Decrease In Molar Volume Research Articles

Crystal structure of the high-pressure phase of calcium hydroxide, portlandite: In situ powder and single-crystal X-ray diffraction study

The crystal structure of a high-pressure phase of calcium hydroxide, Ca(OH)2 (portlandite), was clarified for the first time using the combination of in situ single-crystal and powder X-ray diffraction measurements at high pressure and room temperature. A diamond-anvil cell with a wide opening angle and cell-assembly was improved for single-crystal X-ray diffraction experiments, which allowed us to successfully observe Bragg reflections in a wide range of reciprocal space. The transition occurred at 6 GPa and the crystal structure of the high-pressure phase was determined to be monoclinic at 8.9 GPa and room temperature [ I 121; a = 5.8882(10), b = 6.8408(9), c = 8.9334(15) A, β = 104.798(15)°]. The transition involved a decrease in molar volume by approximately 5.8%. A comparison of the structures of the low- and high-pressure phases indicates that the transition occurs by a shift of CaO6 octahedral layers in the a-b plane along the a -axis, accompanied by up-and-down displacements of Ca atoms from the a-b plane. The crystal structure of this high-pressure phase is considered to be an intermediate state between the low-pressure phase and the high-pressure–high-temperature phase. The complicated diffraction patterns of the high-pressure phase suggest that the phase transition occurred toward three directions around the c -axis of the low-pressure phase. This explains the difficulties encountered in previous structural analyses. The present results will provide key information for discussing the behavior of hydrogen bonds in these hydrous minerals under pressure.

Effect of Bi3+ ions on physical, thermal, spectroscopic and optical properties of Nd3+ doped sodium diborate glasses

Neodymium doped sodium diborate glasses containing bismuth oxide were prepared by melt quenching method. An effort has been made to understand whether the stiffness of tightly bound diborate groups affect upon the addition of heavy metal oxide. The increase in density and decrease in molar volume with increase of Bi2O3 content indicates the opening of diborate glass structure to achieve better packing and bonding. The mixed bonding such as Bi–O–B may occur during glass formation leads to decrease in its glass transition temperature. The increase in oxygen packing density values also indicates the existence of tight packing of the oxide network. The optical properties are measured using UV–visible spectroscopy. The increase in refractive index is attributed to the increasing number of highly polarizing Bi3+ ions with higher atomic weight and coordination number. The decrease in the optical band gap energy with increase in Bi2O3 content is ascribed to shifting of absorption edge to a longer wavelength region. The IR spectra reveal that the glass network consists of tightly bound diborate and BiO6 octahedral units.

Physical, Optical and Structural Properties of xLi2O-(50–x)Bi2O3-10ZnO-40B2O3 Glasses

Glasses with composition xLi2O-(50–x)Bi2O3-10ZnO-40B2O3 have been prepared by conventional melt quenching method. Density and molar volume decrease with increase in Li2O content. The IR and Raman studies indicate that these glasses are made up of [BiO3] [BiO6], [BO3] and [BO4] basic structural units. Li2O acts as a network modifier and modifies the glass structure. The optical absorption studies reveal that optical band gap decreases with Li2O content whereas Urbach energy (ΔE) shows an increasing trend. The metallization criterion is found to be in the range 0.368-0.386, indicating the suitability of these glasses for non-linear optical properties.

The role of lead oxide on structural and physical properties of lithium diborate glasses

Pseudo-binary (100−x)Li2B4O7–xPb3O4, with x=0–70mol% PbO have been prepared and their properties investigated. The glass transition temperature, density and molar volume have been determined as a function of composition. The values of Tg and the molar volume decrease non-linearly while the density increases as the Pb3O4 content is raised. Infrared spectra of the glasses reveal that a strong network consisting of diborate units breaks up by the addition of Pb3O4. The absorption bands below 620cm−1 show that PbO is one of the network formers of the glasses 70⩾Pb3O4⩾10; as they can be associated with vibrations of (PbO4)2− grouping. PbO plays a dual role in the glass network. The calculated values of N4 [the fraction of borons which are tetrahedral] slightly decrease with PbO content up to 30mol% and then increase with Pb3O4 content up to 50mol%, then followed by a decrease as the Pb3O4 content rises further. The Vickers hardness of the glasses varies as a function of the PbO content in the same manner as the variation of N4. The dc conductivity decreases with the Pb3O4 concentration up to about 30mol% and then increases thereafter.

