O2 Bond Research Articles

Foxtail millet bran dietary fibres foster in vitro beneficial gut microbes and metabolites while suppressing pathobionts

Foxtail millet bran soluble dietary fibre (MBSDF) is a dietary compound with various bioactivities, potentially modulated by the gut microbiota. To elucidate this bioregulatory mechanism, this study focused on the structureal composition and in vitro fermentation characteristics of MBSDF. The results revealed that MBSDF has a molecular weight of 18.26 kDa. The main chain is connected through a glycosidic bond in the form of →4)-α-D-Glcp-(1 → 4)-β-D-Xylp-(1→, being branched by →4, 6)-α-D-Glcp-(1 → O-6 and →3, 4)-β-D-Xylp-(1 → O3 bonds. After 24 h fermentation, the carbohydrate utilisation rate reached 59.15 %, with a decreased molecular weight and monosaccharide composition molar mass ratio. Meanwhile, a increase was observed in the short-chain fatty acid, accompanied by an increased relative abundance of Faecalibacterium, Bifidobacterium and Lactobacillus and suppressed growth of pathogenic Enterococcus. Interestingly, the modulation of gut homeostasis probably occurs via butyrate metabolism pathway. Collectively, MBSDF can selectively regulate the gut microbiota and their metabolites.

Core-shell structured composite high-efficiency catalyst Co@Pd/TiO2 with a compressed-strain Pd shell for the direct synthesis of H2O2

Direct synthesis of H2O2 from H2 and O2 still faces the dilemma of low selectivity and productivity due to the O-O bond dissociation. To expedite the resolution of this issue, we introduce a core–shell structured catalyst Co@Pd/TiO2 with a compressed-strain Pd shell. The Co@Pd/TiO2 catalyst demonstrates a superior H2O2 productivity of 6.95 × 103 mmol·gPd-1·h−1 and H2O2 selectivity of 98.1 %, with enhancements of over 192 % and 139 %, respectively, when compared to Pd/TiO2. The construction of the compressed-strain Pd shell on the Co@Pd/TiO2 catalyst induces a winder width (wd) and a lower center (εd) of the Pd d-band, allowing the Co@Pd/TiO2 catalyst to achieve the following benefits for improving H2O2 selectivity and productivity: (1) Reducing the degree of electron back-donation to O2* (* denotes adsorbed state, the same below), thus inhibiting the cleavage of the O-O bond in O2*; (2) Showing a weaker Pd-O bond strength, which stabilizes the OOH* species and suppresses the breakage of the O-O bond therein; (3) Weakening the interaction between the catalyst and chemical substances, thereby restraining H2O2 degradation.

A DFT and Microkinetic Study of Propylene Selective Oxidation on Cu2O(111) Surface with O2: Chlorinum Effect

AbstractSpin‐polarized density functional theory (DFT) +U calculation was performed to study propylene selective oxidation on Cu2O(111) and Cl−Cu2O(111) surfaces. The mechanism included two pathways: the allylic hydrogen stripping (AHS) pathway and the epoxidation pathway, and acrolein, propylene oxide (PO), propanal and acetone can be formed. The calculated results found that the C3H6*+OO*→OOMMP2*→PO* route can be regarded as the preferred formation route of PO on these two surfaces. On clean surface, acrolein can be regarded as the main product, then other products selectivity follows: acetone>PO>propanal. On Cl−Cu2O(111) surface, acrolein was also the main product, and the apparent activation energy of acrolein (1.97 eV) was approximated to the apparent activation energy of PO (2.04 eV), other products selectivity follows: PO>propanal>acetone, which means that the selectivity of PO can be improved by the effect of Cl. Microkinetic simulation confirm that PO selectivity can be elevated qualitatively, and found that OOMMP2*→PO2*+O* is the rate determining step on pure surface and C3H6*+OO*→OOMMP2* is the rate controlling step on the doped−Cl surface. From this work, it can be found the O−O bond in O2 can be activated effectively by the presence of Cl, enhancing the selectivity of PO.

