Average Bond Length Research Articles

Adsorption of rare earth elements on organic matter in coal

The occurrence modes of rare earth elements (lanthanide and yttrium, abbreviated as REY) in coal are important both for coal geochemistry studies and the application potential of REY as a by-product of coal-based resources. In this study, the adsorption behaviors of REY on organic matter in coal were investigated by leaching tests using REY solution and ultra-low ash coal samples. On this basis, the adsorption mechanism of REY on organic matter in coal was also studied by molecular simulation calculations. The leaching tests show that the organic matter in coal has a relatively strong adsorption capacity for REY, and that the average adsorption rate or the net adsorption amount of heavy rare earth elements (HREY: Gd, Tb, Y, Dy, Ho, Er, Tm, Yb and Lu) is always higher than that of the light rare earth elements (LREY: La, Ce, Pr, Nd, Sm and Eu). A molecular model of humic acid (HA) was constructed and the adsorption amount between REY and HA was calculated. The results show that the theoretical adsorption rate of HREY (84.88%) is higher than that of the LREY (84.00%). The analysis of the adsorption distances between REY atoms and various functional groups on HA molecules shows that the minimum adsorption distance of LREY is 0.372 nm on average, which is larger than that of HREY (0.368 nm), indicating that the adsorption capacity of the latter is stronger. In addition, a coal molecule (C18H22O) was also constructed to investigate the adsorption characteristics of various REY atoms on the molecule. As a result, it is found that the average binding energy and bond length between the hydroxyl functional group and LREY atoms are 0.12469 Ha (Hartree, the unit of energy in the atomic unit system) and 0.1407 nm, respectively, while for HREY, 0.12883 Ha and 0.1121 nm, respectively. This confirms that HREY is more stable than LREY in binding on organic matter in coal. To conclude, both leaching tests and molecular simulation calculations reveal that REY has a strong adsorption affinity for organic matter in coal, and in particular, HREY shows a stronger organic adsorption preference in coal than LREY, which is probably due to stronger chemical bonding between the former and the functional groups on the coal molecule.

Feasibility and Limitations of High-Voltage Lithium-Iron-Manganese Spinels

Positive electrodes with high energy densities for Lithium-ion batteries (LIB) almost exclusively rely on toxic and costly transition metals. Iron based high voltage spinels can be feasible alternatives, but the phase stabilities and optimal chemistries for LIB applications are not fully understood yet. In this study, LiFexMn2-xO4 spinels with x = 0.2 to 0.9 were synthesized by solid-state reaction at 800 °C. High-resolution diffraction methods reveal gradual increasing partial spinel inversion as a function of x and early secondary phase formation. Mössbauer spectroscopy was used to identify the Fe valences, spin states and coordination. The unexpected increasing lattice parameters with Fe substitution for Mn was explained considering the anion-cation average bond lengths determined by Rietveld analysis and Mn3+ overstoichiometries revealed by cyclic voltammetry. Finally, galvanostatic cycling of Li-Fe-Mn-spinels shows that the capacity fading is correlated to increased cell polarization for higher upper charging cut-off voltage, Fe-content and C-rate. The electrolyte may also contribute significantly to the cycling limitations.

