Daniel N. Blaschke, John S. Carpenter, Abigail Hunter
Generating high magnetic fields requires materials with not only high electric conductivity, but also good strength properties in order to withstand the necessarily strong Lorentz forces. A number of bi-metal composites, most notably Cu/Nb, are considered to be good candidates for this purpose. Here, we generalize our previous work on Cu/Nb in order to predict, from theory, the dependence of electric conductivity on the microstructure and volume fraction of the less conductive component for a number of other bi-metal composites. Together with information on strength properties (taken from previous literature), the conductivity information we provide in this work can help to identify new promising candidate materials for magnet applications with the highest achievable field strengths.
{"title":"Predicting electrical conductivity in bi-metal composites","authors":"Daniel N. Blaschke, John S. Carpenter, Abigail Hunter","doi":"arxiv-2409.04655","DOIUrl":"https://doi.org/arxiv-2409.04655","url":null,"abstract":"Generating high magnetic fields requires materials with not only high\u0000electric conductivity, but also good strength properties in order to withstand\u0000the necessarily strong Lorentz forces. A number of bi-metal composites, most\u0000notably Cu/Nb, are considered to be good candidates for this purpose. Here, we\u0000generalize our previous work on Cu/Nb in order to predict, from theory, the\u0000dependence of electric conductivity on the microstructure and volume fraction\u0000of the less conductive component for a number of other bi-metal composites.\u0000Together with information on strength properties (taken from previous\u0000literature), the conductivity information we provide in this work can help to\u0000identify new promising candidate materials for magnet applications with the\u0000highest achievable field strengths.","PeriodicalId":501234,"journal":{"name":"arXiv - PHYS - Materials Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142224528","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jonathan S. Paras, Randy D. Curry, James A. Ohlhausen, Michael J. Abere
Continuous Wave Laser Beam (LB) melting offers control over the localized heating and cooling of melt pools for welding, brazing, additive manufacturing, and solidification. Research into laser-liquid metal interactions have primarily focused on the heat and mass transport under large thermal gradients imposed by the localized melting conditions. However, little research has been conducted into varying input laser frequency and scan rate at fixed absorption to understand the effects of laser-light on surface oxide formation. This article conducts laser melting of 304L under Blue (450 nm) and Infrared (IR, 1064 nm) laser frequencies and examines their impact on laser oxide thickness, chemistry, and coloration. We find that laser frequencies induce changes in the oxide layer thickness and chemistry that cannot be explained using conventional thermal absorption shifts and fluid dynamics. We suggest that light coupling may have thermodynamic implications for the chemical potential of the liquid metal which may drive the observed phase behavior.
{"title":"The Effect of Blue and Infrared Laser Melting Frequency on Oxide Morphology in 304L","authors":"Jonathan S. Paras, Randy D. Curry, James A. Ohlhausen, Michael J. Abere","doi":"arxiv-2408.05144","DOIUrl":"https://doi.org/arxiv-2408.05144","url":null,"abstract":"Continuous Wave Laser Beam (LB) melting offers control over the localized\u0000heating and cooling of melt pools for welding, brazing, additive manufacturing,\u0000and solidification. Research into laser-liquid metal interactions have\u0000primarily focused on the heat and mass transport under large thermal gradients\u0000imposed by the localized melting conditions. However, little research has been\u0000conducted into varying input laser frequency and scan rate at fixed absorption\u0000to understand the effects of laser-light on surface oxide formation. This\u0000article conducts laser melting of 304L under Blue (450 nm) and Infrared (IR,\u00001064 nm) laser frequencies and examines their impact on laser oxide thickness,\u0000chemistry, and coloration. We find that laser frequencies induce changes in the\u0000oxide layer thickness and chemistry that cannot be explained using conventional\u0000thermal absorption shifts and fluid dynamics. We suggest that light coupling\u0000may have thermodynamic implications for the chemical potential of the liquid\u0000metal which may drive the observed phase behavior.","PeriodicalId":501234,"journal":{"name":"arXiv - PHYS - Materials Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141948607","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shishir Mundra, Emanuele Rossi, Luka Malenica, Mohit Pundir, Ueli M. Angst
Macroscopic voids at the steel-concrete interface and their degree of saturation with an aqueous electrolyte are known to play an important role in the corrosion of steel in reinforced concrete. Irrespective of the exposure conditions and testing parameters, corrosion products have been reported to consistently precipitate in a unique pattern within these macroscopic voids, preferentially along the void walls and growing inward. The underlying mechanisms governing corrosion product precipitation in macroscopic voids and their effects on long-term durability remain unclear. Through in-situ X-ray computed tomography observations, thermodynamic and kinetic considerations, and numerical modelling of water transport within macroscopic voids, here, we provide plausible hypotheses of the processes responsible for the precipitation of corrosion products along the walls of the voids. Understanding the mechanisms of corrosion product precipitation can offer insights into the development of stresses in and around the macroscopic interfacial void and the durability of reinforced concrete structures. This contribution also discusses opportunities for different avenues for research to elucidate several multiscale processes that influence the durability of reinforced concrete.