Micromechanical properties of (Na,Zn)-sulfophosphate glasses

Elastic constants, hardness and crack initiation resistance of sulfur-bearing sodium-zinc-phosphate glasses were determined by ultrasonic echography and Vickers indentation experiments. Incorporation of up to 35mol% of sulfur into the glass structure resulted in a decrease in molar volume of 23% and an increase of Poisson's ratio up to a value of~0.32. Resistance against permanent deformation and cracking decreased with compaction of the glass structure, i.e. a more brittle character of softer sulfophosphate glasses was observed when tested under normal atmosphere. Under flowing N2 gas only a weak compositional dependence of the crack-to-indent size ratio was evident, which indicates that surface reactions dominate micromechanical crack initiation in sulfophosphate glasses.

Modification in structural and optical properties of ZnO, CeO2 doped Al2O3–PbO–B2O3 glasses

The structural and optical analysis of glasses is carried out by XRD, FTIR, density and UV visible spectroscopic measurement techniques. XRD results have confirmed the glassy nature of the samples. The FTIR spectral analysis reveals that with the combined presence of ZnO and CeO2 contents in Al2O3–PbO–B2O3 glasses, more BO3 groups are transformed into BO4. The optical analysis reveals that optical band gap energy decreases more for CeO2–ZnO–Al2O3–PbO–B2O3 glasses (from 2.28 to 1.84eV). The presence of CeO2 and ZnO in the glass samples causes more compaction of the borate network due to the formation of more BO4 groups and the presence of ZnO4 groups, which results an increase in density, refractive index and decrease of molar volume.

Resolving the contribution due to Förster-type intramolecular electronic energy transfer in closely coupled molecular dyads

This work examines the electronic energy-transfer (EET) processes inherent to a molecular dyad in which aryl polycycles attached to a boron dipyrromethene (Bodipy) dye act as ancillary light harvesters for near-UV photons. The solvent, being methyltetrahydrofuran, is compressed under applied pressure to such an extent that, over the accessible pressure range, there is a 25% decrease in molar volume. This effect serves to increase the effective concentration of the solute and increases fluorescence from Bodipy when this chromophore is excited directly. Illumination into the aryl polycycles, namely pyrene and perylene derivatives, leads to rapid intramolecular EET to Bodipy but fluorescence from these units is partially restored under high pressure. The argument is made that applied pressure restricts torsional motions around the linkages and imposes a near orthogonal geometry for transition dipole moment vectors on the reactants. In turn, this pressure-induced conformational restriction switches off Forster-type EET within the system, leaving the electron-exchange contribution. For the target dyad, the Forster component is ca. 5% for pyrene and ca. 25% for perylene. Such contributions are not inconsistent with calculations made on the basis of Forster theory but modelling is rendered difficult by the absence of accurate information about the nature of the conformational motion. Two possibilities have been considered. In the first case, the appendages remain stiff but pressure reduces the extent of displacement from the lowest-energy position. The results can be accounted for in a quantitative sense on the basis of small deviations from the lowest-energy conformation; the actual amount of displacement needed to explain the pressure effect depends on the method used to compute the Forster rates and ranges from ca. 4° for the ideal dipole approximation to only 0.5° for the extended dipole method. Secondly, pressure is assumed to bend each appendage into a banana-like shape. Again, the full effect of applied pressure can be accounted for by way of minor curvature of the linkage.

Pseudo-critical behavior on the partial molar volume of solutes in the isotropic phase of liquid crystal

Temperature dependence of partial molar volume of 4-amino-4′-nitrobiphenyl (ANB) and 4,4′-dinitrobiphenyl (DNB) in the isotropic phase of 4-n-pentyl-4′-cyanobiphenyl (5CB) was determined. Addition of ANB to 5CB causes increase of isotropic–nematic phase transition temperature (TIN) [1]. The decrease of partial molar volume of ANB was observed while the increase of partial molar volume of DNB and triphenyl phosphite (TPP) [8] was observed with approaching TIN. The anomalous behavior of partial molar volume was discussed using treatments similar to that of other thermodynamic derivatives in the I–N transition.