Two-dimensional Mo3-TiS2 monolayer hosting high moisture resistance and abundant surface-chemisorbed oxygen for effective detection of SF6 decomposition gases: Atomic-scale study

Monitoring the SF6 decomposition gas (DPA) by gas sensors can be used to predict the operating status of power equipment, and the sensitivity performance of gas sensors is deeply influenced by the humidity resistance and surface oxygen adsorption performance of their sensing materials. The present research aims to explore a high‐valence transition‐metal ion doped transition metal dichalcogenide (TMD) monolayer that hosts high moisture resistance and abundant surface-chemisorbed oxygen suitable for detecting DPA. Using first-principles methods, the adsorption behavior of three representative types of gases (HF, SO2, and CO2) in DPA, H2O, and O2 on Mo3-TiS2 monolayer are considered. Our results show that SO2 and CO2 molecules are adsorbed above the Mo3 cluster through chemical adsorption, while HF molecule is physically adsorbed. The desorption times for SO2 and CO2 on Mo3-TiS2 adsorbent are 9.89 s at 348 K and 34.96 s at 398 K, respectively. Introducing dopant Mo3 resulted in better anti-humidity performance of TiS2, as the force of Mo3-TiS2 monolayer towards H2O molecule is weakened compared to the intrinsic adsorption system. Additionally, Mo3-TiS2 monolayer exhibits an exceptionally high affinity for O2 molecule, leading to the rupture of chemical bond in O2, and the chemisorbed oxygen ions are acquired through the charge transfer between Mo3 cluster and O2 molecule. The computational findings in this article offer theoretical backing for advancing the development of gas sensors utilizing Mo3-TiS2 and its utilization in the realm of DPA detection.

How Do the Position and Number of Methyl Substituents Affect the Photochemical Process of Criegee Intermediate? Trajectory Surface-Hopping Dynamics of Four-Carbon CIs.

Electronic-structure calculations combined with nonadiabatic trajectory surface-hopping (TSH) dynamic simulations were carried out on two alkenyl-substituted Criegee intermediates (CIs), i.e., propenyl-substituted CI (PCI) and 1-methyl-propenyl substituted CI (MPCI), in order to investigate the influence of the position and number of substituents on the photochemical process of CI in S1 states. It is found that they play critical roles in the reactivity, dominant product channel, and mechanism of the CIs. More specifically, introducing a methyl group on either C1 (α-C) or C3 (γ-C) position of a vinyl-substituted CI (VCI) skeleton facilitates the rotation of the C1═O1 bond and leads to the formation of a three-membered dioxirane ring; meanwhile, it evidently enhances the reactively of the S1-state molecule. Meanwhile, methyl substitution on the vinyl moiety [i.e., C2 (β-C) and C3 (γ-C) positions] is beneficial for the rotation of the C2═C3 bond and thus facilitates the formation of the five-membered 1,2-dioxole ring, and the substitution on C2 site decreases the reactivity. The cosubstitution of C2 and C3 atoms by methyl groups well balances the features of VCI in the sense of high reactivity, consistently predominant channel, and possible dioxole side-product. The findings here not only deepen the knowledge on the photochemical processes of the CI but also inspire the rethinking of the "old" concept of substitution effect.

Bond dissociation energy of O2 measured by fully state-to-state resolved threshold fragment yield spectra.

We have determined the bond dissociation energy of O2 by measuring fully state-to-state resolved threshold fragment yield spectra in the XUV energy region, O2X3Σg-,N″,J″→O(PJ3)+O(S1o3)/O(S2o5). Our results have yielded a bond dissociation energy value of 41 269.19 ± 0.10cm-1, which is consistent with previous measurements but exhibits a significantly lower uncertainty, approximately five times smaller. It is noteworthy that this study is the first to simultaneously achieve fine structure state resolution for the parent O2molecule and spin-orbit state resolution for the O(3PJ) fragments in the measurement of O2 bond dissociation energy. As a result, our findings have established a solid foundation for the obtained data.

Insight into the Critical Role of Oxygen Vacancies and V=O Bonds Length in V2O5 for Advanced Zinc Ion Storage.