An ab-initio study on two-dimensional semiconductor alloys: Monolayer Mo1-xCrxS2

The formation energy, structure, electronic and magnetic properties of the monolayer (ML) Mo1-xCrxS2 alloy are calculated based on density functional theory calculations within generalized gradient approximation method. It is found that Cr doping in the ML MoS2 is energetically unfavorable. Its lattice constant exhibits a negative bowing coefficient of −0.022 Å. The Mo–S bond length and the average bond length of the ML Mo1-xCrxS2 show a decline trend while the composition dependence of the Cr–S bond length is not monotonic. It is also found that the ML Mo1-xCrxS2 has a direct bandgap at K for any Cr concentration and its bandgap energy monotonically decreases with increasing Cr concentration. When the Cr concentration is no more than 0.6, the bandgap narrowing is due to the upward shift of K VBM and the downward shift of K CBM. If the Cr concentration goes on increasing, the bandgap narrowing is merely due to the upward movement of the K VBM. Besides, the location of the K CBM for Mo1-xCrxS2 is determined by the coupling interaction between the S-3p and Cr-3d states in the conduction band while the K VBM is dominated by two coupling interactions in the valence band. One is the coupling interaction between the S-3p and Cr-3d states. The other is the coupling interaction between the S-3p and Mo-4d states. In order to study the bandgap energy of the ML Mo1-xCrxS2 alloy quantitatively, a physical model is developed. It is observed that the model can give a good estimation by setting EI,Cr−3d,MoS2=1.68 eV, Cp−d=0.55 eV and b1=0.69 eV. The result of the magnetic properties shows that the magnetism of the ML Mo1-xCrxS2 system is very weak.

π-Pimer, π-Dimer, π-Trimer, and 1D π-Stacks in a Series of Benzene Triimide Radical Anions: Substituent-Modulated π Interactions and Physical Properties in Crystalline State

π-Pimer, π-Dimer, π-Trimer, and 1D π-Stacks in a Series of Benzene Triimide Radical Anions: Substituent-Modulated π Interactions and Physical Properties in Crystalline State

First-principles study on the thermodynamic, electronic and mechanical properties of Mg–Al–Si ternary compounds

The alloys used in lightweight equipment such as magnesium (Mg) alloys are not only required the considerable strength but also the good stiffness, i.e., the Young’s modulus (E) is relatively high. Herein, the first-principle density functional theory is adopted to efficiently and economically explore the thermodynamic, mechanical, and electronic properties of Mg-aluminum (Al)-silicon (Si) ternary compounds. The current calculated results show that the Mg–Al–Si ternary compounds are dynamically stable. In addition, the calculated cohesive energies of these compounds are negative, indicating that they are thermodynamically stable. Moreover, the calculated bulk modulus (B) of Mg–Al–Si ternary compounds is gradually enhanced with decreasing Mg content, and Mg2Al3Si6 has the largest B with a value of 72.6 GPa, while MgAlSi has the largest shear modulus, E with values of 44.5 and 109.7 GPa, respectively, which is beneficial for increasing the stiffness of Mg alloys. Electronic density and weighted average bond length are used to probe the electronic basis of mechanical properties, and the results show that the weighted average length of Mg2Al3Si6 is tighter than other compounds, resulting in higher B.

Synthesis, covalency parameters, energy calculations and crystal features of acylpyrazolone derived pentavalent Uranyl complex along with DFT and Hirshfeld analysis

A σ-donating acylpyrazolone DMBPMP (4-(3,5-dimethyl benzoyl) 1-phenyl 3-methyl 5-pyrazolone) ligand and its Uranyl acylpyrazolone complex [UO2(DMBPMP)2(EtOH)] were synthesized to analyze the nature of covalency, reactivity, and redox properties. The structure, pentavalent bipyramidal geometry, and complex composition are mainly scrutinized through their single-crystal x-ray crystal data, molar conductivity, gravimetric estimation, FTIR significant vibrations, δ-values of 1H NMR, 13C NMR and TG-DTA plots. The covalency of the Uranyl complex mainly depends on average bond length values on the pentagonal equatorial plane, Uranyl axial bond lengths, stretching frequency values, coordinated solvent on the fifth coordination site, and different aryl group substitution on the first position of the pyrazolone ring; and it can be confirmed through FTIR, single-crystal, and electronic UV–Vis spectral characterization methods. The UV–Vis data was also valuable for identifying n → π*, π → π*, and LMCT transitions and calculating Sinha’s covalency parameters, which shows that the complex can show maximum covalent character in DMSO solvent and covalency decreases in DMSO > DMF > Ethyl acetate > Ethanol > CHCl3 order. DFT calculations were performed to get an excellent correlation and comparison with all experimental values. This correlation and comparision is helpful to identify global index parameters to get an idea of the physical as well as chemical properties of such systems and to confirm the characteristics theoretically by HOMO-LUMO energy gap, theoretical vibrations, natural electronic configuration, and NBO charges. The Hirshfeld surface analysis was also carried out to identify the crystal strength through interaction energies and energy frameworks in the ligand and intermolecular non-covalent surface interactions with fingerprint plot details in both ligand and complex. Electro-chemical analysis in CV-DPV plots provides information on the redox properties of uranyl moiety.