Influence of Ba2+ ions on defect concentration in bismuth silicate glasses evidenced by FTIR and UV‐visible spectroscopy

AbstractBismuth silicate glasses containing Ba2+ ions were prepared by a normal melt quench technique in a wide range of composition. The present study includes structural and optical characterization of these glasses by using the techniques of IR and UV‐visible spectroscopy. The variation in density and molar volume with Ba2+ ion concentration was related to structural changes occurring in the glass. The large difference in crystalline temperature (TC) and glass transition temperature (Tg) value shows the thermal stability of these glasses. Analysis of IR spectra shows the occurrence of broad and strong band around 456‐471 cm‐1, attributed to both Bi‐O‐ stretching vibrations in distorted linked [BiO6] units and bending vibrations of the silicate network. The shifting of center of the band around 800 ‐ 1100 cm‐1 with the increase in Ba2+ ions concentration in glass matrix suggests a decrease in Si‐O‐Si bond angle and causes glass network shrinkage which is also supported by observed decrease in molar volume. The analysis of optical absorption spectra of these glasses reveals that the position of absorption edge and cutoff wavelength shift towards blue as Ba2+ ion concentration increases in the glass composition. The variation in optical band gap energy (Eg) with change in glass composition may be attributed to the indirect influence of the Ba2+ ions on the band gap and can be evaluated from the Tauc's plots for indirect allowed and indirect forbidden transitions. The increase in optical band gap (Eg) from optical absorption analysis indicates that the glass network becomes more compact and degree of disorder decreases with increase of concentration of Ba2+ ions. The origin of Urbach's energy is associated with phonon‐assisted indirect transitions and its value varies with the random internal electric field either due to lack of long range order or presence of defects. From Urbach energy values, it was concluded that the defect concentration could be controlled by the presence of Ba2+ ions in the present glass system (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dehydration-induced structural transformations of the microporous zirconosilicate elpidite

The structural transformations accompanying the thermal dehydration of natural elpidite, Na2ZrSi6O15 · 3H2O, have been studied by X-ray powder diffraction and IR spectroscopy. The crystal structures of both elpidite (a = 7.1136(1), b = 14.6764(2), c = 14.5977(2) A; sp. Gr. Pbcm) and the dehydration product Na2ZrSi6O15 (a = 14.0899(1), b = 14.4983(1), c = 14.3490(1)A; sp. gr. Cmce = Cmca) are based on a heteropolyhedral Si-Zr-O framework. The Na cations and (in hydrous elpidite) H2O molecules reside in extra-framework sites. The dehydration-induced distortion of the framework leads to a doubling of the a cell parameter, and the water loss is accompanied by a considerable decrease in molar volume.

Isotope effects in ice Ih: A path-integral simulation

Ice Ih has been studied by path-integral molecular dynamics simulations, using the effective q-TIP4P/F potential model for flexible water. This has allowed us to analyze finite-temperature quantum effects in this solid phase from 25 to 300 K at ambient pressure. Among these effects we find a negative thermal expansion of ice at low temperatures, which does not appear in classical molecular dynamics simulations. The compressibility derived from volume fluctuations gives results in line with experimental data. We have analyzed isotope effects in ice Ih by considering normal, heavy, and tritiated water. In particular, we studied the effect of changing the isotopic mass of hydrogen on the kinetic energy and atomic delocalization in the crystal as well as on structural properties such as interatomic distances and molar volume. For D(2)O ice Ih at 100 K we obtained a decrease in molar volume and intramolecular O-H distance of 0.6% and 0.4%, respectively, as compared to H(2)O ice.

Compositional dependence of the structural and dielectric properties of Li2O–GeO2–ZnO–Bi2O3–Fe2O3 glasses

(10Li2O–20GeO2–30ZnO–(40-x)Bi2O3–xFe2O3 where x = 0.0, 3, 6, and 9 mol%) glasses were prepared. A number of studies, viz. density, differential thermal analysis, FT-IR spectra, DC and AC conductivities, and dielectric properties (constant e′, loss tan δ, AC conductivity, σ ac, over a wide range of frequency and temperature) of these glasses were carried out as a function of iron ion concentration. The analysis of the results indicate that, the density and molar volume decrease with an increasing of iron content indicates structural changes of the glass matrix. The glass transition temperature T g and onset of crystallization temperature T x increase with the variation of concentration of Fe2O3 referred to the growth in the network connectivity in this concentration range, while glass-forming ability parameter ΔT decrease with increase Fe2O3 content, indicates an increasing concentration of iron ions that take part in the network-modifying positions. The FT-IR spectra evidenced that the main structural units are BiO3, BiO6, ZnO4, GeO4, and GeO6. The structural changes observed by varying the Fe2O3 content in these glasses and evidenced by FTIR investigation suggest that the iron ions play a network modifier role in these glasses while Bi2O3, GeO2, and ZnO play the role of network formers. The temperature dependence of DC and AC conductivities at different frequencies was analyzed using Mott’s small polaron hopping model and, the high temperature activation energies have been estimated and discussed. The dielectric constant and dielectric loss increased with increase in temperature and Fe2O3 content.