Due to the larger sizes and stronger positive polarity of Zn2+ than dominant univalent ions, Zn2+ sluggish diffusion within V2O5 host electrodes is an essential issue in developing aqueous zinc-ion batteries (ZIBs) of higher energy densities. Herein, a high-performance V2O5 cathode was developed through subtly synthesizing and tuning V2O5 with oxygen vacancies-enriched and elongated apical V=O1 bond by altering the gradient concentration of hydrazine hydrate in the gas-solid reaction system. This strategy can enhance both intrinsic and extrinsic conductivity to a large extent. The electrochemical testing demonstrated the oxygen vacancies-enriched and elongated apical V=O1 bond can not only increase the intrinsic electronic conductivity of V2O5, but also induce additional pseudocapacitance to enhance the Zn2+ diffusion kinetics. We used infrared spectroscopy and Raman spectroscopy to characterize the change in the bond length structure of V2O5. Simultaneously, the long-term cyclability (capacity retention of 76.9 % after 1200 cycles at 4.0 A g-1) and rate capabilities (218 mAh g-1 at 4.0 A g-1) are promoted as well. We believe that our work might shed light on the bond length engineering of V2O5 and provide insights for the reasonable designing of novel cathodes for practical rechargeable ZIBs.

The OH stretching region in infrared spectra of the apatite OH-Cl binary system

Abstract Polarized Fourier Transform Infrared (FTIR) microspectroscopy of the OH stretching region of hydroxylapatite-chlorapatite solid solutions presents novel problems for the assignment of peaks to specific OH-Cl pairs. Crystal structure refinements of Hughes et al. (2016) identified new positions for column anions in synthetic mixed Cl-OH apatites, with three different column anion arrangements depending on composition. These structural refinements, combined with bond valence calculations, allow for interpretation of the OH stretching region. A peak at 3574 cm-1 is identified as that from end member hydroxylapatite. A second major peak at 3548 cm-1 is only found in mixed chlorapatite-hydroxylapatite solid solutions, as is a third peak at 3592 cm-1. Both represent perturbations of the OH stretching vibration as compared to hydroxylapatite, to lower and higher frequency, respectively. Both of the new peaks are the result of a Clb-OH sequence, with adjacent anions in crystallographically similar positions, both above or both below adjacent mirror planes. One configuration has the hydrogen atom pointed towards the chlorine atom. The second has the hydrogen of the OH group pointed away from the chlorine atom. Both configurations present novel problems. The shift to lower wavenumber at 3548 cm-1 is characteristic of hydrogen bonding in fluorapatite-hydroxylapatite mixtures, yet the distance between O(H) and Clb is too great to allow it. The shift of OH stretching vibrations to lower wavenumber is produced through changes in polarization of intervening Cl-Ca2’ (or Ca2) and Ca2(’)-O3 bonds, which are affected by the presence of the large chlorine atom. Lowering the OH stretching vibration mimics the expected effect of a chlorine on a neighboring OH group in the apatite c-axis column, though without hydrogen bonding. The shift to higher wavenumbers, i.e. higher frequency at 3592 cm-1, is the opposite of that expected for hydrogen bonding between column anions in the apatite mineral group. It is ascribed to interaction between an adjacent Clb and the oxygen end of an adjacent OH dipole. This pairing places an oxygen and a chlorine atom in close proximity. Possible means of accommodation are discussed. A ubiquitous peak at 3498 cm-1 represents hydrogen bonding between an OH and the OHa site, with an interoxygen distance of about 2.9 Å. Published modeling supports the hypothesis that the OHa site is occupied by an O rather than an OH. However, no clear counterpart to this pairing is observed in crystal structure refinements for specimens lacking OHa, although the infrared absorbance is present. The existence of oxyapatite is inferred from studies of plasma-sprayed biomaterials, but the crystallographic details of the substitution have remained elusive. A minor shoulder at 3517 cm-1 does not have a clear counterpart in the structural refinements. Sequences of three columnar anions (e.g. OH-Cl-OH or Cl-OH-OH) can be ruled out, but unequivocal assignment awaits further research.