Construction of Synergistic Co and Cu Diatomic Sites for Enhanced Higher Alcohol Synthesis

Construction of Synergistic Co and Cu Diatomic Sites for Enhanced Higher Alcohol Synthesis

Tunable photoluminescence in novel Ca2La1-xGdxNbO6:Bi3+ double perovskite phosphor for the application of luminescent cement-based composite materials

In this study, novel luminescent cement-based composite materials with tunable emission color were prepared. A series of novel Bi3+ doped double perovskite Ca2La1-xGdxNbO6 phosphors were firstly synthesized and the relationships between structure variation and tunable luminescence were discussed. The Gd substitution for La led to the change of crystal compressive strain, average bond length and polyhedron distortion of (Ca/Ln)O6 polyhedron, which caused the emission color of Ca2La1-xGdxNbO6:Bi3+ tuned from (0.2020, 0.2472) to (0.1581, 0.0992). Furthermore, the synthesized Ca2La1-xGdxNbO6:Bi3+ phosphors were combined with cementitious materials, which made the luminescent specimens displayed tunable cyan-blue to blue emission color, and the XRD, SEM and EDS tests presented that the phosphors and cement were uniformly mixed in the cementitious material. These brilliant properties indicated that the synthesized phosphor could be used in exploring novel luminescent cement-based composite materials.

Improved volume variable cluster model method for crystal-lattice optimization: effect on isotope fractionation factor

The isotopic fractionation factor and element partition coefficient can be calculated only after the geometric optimization of the molecular clusters is completed. Optimization directly affects the accuracy of some parameters, such as the average bond length, molecular volume, harmonic vibrational frequency, and other thermodynamic parameters. Here, we used the improved volume variable cluster model (VVCM) method to optimize the molecular clusters of a typical oxide, quartz. We documented the average bond length and relative volume change. Finally, we extracted the harmonic vibrational frequencies and calculated the equilibrium fractionation factor of the silicon and oxygen isotopes. Given its performance in geometrical optimization and isotope fractionation factor calculation, we further applied the improved VVCM method to calculate isotope equilibrium fractionation factors of Cd and Zn between the hydroxide (Zn–Al layered double hydroxide), carbonate (cadmium-containing calcite) and their aqueous solutions under superficial conditions. We summarized a detailed procedure and used it to re-evaluate published theoretical results for cadmium-containing hydroxyapatite, emphasizing the relative volume change for all clusters and confirming the optimal point charge arrangement (PCA). The results showed that the average bond length and isotope fractionation factor are consistent with those published in previous studies, and the relative volume changes are considerably lower than the results calculated using the periodic boundary method. Specifically, the average Si–O bond length of quartz was 1.63 Å, and the relative volume change of quartz centered on silicon atoms was − 0.39%. The average Zn–O bond length in the Zn–Al-layered double hydroxide was 2.10 Å, with a relative volume change of 1.96%. Cadmium-containing calcite had an average Cd–O bond length of 2.28 Å, with a relative volume change of 0.45%. At 298 K, the equilibrium fractionation factors between quartz, Zn–Al-layered double hydroxide, cadmium-containing calcite, and their corresponding aqueous solutions were Delta ^{30/28} {text{Si}}_{{{text{Qtz-H}}_{4} {text{SiO}}_{4} }} = 2.20{permil} , Delta^{18/16} {text{O}}_{ {text{Qtz}}{-} ( {text{H}}_{2} {text{O}} )_{text{n}}} = 36.05{permil}, Delta^{66/64} {text{Zn}}_{ {text{Zn}} {-} {text{Al LDH-Zn}} ( {text{H}}_{2} {text{O}} )_{text{n}}^{2+}} = 1.12{permil} and Delta^{114/110} {text{Cd}}_{ {text{(Cd--Cal)-Cd}} ( {text{H}}_{2} {text{O}} )_ {text{n}}^{2 +} } = - 0.26{permil} respectively. These results strongly support the reliability of the improved VVCM method for geometric optimization of molecular clusters.