众所周知，钢筋混凝土界面上的宏观空隙及其与水性电解质的饱和度对钢筋混凝土中的钢筋锈蚀起着重要作用。据报道，无论暴露条件和测试参数如何，腐蚀产物都会以一种独特的模式在这些宏观空隙中持续析出，并优先沿着空隙壁向内生长。宏观空隙中析出腐蚀产物的基本机制及其对长期耐久性的影响仍不清楚。通过原位 X 射线计算机断层扫描观测、热力学和动力学考虑以及宏观空隙内水传输的数值模拟，我们在此对腐蚀产物沿空隙壁析出的过程提出了合理的假设。了解腐蚀产物析出的机理有助于深入了解宏观界面空隙内部和周围的应力发展以及钢筋混凝土结构的耐久性。本文还讨论了不同研究途径的机会，以阐明影响钢筋混凝土耐久性的多个多尺度过程。
{"title":"Precipitation of corrosion products in macroscopic voids at the steel-concrete interface -- observations, mechanisms and research needs","authors":"Shishir Mundra, Emanuele Rossi, Luka Malenica, Mohit Pundir, Ueli M. Angst","doi":"arxiv-2408.05028","DOIUrl":"https://doi.org/arxiv-2408.05028","url":null,"abstract":"Macroscopic voids at the steel-concrete interface and their degree of\u0000saturation with an aqueous electrolyte are known to play an important role in\u0000the corrosion of steel in reinforced concrete. Irrespective of the exposure\u0000conditions and testing parameters, corrosion products have been reported to\u0000consistently precipitate in a unique pattern within these macroscopic voids,\u0000preferentially along the void walls and growing inward. The underlying\u0000mechanisms governing corrosion product precipitation in macroscopic voids and\u0000their effects on long-term durability remain unclear. Through in-situ X-ray\u0000computed tomography observations, thermodynamic and kinetic considerations, and\u0000numerical modelling of water transport within macroscopic voids, here, we\u0000provide plausible hypotheses of the processes responsible for the precipitation\u0000of corrosion products along the walls of the voids. Understanding the\u0000mechanisms of corrosion product precipitation can offer insights into the\u0000development of stresses in and around the macroscopic interfacial void and the\u0000durability of reinforced concrete structures. This contribution also discusses\u0000opportunities for different avenues for research to elucidate several\u0000multiscale processes that influence the durability of reinforced concrete.","PeriodicalId":501234,"journal":{"name":"arXiv - PHYS - Materials Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141948605","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Flexoelectricity refers to a linear coupling between the electric polarization and the strain gradient, such as bending or asymmetric compression. This effect is enhanced in nano-scale structures, where grain boundaries or dislocation cores induce the strain gradient. In this study, we theoretically investigate the flexoelectric polarization induced by misfit dislocations in a thin film. A nano-scale dislocation structure is modeled in a periodic SrTiO$_3$ supercell, and then the structure is optimized by using neural-network-potential and first-principles approaches. We point out that a pyramidal TiO$_5$ coordination forms near the dislocation cores, which in turn dominantly causes the sizable flexoelectric polarization.