Percarbonate activation by N-doped polyethylene terephthalate (PET)-derived carbon: The role of vacancy and insights into the mechanism

Percarbonate-based advanced oxidation processes catalyzed by carbon materials from plastic waste are rarely reported and lack clarity in their mechanisms. We synthesized N-doped polyethylene terephthalate (PET)-derived carbon materials with surface areas of up to 2190.9 m2/g and nitrogen/oxygen vacancies via urea-assisted pyrolysis. These materials exhibited exceptional adsorption and catalytic activities in a Fenton-like reaction for tetracycline degradation. The N-doped PET-derived catalyst (NPETK-800) achieved a 95 % removal efficiency for tetracycline at 50 mg/L, attributed to synergistic adsorption and oxidation effects via sodium percarbonate activation. NPETK-800 underwent surface hydroxylation through the electrostatic adsorption of OH− from CO32− hydrolysis on N and O vacancies, and its hydroxylated surface converted the adsorption mode of H2O2 to a H-bonded structure. This mode favored cleaving the OH bond over the OO bond in H2O2, generating 1O2 and O2−, crucial for tetracycline degradation. This study unveils the pivotal role of vacancies in tuning the generation of reactive oxygen species in Fenton-like reactions.

First Principles Investigation of C, Cl2 and CO Co-Adsorption on ZrSiO4 Surfaces for Carbochlorination Reaction.

The study of the adsorption behavior of C, CO and Cl2 on the surface of ZrSiO4 is of great significance for the formulation of the technological parameters in the carbochlorination reaction process. Based on first principles, the adsorption structure, adsorption energy, Barder charge, differential charge density, partial density of states and energy barrier were calculated to research the adsorption and reaction mechanism of C and Cl2 on ZrSiO4 surfaces. The results indicated that when C, CO and Cl2 co-adsorbed on the surface of ZrSiO4, they interacted with surface atoms and the charge transfer occurred. The Cl2 molecules dissociated and formed Zr-Cl bonds, while C atoms formed C1=O1 bonds with O atoms. Compared with CO, the co-adsorption energy and reaction energy barrier of C and Cl2 are lower, and the higher the C content, the lower the adsorption energy and energy barrier, which is beneficial for promoting charge transfer and the dissociation of Cl2. The 110-2C-2Cl2 has the lowest adsorption energy and the highest reaction activity, with adsorption energy and energy barriers of -13.45 eV and 0.02 eV. The electrons released by C are 2.30 e, while the electrons accepted by Cl2 are 2.37 e.

Synthesis and characterization of (Pb1−x Sr x )MnBO4: a structural and spectroscopic study

Abstract The presence of ns 2 stereo-chemical active lone electron pairs (LEPs) causes asymmetric atomic environments around a given p-block cation, leading to change the crystal chemistry of a respective system. Here we report a series of mullite-type compounds to understand at what extend Sr2+ replaces the stereochemical active Pb2+ cation in (Pb1−x Sr x )MnBO4. Each member of the solid solution has been synthesized by conventional solid-state method. The polycrystalline samples are characterized using X-ray powder diffraction followed by Rietveld refinement. Substitution of Pb2+ with Sr2+ leads to contraction of the a lattice parameter with slight elongation in the b and c direction. For a difference of 1 pm of the ionic radius between Sr2+ and Pb2+, the cell volume contracts about 4 % between the end members as the spatial requirement of the LEP activity in the MBO4 2− channels significantly decreases. Within the solid solution, two distinct Pb/Sr–O2 bond distances significantly differ, which gradually decreases with increasing strontium content leading to a more symmetric coordination around strontium. The calculated BVS of Pb2+/Sr2+ exhibits a linear correlation with the Wang–Liebau eccentricity parameter, indicating to an increased bonding ability cation. The vibrational properties are characterized by both Raman and FTIR spectroscopy, complementing the XPRD results. Electronic band gaps of selected (Pb1−x Sr x )MnBO4 samples were obtained from diffuse reflectance spectroscopy data. Additionally, the Sr containing samples show higher thermal stability than the Pb containing counterparts.

