Partitioning experiments and the chemistry of iron meteorites indicate that the light element nitrogen could be sequestered into the metallic core of rocky planets during core–mantle differentiation. The thermal conductivity and the mineralogy of the Fe–N system under core conditions could therefore influence the planetary cooling, core crystallization, and evolution of the intrinsic magnetic field of rocky planets. Limited experiments have been conducted to study the thermal properties and phase relations of Fe–N components under planetary core conditions, such as those found in the Moon, Mercury, and Ganymede. In this study, we report results from high-pressure experiments involving electrical resistivity measurements of Fe–N phases at a pressure of 5 GPa and temperatures up to 1400 K. Four Fe–N compositions, including Fe–10%N, Fe–6.4%N, Fe–2%N, and Fe–1%N (by weight percent), were prepared and subjected to recovery experiments at 5 GPa and 1273 K. These experiments show that Fe–10%N and Fe–6.4%N form a single hexagonal close-packed phase (ɛ-nitrides), while Fe–2%N and Fe–1%N exhibit a face-centered cubic structure (γ-Fe). In separate experiments, the resistivity data were collected during the cooling after compressing the starting materials to 5 GPa and heating to ~1400 K. The resistivity of all compositions, similar to the pure γ-Fe, exhibits weak temperature dependence. We found that N has a strong effect on the resistivity of metallic Fe under rocky planetary core conditions compared to other potential light elements such as Si. The temperature-dependence of the resistivity also revealed high-pressure phase transition points in the Fe–N system. A congruent reaction, ε ⇌ γ’, occurs at ~673 K in Fe–6.4%N, which is ~280 K lower than that at ambient pressure. Furthermore, the resistivity data provided constraints on the high-pressure phase boundary of the polymorphic transition, γ ⇌ α, and an eutectoid equilibrium of γ’ ⇌ α + ε. The data, along with the recently reported phase equilibrium experiments at high pressures, enable construction of a phase diagram of the Fe–N binary system at 5 GPa.

On the basis of the van der Pauw method, we developed a new technique for measuring the electrical resistivity of metals in a cubic multi-anvil high-pressure apparatus. Four electrode wires were introduced into the sample chamber and in contact with the pre-pressed metal disk on the periphery. The sample temperature was measured with a NiCr-NiSi (K-type) thermocouple, which was separated from the sample by a thin hexagonal boron nitride layer. The electrodes and thermocouple were electrically insulated from each other and from the heater by an alumina tube as well. Their leads were in connection with cables through the gap between the tungsten carbide anvils. We performed experiments to determine the temperature dependence of electrical resistivity of pure iron at 3 and 5 GPa. The experiments produce reproducible measurements and the results provide an independent check on electrical resistivity data produced by other methods. The new technique provides reliable electrical resistivity measurements of metallic alloys and compounds at high pressure and temperature.

本文将单摆法与电磁感应原理相结合,用永磁球体作为摆球,并且在其正下方放置多匝线圈.当摆球做简谐运动时,线圈内部磁通量对应地发生周期性变化,从而产生周期性的感应电动势.使用滤波器模块过滤噪声,并利用示波器采集周期性信号.通过判读电动势信号即可准确获取单摆的周期信息.进一步通过改变摆球和线圈之间的相对高度衡量电磁阻尼对于测量的影响,发现测量的周期与相对高度无关,说明电磁阻尼是可以忽略的,这与半定量分析结果是一致的.本文测量的重力加速度实验值与本地参考值有很好的一致性.

High-pressure and high-temperature (HPHT) synthesis provides an effective way to tune the band structure of materials and improve their electronic properties. To investigate the influence of synthesis pressure on electronic properties, Mg1.97Al0.03Si samples were synthesized using the HPHT method. The maximum effective mass 0.92m(e) is obtained for the sample prepared with the synthesis pressure of 3 GPa, leading to the biggest Seebeck coefficient -201.3 mu V/K at room temperature. Meanwhile, the 3 GPa sample obtains the higher electron carrier concentration and electrical conductivity, resulting in nearly overall enhancement of power factor. The Density Functional Theory (DFT) calculations evidences that the Conduction Bands Minimum (CBM) can be tuned effectively by applied pressure and the convergence of the CBM leads to a larger effective mass of DOS, which are beneficial to the enhancement of power factors. These results indicate that high-pressure is a powerful tool to tune Mg1.97Al0.03Si band structures. (c) 2019 The Chinese Ceramic Society. Production and hosting by Elsevier B.V.

