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Pressure is a unique thermodynamic variable to explore the phase competitions and novel phases inaccessible at ambient conditions. The resistive switching material GaTa4Se8 displays several quantum phases under pressure, such as a Jeff = 3/2 Mott insulator, a correlated quantum magnetic metal, and d-wave topological superconductivity, which has recently drawn considerable interest. Using high-pressure Raman spectroscopy, X-ray diffraction, extended X-ray absorption, transport measurements, and theoretical calculations, we reveal a complex phase diagram for GaTa4Se8 at pressures exceeding 50 GPa. In this previously unattained pressure regime, GaTa4Se8 ranges from a Mott insulator to a metallic phase and exhibits superconducting phases. In contrast to previous studies, we unveil a hidden correlation between the structural distortion and band gap prior to the insulator-to-metal transition, and the metallic phase shows superconductivity with structural and magnetic properties that are distinctive from the lower-pressure phase. These discoveries highlight that GaTa4Se8 is a unique material to probe novel quantum phases from a structural, metallicity, magnetism, and superconductivity perspective.

Valence transition could induce structural, insulator-metal, nonmagnetic-magnetic and superconducting transitions in rare-earth metals and compounds, while the underlying physics remains unclear due to the complex interaction of localized 4f electrons as well as their coupling with itinerant electrons. The valence transition in the elemental metal europium (Eu) still has remained as a matter of debate. Using resonant x-ray emission scattering and x-ray diffraction, we pressurize the states of 4f electrons in Eu and study its valence and structure transitions up to 160 GPa. We provide compelling evidence for a valence transition around 80 GPa, which coincides with a structural transition from a monoclinic (C2/c) to an orthorhombic phase (Pnma). We show that the valence transition occurs when the pressure-dependent energy gap between 4f and 5d electrons approaches the Coulomb interaction. Our discovery is critical for understanding the electrodynamics of Eu, including magnetism and high-pressure superconductivity.

Local structures play a crucial role in the structural polyamorphism and novel electronic properties of amorphous materials, but their accurate measurement at high pressure remains a formidable challenge. In this article, we use the local structure of network-forming GeO2 glass as an example, to present our recent approaches and advances in high-energy x-ray diffraction, high-pressure x-ray absorption fine structure, and ab initio first-principles density functional theory calculations and simulations. Although GeO2 glass is one of the best studied materials in the field of high pressure research due to its importance in glass theory and geophysical significance, there are still some long-standing puzzles, such as the existence of appreciable distinct fivefold [5]Ge coordination at low pressure and the sixfold-plus [6+]Ge coordination at ultrahigh pressure. Our work sheds light on the origin of pressure-induced polyamorphism of GeO2 glass, and the [5]Ge polyhedral units may be the dominant species in the densification mechanism of network-forming glasses from tetrahedral to octahedral amorphous structures.

Pressure is a unique thermodynamic variable to explore the phase competitions and novel phases inaccessible at ambient conditions. The resistive switching material GaTa

The novel physics, such as the pressure-induced electronic topological transition (ETT), topological superconductivity and Majorana fermions in the isostructural $R\text{\ensuremath{-}}3m$ phase of three-dimensional topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$, holds considerable interest in condensed-matter physics. We carried out a combined investigation of single-crystal x-ray diffraction, high-quality x-ray absorption fine structure, and first-principles theoretical calculations to decipher the puzzling origin of the intriguing electronic states in the isostructural $R\text{\ensuremath{-}}3m$ phase of ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ at high pressure. Three distinct regions with two isostructural phase transitions (IPTs) in the $R\text{\ensuremath{-}}3m$ phase have been identified. The first IPT, which is known as the ETT, occurs at the boundary of region I (0--2 GPa) and region II (2--5 GPa) with a sharp minimum in the $c/a$ ratio of $R\text{\ensuremath{-}}3m$ structure, while the second IPT happens as pressure increases from region II (2--5 GPa) to region III (5--7 GPa). The positions of the Bi ($6c$) and Se ($6c$) sites in the unit cell change rapidly in region II (2--5 GPa), but there is little change at these sites in region III (5--7 GPa). The band-gap closure in region I reflects the pressure-induced metallization. At higher pressures, the band gap opens in region II but remains almost constant after the second IPT in region III, which agrees well with the topological superconductivity of ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$. Our results demonstrate that the combination of local structure, long-range crystal structure, and first-principles calculation is critically important for understanding the isostructural electronic states and the connection between the structure and function as in ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ at high pressure.

