Raman spectroscopy of natural cordierite at high water pressure up to 5 GPa

The high‐pressure behaviour of cordierite, a widespread ring aluminosilicate with channels incorporating fluid compounds (H₂O, CO₂), is characterized by the absence of phase transitions up to 2.5 GPa. However, the distortion of the ring tetrahedra observed previously at 2.3 GPa is supposed to introduce a phase transition at higher pressure, which has not been checked so far. This work presents a high‐pressure Raman spectroscopic study of natural cordierite compressed in water medium up to 4.7 GPa in a diamond anvil cell. At P > 4 GPa, a disordering of both the framework and intrachannel H₂O subsystem is apparent from significant broadening of Raman peaks and the evolution of short‐range order parameters. This is followed by abrupt shifts of the framework and O–H stretching modes at about 4.5 GPa, indicating a first‐order phase transition. Its reversibility is seen from the recovery of the initial spectrum at P < 3 GPa. The shift amplitudes of different framework modes indicate the predominance of distortion over contraction of the framework polyhedra upon this transition. The disordering of the H₂O subsystem in the high‐pressure phase is likely a consequence of distortion of the channel‐forming framework elements, which is supposed to be a driving force of this transition. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydrothermal Synthesis at High Pressure and Temperature of the Mg 7.5 Ni 6 H 3 (AsO 4 ) 8 (OH) 6 and Mg 8 Ni 4 H 6 (PO 4 ) 8 (OH) 6 Compounds

The Mg 7.5 Ni 6 H 3 (AsO 4 ) 8 (OH) 6 and Mg 8 Ni 4 H 6 (PO 4 ) 8 (OH) 6 compounds have been synthesized by using hydrothermal techniques at high pressure and temperature. The crystal structure of the arsenate phase has been refined with the Rietveld method. The compounds are isostructural. The structure consists of a three-dimensional framework in which the presence of triangular and hexagonal channels is observed. Reflectance diffuse measurements confirm the hexacoordination of the Ni(II) ions in both compounds. The magnetic behaviour indicates the presence of antiferromagnetic interactions between the Ni(II) ions placed in the double chains.     

Changes in Volatile Aromatic Compounds of Strawberry Puree Treated by High-pressure During Storage

The changes in volatile flavor components and lipoxygenase and peroxidase enzymatic activity of Cilady strawberry puree during high pressure processing (400 MPa/20 °C/20 min) and storage at 4 °C were evaluated. High pressure processing maintains the original aromatic distribution, but after thirty days of storage an increase in some volatile compounds was observed. After high pressure treatment and storage, a residual lipoxygenase activity was observed, which could explain some slight changes of volatile compounds. On the other hand, the peroxidase was clearly inactivated by high pressure treatment.     

Vapor Pressure Assisted Void Growth and Cracking of Polymeric Films and Interfaces

Pores and cavities form at filler particle-polymer matrix interfaces, at polymer film-silicon substrate interfaces as well as in molding compounds of IC packages. Moisture diffuses to these voids. During reflow soldering, surface mount plastic encapsulated devices are exposed to temperatures between 210 to 260°C. At these temperatures, the condensed moisture vaporizes. The rapidly expanding water vapor can create internal pressures within the voids that reach 3–6 MPa. These levels are comparable to the yield strengths of epoxy molding compounds and epoxy adhesives, whose glass transition temperatures T _g range between 150 to 300°C. Under the combined action of thermal stress and high vapor pressure (relative to the yield strength at T _g), both pre-existing and newly nucleated voids grow rapidly and coalesce. In extreme situations, vapor pressure alone could drive voids to grow and coalesce unstably causing film rupture, film-substrate interface delamination and cracking of the plastic package.Vapor pressure effects on void growth have been incorporated into Gurson's porous material model and a cohesive law. Crack growth resistance-curve calculations using these models show that high vapor pressure combined with high porosity bring about severe reduction in the fracture toughness. In some cases, high vapor pressure accelerates void growth and coalescence resulting in brittle-like interface delamination. Vapor pressure also contributes a strong tensile mode component to an otherwise shear dominated interface loading. An example of vapor pressure related IC package failure, known as popcorn cracking, is discussed.     