Understanding the effect of carbon on the density of hcp (hexagonal-close-packed) Fe-C alloys is essential for modeling the carbon content in the Earth’s inner core. Previous studies have focused on the equations of state of iron carbides that may not be applicable to the solid inner core that may incorporate carbon as dissolved carbon in metallic iron. Carbon substitution in hcp-Fe and its effect on the density have never been experimentally studied. We investigated the compression behavior of Fe-C alloys with 0.31 and 1.37 wt % carbon, along with pure iron as a reference, by in-situ X-ray diffraction measurements up to 135 GPa for pure Fe, and 87 GPa for Fe-0.31C and 109 GPa for Fe-1.37C. The results show that the incorporation of carbon in hcp-Fe leads to the expansion of the lattice, contrary to the known effect in body-centered cubic (bcc)-Fe, suggesting a change in the substitution mechanism or local environment. The data on axial compressibility suggest that increasing carbon content could enhance seismic anisotropy in the Earth’s inner core. The new thermoelastic parameters allow us to develop a thermoelastic model to estimate the carbon content in the inner core when carbon is incorporated as dissolved carbon hcp-Fe. The required carbon contents to explain the density deficit of Earth’s inner core are 1.30 and 0.43 wt % at inner core boundary temperatures of 5000 K and 7000 K, respectively.

We conducted shock wave experiments on iron carbide Fe3C up to a Hugoniot pressure of 245 GPa. The correlation between the particle velocity (u(p)) and shock wave velocity (u(s)) can be fitted into a linear relationship, u(s) = 4.627(+/- 0.073) + 1.614(+/- 0.028) u(p). The density-pressure relationship is consistent with a single-phase compression without decomposition. The inference is further supported by the comparison of the observed Hugoniot density with the calculated Hugoniot curves of possible decomposition products. The new Hugoniot data combined with the reported 300-K isothermal compression data yielded a Gruneisen parameter of gamma = 2.23(7.982/rho)(0.29). The thermal equation of state of Fe3C is further used to calculate the density profile of Fe3C along the Earth's adiabatic geotherm. The density of Fe3C was found to be too low (by similar to 5%) to match the observed density in the Earth's inner core, and Fe3C is unlikely a dominant component of the inner core.

We report Hugoniot measurements on a mixture of cubic boron nitride (cBN) and hexagonal boron nitride (hBN, ∼10% in weight) to investigate the shock compression behavior of BN at Hugoniot stresses up to 110 GPa. We observed a discontinuity at ∼77 GPa along the Hugoniot and interpreted it as the manifestation of the shock-induced phase transition of hBN to cBN. The experimental stress at 77–110 GPa shows significant deviation from the hydrodynamic Hugoniot of cBN calculated using the Mie-Grüneisen model coupled with the reported 300 K-isotherms of cBN. Our investigation reveals that material strength in cBN increases with the experimental stress at least up to 110 GPa. The material strength might be preserved at higher stress if we consider the previously reported high stress data.

The excellent thermal and chemical properties of cubic boron nitride (cBN) indicate that it is potential materials to prepare the thermal dissipate substrate applied in the electronic packaging. The thermal properties of polycrystalline cBN ceramics, however, have not been fully investigated. We report the first sintering experiment on preparing polycrystalline cBN ceramics using cBN powder as starting material without any sintering aids. The microstructure and high bending strength show that the strong combination was achieved among the crystal grains. The measured results, including density, thermal conductivity and thermal expansion coefficient, reveal that the properties of this ceramics depend on the grain size of starting crystal cBN. The PcBN ceramics has low thermal expansion coefficient extremely matching to that of silicon and exhibits moderate thermal conductivity due to its low density and the existence of low thermal conductive phase of hexagonal boron nitride.

Using a two-stage light gas gun and FPGWI (flier-plates with graded wave impedance),the free surface velocities of 93 tungsten alloy (93W)were measured at the impact velocities of 2.12 km/s and 5.02 km/s respectively and the experimental data were analyzed based on the shock wave theory. The results show that at a low impact velocity the pressures and temperatures of 93W alloy after repeated shock compression are higher than those after a single shock compression,and that at a high impact velocity the reverse is true.The phenomenon is results from the change of the Hugoniot parameters and the volume stress after multiple compressions.