The electronic state of layered three-dimensional topological insulators at high pressure is a compelling but a puzzling hot topic. The open question is the structural origins for the pressure-induced novel physics of electronic topological transition (ETT), topological superconductivity, and Majorana fermions in the same isostructural $R\text{\ensuremath{-}}3m$ phase. Here, we report a combined investigation on the local structure and bulk electronic state of topological insulator $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ using x-ray diffraction, high quality x-ray absorption fine-structure spectroscopies both at the $\mathrm{Bi}\phantom{\rule{0.16em}{0ex}}{L}_{3}$ edge and at the Se K edge, and first-principles theoretical calculations. We have found three pressure-induced distinct intermediate states in the isostructural rhombohedral phase of $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$. The bulk electronic structure of the $R\text{\ensuremath{-}}3m$ phase was calculated based on the experimental structure. The corresponding distinct electronic states provide the origins of ETT at \ensuremath{\sim}3 GPa and the metallization at 7--9.5 GPa in the $R\text{\ensuremath{-}}3m$ phase of $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$. Our results demonstrate that the local structure plays a critical role in the electronic states of topological insulator $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$.

One challenge in studying high-temperature superconductivity (HTSC) stems from a lack of direct experimental evidence linking lattice inhomogeneity and superconductivity. Here, we apply synchrotron hard X-ray nanoimaging and small-angle scattering to reveal a novel micron-scaled ribbon phase in optimally doped Bi2Sr2CaCu2O8+δ (Bi-2212, with δ = 0.1). The morphology of the ribbon-like phase evolves simultaneously with the dome-shaped TC behavior under pressure. X-ray absorption studies show that the increasing of TC is associated with oxygen-hole redistribution in the CuO2 plan, while TC starts to decrease with pressure when oxygen holes become immobile. Additional X-ray irradiation experiments reveal that nanoscaled short-range ordering of oxygen vacancies could further lower TC, which indicates that the optimal TC is affected not only by an optimal morphology of the ribbon phase, but also an optimal distribution of oxygen vacancies. Our studies thereby provide for the first time compelling experimental e...

We utilized the pair distribution function method to characterize the pressure-induced polyamorphic transition in Ce60Al20Cu20 and Ce55Al45 metallic glass at room temperature. Using synchrotron high-energy x-ray diffraction we collected scattering information from a large Q-space coverage, which in turn gave a high resolution g(r) that provided accurate local structure information. We observed a sudden change in compressibility and the nearest neighbor distance at 3.50–6.32 GPa for Ce60Al20Cu20 and 2.20–6.89 GPa for Ce55Al45. The origin of the volume collapse seemed to be pressure-induced qualitative changes in bond shortening that corresponded to different coordination spheres. The polyamorphic transitions in these two systems from low-density glass (LDG) to high-density glass (HDG) are associated with local atomic rearrangements.

Pressure-induced phase transitions of monoclinic H-Nb

The honeycomb iridate ${\mathrm{Na}}_{2}{\mathrm{IrO}}_{3}$ has received much attention as a candidate to realize a quantum spin liquid state, but the nature of its insulating state remains controversial. We found that the material exhibits structural transitions at 3 and 10 GPa. The former is accompanied by 166-meV suppression of the activation gap, but the energies for the low-lying interband transitions change by less than 10 meV. This can be reconciled in a picture in which the application of high pressure barely shifts the electronic bands, but rather merely broadens them. First-principles calculations uncover a strong correlation between the band gap and the $\ensuremath{\beta}$ angle of the monoclinic structure, indicating non-negligible interlayer coupling. These results offer clear evidence for a spin-orbit Mott insulating state in ${\mathrm{Na}}_{2}{\mathrm{IrO}}_{3}$ and are inconsistent with the quasimolecular orbital model.

One challenge in studying high-temperature superconductivity (HTSC) stems from a lack of direct experimental evidence linking lattice inhomogeneity and superconductivity. Here, we apply synchrotron hard X-ray nanoimaging and small-angle scattering to reveal a novel micron-scaled ribbon phase in optimally doped Bi

