RESUMEN
Liquid polymorphism is an intriguing phenomenon that has been found in a few single-component systems, the most famous being water. By supercooling liquid Te to more than 130 K below its melting point and performing simultaneous small-angle and wide-angle X-ray scattering measurements, we observe clear maxima in its thermodynamic response functions around 615 K, suggesting the possible existence of liquid polymorphism. A close look at the underlying structural evolution shows the development of intermediate-range order upon cooling, most strongly around the thermodynamic maxima, which we attribute to bond-orientational ordering. The striking similarities between our results and those of water, despite the lack of hydrogen-bonding and tetrahedrality in Te, indicate that water-like anomalies may be a general phenomenon among liquid systems with competing bond- and density-ordering.
RESUMEN
A pressure-induced structural change of a polymer isotactic poly(4-methyl-1-pentene) (P4MP1) in the melted state at 270 °C has been investigated by high-pressure in situ x-ray diffraction, where high pressures up to 1.8 kbar were applied using helium gas. The first sharp diffraction peak (FSDP) position of the melt shows a less pressure dependence than that of the normal compression using a solid pressure transmitting medium. The contraction using helium gas was about 10% at 2 kbar, smaller than about 20% at the same pressure using a solid medium. The result indicates that helium entered the interstitial space between the main chains. The helium/monomer molar ratio was estimated to be 0.3 at 2 kbar from the FSDP positions. These results suggest that the compressibility of the P4MP1 melt can be largely dependent on the pressure transmitting media. As the pore size is reversibly and continuously controllable by compression, we suggest that the P4MP1 melt can be an ideal porous liquid for investigating a novel mechanical response of the pores in a non-crystalline substance.
RESUMEN
We performed small-angle x-ray scattering measurements of liquid Te using a synchrotron radiation facility and observed maximum scattering intensity near 620 K in the supercooled region (melting temperature 723 K). This indicates that density inhomogeneity exists in liquid Te, and the fact that this temperature coincides with the temperature at which the specific heat, sound velocity, and thermal expansion coefficient reach their maxima means that this density inhomogeneity is the cause of these thermodynamic anomalies. The thermodynamic anomalies in liquid Te had already been shown in the 1980s to be comprehensively explained by the inhomogeneity associated with the continuous liquid-liquid phase transition (LLT), but direct experimental evidence for the existence of the inhomogeneity had not been obtained. The present results, together with those already obtained for mixture systems (Te-Se, Te-Ge), indicate the existence of inhomogeneity associated with LLT in liquid Te systems, and strongly support the model. Recently, similar maximum scattering intensity has also been observed in supercooled liquid water, which exhibits thermodynamic anomalies similar to those of Te, indicating the universality of the inhomogeneous model or LLT scenario to explain the thermodynamics of such 'anomalous liquids'. Further development of the LLT scenario is expected in near future.
RESUMEN
Inelastic x-ray scattering (IXS) measurements were performed for observing the excitation of bulk plasmons in metallic liquid silicon (Si). The peak due to plasmon excitation was observed within the energy loss around 17 eV. Combined with IXS data of crystalline Si measured at several elevated temperatures, it was found that temperature dependence of the excitation energy in the crystalline solid state is explained by the electron gas including the band gap effect, whereas in the metallic liquid state near the melting point, it exhibits a departure from the electron gas; the plasmon energy takes a lower value than that of the electron gas. Such lowering of plasmon energies is reasonably explained by a model incorporating semiconducting component to the electron gas. Non-simple metallic nature in liquid silicon is highlighted by the observation of electron collective dynamics.
RESUMEN
The dynamic structure factorS(Q,E), whereQandEare momentum and energy transfer, respectively, has been measured for liquid Eu8Ga16Ge30(EGG), using inelastic x-ray scattering. The excitation energy of the longitudinal acoustic mode in the liquid was scaled to that in liquid Ba8Ga16Sn30(BGS) with the effective mass. This result means that the local structure in both liquids are similar. The longitudinal acoustic excitation energy of type-I clathrate compound EGG disperses faster than that in the liquid, suggesting that the interatomic force is weakened on melting. The lower energy excitation was observed in both liquid EGG and liquid BGS. In comparison with the longitudinal phonon dispersion in crystalline clathrate compound EGG obtained by density functional theory-based calculations, the lower energy in the liquid was found to be near the optical mode energy. The result indicates that the lower energy mode arises from the relative motion between Eu and (Ga, Ge) atoms.
RESUMEN
X-ray scattering measurements of an expanded liquid Se(80)Te(20) mixture in the temperature range between 300 and 1000 °C and at pressures of 10, 200, and 1600 bar have been carried out. The reverse Monte Carlo simulation and Voronoi-Delaunay void analyses have been applied to clarify the relationship between the voids and chain geometries in the intermediate scale near the semiconductor to metal (SC-M) transition at 800 °C under 200 bar accompanied by a shrinkage of molar volume. The structure of the liquid mixture can be envisaged in terms of a packing of covalently bonded chains and interstitial voids. The thermal expansion leads to a decrease in the number of chains around a chain and is compensated for by empty spaces (voids). The packing density of helical chains decreases and so voids supported by chains increase with rising temperature. At high temperature the shortening of chains and frequent transfer of lone pair electrons on Se (or Te) atoms cause modification of the helical chain to ring and zigzag chain conformations. The stacking of zigzag chains, joined to layers above 800 °C, leads to the formation of metallic domains separated by voids. The shrinkage of molar volume near the SC-M transition arises through the progressive filling of the voids around chains with (Se, Te)(5, 6, 7, 8) rings.