New materials from high pressure experiments: Challenges and opportunities

Recent improvements in high pressure techniques have led to new scientific discoveries in fields ranging from Earth and Planetary Science, to fundamental physics and biology. Here we examine the possibilities for development of new technologically-important materials based on high pressure research.     

On the structure of alkali halide solutions

Summary The structure factors of NaI solutions have been determined by employing both neutron and X-ray scattering. The results have been analysed in terms of the structure of hydration spheres of both Na⁺ and I⁻ ions. No concentration or temperature dependences of the size of the hydration shells have been evidentiated in the present experiment, while the structure of the free water appears to be affected, at least at small distances.

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Riassunto I fattori di struttura delle soluzioni acquose di NaI sono stati misurati impiegando la diffrazione di raggi X e neutroni. I risultati sono stati analizzati per caratterizzare le sfere di idratazione degli ioni Na⁺ ed I⁻. Nessuna dipendenza dalla temperatura o concentrazione è stata evidenziata per le sfere di idratazione, mentre alle piccole distanze si osservano effetti della concentrazione sulla sutruttura dell'acqua libera.

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Резюме Используя дифракцию нейтронов и рентгеновских лучей, определяются структурные факторы растворов NaI. Полученные результаты анализируются в терминах структуры сферы гидратации ионов Na⁺ и I⁻. В проведенных экспериментах не обнаружено зависимостей от концентрации или темиературы для сферы гидратации, тогда как, по крайней мере, на малых расстояниях обнаружено влияние концентрации на структуру свободной воды.

     

Near-Infrared spectral study of aqueous solutions of ethyl alcohol

Summary The 1450 nm band of water, usually assigned tov ₁+v ₃(v ₁ is the symmetric stretching andv ₃ the asymmetric stretching mode of water molecules), has been measured in aqueous ethanol solutions as a function of alcohol concentration at 25°C. A simple analysis of these spectra illustrates the qualitative similarity between the effects of ethanol and those of a temperature decrement on the spectrum of water. The results are compared with other physicochemical measurements available for these mixtures and, on the whole, support the hypothesis that at low concentrations the added ethanol enhances water-water interactions so that the liquid structure resembles an alcohol clathrate of type II of composition ethanol-17H₂O. To speed up publication, the author of this paper has agreed to not receive the proofs for correction.     

Goethe's Science: An Approach to Research in American Indian Studies

In The Wholeness of Nature (1996), Henri Bortoft shows how a Goethean science of qualitative wholeness complements the analytic and causal- explanatory framework that underlies most research in the natural and social sciences. Goethe's insights and methods suggest that a better understanding of Indian tribes may occur when a tribe is regarded as its own abstraction and its own explanation. In Goethe's approach to science, the human mind is an organ of perception and researchers are active participants in the way they see the world. Consider an Indian tribe and the goal of Goethean science is to intuitively see patterns of interpenetrating relationships in a dynamic process of self-organization that is the tribe. While analytic science and Goethe's science of wholeness are incommensurable, both are true, and neither is comprehensive.     

First principles study of structural,magnetic and electronic properties of half-metallic CrO<Subscript>2</Subscript> under pressure

A first-principles tight-binding linear muffin tin orbital (TB-LMTO) method within the local-density approximation is used to calculate the total energy, lattice parameter, bulk modulus, magnetic moment, density of states and energy band structures of half-metallic CrO₂ at ambient as well as at high pressure. The magnetic and structural stabilities are determined from the total energy calculations. From the present study we predict a magnetic transition from ferromagnetic (FM) state to a non-magnetic (NM) state at 65 GPa, which is of second order in nature. We also observe from our calculations that CrO₂ is more stable in tetragonal phase (rutile-type) at ambient conditions and undergoes a transition to an orthorhombic structure (CaCl₂-type) at 9.6 GPa, which is in good agreement with the experimental results. We predict a second structural phase transition from CaCl₂- to fluorite-type structure at 89.6 GPa with a volume collapse of 7.3%, which is yet to be confirmed experimentally. Interestingly, CrO₂ shows half metallicity under ambient conditions. After the first structural phase transition from tetragonal to orthorhombic, half metallicity has been retained in CrO₂ and it vanishes at a pressure of 41.6 GPa. Ferromagnetism is quenched at a pressure of 65 GPa.     

Structural and magnetic properties of polymerized C<Subscript>60</Subscript> with Fe

We provide evidence that high-pressure high-temperature (2.5 GPa and 1040 K) treatment of mixtures of iron with fullerene powders leads to the complete transformation of iron into iron carbide Fe₃C. The comparison of the magnetic properties (Curie temperature and magnetic moment) of the here studied samples and those for the ferromagnetic polymer Rh-C₆₀ indicates that the main ferromagnetic signal reported in those samples is due to Fe₃C and not related to the ferromagnetism of carbon as originally interpreted. Taking into account the results obtained in this study the original paper on “Magnetic carbon" [Nature 413, 716 (2001)] was recently retracted.     

阴离子型层柱材料研究进展

介绍了阴离子型层柱材料（ＬＤＨｓ）的结构、性能、制备方法和应用。ＬＤＨｓ是一类具有酸性、生篱子交换性能的层柱材料。它可以用作催化剂、催化剂载体、离子交换剂、吸附剂等,在医药上用作为抗酸药,在功能高分子材料添加剂方面可以用作红外吸收材料、紫外吸收和阻隔材料、结构完整性无机分散相、新型杀菌材料、聚氯乙烯稳定剂等。     

Glass like magnetic alternating field susceptibility behavior of structurally frozen ferrofluids

Four ferrofluids, distinct in size distribution and aggregate structure, were investigated. The relaxation time ,related to the temperature of susceptibility maximum, was fitted to a Vogel-Fulcher law. A mean ordering temperature, T₀, was calculated using magnetic particle parameters derived from the structure. It is assumed that at T₀ the particle moments of particle clusters correlate, leading to a spin glass-like transition. Hence, then dynamic slows down considerably, as indicated by a strong broadening of relaxation-time distribution. T₀ roughly agrees with the energy of competing interaction between particle moments, as calculated from the structure of particle aggregates. Differences between particle arrangements clearly influence the dispersion and absorption, particularly within the cluster phase. Received 15 July 1998     

Theoretical Studies of PCl3/H2 Gas Chromatography Mechanism

Density functional theory B3LYP method was firstly applied to fully optimize the geometrical configuration of each stable point on PCl3/H2 gas chromatography reaction potential energy surface on the 6-311G** basis set, and single point energy was computed at the QCISD(T)/ 6-311G** level, then the transition state was validated by analyzing the unique imaginary vibration modes of each transition state and calculating intrinsic reaction coordinate (IRC), and the major reaction and competing reaction paths of PCl3/H2 gas chromatography reaction were presented through comparing active energy barrier, and phosphor was finally gained from the reaction of PH and PCl.     

Synthesis and Study of the Thermal Epimerization of r -2-Ethoxy- cis -4- cis -5-Dimethyl-1,3,2-λ 3 -Dioxaphospholane Using 31 P NMR

The exclusive synthesis of r -2-ethoxy- cis -4- cis -5-dimethyl-1,3,2- u 3 -dioxaphospholane ( cis - 1 ) is reported. The kinetic measurements of the epimerization of cis - 1 to trans - 1 were performed by 31 P NMR from 50 to 80;C in toluene. The energy of activation (E a ) of the epimerization process was calculated from Arrhenius plot. The thermodynamic parameters of the transition state led us to conclude that the activation barrier of the inversion at phosphorus is driven by the enthalpy and by a large and negative entropy of activation.