Pure larnite (β-Ca2SiO4; Lrn) was synthesized at 6 GPa and 1473 K for 6 h by using a cubic press, its thermal expansivity was investigated up to 923 K by using an X-ray powder diffraction technique (ambient P ), and its compressibility was investigated up to ~16 GPa by using a diamond-anvil cell coupled with synchrotron X-ray radiation (ambient T ). Its volumetric thermal expansion coefficient (α V ) and isothermal bulk modulus ( K T) were constrained as α V = 4.24(4) × 10−5 K−1 and K T = 103(2) GPa [the first pressure derivative K T′ obtained as 5.4(4)], respectively. Its compressibility was further studied with the CASTEP code using density functional theory and planewave pseudopotential technique. We obtained the K T values as 123(3) GPa (LDA; high boundary) and 92(2) GPa (GGA; low boundary), with the values of the K T′ as 4.4(9) and 4.9(5), respectively. The phonon dispersions and vibrational density of states (VDoS) of Lrn were simulated using density functional perturbation theory, and the VDoS was combined with a quasi-harmonic approximation to compute the isobaric heat capacity ( C P ) and standard vibrational entropy ( S 298), yielding C P = 212.1(1) – 9.69(5) × 102 T −0.5 – 4.1(3) × 106 T −2 + 5.20(7) × 108 T −3 J/(mol·K) for the T range of ~298–1000 K and S 298 = 129.8(13) J/(mol·K). The microscopic and macroscopic thermal Gruneisen parameters of Lrn at 298 K were calculated to be 0.75(6) and 1.80(4), respectively.

Compressional behavior of a natural hypersthene has been investigated at pressures up to 10.1 GPa at room temperature using in situ synchrotron X-ray diffraction in a diamond anvil cell. No phase transition was observed within the experimental pressure range. The pressure–volume data have been fitted with a third-order Birch–Murnaghan equation of state, resulting in K0 = 113.6(6.2) GPa and K0′=7.7(2.0) for the bulk modulus and its pressure derivative with a fixed unit-cell volume V0 = 854.0(6) A3. The unit-cell parameters, a, b, and c, decrease nonlinearly with elevated pressure and show an anisotropic axial compressibility with a ratio βa: βb: βc: =1:2.05:1.3. The comparison with previous results of orthopyroxene reveals that Al substitution causes a decrease in unit-cell volume and an increase in the bulk modulus, whereas the incorporation of Fe has opposite effects. The relation between unit-cell volume and En/Ts contents has been obtained, V0 (A3) = 873.7(1.1) − 40.8(1.44) × En-90.6(14.7) ×...

Using a diamond-anvil cell and synchrotron X-ray diffraction, the compressional behavior of a synthetic ulvospinel (Fe1.94Ti0.03)Ti1.00O4.00 has been investigated up to about 7.05 GPa at 300 K. The pressure–volume data fitted to the second-order Birch–Murnaghan equation of state yield an isothermal bulk modulus (K T ) of 147(4) GPa (K′ T fixed as 4). This value is slightly larger than that previously determined by an ultrasonic pulse echo method (121(2) GPa; Syono et al., J Phys Soc Jpn 31:471–476, 1971), but substantially smaller than that recently determined by a synchrotron X-ray diffraction technique (251(3) GPa; Yamanaka et al., Phys Rev B 80:134120, 2009; Am Mineral 98:736–744, 2013). Combined with the K T of magnetite (Fe3O4; ~182(3) GPa), our finding suggests that the bulk modulus of the solid solutions Fe3−x Ti x O4 (0 ≤ x ≤ 1) along the join magnetite–ulvospinel decreases by ~20 %.

Pressure-induced phase transitions of monoclinic H-Nb2O5 have been studied by in situ synchrotron x-ray diffraction, pair distribution function (PDF) analysis, and Raman and optical transmission spectroscopy. The initial monoclinic phase is found to transform into an orthorhombic phase at ~9 GPa and then change to an amorphous form above 21.4 GPa. The PDF data reveal that the amorphization is associated with disruptions of the long-range order of the NbO6 octahedra and the NbO7 pentagonal bipyramids, whereas the local edge-shares of octahedra and the local linkages of pentagonal bipyramids are largely preserved in their nearest neighbors. Upon compression, the transmittance of the sample in a region from visible to near infrared (450-1000 nm) starts to increase above 8.0 GPa and displays a dramatic enhancement above 22.2 GPa, indicating that the amorphous form has a high transmittance. The pressure-induced amorphous form is found to be recoverable under pressure release, and maintain high optical transmittance property at ambient conditions. The recoverable pressure induced amorphous material promises for applications in multifunctional materials.