Electronic Structure,Optical Properties,and Pressure Behavior of the CdB<Subscript>4</Subscript>O<Subscript>7</Subscript> and HgB<Subscript>4</Subscript>O<Subscript>7</Subscript> Compounds

Ab initio calculations of the structural, electronic, and optical properties of the CdB₄O₇ and HgB₄O₇ tetraborate compounds in three structural modifications with the Pbca, Cmcm, and Pmn2₁ symmetry have been performed in the framework of the density functional theory using the VASP package. The calculations of the electronic band structure showed that these compounds in all the investigated modifications are dielectrics with a band gap of 2–4 eV. The calculation of the structural properties of the tetraborates under pressure showed that the phase transition between the Pbca and Pmn2₁ structures in cadmium and mercury tetraborates occurs under pressures of 4.8 and 4.7 GPa, respectively.     

高压下氢基高温超导体研究的新进展

富氢材料被认为是室温超导体的最佳候选体系,是物理学、材料科学等多学科的热点研究领域之一。理论和实验研究发现的新型共价氢化物H3S和笼状氢化物LaH10的超导转变温度(T_c)均超过200 K,进一步推动了对富氢化合物超导电性的探索。最近,通过高压实验合成的碳质硫氢化物在288 K的室温下实现了零电阻,让人们看到了室温超导的曙光。本文结合课题组在此领域的主要成果,介绍了3类典型富氢化合物的结构及超导特性,包括近期首次在层状氢化物中发现的具有类五角石墨烯结构的富氢超导体HfH₁₀,其超导转变温度高达213~234 K。     

Novel rubidium polyfluorides with F_3, F_4, and F_5 species

Pressure has an important effect on chemical bonds and their chemical properties. The atypical compounds NaCl_3 and CsF_3 are predicted to be stable at high pressure and show unique physical and chemical properties. By using ab initio random structure searching and density functional theory calculations, we predicted multiple thermodynamically stable atypical compounds, which are RbF_2, RbF_3, RbF_4, and RbF_5 in the pressure range of 0–300 GPa. In these stable compounds, homonuclear bondings of F_3, F_4, and F_5 species are easily formed. The electron structure calculation showed that except for Fd-3 m phase of RbF_2, these stable compounds are insulators and F 5 p orbitals play an important role in the Fermi level. It is interesting that the compounds RbF_5 could be stable at nearly ambient pressure and 0 K which will stimulate experimental studies in the future.     

XPS study of CeTbO3+δ synthesized by high pressure and temperature method

The samples of CeTbO₃₊ synthesized by high pressure and high temperature method were studied by XPS. It was found that Tb⁴⁺ ion began to transform to Tb³⁺ at about 600° C and Ce⁴⁺ to Ce³⁺ about 800° C. Single phase compound of CeTbO₃₊ having fluorite structure was formed at 1000° C, and in the compound the Ce ions had been in mixed valence state. Existence of Ce³⁺ ions in compounds could be detected with the shift of the 888 eV peak and the change of relative intensity of it to the 882 eV peak. The duration stability of CeTbO₃₊ synthesized by high pressure and temperature method was investigated.The project supported by National Natural Science Foundation of China     

Structural study of pressure-induced magnetic phase transitions in manganites Pr0.7Ca0.3Mn1-y Fe y O3 (y?=?0, 0.1)

A crystal and magnetic structure of manganites Pr_0.7Ca_0.3Mn_1?y Fe _y O₃ (y = 0, 0.1) has been studied by means of powder neutron diffraction at pressures up to 4 GPa in the temperature range 15-300 K. Under high pressure, an appearance of A-type antiferromagnetic state in both systems was observed. Both compounds exhibit anisotropic compression of the lattice which leads to the apical compression of MnO₆ octahedra along the crystallographic b-axis. The calculated from obtained structural data pressure dependence of the charge-carrier bandwidth is in a qualitative agreement with observed pressure behavior of insulator-metal transition temperature within the framework of the double-exchange model.     