Effect of Additives on the Refractive Index of B2O3-SiO2-Al2O3 Glasses for Photolithographic Process in Electronic Micro Devices

In fabricating plasma display panels, the photolithographic process is used to form patterns of barrier ribs with high accuracy and high aspect ratio. It is important in the photolithographic process to control the refractive index of the photosensitive paste. The composition of this paste for photolithography is based on the B2O3-SiO2-Al2O3 glass system, including additives of alkali oxides and rare earth oxides. In this work, we investigated the density, structure and refractive index of glasses based on the B2O3-SiO2-Al2O3 system with the addition of Li2O, K2O, Na2O, CaO, SrO, and MgO. The refractive index of the glasses containing K2O, Na2O and CaO was similar to that of the [BO3] fraction while that of the SrO, MgO and Li2O containing glasses were not correlated with the coordination fraction. The coordination number of the boron atoms was measured by MAS NMR. The refractive index increased with a decrease of molar volume due to the increase in the number of non-bridging oxygen atoms and the polarizability. The lowest refractive index (1.485) in this study was that of the B2O3-SiO2-Al2O3-K2O glass system due to the larger ionic radius of K+. Based on our results, it has been determined that the refractive index of the B2O3-SiO2-Al2O3 system should be controlled by the addition of alkali oxides and alkali earth oxides for proper formation of the photosensitive paste.

High-pressure phase relations in the system CaAl 4Si 2O 11–NaAl 3Si 3O 11 with implication for Na-rich CAS phase in shocked Martian meteorites

High-pressure phase relations in the system NaAl 3Si 3O 11–CaAl 4Si 2O 11 were examined at 13–23 GPa and 1600–1900 °C, using a multianvil apparatus. A Ca-aluminosilicate with CaAl 4Si 2O 11 composition, designated CAS phase, is stable above about 13 GPa at 1600 °C. In the system NaAl 3Si 3O 11–CaAl 4Si 2O 11, the CAS phase dissolving NaAl 3Si 3O 11 component coexists with jadeite, corundum and stishovite below 22 GPa, above which the CAS phase coexists with Na-rich calcium ferrite, corundum and stishovite. At 1600 °C, the solubility of NaAl 3Si 3O 11 component in the CAS solid solution increases with increasing pressure up to about 50 mol% at about 22 GPa, above which the solubility decreases with pressure. The maximum solubility of NaAl 3Si 3O 11 component in the CAS phase increases with temperature up to around 70 mol% at 1900 °C at 22 GPa. The dissociation of NaAlSi 2O 6 jadeite to NaAlSiO 4 calcium ferrite plus stishovite occurs at about 22 GPa. Lattice parameters of the CAS phase with the hexagonal Ba-ferrite structure change with increase of the NaAl 3Si 3O 11 component: a-axis decreases and c-axis slightly increases, resulting in decrease of molar volume. Enthalpies of the CAS solid solutions were measured by high-temperature drop-solution calorimetry techniques. The results show that enthalpy of hypothetical NaAl 3Si 3O 11 CAS phase is much higher than the mixture of NaAlSi 2O 6 jadeite, corundum and stishovite and is close to that of the mixture of NaAlSiO 4 calcium ferrite, corundum and stishovite. When we adopt the Na:Ca ratio of 75:25 of the natural Na-rich CAS phase in a shocked Martian meteorite, Zagami, the phase relations determined above suggest that the natural CAS phase crystallized from melt at pressure around 22 GPa and temperature close to or higher than 2000–2200 °C. The inferred P, T conditions are consistent with those estimated using other high-pressure minerals in the shocked meteorite.

A new high-pressure polymorph of Ti2O3: implication for high-pressure phase transition in sesquioxides

The post-corundum phase transition has been investigated in Ti2O3 on the basis of synchrotron X-ray diffraction in a diamond anvil cell and transmission electron microscopy. The new polymorph of Ti2O3 was found at about 19 GPa and 1850 K, and this phase was stable even at about 40 GPa. A new polymorph of Ti2O3 can be indexed on a Pnma orthorhombic cell, and the unit-cell parameters are a=7.6965 (19) Å, b=2.8009 (9) Å, c=7.9300 (23) Å, V=170.95 (15) Å3 at 19 GPa, and a=7.8240 (2) Å, b=2.8502 (1) Å, c=8.1209 (3) Å, V=181.10 (1) Å3 at ambient conditions. The Birch–Murnaghan equation of state yields K 0=206 (3) GPa and K′0=4 (fixed) for corundum phase, and K 0=296 (4) GPa and K′0=4 (fixed) for the post-corundum phase. The molar volume decreases by 12% across the phase transition at around 20 GPa. The structural identification was carried out on a recovered sample by the Rietveld method, and a new polymorph of Ti2O3 can be identified as Th2S3-type rather than U2S3-type structure. The transition from corundum-type to Th2S3-type structure accompanies the drastic change of the form of polyhedron: from TiO6 octahedron in the corundum-type to TiO7 polyhedron in the Th2S3-type structures.