SummaryIbalizumab is a humanized, anti-CD4 monoclonal antibody. It potently blocks HIV-1 infection and targets an epitope in the second domain of CD4 without interfering with immune functions mediated by interaction of CD4 with major histocompatibility complex (MHC) class II molecules. We report here the crystal structure of ibalizumab Fab fragment in complex with the first two domains (D1-D2) of CD4 at 2.2 Å resolution. Ibalizumab grips CD4 primarily by the BC-loop (residues 121–125) of D2, sitting on the opposite side of gp120 and MHC-II binding sites. No major conformational change in CD4 accompanies binding to ibalizumab. Both monovalent and bivalent forms of ibalizumab effectively block viral infection, suggesting that it does not need to crosslink CD4 to exert antiviral activity. While gp120-induced structural rearrangements in CD4 are probably minimal, CD4 structural rigidity is dispensable for ibalizumab inhibition. These results could guide CD4-based immunogen design and lead to a better understanding of HIV-1 entry.

We report development of micro-focusing optics for high-energy x-rays by combining a sagittally bent Laue crystal monchromator with Kirkpatrick-Baez (K–B) X-ray focusing mirrors. The optical system is able to provide a clean, high-flux X-ray beam suitable for pair distribution function (PDF) measurements at high pressure using a diamond anvil cell (DAC). A focused beam of moderate size (10–15 μm) has been achieved at energies of 66 and 81 keV. PDF data for nanocrystalline platinum (n-Pt) were collected at 12.5 GPa with a single 5 s X-ray exposure, showing that the in-situ compression, decompression and relaxation behavior of samples in the DAC can be investigated with this technique. PDFs of n-Pt and nano Au (n-Au) under quasi-hydrostatic loading to as high as 71 GPa indicate the existence of substantial reduction of grain or domain size for Pt and Au nanoparticles at pressures below 10 GPa. The coupling of sagittally bent Laue crystals with K–B mirrors provides a useful means to focus high-energy synchrotron X-rays from a bending magnet or wiggler source.

In this paper, we report recent progress in high-energy X-ray focusing by using Kirkpatrick-Baez (K–B) mirrors in combination with a sagittally bent Laue monochromator. This combination of optics provides a high flux X-ray beam, which can significantly reduce the data acquisition time for high-pressure pair distribution function (HP-PDF) measurements using the diamond anvil cell (DAC). Demonstration of the HP-PDF technique for the compression/relaxation of nanocrystalline platinum at high pressures is presented.

In this paper, we report recent development of the high-pressure pair distribution function (HP-PDF) measurement technique using a focused high-energy X-ray beam coupled with a diamond anvil cell (DAC). The focusing optics consist of a sagittally bent Laue monochromator and Kirkpatrick-Baez (K–B) mirrors. This combination provides a clean high-energy X-ray beam suitable for HP-PDF research. Demonstration of the HP-PDF technique for nanocrystalline platinum under quasi-hydrostatic condition above 30 GPa is presented.

In this paper, we report some recent developments of the diffraction-based absolute X-ray energy calibration method. In this calibration method, high spatial resolution of the measured detector offset is essential. To this end, a remotely controlled long-translation motorized stage was employed instead of the less convenient gauge blocks. It is found that the precision of absolute X-ray energy calibration (ΔE/E) is readily achieved down to the level of 10−4 for high-energy monochromatic X-rays (e.g. 80 keV). Examples of applications to pair distribution function (PDF) measurements and energy monitoring for high-energy X-rays are presented.

The structure of fluid Hg during the metal–non-metal transition has been modelled by Reverse Monte Carlo simulation in terms of the structural factors S ( Q ) measured by X-ray diffraction at SPring-8. The full region of S ( Q ) including S (0) was employed in the simulation so as to take the effect of fluctuation phenomenon into account. The modelling reveals that as the M–NM transition is approached, the distribution of coordination numbers, P ( N ), of the first-neighbor shell broadens obviously and shifts to lower values, supporting the speculation of Franz’s model. Furthermore, the coordination number P S ( N ), denoted for atoms with a shorter bond, changes markedly in width and average value, while much smaller is found for that of longer bond as the density decreases. The variation of P S ( N ) of the atoms with the shorter bond are directly related to the M–NM transition of fluid Hg.

One fascinating high-pressure behavior of tetrahedral glasses and melts is the local coordination change with increasing pressure, which provides a structural basis for understanding numerous anomalies in their high-pressure properties. Because the coordination change is often not retained upon decompression, studies must be conducted in situ . Previous in situ studies have revealed that the short-range order of tetrahedrally structured glasses and melts changes above a threshold pressure and gradually transforms to an octahedral form with further pressure increase. Here, we report a thermal effect associated with the coordination change at given pressures and show distinct thermal behaviors of GeO 2 glass in tetrahedral, octahedral, and their intermediate forms. An unusual thermally induced densification, as large as 16%, was observed on a GeO 2 glass at a pressure of 5.5 gigapascal (GPa), based on in situ density and x-ray diffraction measurements at simultaneously high pressures and high temperatures. The large thermal densification at high pressure was found to be associated with the 4- to 6-fold coordination increase. Experiments at other pressures show that the tetrahedral GeO 2 glass displayed small thermal densification at 3.3 GPa arising from the relaxation of intermediate range structure, whereas the octahedral glass at 12.3 GPa did not display any detectable thermal effects.