Nitrogen-Rich Molybdenum Nitride Synthesized in a Crucible under Air.

The triple bond in N2 is significantly stronger than the double bond in O2, meaning that synthesizing nitrogen-rich nitrides typically requires activated nitrogen precursors, such as ammonia, plasma-cracked atomic nitrogen, or high-pressure N2. Here, we report a synthesis of nitrogen-rich nitrides under ambient pressure and atmosphere. Using Na2MoO4 and dicyandiamide precursors, we synthesized nitrogen-rich γ-Mo2N3 in an alumina crucible under an ambient atmosphere, heated in a box furnace between 500 and 600 °C. Byproducts of this metathesis reaction include volatile gases and solid Na(OCN), which can be washed away with water. X-ray diffraction and neutron diffraction showed Mo2N3 with a rock salt structure having cation vacancies, with no oxygen incorporation, in contrast to the more common nitrogen-poor rock salt Mo2N with anion vacancies. Moreover, an increase in temperature to 700 °C resulted in molybdenum oxynitride, Mo0.84N0.72O0.27. This work illustrates the potential for dicyandiamide as an ambient-temperature metathesis precursor for an increased effective nitrogen chemical potential under ambient conditions. The classical experimental setting often used for solid-state oxide synthesis, therefore, has the potential to expand the nitride chemistry.

A variable temperature neutron diffraction study of dual ion conducting Sr3V2O8

Sr3V2O8 exhibits sizeable oxide ion and proton conductivity at 800 °C. In order to investigate any correlation between the crystal structure and electrical properties of Sr3V2O8, a variable temperature neutron diffraction study has been performed. Results show that there is no change in crystal symmetry upon heating. However, the VO4 tetrahedra are observed to become more distorted upon heating and more oblate in shape. The distortion arises due to a shortening of the apical V–O1 bond length and accompanying increase of the V–O2 bond length with temperature. Bond valence site energy analysis show that there is a reduction in the energy of the migration pathways for movement of the oxide ions as the Sr–V–Sr bottlenecks expand upon heating.

Robust iron-doped manganese oxide nanoparticles from facile fabrication to photo-catalytic degradation application of binary dyes mixture

The manganese oxide (MnO2 and iron-doped manganese oxide (Fe–MnO2) nanoparticles (NPs) with reduced band gap (Eg) were fabricated through the co-precipitation process. They used to degrade Indigo Carmine (IC) and Rhodamine B (RB) binary mixture in an aqueous medium under solar light irradiation. From FT-IR, the twisting modes of the Mn–O bond and the stretching vibrations of the Fe–Mn–O2 bond were confirmed from the peaks observed at 480 cm−1,584 cm−1,675 cm−1, and 900 cm−1, 1150 cm−1, and 1200 cm−1 respectively. The MnO2 has an optical band gap of 3.2 eV, which was decreased to 3 eV in Fe–MnO2. The zero charge (PZC) point was 8 for Fe–MnO2 and 7 for MnO2. The BET surface area for Fe–MnO2 was 398 m2/g, relatively higher than MnO2 particles, having a surface area of 384 m2/g. The average crystallite sizes calculated from Scherer formulae were 37 nm for MnO2 and 31 nm for Fe–MnO2 NPs. SEM confirmed the irregular morphology of the prepared particles. It was analyzed that agglomeration occurs in MnO2 than the Fe–MnO2. The maximum degradation of IC dye was 99%, and that of RB was 98% at the optimum conditions. The data were best fitted to second-order kinetics.

A Theoretical Study on the Degradation Mechanism, Kinetics, and Ecotoxicity of Metronidazole (MNZ) in •OH- and SO4•--Assisted Advanced Oxidation Processes.