Li3N在生成BN反应中的作用

研究了常压高温下Li3N在B4C与含氮化合物生成BN反应中的作用。实验结果表明,在950℃高温下,B4C与Si3N4反应不生成hBN,B4C与NH4Cl反应只生成少量hBN。在该两种原料中加入Li3N后,反应产物中hBN生成量都明显增多。但Li3N本身没有与B4C生成hBN的反应。由此推断,Li3N在上述B4C与含氮化合物生成hBN的反应中表现出了催化作用。此外,在以hBN为原料,以Li3N为催化剂合成出cBN的温度压力区域内,对B4C-Si3N4-Li3N体系所做的高温高压实验没有合成出hBN或cBN。还讨论了在低压条件下原位合成cBN的探索实验中,应如何选择硼源和氮源的问题。     

高温高压下Ag-Mg-Zn合金中金属间化合物的微观结构与热动力学性质的第一性原理计算

采用基于密度泛函理论的第一性原理计算方法,研究了Ag-Mg-Zn合金中金属间化合物AgMg,Mg4Zn8和Ag8Mg4Zn4在高温高压下的结构稳定性、弹性性能和热动力学性质.理论计算结果与实验值和其他的理论结果符合得非常好.研究表明:金属间化合物AgMg,Mg4Zn8和Ag8Mg4Zn4在零温零压下是力学稳定的;Mg4Zn8和Ag8Mg4Zn4为延性相,而AgMg则为脆性相;在这三种金属间化合物中,Ag8Mg4Zn4的塑性最好,AgMg的塑性最差.利用准谐Debye模型,讨论了高温高压下Ag-Mg-Zn合金中金属间化合物的摩尔振动内能Uvib,m,摩尔Helmholtz振动自由能Avib,m,摩尔振动熵Svib,m,摩尔定容热容Cv,m,摩尔定压热容Cp,m,热膨胀系数α,Griüneisen 参量γ和Debye温度(O).     

Ultrasonic-assisted synthesis of the nanostructures of a Co(II) metal organic framework as a highly sensitive fluorescence probe of phenol derivatives

Nanostructures of a metal-organic framework with chemical formula, [Co(BDC)(L*)]_n.DMF (TMU-40), BDC = 1,4-benzendicarboxylate, L* = 5,6-dipyridin-4-yl-1,2,3,4-tetrahydropyrazine, under ultrasonic irradiation at ambient temperature and atmospheric pressure were prepared and characterized by Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Sonication time, concentration of initial reagents and ultrasonic generator power effects on the size and morphology of nano-structured compounds were studied. TMU-40 (for Tarbiat Modares University) displayed a good potential as a luminescent sensor against phenol derivatives consist of phenol, 4-aminophenol, 4-methylphenol and 4-chlorophenol. Nano-sized TMU-40 showed the better sensing performance in comparison to its bulk phase. The nano TMU-40 displayed very selective and sensitive in detection of phenol derivatives. The detection limit amounts of 15 nM and 63 nM were achieved for 4-aminophenol in nano TMU-40 and bulk TMU-40, respectively. The special structure and fluorescent character of L* ligand and high surface area of nano MOF provide an effective interaction between MOF and phenolic analytes to selectively and sensitively detect of the analyte molecules.     

Effect of pressure on the M?ssbauer isomer shift and quadrupole splitting in Au(I)-cyanides

The effect of pressure on the Mössbauer isomer shift and quadrupole splitting was studied with the 77 keV resonance of¹⁹⁷Au in the Au(I)-cyanides AuCN and KAu(CN)₂ at 4.2 K under pressures up to 80 kbar. We observe an increase of the electron density and a decrease of the absolute value of the electric field gradient at the Au nuclei in both compounds with pressure. This variation is different from the correlation that has been established for these parameters within the chemical series of Au(I) compounds at ambient pressure. It indicates that the-bonding increases strongly under pressure. X-ray diffraction studies on AuCN under pressures up to 115 kbar together with investigations of the Goldanskii-Karyagin-effect on AuCN at ambient pressure support the previous assumption that the sign of the electric field gradient at the Au(I) sites is negative.     