Perovskite-structure materials generally exhibit local structural distortions that are distinct from long-range, average crystal structure. The characterization of such distortion is critical to understanding the structural and physical properties of materials. In this work, we combined Pair Distribution Function (PDF) technique with Raman spectroscopy and electrical resistivity measurement to study Bi(Ni1/2Ti1/2)O3 perovskite under high pressure. PDF analysis reveals strong local structural distortion at ambient conditions. As pressure increases, the local structure distortions are substantially suppressed and eventually vanish around 4 GPa, leading to concurrent changes in the electronic band structure and anomalies in the electrical resistivity. Consistent with PDF analysis, Raman spectroscopy data suggest that the local structure changes to a higher ordered state at pressures above 4 GPa.

The topological shape of the integral membrane protein light-harvesting complex LH2 from photosynthetic bacteria Rhodobacter spheroides 2.4.1 in detergent solution has been determined from synchrotron small-angle X-ray scattering data using direct curve-fitting by the ellipsoid, ab initio shape determination methods of simulated annealing algorithm and multipole expansion, respectively. The results indicate that the LH2 protein in aqueous solution is encapsulated by a monolayered detergent shell. The detergent-stabilized structure has the shape of an oblate plate, with a thickness of 40 Å, a long axis of 110 Å, and a short axis of 85 Å . After correction for the detergent shell, the shape of the LH2 core is also an oblate plate with a height of 40 Å, a long axis of 80 Å, and a short axis of 55 Å. In contrast to the cylindrical crystal structure with a height of 40 Å and a diameter of 68 Å, the molecular shape of the LH2 complex in detergent solution clearly deviates from the ringlike crystal structure, with an eccentricity found to be 0.59—consistent with the result of single molecular spectroscopy study of the isolated single LH2 molecules.

X-ray diffraction measurements for expanded fluid mercury have been carried out in a wide density region from the liquid to dense vapour region using synchrotron radiation at SPring-8. We have developed a new high-pressure vessel with seven windows to collect the scattered X-rays for energy-dispersive X-ray diffraction measurements under high temperature and high pressure, and present the new data. It was found that the reliability of the structure factors, S(k), and the accuracy of the pair distribution functions, g(r), are much better. Reliable relations of the coordination number and the correlation distance with the density of fluid Hg were obtained. Structural changes with decreasing density are discussed in relation to the metal–non-metal transition in fluid Hg based on the new results.

Small angle X-ray scattering measurements for supercritical fluid metals such as selenium and mercury have been carried out using synchrotron radiation at SPring-8 to study density fluctuations near the liquid–vapor critical points. The absolute value of the scattering intensity was estimated from measurements on compressed He gas, a method developed using the in-house X-ray source at Hiroshima University. The observed scattering intensity of fluid selenium increases when one approaches the isochore of the critical density with decreasing pressure. The correlation length of the density fluctuations and the long wave length limit of the structure factor, S (0), are deduced to be 16.5 A and 31 at 1680 °C and 459 bar using the Ornstein–Zernike formula. Based on these data, the density fluctuations in fluid selenium are discussed.

X-ray diffraction measurements for expanded fluid selenium have been carried out in a wide density region from the liquid to the dense vapor using synchrotron radiation at SPring-8. We have developed a new high pressure vessel with seven windows to measure scattered X-rays and the reliability of the structure factors becomes much better. The measurements were made in the semiconductor–metal (SC–M) transition region from 600 to 1500 °C near 800 bar. The structure factors in the dense vapor region from 300 to 441 bar at 1650 °C are obtained for the first time. Structural changes in the SC–M transition region and the structure of the dense selenium vapor are discussed, based on these new results.

Understanding the structural phase diagram of nano scale SrTiO3 has important implications on the basic physics and applications of the general class of transition metal oxide perovskites. Pressure dependent structural measurements on monodispersed nanoscale SrTiO3 samples with average diameters of 10 to ~80 nm were conducted. A robust pressure independent polar structure was detected in the 10 nm sample for pressures of up to 13 GPa while a size dependent cubic to tetragonal transition occurs (at P = Pc) for larger particle sizes. The results suggest that the growth of ~10 nm STO particles on substrates with large lattice mismatch will not alter the polar state of the system for a large range of strain values, possibly enabling device use.

