-inorganic hybrid copper(I)-halide with broadband emission

Organic-inorganic perovskite materials have shown excellent performance and strong competitiveness in high-performance photovoltaic and optoelectronic devices. Besides the color-tunable and narrow-band emissions realized in hybrid perovskites, broadband emission from lead-halide perovskites has also attracted strong interest for applications in the next generation of solid-state lighting. Although great progress has been made in lead halide perovskites, a very important aspect that hinders their commercial exploitation is the severe lead toxicity. In this research, a lead-free copper(I)-iodine hybrid was synthesized by a solution evaporation method at room temperature. Single crystal X-ray diffraction shows that this hybrid possesses the chemical formula of C6H5CH2CH2NH3CuI2. The C6H5CH2CH2NH3CuI2 belongs to the monoclinic phase with the C2/c space group, where the edge-sharing [CuI4] tetrahedral chains are separated by organic C6H5CH2CH2NH3+ ions, exhibiting one-dimensional (1D) crystal structure. The optical band-gap of C6H5CH2CH2NH3CuI2 was determined to be 4.02 eV. The photoluminescence (PL) spectrum shows a broadband emission ranging from 380 nm to 780 nm and peaks at 542 nm together with a small peak at 336 nm, which can be attributed to the emission of self-trapped exciton (STE) and free exciton (FE), respectively. The large Stokes shift of 230 nm between the PL and photoluminescence excitation (PLE) as well as the broad emission was ascribed to the Jahn–Teller lattice distortion of [CuI4] tetrahedra. The reduced 1D characteristic facilitates the tetrahedral distortion. PL decay analysis shows that the average lifetime of STE is about 66.9 ns? Temperature and time-dependent PL measurements show that the normal working temperature of this luminescent material should be no higher than 100 °C. Theoretical calculations were performed to better understand this compound. The successful synthesis and preliminary optical investigations on C6H5CH2CH2NH3CuI2 can be of great significance for offering more environmental-benign options in both solid-state lighting and other perovskite optoelectronic devices.

Lanthanum phosphate as catalyst in the reaction of 5-HMF formation

Lanthanum phosphate (LP) has been synthesized by sol-gel method at room temperature. The synthesized catalyst was characterized by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), pyridine adsorption FTIR, N2 adsorption-desorption and SEM-EDX. The XRD results show that LP has a hexagonal structure. The FTIR spectra of LP showed O=P-O bending vibrations, P-O vibrations (from phosphate tetrahedral distortion), P-O symmetrical strain vibrations and PO43- bending vibrations, each of which was characterized by the appearance of a peak at 613, 530-620, 950 and 538-621 cm-1. The presence of the OH functional group was indicated by a peak at 3450-3700 cm-1, which was strengthened by the H-O-H bending vibration that appeared at 1629 cm-1. The surface area, pore volume and pore diameter of LP are 51.04 m2/g, 0.21 cm3/g and 13.31 nm, respectively. SEM image showed that agglomerated solids with irregular shapes were obtained from the synthesis. Catalytic testing indicates that the acidity of the catalyst has main role in the formation of 5-HMF.

Luminescence properties and spectral modulation of the ultra-broadband, highly efficient near-infrared luminescent material CaGa4O7:Cr3+, Cr4+, Yb3+

Recently, near-infrared phosphors have received a lot of attention due to their wide application in the field of detection and analysis, and it is urgent to develop efficient broadband NIR phosphors. In this paper, a conventional high-temperature solid-phase method was used to prepare a novel near-infrared phosphor CaGa4O7:Cr3+, Cr4+, which provides two emission bands ranging from 600 to 1000 nm and 1100–1600 nm. Although there are only four and five coordination sites in the CaGa4O7 (CGO) lattice, the doping of the Cr3+ ions in the CGO causes the Ga–O tetrahedral distortion into an octahedron, providing a favorable environment for the emission of the Cr3+ ions. Under blue light excitation, Cr3+ emits luminescence in the NIR I region from 600 to 1000 nm with a half-height width of up to 148 nm. With increasing Cr ion concentration, more and more Cr4+ preferentially occupy the four coordinated Ga3+ sites, and the intensity of the ultra-broad emission band in the NIR II region (1100 nm–1600 nm) increases with a full width at half maximum (FWHM) of 262 nm. To further optimize the emission spectrum, Yb3+ was codoped into CGO: Cr3+, Cr4+, the energy transfers from Cr3+ to Yb3+ in CGO was found, thus filling the gap between 1000 and 1100 nm in the CGO emission spectrum and obtaining a more complete ultra-wide spectrum. Moreover, the luminescence mechanism, energy transfer efficiency, and quantum yield are also studied in detail, and the ability of CaGa4O7:Cr3+, Cr4+, and Yb3+ luminescent materials to achieve ultra-broadband efficient near-infrared emission was demonstrated.