High pressure: a tool to improve the enzymatic production of glycosides

Naringinase, an enzyme complex that expresses α -l-rhamnosidase and β -d-glucosidase activities in native state, can be used to deglycosylate natural glycosides. The selective inactivation of one of these activities will allow the biosynthesis of different bioactive compounds in a simple, effective and cheap way. In this work, pressure and temperature were the tools used to selectively inactivate the activities expressed by naringinase. The main goal was the identification of pressure–temperature conditions to acquire conditions for the maximization of enzymatic hydrolysis of substrates with different numbers of glycosidic residues. α -l-Rhamnosidase was 32-fold more resistant against inactivation at 250 MPa than at atmospheric pressure. The best pressure condition to reduce β -d-glucosidase inactivation at 75°C was 173 MPa, while in the case of α -l-rhamnosidase inactivation at 85°C, it was above 250 MPa. Moreover, a selective inactivation of β -d-glucosidase activity of naringinase was attained, allowing an easy and cheap method with which to produce prunin and other expensive glycosides. The present work highlights the effect of high pressure on enzyme protection against thermal inactivation, demonstrating its potential as a powerful tool in biosynthesis.     

Effect of pressure on the Mössbauer isomer shift and quadrupole splitting in Au(I)-cyanides

The effect of pressure on the Mössbauer isomer shift and quadrupole splitting was studied with the 77 keV resonance of¹⁹⁷Au in the Au(I)-cyanides AuCN and KAu(CN)₂ at 4.2 K under pressures up to 80 kbar. We observe an increase of the electron density and a decrease of the absolute value of the electric field gradient at the Au nuclei in both compounds with pressure. This variation is different from the correlation that has been established for these parameters within the chemical series of Au(I) compounds at ambient pressure. It indicates that the-bonding increases strongly under pressure. X-ray diffraction studies on AuCN under pressures up to 115 kbar together with investigations of the Goldanskii-Karyagin-effect on AuCN at ambient pressure support the previous assumption that the sign of the electric field gradient at the Au(I) sites is negative.     

NMR of Colossal Magnetoresistive Manganites and Expanded Lattice Intermetallics at High Pressure

A survey is given of NMR studies of colossal magnetoresistive manganese perovskites (RE,Ca,Sr,Ba)MnO₃ (RE = rare earth) and the interstitially modified permanent magnet materials, RE₂Fe₁₇A _x (A = N,C,H) at ambient pressure and at applied pressures of up to 10 kbar. The different pressure behavior of the Mn hyperfine field found in the metallic and in the insulating manganite compounds is discussed and related to the micro- and macroscopic properties of these magnetically inhomogeneous materials. In the RE₂Fe₁₇A _x compounds a different pressure behavior of the hyperfine field at the RE sites with different number and type of interstitial atom neighbors is discussed in terms of local compressibility. The influence of the interstitial modification and the applied pressure on the RE hyperfine field and quadrupole splitting is analyzed and the impact of the chemical pressure and covalent effects on these quantities is compared. A comparison of the behavior of the magnetic state of the 4f electron shell with pressure and with interstitial modification is made and the relation to the magnetocrystalline anisotropy is discussed.     

Li_3N在生成BN反应中的作用

研究了常压高温下Li3N在B4 C与含氮化合物生成BN反应中的作用。实验结果表明 ,在 950℃高温下 ,B4 C与Si3N4 反应不生成hBN ,B4 C与NH4 Cl反应只生成少量hBN。在该两种原料中加入Li3N后 ,反应产物中hBN的生成量都明显增多。但Li3N本身没有与B4 C生成hBN的反应。由此推断 ,Li3N在上述B4 C与含氮化合物生成hBN的反应中表现出了催化作用。此外 ,在以hBN为原料 ,以Li3N为催化剂合成出cBN的温度压力区域内 ,对B4 C Si3N4 Li3N体系所做的高温高压实验没有合成出hBN或cBN。还讨论了在低压条件下原位合成cBN的探索实验中 ,应如何选择硼源和氮源的问题     

Effect of pressure on structure of oxide glasses at high pressure: Insights from solid-state NMR of quadrupolar nuclides