Energy-dispersive X-ray diffraction measurements using synchrotron radiation at SPring-8 for fluid Se have been carried out at temperatures up to 1650 °C and pressures up to 878 bar, including the dense vapour region, to investigate the structural change in the semiconductor-to-metal (SC–M) transition in expanded fluid Se. We obtained the structure factors, S ( k ), and the pair distribution functions, g ( r ), with a fairly good accuracy. Besides confirming the preservation of twofold-co-ordinated structure, the contraction of nearest co-ordination distance and the existence of asymmetry of the first peak in the g ( r ) in the metallic fluid region, it was found that the line shape of the first peak in the g ( r ) changes as well as the value of the first minimum in the g ( r ) increases obviously with increasing metallic properties. These results indicate that both the existence of different intrachain bonds and the interchain interaction are important for the mechanism of SC–M transition in fluid Se.

The amorphous Sm2Fe15Ga2C2 ribbons were rapidly thermal annealed at various temperatures for various times. From the X-ray diffraction patterns, two phases, i.e. 2 : 17 phase and alpha-Fe, were always found when the ribbons were annealed at temperature above 700 degrees C. The demagnetization curves also verified this two-phase behavior. However, from the TEM studies, only 2: 17 phase was found. This led to the suggestion that the alpha-Fe precipitates were caused by the oxidation of Sm and only took place at the surface of the annealed ribbons. Moreover, from the TEM images, crystallization of 2 : 17 phase was found to begin at about 600 degrees C. The ribbons annealed at 700 or 900 degrees C for 1 min showed well-defined grains in the absence of alpha-Fe. Their grain sizes were measured to be about 100 nm for 700 degrees C x 1 min and 250 nm for 900 degrees C x 1 min, respectively. It was thus suggested that the Sm2Fe15Ga2C2 2 : 17 type structure obtained from the melt-spinning technique remains stable up to at least 900 degrees C. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

We have studied the physical properties such as the viscosity, eta, density, rho, and surface tension, gamma, of Li2O-4B(2)O(3) melt at a high temperature of 860 degrees C up to 1150 degrees C in air ambient atmosphere. From the viscosity measurement, it has been found that the activation energy, E-a, of the melt, with slight relaxation, shows a distinct change around 970 degrees C. The existence of this anomalous point at around 970 degrees C was also clearly verified by the density and surface tension measurements. The temperature coefficients of these properties at low- and high-temperature side of the point are E-a: 150 kJ/mol, d rho/dT: - 5.54 x 10(-4) g/cm(3) K, d gamma/dT 0, respectively. Our results are informative for understanding the molten state of Li2O-4B(2)O(3) melt as well as helpful in growing LBO crystals. (C) 1999 Elsevier Science B.V. All rights reserved.

Using the double-wire torsion pendulum method, we have measured the viscosity of BaB2O4, BaB2O4-NaF and BaB2O4-Na2O melts, respectively, at high temperature of circa 910 degrees C up to 1150 degrees C in air ambient atmosphere. It was found that at the reported growth temperature (1050 degrees C), the viscosity of BaB2O4 was as high as 197.2 Pa s, and the addition rate of the logarithmic viscosity becomes bigger in the supercooling region than that of the normal melt. Both the activation energy and the volume of how unit are different around the growth temperature of beta-BaB2O4 crystal. With the addition of NaF or Na2O as flux to the BaB2O4 melt, both the viscosity and the activation energy of the melt decrease severely. Density of the melts with the fluxes was also determined, showing that similar obvious variations of density and its temperature dependence were observed. In terms of the Stokes-Einstein equation and the estimated volumes of the flow units in the melt, the role of NaF and Na2O fluxes on the BaB2O4 crystal growth was discussed. (C) 1998 Elsevier Science B.V. All rights reserved.