Investigations on the local structure and the spin Hamiltonian parameters for Cu2+ in xCuO-(68-x)V2 O5 -32TeO2 glasses.

The defect structure, spin Hamiltonian parameters (SHPs: anisotropic factors and and the hyperfine structure constants and ), and their compositional dependence of in ( = 5, 10, 20, 30 mol%) glasses are quantitatively analyzed by using the higher-order perturbation formula of octahedral complex with tetrahedral elongation distortion. Due to the Jahn-Teller effect, the group is subjected to tetragonal elongation distortion of varying degrees. , and show nonlinear changes with the concentrations of . When = 10 mol% CuO, the degree of distortion ( ) is the smallest; when = 30 mol% CuO, the degree of distortion ( ) is the largest, which indicates that excessive distortion leads to the appearance of -axis oxygen vacancies and the coordination number of copper ions from six to four. The increasing tendency of the evaluated and reveals decreasing covalency of the whole glass system. Present theoretical studies would be useful to the explore the structural properties and optical applications of glass with different concentrations.

Sintering behavior, structure and dielectric properties of CuO-ZnO-MgO-B2O3 glass-ceramics for ULTCC applications

High performance ultra-low temperature co-fired ceramic (ULTCC) materials were prepared from CuO- MgO- ZnO- Al2O3- B2O3- Li2O glass-ceramics. The sintering behaviors, crystalline phase evolution, microstructure and dielectric properties, as well as their compatibility with Ag and Al electrodes, were investigated. With the suitable substitution of MgO for ZnO, the dielectric properties of glass-ceramics were improved. It is mainly associated with the fine microstructure, highly crystallinity, and decrease in tetrahedral distortion in the crystal lattice. All the glasses completed the densification at 575–600 °C, and ZnB4O7 is the only crystalline phase precipitated from the glasses. Moreover, the glass-ceramic with 1 wt% MgO sintered at 575 °C for 5 h, exhibited low relative permittivity ~ 7.1 and low dielectric loss ~ 6.40 × 10−4. And the glass-ceramic with 4 wt% MgO sintered at 600 °C for 5 h, also displayed low relative permittivity ~ 7.1 and low dielectric loss ~ 5.77 × 10−4. Both two glasses have good sintering compatibility with silver and aluminum electrodes, which provided high potential for ULTCC application.

Impact of erbium (Er) doping on the structural and magnetic properties of Ni-Cu (Ni0.1Cu0.9Fe2O4) nanoferrites