Revealing the structure of oxide glasses at high pressure remains a fundamental yet difficult problem in modern physical and chemical sciences. The recent advances in solid-state NMR techniques used for quadrupolar nuclides offer a considerably improved resolution of atomic sites, unveiling previously unknown structural details of oxides glasses at high pressure. Here, we present an overview of the recent progress and insights by high-resolution multi-nuclear triple quantum magic angle spinning (3QMAS) NMR into pressure-induced changes in coordination number, connectivity, and topological disorder in oxide glasses quenched from melts at high pressure. (11)B and (27)Al 3QMAS NMR studies of oxide glasses show that the formation of highly coordinated Al (([5,6])Al) and four coordinated ([4])B are prevalent at high pressure up to 8 GPa. The formation of oxygen clusters linking these highly coordinated framework units and Si (e.g., ([5,6])Al-O-([4])Si, ([5,6])Si-O-([4])Si, and Na-O-([5,6])Si) is observed in the (17)O NMR spectra at higher pressure, leading to an overall increase in the degree of polymerization with pressure. (23)Na MAS NMR spectra of diverse oxide glasses at high pressure and high magnetic field also indicate that the Na-O bond distance may decrease with pressure. Pressure-induced changes in structurally relevant NMR parameters such as the (17)O quadrupolar coupling product (P(q)) for the Si-O-Si cluster and (27)Al P(q) for Al sites in oxide glasses indicate the occurrence of pressure-induced reductions in the Si-O-Si angle and an increase in the Al-O bond length distribution with pressure, indicating an increase in the overall topological disorder in oxide glasses with pressure. All the pressure-induced changes in structure and topology are characterized by strong composition dependence. These experimental results highlight a new opportunity to investigate the molecular structures of silicate melts at high pressure and reveal connections between the microscopic signatures of anomalous and non-linear changes in the macroscopic properties of the corresponding liquids. While many challenges still remain in the synthesis of oxide glasses with wider range of melt composition at higher pressure above 12 GPa, recent progress in enhancement of sensitivity and resolution in the solid state NMR hold strong promise for study exploring additional details of connectivity among quadrupolar nuclides and medium-range order of the more complex, multi-components glasses at high pressure.     

Synthesis and Structural Characterization of a New Phase of GaAsO 4

A new polymorph of GaAsO 4 has been synthesised at high pressure and temperature (60 kbar and 1273 K). Samples were characterised by powder X-ray diffraction, scanning electron microscopy and EDAX spectroscopy. This material shows an hexagonal symmetry with cell parameters, a =8.1931(4) Å and c =4.3744(2) Å; particles are of hexagonal shape with a narrow size distribution around 2-3 w m and composition close to the Ga:As atomic ratio=1:1. This new high pressure phase of GaAsO 4 represents a new transition path for the ABO 4 compounds.     

Predictions of pressure-induced structural transition,mechanical and thermodynamic properties of α-and β-Si₃N₄ ceramics:ab initio and quasi-harmonic Debye modeling

The plane-wave pseudo-potential method within the framework of ab initio technique is used to investigate the structural and elastic properties of α-and β-Si3N4.The ground-state parameters accord quite well with the experimental data.Our calculation reveals that α-Si3N4 can retain its stability to at least 40 GPa when compressed at 300 K.The α→β phase transformation would not occur in a pressure range of 0-40 GPa and a temperature range of 0-300 K.Actually,the α→β transition occurs at 1600 K and 7.98 GPa.For α-and β-Si3N4,the c axes are slightly more incompressible than the a axes.We conclude that β-Si3N4 is a hard material and ductile in nature.On the other hand,β-Si3N4 is also found to be an ionic material and can retain its mechanical stability in a pressure range of 0-10 GPa.Besides,the thermodynamic properties such as entropy,heat capacity,and Debye temperature of α-and β-Si3N4 are determined at various temperatures and pressures.Significant features in these properties are observed at high temperature.The calculated results are in good agreement with available experimental data and previous theoretical values.Many fundamental solid-state properties are reported at high pressure and high temperature.Therefore,our results may provide useful information for theoretical and experimental investigations of the Si3N4 polymorphs.