Synthesis and crystal structure of di-aqua-(1,4,8,11-tetra-aza-cyclo-tetra-deca-ne)zinc(II) bis-(hydrogen 4-phospho-natobiphenyl-4'-carboxyl-ato)(1,4,8,11-tetra-aza-cyclo-tetra-deca-ne)zinc(II).

In the asymmetric unit of the title compound, trans-di-aqua-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N 1,N 4,N 8,N 11)zinc(II) trans-bis-(hydrogen 4-phospho-natobiphenyl-4'-carboxyl-ato-κO)(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N 1,N 4,N 8,N 11)zinc(II), [Zn(C10H24N4)(H2O)2][Zn(C13H9O5P)2(C10H24N4)], both Zn atoms lie on crystallographic inversion centres and the atoms of the macrocycle in the cation are disordered over two sets of sites. In both macrocyclic units, the metal ions possess a tetra-gonally elongated ZnN4O2 octa-hedral environment formed by the four secondary N atoms of the macrocyclic ligand in the equatorial plane and the two trans O atoms of the water mol-ecules or anions in the axial positions, with the macrocyclic ligands adopting the most energetically favourable trans-III conformation. The average Zn-N bond lengths in both macrocyclic units do not differ significantly [2.112 (12) Å for the anion and 2.101 (3) Å for the cation] and are shorter than the average axial Zn-O bond lengths [2.189 (4) Å for phospho-nate and 2.295 (4) Å for aqua ligands]. In the crystal, the complex cations and anions are connected via hydrogen-bonding inter-actions between the N-H groups of the macrocycles, the O-H groups of coordinated water mol-ecules and the P-O-H groups of the acids as proton donors, and the O atoms of the phospho-nate and carboxyl-ate groups as acceptors, resulting in the formation of layers lying parallel to the (110) plane.

K replaces Rb towards cyan to red ultra-wideband perovskite-type phosphors for full-spectrum lighting

Near-ultraviolet-excited high-performance broad-emission phosphors are still an important challenge in full-spectrum LED lighting. According to the perovskite structure Rb2CaPO4F and K2CaPO4F, the broadband phosphor Rb2-wKwCaPO4F: Eu2+ (w = 0–2) suitable for near-ultraviolet excitation was studied, especially the phosphors with w of 0.5, 1 and 1.5. These three phosphors emit green, yellow and red light under excitation at 395 nm, and the full width at half maximum (FWHM) is 144 nm, 182 nm, and 174 nm, respectively, which is wider than the FWHM of commercial phosphors. Through the calculation of the formation energy and the change of the average bond length after Eu2+ doping, it can be determined that Eu2+ mainly occupies Ca2+ site. As K replaces Rb to change the coordination environment of Eu2+, the emission wavelength is continuously red-shifted and the FWHM is also changed. The series of phosphors Rb2-wKwCaPO4F: Eu2+ (w = 0–2) have high quantum efficiency and excellent thermal stability (more than 80%@150 °C of the integrated emission intensity at room temperature). The white LED synthesized by using the series of phosphors have a high color rendering index (Ra is greater than 90), a wide spectral range and a suitable correlated color temperature. These results indicate that Rb2-wKwCaPO4F: Eu2+ (w = 0–2) phosphors have great potential in full-spectrum LED lighting applications. This research also verifies that the photoluminescence adjustment strategy through cation substitution is the key to achieve tunable emission.