{"title":"Dislocation-induced flexoelectricity in SrTiO$_3$ nanostructure from first principles","authors":"Kunihiko Yamauchi, Thi Phuong Thao Nguyen, Tamio Oguchi","doi":"arxiv-2408.04985","DOIUrl":"https://doi.org/arxiv-2408.04985","url":null,"abstract":"Flexoelectricity refers to a linear coupling between the electric\u0000polarization and the strain gradient, such as bending or asymmetric\u0000compression. This effect is enhanced in nano-scale structures, where grain\u0000boundaries or dislocation cores induce the strain gradient. In this study, we\u0000theoretically investigate the flexoelectric polarization induced by misfit\u0000dislocations in a thin film. A nano-scale dislocation structure is modeled in a\u0000periodic SrTiO$_3$ supercell, and then the structure is optimized by using\u0000neural-network-potential and first-principles approaches. We point out that a\u0000pyramidal TiO$_5$ coordination forms near the dislocation cores, which in turn\u0000dominantly causes the sizable flexoelectric polarization.","PeriodicalId":501234,"journal":{"name":"arXiv - PHYS - Materials Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141948606","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. Yang, X. Zhang, H. Wang, N. Lei, J. Wang, Y. Sun, L. Liu, Z. Zhao, Y. Yang, D. Wei, D. Pan, J. Zhao, J. Shen, W. g Zhao, H. Lu, W. Wang, H. Yu
The Dzyaloshinskii-Moriya interaction (DMI) plays a critical role in stabilizing topological spin textures, a key area of growing interest in oxide-based spintronics. While most of reported topological phenomena found in manganites are related to the bulk-like DMI, the understanding of interfacial DMI and its origin in oxide interfaces remain limited. Here we experimentally investigate the interfacial DMI of La_{0.7}Sr_{0.3}MnO_{3} (LSMO) films grown on various substrates by employing spin-wave propagation with drift velocities at room temperature. Our findings reveal a giant interfacial DMI coefficient (mathit{D} _{s}) of 1.96 pJ/m in LSMO/NdGaO_{3}(110) system, exceeding previously reported values in oxides by one to two orders of magnitude. First-principles calculations further show that with the aid of 6mathit{s} electrons, the 4mathit{f} electrons from Nd play a key role in enhancing the spin-orbit coupling of the 3mathit{d} electrons in Mn, ultimately leading to the observed giant interfacial DMI. This discovery of giant interfacial DMI through engineering the interface of oxides provides valuable insights for advancing functional chiral magnonics and spintronics.
{"title":"Giant interfacial Dzyaloshinskii-Moriya Interaction in perovskite La_{0.7}Sr_{0.3}MnO_{3} films","authors":"L. Yang, X. Zhang, H. Wang, N. Lei, J. Wang, Y. Sun, L. Liu, Z. Zhao, Y. Yang, D. Wei, D. Pan, J. Zhao, J. Shen, W. g Zhao, H. Lu, W. Wang, H. Yu","doi":"arxiv-2408.04959","DOIUrl":"https://doi.org/arxiv-2408.04959","url":null,"abstract":"The Dzyaloshinskii-Moriya interaction (DMI) plays a critical role in\u0000stabilizing topological spin textures, a key area of growing interest in\u0000oxide-based spintronics. While most of reported topological phenomena found in\u0000manganites are related to the bulk-like DMI, the understanding of interfacial\u0000DMI and its origin in oxide interfaces remain limited. Here we experimentally\u0000investigate the interfacial DMI of La_{0.7}Sr_{0.3}MnO_{3} (LSMO) films grown\u0000on various substrates by employing spin-wave propagation with drift velocities\u0000at room temperature. Our findings reveal a giant interfacial DMI coefficient\u0000(mathit{D} _{s}) of 1.96 pJ/m in LSMO/NdGaO_{3}(110) system, exceeding\u0000previously reported values in oxides by one to two orders of magnitude.\u0000First-principles calculations further show that with the aid of 6mathit{s}\u0000electrons, the 4mathit{f} electrons from Nd play a key role in enhancing the\u0000spin-orbit coupling of the 3mathit{d} electrons in Mn, ultimately leading to\u0000the observed giant interfacial DMI. This discovery of giant interfacial DMI\u0000through engineering the interface of oxides provides valuable insights for\u0000advancing functional chiral magnonics and spintronics.","PeriodicalId":501234,"journal":{"name":"arXiv - PHYS - Materials Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141948608","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Marius Weber, Stephan Wust, Luca Haag, Akashdeep Akashdeep, Kai Leckron, Christin Schmitt, Rafael Ramos, Takashi Kikkawa, Eiji Saitoh, Mathias Kläui, Libor Šmejkal, Jairo Sinova, Martin Aeschlimann, Gerhard Jakob, Benjamin Stadtmüller, Hans Christian Schneider
