Atomic Linkages Research Articles

Preparation, uniaxial negative thermal expansion and Raman study in semiconductor oxide Nb2WO8 ceramic

Negative thermal expansion materials exhibit important promising to tailor thermal expansion due to their abnormal thermal shrinkage characteristics. Here, the Nb2WO8 ceramic has been synthesized, which exhibits axial negative thermal expansion (αa = −2.05 × 10−6 K−1) from 300 to 1000 K without water absorption or phase transformation. Along a axis, the one O atom is located between two identical Nb atoms and the Nb–O–Nb atomic linkages are formed, in which the Nb2–O2–Nb2 bond angle decreases upon heating, resulting in the negative thermal expansion of a axis. Although the b axis and c axis show positive thermal expansion, the low thermal expansion (αl = 2.30 × 10−6 K−1, 173–1073 K) occurs in unit cell volume due to the negative thermal expansion of a axis. The variable pressure Raman shows that the translational and rotational modes of the polyhedron play a key role in axial negative thermal expansion. This work shows potential application prospects of Nb2WO8 as a low thermal expansion semiconductor ceramic.

Network structure and thermal properties of bioactive (SiO2\u2013CaO\u2013Na2O\u2013P2O5) glasses

Ca- and P-based bioactive glasses are excellent candidates for design and manufacture of biomaterials. Understanding the structure and physico-chemical–thermal behaviour of bioactive glasses is a fundamental step towards the design of a new generation of biocompatible materials. In this study, the structure of SiO2–CaO–Na2O glasses and its derivatives, obtained by substituting Na2O with P2O5 and prepared by melt–quench technique, was studied with neutron and electron diffraction techniques combined with thermal analysis, high-resolution electron microscopy and X-ray photoelectron spectroscopy. Neutron and electron diffraction data were analysed with reverse Monte Carlo simulation and pair distribution function analysis, respectively. Bioactivity of P2O5 substituted glasses was also investigated and proven in vitro using simulated body fluid. Based on the structural analysis, it was found that Si and P atoms are in well-defined tetrahedral units with a bond distance of 1.60 Å for both Si–O and P–O bonds, although P exhibits a higher average coordination number than Si. With increasing phosphate content, tendentious changes in the glass behaviour were observed. Linear increase in Tg, supported by the changes in the average coordination numbers of Si and P, indicates strengthening of network structure with increasing P content and formation of P–O–Ca atomic linkages, which lead to Ca–P-rich atomic environments in the silicate network. These Ca–P-rich environments trap volatile elements and thus decrease the total weight loss during heating at higher P concentrations. In the case of the highest investigated P2O5 content (5 mol%), nanoscale structural inhomogeneity and the formation of Ca–P-rich clusters were also revealed by electron diffraction and atomic resolution imaging. This type of Ca–(Na)–P clustering has a key role in the behaviour of phosphate-substituted silicate glasses under physiological conditions.

The pressure-induced phase transition(s) of $$\hbox {ZrSiO}_4$$: revised

The existence of a new high-pressure low-symmetry (HPLS) $$\hbox {ZrSiO}_4$$ phase (space group $$I\bar{4}2d$$ ), which has been predicted by density-functional-theory (DFT) calculations (Stangarone et al. in Am Mineral, 2019b), is experimentally confirmed by in situ high-pressure Raman spectroscopic analysis up to 25.3 GPa. The new $$\hbox {ZrSiO}_4$$ polymorph is developed from zircon via a soft-mode-driven displacive phase transition. The Cochran-law-type pressure dependency of the soft-mode wavenumber reveals a zircon-to-HPLS critical pressure $$p_{{\mathrm{c}}}$$ = 20.98 ± 0.02 GPa. The increase in the phonon compressibilities of the zircon hard mode near $$\hbox {202 cm}^{-1}$$ at $$p>p_{{\mathrm{r}}}=10.0$$ GPa as well as of the reidite hard mode near $$\hbox {349 cm}^{-1}$$ at $$p<p_{\mathrm {r}}$$ marks the pressure above which zircon becomes thermodynamically metastable with respect to reidite; the experimentally determined value of $$p_{\mathrm {r}}$$ is in good accordance with the equilibrium zircon–reidite transition pressure derived from DFT simulations. However, at room temperature, there is not enough driving force to rebuild the atomic linkages and the reconstructive transition to reidite happens $$\sim$$ 1.4 GPa above $$p_{\mathrm {c}}$$ , indicating that at room temperature, the HPLS phase is a structural bridge between zircon and reidite. The pressure dependencies of the phonon modes in the range $$\hbox {350--460 cm}^{-1}$$ reveal that the reconstructive phase transition in the $$\hbox {ZrSiO}_4$$ system is triggered by energy resonance and admixture of hard modes from the parent and resultant phase.

Atomic Linkage Flexibility Tuned Isotropic Negative, Zero, and Positive Thermal Expansion in MZrF6 (M = Ca, Mn, Fe, Co, Ni, and Zn).

The controllable isotropic thermal expansion with a broad coefficient of thermal expansion (CTE) window is intriguing but remains challenge. Herein we report a cubic MZrF6 series (M = Ca, Mn, Fe, Co, Ni and Zn), which exhibit controllable thermal expansion over a wide temperature range and with a broader CTE window (-6.69 to +18.23 × 10-6/K). In particular, an isotropic zero thermal expansion (ZTE) is achieved in ZnZrF6, which is one of the rarely documented high-temperature isotropic ZTE compounds. By utilizing temperature-dependent high-energy synchrotron X-ray total scattering diffraction, it is found that the flexibility of metal···F atomic linkages in MZrF6 plays a critical role in distinct thermal expansions. The flexible metal···F atomic linkages induce negative thermal expansion (NTE) for CaZrF6, whereas the stiff ones bring positive thermal expansion (PTE) for NiZrF6. Thermal expansion could be transformed from striking negative, to zero, and finally to considerable positive though tuning the flexibility of metal···F atomic linkages by substitution with a series of cations on M sites of MZrF6. The present study not only extends the scope of NTE families and rare high-temperature isotropic ZTE compounds but also proposes a new method to design systematically controllable isotropic thermal expansion frameworks from the perspective of atomic linkage flexibility.

