اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThermal Transfer in Amorphous Superionic Systems
101
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Using direct atomic simulations, the vibration scattering time scales are characterized, and then the nature and the quantitative weight of thermal excitations are investigated in an example system Li2S from its amorphous solid state to its partial-solid partial-liquid and, liquid states. For the amorphous solid state at 300 K, the vibration scattering time ranges a few femtoseconds to several picoseconds. As a result, both the progagons and diffusons are the main heat carriers and contribute largely to the total thermal conductivity. The enhancement of scattering among vibrations and between vibrations and free ions flow due to the increase of temperature, will lead to a large reduction of the scattering time scale and the acoustic vibrational thermal conductivity, i.e., 0.8 W/mK at 300 K to 0.56 W/mK in the partial solid partial liquid Li2S at 700 K. In this latter state, the thermal conductivity contributed by convection increases to the half of the total, as a result of the usually neglected cross-correlation between the virial term and the free ions flow. The vibrational scattering time can be as large as ~ 1.5 picoseconds yet, and the vibrational conductivity is reduced to a still significant 0.42 W/mK highlighting the unexpected role of acoustic transverse and longitudinal vibrations in liquid Li2S at 1100 K. At this same temperature, the convection heat transfer takes overreaching 0.63 W/mK. Our study provides a fundamental understanding of the thermal excitations at play in amorphous materials from solid to liquid.
قيم البحث
اقرأ أيضاً
Quantifying the correlation between the complex structures of amorphous materials and their physical properties has been a long-standing problem in materials science. In amorphous Si, a representative covalent amorphous solid, the presence of a mediu
m-range order (MRO) has been intensively discussed. However, the specific atomic arrangement corresponding to the MRO and its relationship with physical properties, such as thermal conductivity, remain elusive. Here, we solve this problem by combining topological data analysis, machine learning, and molecular dynamics simulations. By using persistent homology, we constructed a topological descriptor that can predict the thermal conductivity. Moreover, from the inverse analysis of the descriptor, we determined the typical ring features that correlated with both the thermal conductivity and MRO. The results provide an avenue for controlling the material characteristics through the topology of nanostructures.
Superionic hydrogen was previously thought to be an exotic state predicted and confirmed only in pure H2O ice. In Earths deep interior, H2O exists in the form of O-H groups in ultra-dense hydrous minerals, which have been proved to be stable even at
the conditions of the core-mantle boundary (CMB). However, the superionic states of these hydrous minerals at high P-T have not been investigated. Using first-principles calculations, we found that pyrite structured FeO2Hx (0 <= x <= 1) and d-AlOOH, which have been proposed to be major hydrogen-bearing phases in the deep lower mantle (DLM), contain superionic hydrogen at high P-T conditions. Our observations indicate a universal pathway of the hydroxyl O-H at low pressure transforming to symmetrical O-H-O bonding at high-P low-T, and a superionic state at high-P high-T. The superionicity of hydrous minerals has a major impact on the electrical conductivity and hydrogen transportation behaviors of Earths lower mantle as well as the CMB.
Water is abundant in natural environments but the form it resides in planetary interiors remains uncertain. We report combined synchrotron X-ray diffraction and optical spectroscopy measurements of H2O in the laser-heated diamond anvil cell up to 150
gigapascals (GPa) and 6500 kelvin (K) that reveal first-order transitions to ices with body-centered cubic (bcc) and face-centered cubic (fcc) oxygen lattices above 900 (1300) K and 20 (29) GPa, respectively. We assigned these structures to theoretically predicted superionic phases based on the distinct density, increased optical conductivity, and greatly decreased enthalpies of fusion. Our measurements address current discrepancies between theoretical predictions and various static/dynamic experiments on the existence and location of melting curve and superionic phase(s) in the pressure-temperature phase diagram indicating a possible presence of the conducting fcc-superionic phase in water-rich giant planets, such as Neptune and Uranus.
The magnetization processes in binary magnetic/nonmagnetic amorphous alloy Hf_{57}Fe_{43} are investigated by the detailed measurements of magnetic hysteresis loops, temperature dependence of magnetization, relaxation of magnetization and magnetic ac
susceptibility, including a nonlinear term. Blocking of magnetic moments at lower temperatures is accompanied with the slow relaxation of magnetization and magnetic hysteresis loops. All of the observed properties are explained with the superparamagnetic behaviour of the single domain magnetic clusters inside the nonmagnetic host, their blocking by the anisotropy barriers and thermal fluctuation over the barriers accompanied by relaxation of magnetization. From magnetic viscosity analysis based on thermal relaxation over the anisotropy barriers it is found out that magnetic clusters occupy the characteristic volume from 25 up to 200 nm3 . The validity of the superparamagnetic model of Hf_{57}Fe_{43} is based on the concentration of iron in the Hf_{100-x}Fe_{43} system that is just below the threshold for the long range magnetic ordering. This work throws more light on magnetic behaviour of other amorphous alloys, too.
We present an extensive numerical study of dynamical heterogeneities and their influence on diffusion in an athermal mesoscopic model for actively deformed amorphous solids. At low strain rates the stress dynamics are governed by cooperative regions
of plastic events. On the basis of scaling arguments as well as an extensive numerical study of an athermal elasto-plastic model, we show that there is a direct link between the self-diffusion coefficient and the size of cooperative regions at low strain rates. Both depend strongly on rate and on system size. A measure of the mean square displacement of passive tracers in deformed amorphous media thus gives information about the microscopic rheology, such as the geometry of the cooperative regions and their scaling with strain rate and system size.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