Rare earth erbium (Er) doped spinel Ni-Cu nanoferrites having chemical composition Ni0.1Cu0.9ErxFe2-xO4 (x = 0.00, 0.010, 0.015, 0.020, 0.025 and 0.030) were prepared by standard citrate-gel auto combustion (CGAC) technique. X-ray diffraction spectroscopy (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), UV–visible spectroscopy, and vibrating sample magnetometer (VSM) were used to characterize the structural, optical, and magnetic properties of these ferrites. X-ray diffraction spectra clearly revealed that the pure Ni-Cu ferrite shows a tetrahedral distortion due to John Tellar ion (Cu2+) subsequently erbium doping transformed the tetragonal phase in to the cubic spinel phase with minor traces of impurity phase. Using Scherer's equation, the average crystallite size was found to be between 7.39 and 27.78 nm. The average crystallite size (7.39–27.78 nm) obtained from XRD and average grain size (64.84–83.36 nm) measured from FESEM confirmed the nano structure of prepared samples. Energy dispersive analysis X-ray (EDAX) spectra with elemental analysis verified the existence of Ni, Cu, Er, Fe, and O elements without any impurities. Two prominent absorption bands detected in FTIR spectra within the wave number range of 575.54–586.73 cm−1 (υ1) and 370.24–372.53 cm−1 (υ2) indicate the stretching vibrations of Fe3+-O2− complexes in tetrahedral and octahedral sites of spinel structure respectively. TG and DTA techniques were used to analyze the thermal behavior of the composition x = 0.030. It was observed that exhibiting a rapid loss in weight after 900 °C promotes the formation of pure phase nanoferrite. Direct and indirect optical band gap values were computed from UV absorption studies with Tauc plots. The obtained band gap values revealed the semiconducting behavior of the prepared samples. VSM was used to explore the magnetization of samples as a function of field at temperatures of 15 K and 300 K. The maximum saturation magnetization (Ms) was observed for x = 0.030 composition and it was estimated as 31.18 emu/g at 15 K and 26.80 emu/g at 300 K temperatures. The experimental and theoretical values of lattice parameter and room temperature magnetic moment are good agreement with suggested cation distribution.

Products of Prolonged Autoxidation of Simple Dihydric Phenols in the Presence of Copper(II) Ions – An Electron Spin Resonance Study

Electron spin resonance (ESR) spectroscopy was used for characterizing the products obtained by prolonged autoxidation of simple dihydric phenols (hydroquinone, catechol, and 4-methylcatechol) in the presence of copper(II) ions. Room temperature ESR spectra revealed that both paramagnetic copper(II) ions and organic radicals are present in obtained autoxidation products similarly to the humic acid complexed copper(II) ions. The ratio of organic radical signal intensity to the copper(II) ion signal intensity suggests that the smallest amount of copper(II) ions is incorporated in the hydroquinone autoxidation product while the highest amount of copper(II) ions is incorporated in the autoxidation product of catechol. Satisfactory computer simulations of experimental ESR spectra were obtained by considering only one type of copper(II) ion binding site for hydroquinone autoxidation product and two distinct types of copper(II) ion binding sites for catechol and 4-methylcatechol autoxidation products. Parameters obtained by the computer simulation of ESR spectra indicated prevalent ionic bonding of copper(II) ions in polymeric matrices with tetrahedral distortion at copper(II) ion binding sites and negligible exchange interactions between them. Products obtained by the hydroquinone and catechol autoxidation have more similar characteristics in comparison to the product obtained by the 4-methylcatechol autoxidation where more expressed ionic bonding of copper(II) ions, and smaller tetrahedral distortion are present. Due to the dipolar interactions of oxygen-centered organic radicals in autoxidation products with paramagnetic copper(II) ions, their ESR linewidths are larger and g-values smaller in comparison to the values found in humic acids from various soil types.

Intense Blue Chromophores in Cobalt Doped Phenacite‐Type Zinc Germanate System through Jahn‐Teller Distortion of Co Tetrahedron

AbstractIn the quest for new blue chromophores with less usage of cobalt alternatives to the carcinogenic and expensive zinc‐cobalt aluminate system, we developed cobalt doped phenacite type zinc germanate system. Rietveld analysis reveals that the CoO4 tetrahedron intensely experienced Jahn‐Teller distortions leading to irregular geometry on substitution. The UV‐vis‐IR absorption spectra exhibit intense Co2+ d‐d transitions with three fold splitting associated with the CoO4 tetrahedron in the visible and IR region, indicating low symmetry. The crystal field strength 10Dq, Racah parameter and Nephelauxetic ratio variations reflect on the improved covalency of the Co2+ environment. Thus the synergetic effect of Jahn‐Teller distortions and covalency of the CoO4 tetrahedron lead to strong absorptions in the green to red region resulting in intense blue colors with low cobalt content (2.2 to 8.9 mol %). The typical composition Zn1.6Co0.4GeO4 exhibits intense blue hue b*=−58.64, much higher than that of the commercial CoAl2O4 system.