Metronidazole (MNZ), a typical example of nitroimidazole antibiotics, is widely used in the treatment of infectious diseases caused by anaerobic bacteria. The degradation mechanism and kinetics of MNZ in the presence of HO• and SO4•- were studied using density functional theory (DFT). It was confirmed that both HO• and SO4•- easily added to the carbon atom bonded to the NO2 group in the MNZ molecule as the most feasible reaction channel. This study shows that subsequent reactions of the most important product (M-P) include the O2 addition, hydrogen abstraction and bond breakage mechanisms. The rate constants of HO• and SO4•--initiated MNZ in the aqueous phase were calculated in the temperature range of 278-318 K. The total rate constants of MNZ with HO• and SO4•- were determined to be 8.52 × 109 and 1.69 × 109 M-1s-1 at 298 K, which were consistent with experimental values of (3.54 ± 0.42) × 109 and (2.74 ± 0.13) × 109 M-1s-1, respectively. The toxicity of MNZ and its degradation products to aquatic organisms has been predicted. The results proposed that the toxicity of the initial degradation product (M-P) was higher than that of MNZ. However, further degradation products of MNZ induced by HO• were not harmful to three aquatic organisms (fish, daphnia, and green algae). This study provides a comprehensive theoretical basis for understanding the degradation behavior of MNZ.

Co/VN heterojunction anchored on multi-dimensional N-doped carbon for high-performance zinc–air batteries

Thanks to high electroconductivity and excellent electrochemical durability, the vanadium nitride (VN) is gradually developed as an electrocatalyst. However, the oxygen dissociation ability of VN species is usually weak due to the lack of d-orbital electrons in the vanadium. Herein, Co nanoparticles with abundant 3d-orbital electrons were utilized to construct the heterojunction with the VN (Co/VN), which anchored on the multi-dimensional N-doped carbon (CoVN/NC) for oxygen reduction reaction (ORR). The heterogeneous interface within the Co/VN increased more active sites and was conducive to adsorbing more O-containing intermediates. The oxygen dissociation ability of intermediates was improved on the VN surface. Based on “3d-orbital electron complementary effect”, the Co nanoparticles transferred d-orbit electrons to the VN and regulated the electronic configuration of VN components. The continuity of the V 3dz2 orbitals within the Co/VN was enhanced near the Fermi level, which promoted the formation of strong σ bonds between the CoVN/NC and O pz orbitals. Therefore, the O–O bond of O2 was more easily broken on the CoVN/NC surface. The CoVN/NC displayed the half-wave potential of 0.85 V for ORR. The zinc-air battery with the CoVN/NC possessed a power density of 200.7 mW cm−2 and a cycle stability of 180 h. This work would provide a practical reference for improving electrocatalytic activities of VN species.

Advantages and limitations of hydrogen peroxide for direct oxidation of methane to methanol at mono-copper active sites in Cu-exchanged zeolites

The efficiency of direct catalytic oxidation of methane to methanol (DMTM) is significantly influenced by oxidants. However, realizing a one-pot DMTM using dioxygen remains challenging. Hydrogen peroxide is still the most frequently reported green oxidant for DMTM, with high selectivity for methanol. To gain insight into the influence of oxidants on DMTM performance, we computationally investigated the reaction mechanisms involved in DMTM using H2O2 at mono-copper sites in three types of Cu-exchanged zeolites with different micropore sizes. We identified the advantages and limitations of H2O2 as an oxidant. In contrast to the O–O bond in O2, the O–O bond in H2O2 can be easily broken to produce reactive surface oxygen species, which enable the facile C–H bond activation of methane at a low temperature. However, because of the radical-like process of C–H bond activation at mono-copper sites, actualizing the preferential C–H bond activation of methane is kinetically challenging compared to that of methanol. Moreover, the lower O–H bonding energy of H2O2 would result in self-decomposition of H2O2. Despite these bottlenecks, kinetic analysis shows that improving catalysts to boost the DMTM performance using H2O2 is a promising approach.