A theoretical study of the intermolecular interactions of H2–CuF complex: Intermolecular vibrations, isotope effects, and rotational structure

In this paper, a theoretical study has been made on the intermolecular interactions of the H2–CuF complex, including binding energy, intermolecular vibrations, isotope effects, and rotational structure. Based on different bond lengths of H2 and CuF monomers, three intermolecular potential energy surfaces (PESs) were constructed at the level of single and double excitation coupled-cluster method with a non-iterative perturbation treatment of triple excitations [CCSD(T)] with aug-cc-pVTZ basis set supplemented with bond functions. A global minimum on the PESs show that H2–CuF complex belongs to C2ν point group with a T-shaped structure. The obtained binding energy ranges from 8890 to 10050 cm−1, which increases as the increment of H–H bond length, but opposite case has been determined as the increment of Cu–F bond length. The accuracy of PESs was examined by the available data of 101–000 transition. The predicted rotational transition frequency obtained from bound state calculations can reproduce the experimental observation very well, and the predicted error is 0.1% based on the PES1 constructed with rH2 and rCuF fixed at 0.838 and 1.7409 Å. By analyzing the wave function of the bound state, the intermolecular vibrational modes were assigned unambiguously. Isotope effects were also studied and the largest error is also 0.1% compared with the available 101–000 transition data. A set of spectroscopic parameters were obtained for six isotopologues to determine rotational structure of H2–CuF complex. Upon the complex formation, the obtained structure parameters show that H–H bond length is elongated by 0.081 Å, while Cu–F value is shortened by 0.008 Å from the respective average bond lengths of free monomer.

Strain-Assisted Single Pt Sites on High-Curvature MoS 2 Surface for Ultrasensitive H 2 S Sensing

Strain-Assisted Single Pt Sites on High-Curvature MoS ₂ Surface for Ultrasensitive H ₂ S Sensing

Structure of the TiO2−MgO-Al2O3 system: Insights from molecular dynamics simulations

Molecular dynamics simulations were adopted to characterize the structure of the TiO2−MgO-Al2O3 system. The average bond lengths of Ti-O and Al-O keep unchanged and the average bond length of Mg-O increases from 1.98 Å to 2.01 Å, when the TiO2 content increases from 40% to 85%. The [TiO6] octahedron is dominating in all the [TiOn] polyhedra. Most of Ti-O-Ti bond angles keep unchanged at 101.25°, while small part of Ti-O-Ti bond angles decrease from 127.68° to 126.30°, when the TiO2 content increases from 40% to 85%. The proportions of Ti-O-Ti oxygen connections increase from 16.58% to 65.80%, the proportions of Mg-O-Ti oxygen connections decrease from 36.24% to 5.44%, and the viscosity of the system increases from 0.042 Pa s to 0.118 Pa s, when the TiO2 content increases from 40% to 85%. This work will lay the foundation for predicting the viscosity of titanium slag melt, increasing the preparation efficiency of titanium slag, and improving the product quality of titanium slag.

Wet-etching mechanism of a semi-sphere pattern on sapphire substrate

A semi-spherical pattern can be converted to a triangular pyramid comprising three r-planes using chemical wet etching with a mixture of sulfuric and phosphoric acids. The apex Al atom on the triangular pyramid with numerous dangling bonds can be subject to etching with prolonged exposure. After removing the apex Al atoms, Al atoms underneath the r-plane can be readily etched and low incline-angle, side-facet planes are developed. The concentrations of SO42- and PO43- ions in the mixed etching solution greatly affect the etching rate on the patterns on the sapphire surface. The SO42- and PO43- etchant ions in the etching solution will react with the etching site (surface Al atoms) and form Al2(SO4)3 and AlPO4. The molar ratios of the reactants (surface Al etching sites and acid molecules) are different. Given the size of the SO42- radicals (the average bond length of the sulfate ion is 1.49 Å), the other surface Al atoms next to the Al atoms engaging with the SO42- radicals cannot be close to any free SO42- radicals in the etching solution. This effect is called the “screening effect” or “spatial barrier effect.” For forming AlPO4, one PO43- ion can bond with one etching Al site without being limited by the spatial screening effect. There is no spatial screening effect for the phosphoric acid etching of a sapphire surface. Thus, phosphoric acid would have a higher etching rate of a sapphire surface than sulfuric acid. In this study, the bottom of the triangular pyramid is not an equilateral triangle. Instead, the sides of the bottom triangular of the triangular pyramid are curved. The availability of etching Al sites on the etching side-facet surface and ridges of the triangular pyramid can explain the curved sides of the bottom triangle of the triangular pyramid.