Sulfonic acid functionalized deoxycellulose catalysts for glycerol acetylation to fuel additives

Various forms of sulfonic acid (SO3H) functionalized cellulose-based heterogeneous catalysts were prepared, and their properties on glycerol acetylation reactions to mono-, di-, and triacetin products were investigated. Superior catalytic activity and stability for the reactions was observed on SO3H-NDOC catalyst that is obtained by (i) crosslinking of the cellulose units with epichlorohydrin into a three-dimensionally-networked deoxycellulose-matrix and (ii) sulfonic acid functionalization on the crosslinked deoxycellulose support via CS atomic linkages (CSO3H). It was found that sulfonic acid functionalization via an ether type OS atomic linkage (COSO3H) or the direct utilization of the pristine cellulose support without a fortification by crosslinking led to significant deactivation of the catalysts by substantial acidity loss. The intrinsic glycerol conversion turnover rate on SO3H-NDOC was comparable to that of commercial Amberlyst-15 solid resin, demonstrating the effectiveness of this renewable cellulose-derived heterogeneous catalyst for glycerol acetylation to fuel additives.

Effect of Artificial Saliva on the Apatite Structure of Eroded Enamel

Citric acid‐induced changes in the structure of the mineral component of enamel stored in artificial saliva were studied by attenuated total reflectance infrared spectroscopy as well as complementary electron probe microanalysis and scanning electron microscopy. The results indicate that the application of artificial saliva for several hours (the minimum time period proved is 4 h) leads to slight, partial recovering of the local structure of eroded enamel apatite. However, artificial saliva surrounding cannot stop the process of loosening and breaking of P–O–Ca atomic linkages in enamel subjected to multiple citric acid treatments. Irreversible changes in the atomic bonding within 700 nm thick enamel surface layer are observed after three times exposure for 1 min to aqueous solution of citric acid having a pH value of 2.23, with a 24‐hour interval between the individual treatments. The additional treatment with basic fluoride‐containing solutions (1.0% NaF) did not demonstrate a protective effect on the enamel apatite structure per se.

Optical band gap and Raman spectra in some (Bi 2O 3) x(WO 3) y(TeO 2) 100−x−y and (PbO) x(WO 3) y(TeO 2) 100−x−y glasses

The glasses representing (Bi 2O 3) x (WO 3) y (TeO 2) 100− x − y and (PbO) x (WO 3) y (TeO 2) 100− x − y systems were prepared. The dilatometric glass-transition temperatures of examined glass samples were found in the region 383–434 °C, the coefficient of thermal expansion varied from 12 to 16 ppm/°C and the density ranged from 6.30 2 to 6.80 8 g/cm 3. From the optical transmission measurements of thin glassy bulk samples prepared by a glass blowing, the optical gap values were found in the narrow region 3.21–3.36 eV. For the temperature interval 300–480 K, the values of the temperature coefficient of the optical band gap varied from 3.7 × 10 −4 to 5.24 × 10 −4 eV/K. It is suggested that Raman feature observed at around 350 cm −1 can be assigned to an overlap of Raman bands attributed to WO 6 corner shared octahedra and to the following three atomic linkages: Bi–O–Te, Pb–O–Te and W–O–Te.

Heats of combustion and of formation of the normal aliphatic alcohols in the gaseous and liquid states, and the energies of their atomic linkages

Heats of combustion and of formation of the normal aliphatic alcohols in the gaseous and liquid states, and the energies of their atomic linkages

Heats-of-combustion and of formation of the normal paraffin hydrocarbons in the gaseous state, and the energies of their atomic linkages

Heats-of-combustion and of formation of the normal paraffin hydrocarbons in the gaseous state, and the energies of their atomic linkages

The Energies of the Atomic Linkages in the Normal Paraffin Hydrocarbons

The Energies of the Atomic Linkages in the Normal Paraffin Hydrocarbons

The Energies of the Atomic Linkages in Methane, Ethane, Methanol and Ethanol

The Energies of the Atomic Linkages in Methane, Ethane, Methanol and Ethanol

Some Physical Aspects of Atomic Linkages.

ADVERTISEMENT RETURN TO ISSUEPREVArticleSome Physical Aspects of Atomic Linkages.C. H. Douglas. ClarkCite this: Chem. Rev. 1932, 11, 2, 231–271Publication Date (Print):October 1, 1932Publication History Published online1 May 2002Published inissue 1 October 1932https://doi.org/10.1021/cr60039a002RIGHTS & PERMISSIONSArticle Views77Altmetric-Citations6LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

The molecular scattering of light from certain organic liquids

An attempt is made to discover in the molecular scattering of light a method by which atomic linkages in molecules may be recognized. The essential features of the method are described. There are rather serious difficulties in its application to complex molecules, two of which are suggested. Nevertheless, it may be claimed that the work is not without result, because frequencies attributable to linkages which hold externally substituted atoms or groups seem to be relatively undisturbed by positional effects. In conclusion, the authors wish to express their indebtedness to Mr. G. M. J. Mackay whose interest in this problem made the present work possible.