Mg2Si0.995Sb0.005 compound was prepared by the high-pressure high-temperature (HPHT) method. The simultaneous synthesis and consolidation in one step could be completed in <15 min. The effects of pressure and temperature on the thermoelectric properties of Mg2Si0.995Sb0.005 were analyzed in this work. With the pressure and temperature increasing, the electrical conductivity rises markedly, while the Seebeck coefficient changes slightly, which results in significant enhancement of the power factor. The Mg2Si0.995Sb0.005 sample prepared under the condition of 1073 K and 2 GPa achieves the highest power factor of ∼2.12 × 10−3 W m−1 K−2 at 575 K. As the sample prepared at 973 K and 2 GPa retains a lower thermal conductivity, it obtains the highest thermoelectric figure-of-merit ZT ∼0.62 at 800 K. In conclusion, the HPHT method can serve as a route to prepare Sb-doped Mg2Si thermoelectric materials efficiently.

Investigation of crystal structure, dielectric, magnetic and local ferroelectric properties of the diamagnetically substituted (1-x)BiFeO3-xBi (Ti0.5Ni0.5)O3 solid solutions samples have been carried out. The solid solutions have been found to possess a rhombohedrally distorted perovskite structure described by the space group R3c. Compared with pure BiFeO3 compound, both ferroelectric and magnetic properties are much improved by solid solution with Bi (Ti0.5Ni0.5)O3 with saturation hysteresis loops observed. Among all the samples, the x=0.1 samples shows the optimal ferromagnetism with Mr~0.56531emμ/g and the optimal ferroelectricity with Pr~5.767μC/cm2 at room temperature.

Multiferroic properties and exchange bias (EB) in Bi1-xSrxFeO3 (x = 0-0.6) ceramics synthesized by a modified Pechini method are investigated. Sr concentration dependence of structure distorting, ferroelectric properties, and dielectric properties were studied at room temperature. Appropriate Sr doping (x = 0.05-0.2) has been found to decrease the conductivity, enhance ferroelectric properties and give rise to high dielectric constant. Compared with antiferromagnetic BiFeO3 compound, BSFO-x (0 <= x <= 0.4) ceramics show weak ferromagnetism at room temperature, and their exchange bias field and vertical magnetization shift are observed and exhibit a strong dependence on the content of Sr. This observed EB effect which keeps stable in BSFO ceramics at 10 K tend to vanish at room temperature with Sr concentration over 0.4.

Using a two‐stage light gas gun, we obtained new shock wave Hugoniot data for an iron‐sulfur alloy (Fe‐11.8wt%S) over the pressure range of 94–204 GPa. A least‐squares fit to the Hugoniot data yields a linear relationship between shock velocity DS and particle velocity u, DS (km/s) =3.60(0.14) +1.57(0.05) u. The measured Hugoniot data for Fe‐11.8wt%S agree well with the calculated results based on the thermodynamic parameters of Fe and FeS using the additive law. By comparing the calculated densities along the adiabatic core temperature with the PREM density profile, an iron core with 10 wt.% sulfur (S) provides the best solution for the composition of the Earth's outer core.

Reduced circumstances in Earth's core Earth's liquid outer core consists mainly of liquid iron alloyed with about 10% (by weight) of light elements. Oxygen has been proposed as a major light element in the core, based on cosmochemical arguments and chemical reactions during accretion, but here Huang et al . report data that virtually rule out oxygen as a major light element in the liquid outer core. They compare density and sound-velocity measurements in shock-wave experiments in the Fe–S–O system of Earth's core with geophysical observations. Their findings are consistent with an oxygen-depleted core, and a reduced environment during early Earth accretion, with important implications for early Earth accretion models.

Shock compressed to pressures from 106 GPa to 232 GPa, the sound velocities were determined in Fe‐O‐S (90/8/2 in wt. %), regarded as the candidate compositions of the Earth's outer core. A discontinuity in sound velocity versus pressure relation was observed, which indicated that the shocked sample is initially melted at 149 GPa and completely melted at 167 GPa. On the basis of an energy conservation formulation, the calculated equilibrium melting temperature is about 3880 ± 500 K at 167 GPa. Taking this point as a reference, a high‐pressure melting curve can be inferred through Lindemann Law, which is again confirmed by the release melting temperatures of 3020 ± 500 K and 3200 ± 500 K measured at 90 GPa and 106 GPa, respectively. When extrapolating this melting curve to inner core‐outer core boundary (330 GPa), the melting temperature of this Fe‐O‐S composition is about 5400 ± 500K. Compared with the melting temperature 6000 K for pure iron at 330 GPa, the corresponding melting temperature depression is about 600 K due to the effect of O and S.

针对静压法人工合成纳米金刚石面临着过高的压力和温度,其合成条件在国产六面顶金刚石压机上很难实现的问题,介绍了纳米金刚石的特殊性能和应用状况,概述了纳米金刚石的几种主要合成方法,在此基础上分析了合成过程中影响金刚石成核以及颗粒粒径的因素,提出了静压法制备纳米金刚石的可行性.