Chemical and Structural Alterations in the Amorphous Structure of Obsidian due to Nanolites.

Obsidian is volcanic glass that results from the rapid cooling of silica-rich melt. Nanoscale crystallites precipitate out of the melt prior to solidification and remain embedded in the amorphous matrix. These crystallites provide information on the flow kinetics and composition of the melt. Due to the sparsity and size of nanolites, studies often focus on supramicron crystallites. This research takes advantage of the conchoidal fracture of obsidian by knapping samples with nanometer-thin edges for transmission electron microscopy characterization. Nanolites in the amorphous matrix are studied using energy-dispersive spectroscopy (EDS) and electron diffraction. Certain alkali and alkaline-earth cations exhibit patterns of depletion near Fe-oxide nanolites. EDS is used to identify nanolites and variations in the composition of the matrix. Parallel beam diffraction and radial distribution function analysis of nearest-neighbor distances determine average bond lengths in the matrix near nanolites, showing that nanolites influence the nearby short-range ordering and atomic character of the matrix. Analysis reveals decreased mean nearest-neighbor distances in the matrix adjacent to nanolites compared to the bulk. Our methods exhibit the required sensitivity to detect variations in the composition and structure near nanolites, and our findings indicate that obsidian nanolites contribute to quantifiable localized changes in the amorphous structure.

Pressure and concentration effects on intermineral calcium isotope fractionation involving garnet

To better understand the behaviors of calcium (Ca) isotopes during igneous and metamorphic processes that differentiate the Earth and other rocky planets, we investigated the effects of pressure and Ca/Fe concentration on the average CaO bond length and the reduced partition function ratio of 44Ca/40Ca (103ln44/40Caβ) in garnet using first-principles calculations. Our calculations show that (1) the average CaO bond length increases and 103ln44/40Caβ decreasing (approximately 0.41‰ at 1000 K from a Ca/(Fe + Ca + Mg) of 1/24 to 12/12) with increasing Ca concentrations. In contrast to orthopyroxene and forsterite, whose CaO bond lengths and 103ln44/40Caβ are sensitive to Ca concentrations only in narrow range, the garnet CaO bond length and 103ln44/40Caβ vary with Ca concentrations in wide ranges. (2) The average CaO bond length increases and 103ln44/40Caβ decreases with increasing Fe concentrations (by 0.12‰ at 1000 K, FeO content of 12.4 wt%). (3) The average CaO bond length decreases by ~0.014 Å, and 103ln44/40Caβ increases by 0.1‰–0.2‰ at 1000 K when the pressure increases from 0 to 3 GPa. (4) However, the pressure effect on 103ln44/40Caαgarnet–clinopyroxene is insignificant.Using our new results of the effects of pressure and Ca/Fe concentration on 103ln44/40Caαgarnet–clinopyroxene, we evaluated the observed difference in Ca isotope compositions between garnet and clinopyroxene in natural samples. Most have reached equilibrium, whereas some samples exceed our prediction, which might reflect the majorite effect or kinetic fractionation.

Investigation of the Solid-Solution Limit, Crystal Structure, and Thermal Quenching Mitigation of Sr-Substituted Rb2CaP2O7:Eu2+ Phosphors for White LED Applications.