The recently discovered altermagnets exhibit collinear magnetic order with zero net magnetization but with unconventional spin-polarized d/g/i-wave band structures, expanding the known paradigms of ferromagnets and antiferromagnets. In addition to novel current-driven electronic transport effects, the unconventional time-reversal symmetry breaking in these systems also makes it possible to obtain a spin response to linearly polarized fields in the optical frequency domain. We show through ab-initio calculations of the prototypical d-wave altermagnet RuO$_2$, with $[C_2|C_{4z}]$ symmetry combining twofold spin rotation with fourfold lattice rotation, that there is an optical analogue of a spin splitter effect, as the coupling to a linearly polarized exciting laser field makes the d-wave character of the altermagnet directly visible. By magneto-optical measurements on RuO$_2$ films of a few nanometer thickness, we demonstrate the predicted connection between the polarization of an ultrashort pump pulse and the sign and magnitude of a persistent optically excited electronic spin polarization. Our results point to the possibility of exciting and controlling the electronic spin polarization in altermagnets by such ultrashort optical pulses. In addition, the possibility of exciting an electronic spin polarization by linearly polarized optical fields in a compensated system is a unique consequence of the altermagnetic material properties, and our experimental results therefore present an indication for the existence of an altermagnetic phase in ultrathin RuO$_2$ films.
{"title":"All optical excitation of spin polarization in d-wave altermagnets","authors":"Marius Weber, Stephan Wust, Luca Haag, Akashdeep Akashdeep, Kai Leckron, Christin Schmitt, Rafael Ramos, Takashi Kikkawa, Eiji Saitoh, Mathias Kläui, Libor Šmejkal, Jairo Sinova, Martin Aeschlimann, Gerhard Jakob, Benjamin Stadtmüller, Hans Christian Schneider","doi":"arxiv-2408.05187","DOIUrl":"https://doi.org/arxiv-2408.05187","url":null,"abstract":"The recently discovered altermagnets exhibit collinear magnetic order with\u0000zero net magnetization but with unconventional spin-polarized d/g/i-wave band\u0000structures, expanding the known paradigms of ferromagnets and antiferromagnets.\u0000In addition to novel current-driven electronic transport effects, the\u0000unconventional time-reversal symmetry breaking in these systems also makes it\u0000possible to obtain a spin response to linearly polarized fields in the optical\u0000frequency domain. We show through ab-initio calculations of the prototypical\u0000d-wave altermagnet RuO$_2$, with $[C_2|C_{4z}]$ symmetry combining twofold\u0000spin rotation with fourfold lattice rotation, that there is an optical analogue\u0000of a spin splitter effect, as the coupling to a linearly polarized exciting\u0000laser field makes the d-wave character of the altermagnet directly visible. By\u0000magneto-optical measurements on RuO$_2$ films of a few nanometer thickness, we\u0000demonstrate the predicted connection between the polarization of an ultrashort\u0000pump pulse and the sign and magnitude of a persistent optically excited\u0000electronic spin polarization. Our results point to the possibility of exciting\u0000and controlling the electronic spin polarization in altermagnets by such\u0000ultrashort optical pulses. In addition, the possibility of exciting an\u0000electronic spin polarization by linearly polarized optical fields in a\u0000compensated system is a unique consequence of the altermagnetic material\u0000properties, and our experimental results therefore present an indication for\u0000the existence of an altermagnetic phase in ultrathin RuO$_2$ films.","PeriodicalId":501234,"journal":{"name":"arXiv - PHYS - Materials Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141948603","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Alfredo Fiorentino, Paolo Pegolo, Stefano Baroni, Davide Donadio
Semiconducting alloys, in particular SiGe, have been employed for several decades as high-temperature thermoelectric materials. Devising strategies to reduce their thermal conductivity may provide a substantial improvement in their thermoelectric performance also at lower temperatures. We have carried out an ab initio investigation of the thermal conductivity of SiGe alloys with random and spatially correlated mass disorder employing the Quasi-Harmonic Green-Kubo (QHGK) theory with force constants computed by density functional theory. Leveraging QHGK and the hydrodynamic extrapolation to achieve size convergence, we obtained a detailed understanding of lattice heat conduction in SiGe and demonstrated that colored disorder suppresses thermal transport across the acoustic vibrational spectrum, leading to up to a 4-fold enhancement in the intrinsic thermoelectric figure of merit.