Two magnetic ordering transitions are found in InMnO3, the paramagnetic to antiferromagnetic transition near ~118 K and a lower possible spin rotation transition near ~42 K. Multiple length scale structural measurements reveal enhanced local distortion found to be connected with tilting of the MnO5 polyhedra as temperature is reduced. Strong coupling is observed between the lattice and the spin manifested as changes in the structure near both of the magnetic ordering temperatures (at ~42 K and ~ 118 K). External parameters such as pressure are expected to modify the coupling., Comment: 14 Figures

Using the double-wire torsion pendulum method, we have measured the viscosity of a potassium niobate molten system with excess K2O from 50 to 56 mol% at temperatures up to 1190 degrees C in air. Both the viscosity and its activation energy show strong time dependence. While the values for viscosity increase for melts with 50 and 51 mol% K2O, which are annealed at 1150 degrees C in air, the viscosity, however, of the melt with more than 2 mol% excess K2O shows a completely different time dependence, i.e. drastic decrease with annealing time. A similar striking reversed variation of temperature-dependent viscosity with annealing time is observed when the K2O content in the melt is up to 52 mol%. These anomalous variations in viscosity give clear evidence why the KNbO3 single crystal should be grown from mother melts with excess K2O above 51 mol%, and after being annealed for a long time. This result also confirms that the double-wire torsion pendulum method is a useful tool to study the time-dependent viscosity of melts at high temperature in air.

Rare earth phosphors have been widely studied because of their sharp emission lines and excellent optical performance. However, photoluminescence (PL) tuning by crystal field in Er3+ embedded phosphors has always been a challenge. Here, we demonstrate that pressure can help to enhance the red and green light emission simultaneously in Er:GdVO4. Synchrotron X-ray diffraction investigations revealed that a structural phase transition was responsible for the enhancement. Our work brightens the future prospects for applications of Er3+-based PL materials in various fields, such as high power lasers and (bio) medical imaging.

A new method of measuring the viscosity of liquid, which is named the double‐wire torsion pendulum method in contrast to the conventional torsion pendulum method, is described in this paper. It was found that the damping factor αl changes nearly linearly with the kinematical viscosity η/ρ of the standard oil in the range from 1.55 to 1.15×104 cp. An empirical formula is derived for the damping factor αl and the viscosity η/ρ, and which factors can influence this empirical formula are also presented. The apparatus as constructed is capable of measuring the viscosity and its activation energy over a wide range of temperatures, and is especially suitable for melts at high temperatures with a wide, accurate, dynamic viscosity range. Applying this method, we have observed that the viscous activation energy of a supercooled Li2B8O13 melt is obviously different from that of the normal melt.

Improvements on a torsion pendulum suitable for viscosity measurements of a melt at high temperature are described. Two torsion wires to replace the single torsion wire of a conventional torsion pendulum were used. This improvement enhanced both the anti-disturbance and repeatability of the experimental curves, and made it possible to measure the molten viscosity of oxide melt in air ambience. It was found that the damping factor α1 changes nearly linearly with the kinematical viscosity. An empirical formula was derived for the damping factor α1 and the viscosity. As an application of this method, the soaking effect on the viscosity of molten Li2B8O13 was investigated. The soaking process induces the decrease of viscosity and its activation energy of molten Li2B8O13. The torsion pendulum method shows high potential to the study of the relationship between the molten viscosity and composition, atmosphere, temperature and heat history of the melt.

The density and surface tension of the K2O-Nb2O5 molten system between 50 and 56 mol% K2O melts were measured from 1080 to 1180 degrees C. Excess K2O in the melt can reduce both density and surface tension, and there is a minimum both in the composition dependence and in the temperature dependence of the density within this composition range. It was found that the temperature coefficient of surface tension -d tau/dT was the smallest around the 52 mol% K2O region. The surface tension was observed to increase with soak time, but the temperature coefficient -d tau/dT decreased by the soak process. These properties and variations may explain why a KNbO3 crystal should be grown from the melt with a composition of 52 to 54 mol% K2O at a soak temperature above 1150 degrees C after several days.

The pair-distance distribution function P(r) is a measure of the frequency of interatomic vector lengths within a protein molecule, and can provide information about the shape and intra-structure of the scattering particle. P(r) function has long been recognized as a smooth curve, and the oscillation at low distance is mainly due to unphysical truncation ripples in Fourier transformation.Recently, we have developed an effective method and succeeded in collecting high-quality SAXS and WAXS of protein solutions, showing negligible radiation damage (1) (2) (3). A high resolution pair-distance distribution function, P(r), of protein molecules has been obtained from the complete solution scattering curve made by combining accurate small-angle and wide-angle X-ray scattering data out to crystallographic resolution (2 A).Both indirect and direct Fourier transforms exhibit two distinct peaks at 1.4 A and 5.1 A in P(r). X-ray crystallographic data demonstrate that these peaks correspond to two intramolecular distances: the average bond length between C, N and O atoms and the pitch of an α-helix, respectively. Hence some high resolution aspects of the structure and function of a protein can be investigated in solution.Reference:1. X. Hong and Q. Hao. 2009. Measurements of accurate x-ray scattering data of protein solutions using small stationary sample cells. Review of Scientific Instruments 80:014303.2. X. Hong and Q. Hao. 2009. High resolution pair-distance distribution function P(r) of protein solutions. APPLIED PHYSICS LETTERS 94:083903-083903.3. X. Hong and Q. Hao. 2009. Combining solution wide-angle X-ray scattering and crystallography: determination of molecular envelope and heavy-atom sites. Journal of Applied Crystallography 42:259-264.