Rb2CaP2O7:Eu2+ is a bright reddish-orange-emitting phosphor, but its luminescence thermal stability is poor. In this study, we investigated the solid-solution limit and thermal quenching mitigation of Rb2CaP2O7:Eu2+ phosphors by cation substitution with Sr2+ and revisited their crystal structure. First, we carefully investigated the solid solution limit of Sr in the structure of Rb2CaP2O7. The results show that up to 80% of Ca can be substituted by Sr, whereas Ca hardly resides in the structure of Rb2SrP2O7. Consequently, the photoluminescence was fine-tuned from reddish-orange (612 nm) to yellow (580 nm) light emission by increasing the Sr2+ concentration in the solid-solution phosphors Rb2Sr1-xCaxP2O7:Eu2+ under excitation at 342 nm. The mechanism for the blue shift of the emission spectrum was discussed. With the associated modification of the local environment of the activator (as reflected by the changes in the effective coordination number, average bond length, distortion index, and quadratic elongation), the luminescence thermal quenching issue of Rb2CaP2O7:Eu2+ was mitigated by substituting 20% Sr into the Ca site (Rb2Ca0.8Sr0.2P2O7:Eu2+). The integrated intensity of bright orange-emitting Rb2Ca0.8Sr0.2P2O7:Eu2+ (603 nm) at 150 °C retained 53% of its initial value, 1.64 times that of Rb2CaP2O7:Eu2+ (32.3%). Such an enhancement could be attributed to the improved rigidity of the crystal structure due to the local structure modification as evidenced by Rietveld refinement. The cation substitution is an effective approach for mitigating the thermal quenching issue of phosphors.

Tailoring Thermal Expansion of (LiFe)0.5xCu2-xP2O7 via Codoping LiFe Diatoms in Cu2P2O7 Oxide.

Tailoring the thermal expansion coefficient of negative thermal expansion (NTE) materials to achieve near-zero thermal expansion has attracted great attention recently. Here, LiFe diatoms are adopted to substitute Cu in Cu2P2O7 oxide to design Li-O-P and Fe-O-P linkages, with the stronger bond strength of Li-O and Fe-O compared to Cu-O and hence lowering the bond strength of P-O. With increasing the diatomic LiFe in (LiFe)0.5xCu2-xP2O7, new Raman bands corresponding to LiFeP2O7 appear and the NTE coefficient decreases gradually to near-zero thermal expansion at x = 1 (αv = -0.90 × 10-6 °C-1, -100 to 55 °C). Comparing (LiFe)0.5CuP2O7 with Cu2P2O7 and LiFeP2O7, the average bond length of P-O increases while the bond angle of P-O-P decreases, and this is verified by some weakened vibrational energies of terminal PO3 and P-O-P, resulting in the obvious red shift of Raman bands. Ceramic (LiFe)0.5CuP2O7 presents a lower difference in grain size and a higher relative density than Cu2P2O7 and LiFeP2O7.

Non-metallic atom doped GaN nanotubes: Electronic structure, transport properties, and gate voltage regulating effects

GaN is known as the third generation of semiconductor and holds promising applications. In this present work, one-dimensional zigzag nanotubes derived from GaN are studied in depth, mainly focusing on their chemical bondings, electronic structures, transport properties, and the regulating effects under gate voltage for nanotubes doped with low-concentration non-metallic atoms in main-groups IIIA-VIIA. Some important findings are obtained, such as the chemical bonds around a heteroatom atom, and their average bond length, binding energy, and chemical formation energy are closely related to the atomic number (the atomic radius), and the charge transfer between heteroatom and nanotubes is directly related to their relative electronegativity. More importantly, we find that although the intrinsic nanotube is a semiconductor, when it is doped with non-metallic atoms, the electronic phase of nanotube possesses an obvious odd-even effect. Namely, after being doped by hetero-atoms in main-groups IIIA, VA, VIIA, nanotubes are semiconductors, but they becomes metals after having been doped with hetero-atoms in main-groups IVA and VIA. This phenomenon has a close relation with the lone-paired electronic state. And also, It is found that with atom doping, the difference between carriers’ mobilities (the hole mobility and electron mobility) of semiconducting tubes can be regulated to reach one order of magnitude, especially the hole mobility and electron mobility can be obviously enhanced by a higher gate voltage. For example, when the gate voltage is increased to 18 V, the hole mobility rises nearly 20 times compared with the case without gate voltage.