{"title":"Effects of colored disorder on the heat conductivity of SiGe alloys from first principles","authors":"Alfredo Fiorentino, Paolo Pegolo, Stefano Baroni, Davide Donadio","doi":"arxiv-2408.05155","DOIUrl":"https://doi.org/arxiv-2408.05155","url":null,"abstract":"Semiconducting alloys, in particular SiGe, have been employed for several\u0000decades as high-temperature thermoelectric materials. Devising strategies to\u0000reduce their thermal conductivity may provide a substantial improvement in\u0000their thermoelectric performance also at lower temperatures. We have carried\u0000out an ab initio investigation of the thermal conductivity of SiGe alloys with\u0000random and spatially correlated mass disorder employing the Quasi-Harmonic\u0000Green-Kubo (QHGK) theory with force constants computed by density functional\u0000theory. Leveraging QHGK and the hydrodynamic extrapolation to achieve size\u0000convergence, we obtained a detailed understanding of lattice heat conduction in\u0000SiGe and demonstrated that colored disorder suppresses thermal transport across\u0000the acoustic vibrational spectrum, leading to up to a 4-fold enhancement in the\u0000intrinsic thermoelectric figure of merit.","PeriodicalId":501234,"journal":{"name":"arXiv - PHYS - Materials Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141948609","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zhenlong Zhang, Xuehan Di, Charles Paillard, Laurent Bellaiche, Zhijun Jiang
First-principles calculations are performed to investigate the electro-optic (EO) and elasto-optic effects of the three-dimensional (bulk) and two-dimensional (monolayer) ferroelectric NbOI$_{2}$. Remarkably large linear EO and elasto-optic coefficients are discovered in both systems, when under stress-free conditions. We further found that the EO responses of bulk and monolayer NbOI$_{2}$ can be further enhanced with epitaxial strain, because of a strain-driven ferroelectric-to-paraelectric transition that originates from the softening of some polar optical modes. Our findings thus point out that NbOI$_{2}$, as well as other niobium oxide dihalides are highly promising for paving the way for potentially efficient nonlinear optical device applications.
通过第一性原理计算，研究了三维（块状）和二维（单层）铁电 NbOI$_{2}$ 的电光效应和弹光效应。我们发现，在无应力条件下，这两个系统的线性光电效应和弹性光电效应系数都非常大。我们进一步发现，体层和单层 NbOI$_{2}$ 的 EO 响应可以随着外延应变的增加而进一步增强，这是因为应变驱动了铁电到准电的转变，这种转变源于某些极性光学模式的软化。因此，我们的研究结果表明，NbOI$_{2}$ 以及其他氧化铌二卤化物极有希望为潜在的高效非线性光学器件应用铺平道路。
{"title":"Giant electro-optic and elasto-optic effects in ferroelectric NbOI$_{2}$","authors":"Zhenlong Zhang, Xuehan Di, Charles Paillard, Laurent Bellaiche, Zhijun Jiang","doi":"arxiv-2408.04225","DOIUrl":"https://doi.org/arxiv-2408.04225","url":null,"abstract":"First-principles calculations are performed to investigate the electro-optic\u0000(EO) and elasto-optic effects of the three-dimensional (bulk) and\u0000two-dimensional (monolayer) ferroelectric NbOI$_{2}$. Remarkably large linear\u0000EO and elasto-optic coefficients are discovered in both systems, when under\u0000stress-free conditions. We further found that the EO responses of bulk and\u0000monolayer NbOI$_{2}$ can be further enhanced with epitaxial strain, because of\u0000a strain-driven ferroelectric-to-paraelectric transition that originates from\u0000the softening of some polar optical modes. Our findings thus point out that\u0000NbOI$_{2}$, as well as other niobium oxide dihalides are highly promising for\u0000paving the way for potentially efficient nonlinear optical device applications.","PeriodicalId":501234,"journal":{"name":"arXiv - PHYS - Materials Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141969734","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The transport properties (electrical resistivity, thermal conductivity, and viscosity) of iron-hydrogen alloy are of great significance in the stability and evolution of planetary magnetic fields. Here, we investigate the thermal transport properties of iron doped with varying hydrogen content as functions of pressure (P) and temperature (T) for the top and bottom of Earth's outer core and beyond, corresponding to pressures of about 130 to 300 GPa and temperatures of 4000 to 7000 K. Using first-principles density functional theory molecular dynamic simulations (FPMD), we verify that crystalline FeH$_x$ is superionic with H diffusing freely. We find a low frequency viscosity of 10-11 mPa$cdot$s for liquid Fe-H alloys at Earth's outer core conditions by the linear response Green-Kubo formula. Using the KKR method within density functional theory (DFT) plus Dynamical mean-field Theory (DMFT), we find saturation of electrical resistivity with increasing temperatures in liquid iron at outer core conditions. The effect of H on electrical and thermal transport we find is small, so that the exact H content of the core is not needed. The primary effect of H is on the equation of state, decreasing the density at constant P and T. We find the Lorenz number is smaller than the ideal value, and obtain for X(H)= 0.20, or 0.45 wt% H , thermal conductivity $kappa$ of $sim$105 and $sim$190 $Wm^{-1}K^{-1}$, respectively, at conditions near the core-mantle and inner-outer core boundary.
铁氢合金的传输特性（电阻率、热导率和粘度）对行星磁场的稳定和演化具有重要意义。利用第一原理密度泛函理论分子动力学模拟（FPMD），我们验证了结晶的 FeH$_x$ 是超离子的，H 可以自由扩散。通过线性响应格林-久保公式，我们发现液态 Fe-H 合金在地球外核条件下的低频粘度为 10-11 mPa$cdot$s。利用密度函数理论（DFT）和动态平均场理论（DMFT）中的 KKR 方法，我们发现外核条件下液态铁的电阻率会随着温度的升高而饱和。我们发现 H 对电学和热学传输的影响很小，因此不需要确切的铁芯 H 含量。我们发现洛伦兹数小于理想值，并得到了 X(H)= 0.20 或 0.45 wt% H 的热导率$kappa$分别为$sim$105 和$sim$190 $Wm^{-1}K^{-1}$，其条件靠近内核-外核边界。
{"title":"Electrical resistivity, thermal conductivity, and viscosity of Fe-H alloys at Earth's core conditions","authors":"Cong Liu, Ronald Cohen","doi":"arxiv-2408.04521","DOIUrl":"https://doi.org/arxiv-2408.04521","url":null,"abstract":"The transport properties (electrical resistivity, thermal conductivity, and\u0000viscosity) of iron-hydrogen alloy are of great significance in the stability\u0000and evolution of planetary magnetic fields. Here, we investigate the thermal\u0000transport properties of iron doped with varying hydrogen content as functions\u0000of pressure (P) and temperature (T) for the top and bottom of Earth's outer\u0000core and beyond, corresponding to pressures of about 130 to 300 GPa and\u0000temperatures of 4000 to 7000 K. Using first-principles density functional\u0000theory molecular dynamic simulations (FPMD), we verify that crystalline FeH$_x$\u0000is superionic with H diffusing freely. We find a low frequency viscosity of\u000010-11 mPa$cdot$s for liquid Fe-H alloys at Earth's outer core conditions by\u0000the linear response Green-Kubo formula. Using the KKR method within density\u0000functional theory (DFT) plus Dynamical mean-field Theory (DMFT), we find\u0000saturation of electrical resistivity with increasing temperatures in liquid\u0000iron at outer core conditions. The effect of H on electrical and thermal\u0000transport we find is small, so that the exact H content of the core is not\u0000needed. The primary effect of H is on the equation of state, decreasing the\u0000density at constant P and T. We find the Lorenz number is smaller than the\u0000ideal value, and obtain for X(H)= 0.20, or 0.45 wt% H , thermal conductivity\u0000$kappa$ of $sim$105 and $sim$190 $Wm^{-1}K^{-1}$, respectively, at\u0000conditions near the core-mantle and inner-outer core boundary.","PeriodicalId":501234,"journal":{"name":"arXiv - PHYS - Materials Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141948610","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tadataka Watanabe, Kazuya Takayanagi, Ray Nishimura, Yoshiaki Hara, Dharmalingam Prabhakaran, Roger D. Johnson, Stephen J. Blundell