Hydrogenation of furfural to 1,5-pentanediol over CuCo bimetallic catalysts

AbstractA series of CuxCo3–xAl hydrotalcite-like catalysts with different Cu/Co molar ratios were synthesized by the urea homogeneous precipitation method and used for the direct hydrogenation-hydrogenolysis of furfural to 1,5-pentanediol. The results showed that the Cu/Co molar ratio of the catalyst had a significant effect on its textural properties and catalytic performance. The catalyst exhibited excellent catalytic performance when the molar ratio of Cu/Co was 1:29 (Cu0.1Co2.9Al), and the conversion of furfural was 100% together with 51.1% yield of pentanediol among which the yield of 1,5-pentanediol was 41.1%, under the reaction condition of 140 °C, 4 MPa H2 for 6 h. Extensive characterization techniques, including temperature-programmed reduction (H2-TPR), temperature-programmed desorption (H2-TPD), X-Ray photoelectron spectroscopy (XPS) and Raman confirmed that the excellent catalytic activity of Cu0.1Co2.9Al catalyst was attributed to the highest content of Cu0 and CoOx on its surface, and a synergistic catalytic effect was present between them. Typically, Cu0 was used to adsorb and activate H2, and CoOx with much oxygen vacancies promoted the adsorption and activation of C=O groups in furfural molecules, leading to the quick conversion of furfural to furfuryl alcohol. In addition, the oxygen vacancies anchored the –OH in the intermediate furfuryl alcohol to produce a C2-terminal oblique adsorption on the catalyst surface. Then it promoted the hydrogenation of C2=C3 with the weakening and cleavage of C2–O1 bond, and enhanced the selectivity of 1,5-pentanediol.

Developing high performance, low temperature sintering and temperature stable K40 material in Co2O3/Nb2O5-modified Ba3Ti4Nb4O21 microwave dielectric ceramics for 5G-LTCC communication devices

The comprehensive properties and sintering temperature of microwave dielectric ceramics are the key factors limiting their practical application. In this work, a novel strategy of complex (Co1/3Nb2/3)4+ ions substituted and adding glass (Li2O-B2O3- SiO2-CaO-Al2O3: LBSCA) was proposed to greatly enhance the microwave dielectric properties of Ba3Ti4-x(Co1/3Nb2/3)xNb4O21 (0 ≤ x ≤ 12 mol%, xCN-BTN) ceramics. A new ceramic of (Co1/3Nb2/3)4+ substitution improved hexagonal phase BTN was successfully fabricated and systematically investigated. As the increased of (Co1/3Nb2/3)4+ ions concentration, the Q×f was greatly increased because of higher packing fraction, and the reduction in the [Nb1/Ti1O6] octahedral distortion caused great changes of τf. Besides, the P-V-L theory revealed that the Ti/Nb ratio greatly contributed in permittivity εr, and the Nb-O bonds mainly affected dielectric loss, especially in Nb(1)-O2(1) bond. As a result, the superior microwave dielectric properties were obtained in 6CN-BTN ceramic sintered at 950 °C: εr∼40.99 ± 0.48, Q×f∼17,310 ± 565 GHz, and τf∼8.62 ± 4.34 ppm/°C. More encouragingly, 6CN-BTN showed good compatibility with silver, making it a promising K40 LTCC material for filter and dielectric resonators. This study presented a new strategy to improve the properties of BTN-based materials by complex ions substitution, which was expected to provide a general approach for the design of advanced microwave dielectric ceramics for other material systems.

Electron density distribution and microstructural spherical harmonic calculation of BaTiO3 powders and ceramics

BaTiO3 ferroelectric powders with initial tetragonal and orthorhombic phases were high energy milled and sintered by plasma spark sintering. Structural and microstructural characterization were made by Rietveld refinement. The milling process produced an increase in the weight fraction of the tetragonal phase and a decrease in the orthorhombic and all lattice parameters increased. The Ti–O1 and Ti–O2 bond lengths increased according to the Ti-polyhedral volume, due to the microstrains enchanced (≈700%) and an average crystallite size reduction (≈600%). The electronic density for all crystalline structure atoms decreased due the increment in the bond length, the atomic displacement and the unit-cell volume. For the sintered ceramics, the behavior in the structural and microstructural parameters was the opposite as those exhibited from the powders which could be linked to improved piezoelectric properties by the non-centrosymmetric variation.