Electrical conductivity of lithium borosilicate glasses modified with TiO2

The variation of electrical conductivity with addition of TiO2 in lithium borosilicate system has been studied. The addition of TiO2 to the optimum conducting composition in lithium borosilicate system further enhances the conductivity. A maximum conductivity is obtained at 10 mol% TiO2. Also the TiO2 addition results in increase in density and decrease in molar volume. The variation in glass transition temperature Tg and CTE with addition of TiO2 is explained on the basis of changes in glass structure.

Principal component analysis on properties of binary and ternary hydrides and a comparison of metal versus metal hydride properties

Principal component analysis (PCA) is used to investigate interrelationship among material properties of hydrides. Property data which consist of ∼200 compounds (binary and ternary metal hydrides) were analyzed. A comparative study was carried out among the metal properties with that of their hydrides. The observed decrease or increase of entropy, molar volume and specific heat of hydrides from that of the metals can be attributed to hydrogen bond formation, charge transfer and corresponding change in crystal structure.

Structure and thermal stability of arc evaporated (Ti 0.33Al 0.67) 1 − xSi xN thin films

(Ti 0.33Al 0.67) 1 − x Si x N (0 ≤ x ≤ 0.29) thin solid films were deposited onto cemented carbide substrates by arc evaporation and analyzed using analytical electron microscopy, X-ray diffraction, nanoindentation, and density functional theory. As-deposited films with x ≤ 0.02 consisted mainly of a metastable c-(Ti,Al)N solid solution for which Si serves as a veritable grain refiner. Additional Si promoted growth of a hexagonal wurtzite (Al,Ti,Si)N solid solution, which dominated at 0.02 < x < 0.17. For x ≥ 0.17, the films were X-ray amorphous. Despite these widely different microstructures, all as-deposited films had nanoindentation hardness in the narrow range of 22–25 GPa. Isothermal annealing of the x = 0.01 alloy film at a temperature of 900 °C, corresponding to that in turning operation, resulted in spinodal decomposition into c-AlN and TiN and precipitation of h-AlN. For x = 0.09 films, annealing between 600 °C and 1000 °C yielded c-TiN precipitation from the h-(Al,Ti,Si)N phase. Furthermore, the x = 0.01 and x = 0.09 films exhibited substantial age hardening at 900 °C, to 34 GPa and 29 GPa due to spinodal decomposition and c-TiN precipitation, respectively. Films with a majority of c-(Ti,Al)N phase worked best in steel turning tests, while films with x > 0.02 developed cracks during such operation. We propose that the cracks are due to tensile strain which is caused by a decrease in molar volume during the phase transformation from hexagonal wurtzite (Al,Ti,Si)N into cubic TiN phase, which results in degradation in machining performance.

Thermal Conductivity of Aqueous Sugar Solutions under High Pressure

Molecular energy transport in aqueous sucrose and glucose solutions of different mass fractions and temperatures is investigated up to 400 MPa, using the transient hot-wire method. The results reveal an increasing thermal conductivity with increasing pressure and decreasing mass fraction of sugar. No significant differences between sucrose and glucose solutions were observed. Different empirical and semi-empirical relations from the literature are discussed to describe and elucidate the behavior of the solutions with pressure. The pressure-induced change of the thermal conductivity of sugar solutions is mainly caused by an increase of the thermal conductivity and the decrease of molar volume of the water fraction. A simple pressure adapted mass fraction model permits an estimation of the thermal conductivity of the investigated solutions within an uncertainty of about 3%.

Thermal and optical properties of CuO–BaO–B2O3–P2O5 glasses

CuO-doped barium borophosphate glasses in a series of xCuO–(45−x)BaO–10B2O3–45P2O5 in molar ratio with x=0–15mol% were prepared by a melt-quenching technique. All the glasses had excellent thermal stability against crystallization. Glass transition temperature, thermal expansion coefficient and molar volume decrease with increasing CuO concentration. The linear relationship between the absorption coefficient and CuO concentration exists for a peak wavelength in the transitions of 2A1g→2B1g, 2B2g→2B1g, 2Eg→2B1g. The relationship between the properties and glass structure evaluated by Raman spectroscopy is discussed.