We describe an approach for acquiring high quality x-ray absorption fine structure (XAFS) spectroscopy spectra with wide energy range at high pressure using diamond anvil cell (DAC). Overcoming the serious interference of diamond Bragg peaks is essential for combining XAFS and DAC techniques in high pressure research, yet an effective method to obtain accurate XAFS spectrum free from DAC induced glitches has been lacking. It was found that these glitches, whose energy positions are very sensitive to the relative orientation between DAC and incident x-ray beam, can be effectively eliminated using an iterative algorithm based on repeated measurements over a small angular range of DAC orientation, e.g., within +/-3 degrees relative to the x-ray beam direction. Demonstration XAFS spectra are reported for rutile-type GeO2 recorded by traditional ambient pressure and high pressure DAC methods, showing similar quality at 440 eV above the absorption edge. Accurate XAFS spectra of GeO2 glass were obtained at high pressure up to 53 GPa, providing important insight into the structural polymorphism of GeO2 glass at high pressure. This method is expected be applicable for in situ XAFS measurements using a diamond anvil cell up to ultrahigh pressures.

Solving the phase problem remains central to crystallographic structure determination. A six-dimensional search method of molecular replacement (FSEARCH) can be used to locate a low-resolution molecular envelope determined from small-angle X-ray scattering (SAXS) within the crystallographic unit cell. This method has now been applied using the higher-resolution envelope provided by combining SAXS and WAXS (wide-angle X-ray scattering) data. The method was tested on horse hemoglobin, using the most probable model selected from a set of a dozen bead models constructed from SAXS/WAXS data using the program GASBOR at 5 Å resolution (q max = 1.25 Å -1) to phase a set of single-crystal diffraction data. It was found that inclusion of WAXS data is essential for correctly locating the molecular envelope in the crystal unit cell, as well as for locating heavy-atom sites. An anomalous difference map was calculated using phases out to 8 Å resolution from the correctly positioned envelope; four distinct peaks at the 3.2σ level were identified, which agree well with the four iron sites of the known structure (Protein Data Bank code 1ns9). In contrast, no peaks could be found close to the iron sites if the molecular envelope was constructed using the data from SAXS alone (q max = 0.25 Å -1). The initial phases can be used as a starting point for a variety of phase-extension techniques, successful application of which will result in complete phasing of a crystallographic data set and determination of the internal structure of a macromolecule to atomic resolution. It is anticipated that the combination of FSEARCH and WAXS techniques will facilitate the initial structure determination of proteins and provide a good foundation for further structure refinement. © International Union of Crystallography 2009., link_to_subscribed_fulltext

In this paper, we report a method of precise in situ x-ray scattering measurements on protein solutions using small stationary sample cells. Although reduction in the radiation damage induced by intense synchrotron radiation sources is indispensable for the correct interpretation of scattering data, there is still a lack of effective methods to overcome radiation-induced aggregation and extract scattering profiles free from chemical or structural damage. It is found that radiation-induced aggregation mainly begins on the surface of the sample cell and grows along the beam path; the diameter of the damaged region is comparable to the x-ray beam size. Radiation-induced aggregation can be effectively avoided by using a two-dimensional scan (2D mode), with an interval as small as 1.5 times the beam size, at low temperature (e.g., 4 °C). A radiation sensitive protein, bovine hemoglobin, was used to test the method. A standard deviation of less than 5% in the small angle region was observed from a series of nine spectra recorded in 2D mode, in contrast to the intensity variation seen using the conventional stationary technique, which can exceed 100%. Wide-angle x-ray scattering data were collected at a standard macromolecular diffraction station using the same data collection protocol and showed a good signal/noise ratio (better than the reported data on the same protein using a flow cell). The results indicate that this method is an effective approach for obtaining precise measurements of protein solution scattering. © 2009 American Institute of Physics., link_to_subscribed_fulltext