Orthorhombic pseudobrookites CoTi$_2$O$_5$ and FeTi$_2$O$_5$ have a low-symmetry crystal structure comprising magnetic Co$^{2+}$/Fe$^{2+}$ ions and nonmagnetic Ti$^{4+}$ ions, where the orbital-nondegenerate Co$^{2+}$/Fe$^{2+}$ ions form one-dimensional chains running along the orthorhombic $a$ axis. These compounds undergo an antiferromagnetic phase transition at $T_N sim$ 26 K for CoTi$_2$O$_5$ and $T_N sim$ 40 K for FeTi$_2$O$_5$. We perform ultrasound velocity measurements on single crystals of CoTi$_2$O$_5$ and FeTi$_2$O$_5$. The measurements of these compounds reveal that the symmetry-lowering elastic modes of shear elastic moduli exhibit unusual elastic softness in the paramagnetic phase above $T_N$. This elastic softness indicates the presence of spin-lattice-coupled fluctuations above $T_N$ that should be a precursor to the symmetry-lowering lattice distortion at $T_N$. Furthermore, it is revealed that the magnitude of the unusual elastic softness is larger in CoTi$_2$O$_5$ than in FeTi$_2$O$_5$, which indicates that the spin-lattice coupling is stronger in CoTi$_2$O$_5$ than in FeTi$_2$O$_5$. The present study suggests that CoTi$_2$O$_5$ and FeTi$_2$O$_5$ are unique spin Jahn--Teller systems with low crystal symmetry, where, although the nature of exchange interactions is quasi-one-dimensional, the three-dimensional spin-lattice coupling releases the frustration by further lowering the crystal symmetry.
{"title":"Hidden elastic softness of low-symmetry frustrated $A$Ti$_2$O$_5$ ($A$ = Co, Fe)","authors":"Tadataka Watanabe, Kazuya Takayanagi, Ray Nishimura, Yoshiaki Hara, Dharmalingam Prabhakaran, Roger D. Johnson, Stephen J. Blundell","doi":"arxiv-2408.03783","DOIUrl":"https://doi.org/arxiv-2408.03783","url":null,"abstract":"Orthorhombic pseudobrookites CoTi$_2$O$_5$ and FeTi$_2$O$_5$ have a\u0000low-symmetry crystal structure comprising magnetic Co$^{2+}$/Fe$^{2+}$ ions and\u0000nonmagnetic Ti$^{4+}$ ions, where the orbital-nondegenerate Co$^{2+}$/Fe$^{2+}$\u0000ions form one-dimensional chains running along the orthorhombic $a$ axis. These\u0000compounds undergo an antiferromagnetic phase transition at $T_N sim$ 26 K for\u0000CoTi$_2$O$_5$ and $T_N sim$ 40 K for FeTi$_2$O$_5$. We perform ultrasound\u0000velocity measurements on single crystals of CoTi$_2$O$_5$ and FeTi$_2$O$_5$.\u0000The measurements of these compounds reveal that the symmetry-lowering elastic\u0000modes of shear elastic moduli exhibit unusual elastic softness in the\u0000paramagnetic phase above $T_N$. This elastic softness indicates the presence of\u0000spin-lattice-coupled fluctuations above $T_N$ that should be a precursor to the\u0000symmetry-lowering lattice distortion at $T_N$. Furthermore, it is revealed that\u0000the magnitude of the unusual elastic softness is larger in CoTi$_2$O$_5$ than\u0000in FeTi$_2$O$_5$, which indicates that the spin-lattice coupling is stronger in\u0000CoTi$_2$O$_5$ than in FeTi$_2$O$_5$. The present study suggests that\u0000CoTi$_2$O$_5$ and FeTi$_2$O$_5$ are unique spin Jahn--Teller systems with low\u0000crystal symmetry, where, although the nature of exchange interactions is\u0000quasi-one-dimensional, the three-dimensional spin-lattice coupling releases the\u0000frustration by further lowering the crystal symmetry.","PeriodicalId":501234,"journal":{"name":"arXiv - PHYS - Materials Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141948612","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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