Materials representation plays a key role in machine learning based prediction of materials properties and new materials discovery. Currently both graph and 3D voxel representation methods are based on the heterogeneous elements of the crystal structures. Here, we propose to use electronic charge density (ECD) as a generic unified 3D descriptor for materials property prediction with the advantage of possessing close relation with the physical and chemical properties of materials. We developed an ECD based 3D convolutional neural networks (CNNs) for predicting elastic properties of materials, in which CNNs can learn effective hierarchical features with multiple convolving and pooling operations. Extensive benchmark experiments over 2,170 Fm-3m face-centered-cubic (FCC) materials show that our ECD based CNNs can achieve good performance for elasticity prediction. Especially, our CNN models based on the fusion of elemental Magpie features and ECD descriptors achieved the best 5-fold cross-validation performance. More importantly, we showed that our ECD based CNN models can achieve significantly better extrapolation performance when evaluated over non-redundant datasets where there are few neighbor training samples around test samples. As additional validation, we evaluated the predictive performance of our models on 329 materials of space group Fm-3m by comparing to DFT calculated values, which shows better prediction power of our model for bulk modulus than shear modulus. Due to the unified representation power of ECD, it is expected that our ECD based CNN approach can also be applied to predict other physical and chemical properties of crystalline materials.
We discuss the mechanisms of spin–phonon coupling (SPC) in 2D MX3 (M = Fe, Ru; X = Cl, Br, I), and find that the spin induced thermal conductivity variation ranges from −130% to 573%, showing a strong composition effect.
To develop Si structures for multifunctional applications, here we proposed four new low-density silicon clathrates (Si-CL-A, Si-CL-B, Si-CL-C, and Si-CL-D) based on the same bonding topologies of clathrate hydrates. The electronic and thermal properties have been revealed by first-principles calculations. By computing their equation of states, phonon dispersion, and elastic constants, the thermodynamic, dynamic, and mechanical stabilities of Si-CL-A, Si-CL-B, Si-CL-C, and Si-CL-D allotropes are confirmed. In the low-density region of the phase diagram, Si-CL-B, Si-CL-D, and Si-CL-C would overtake diamond silicon and type II clathrate (Si-CL-II) and emerge as the most stable Si allotropes successively. Among them, the two direct semiconductors with bandgaps of 1.147 eV (Si-CL-A) and 1.086 eV (Si-CL-D) are found. The suitable bandgaps close to the optimal Shockley-Queisser limit result in better absorption efficiency in solar spectrum than conventional diamond silicon. Owing to the unique cage-based framework, the thermal conductivity of these Si allotropes at room temperature are very low (2.7–5.7 Wm−1 K−1), which are lower than that of diamond structured Si by two orders of magnitude. The suitable bandgaps, small effective masses, and low thermal conductivity of our new silicon allotropes are anticipated to find applications in photovoltaic and thermoelectric devices.
The spin-phonon coupling (SPC) effect is one of the most important interactions that provides a powerful tool for advancing 2D spintronic devices. 2D NiPS3 stands out from the synthesized 2D magnets because it is an XY-type antiferromagnet semiconductor with the highest Néel temperature. In this work, we investigate the SPC effect on 2D NiPS3 nanosheets by examining the thermal transport properties linked to the magnetic order and the magnetic properties influenced by strain. Our findings reveal the significant variation of magnetic ordering on phonon vibrations. Remarkably, the spin-phonon coupling constant is measured to be 29.85 cm–1, which is 1 order of magnitude greater than that of most other 2D magnets. We discovered that the formation of long-range antiferromagnetic order in NiPS3 notably boosts the lattice thermal conductivity, with increases of 736.54% at 10 K, 32.95% at 150 K, and 31.41% at 300 K. The enhancement in thermal conductivity in the AFM NiPS3 nanosheets predominantly originates from the phonon lifetime and phonon anharmonicity. Moreover, taking advantage of the SPC effect, we also observe that the XY-type AFM is suppressed under the tensile strain. This study not only contributes to a better understanding of the interplay between lattice and spin degrees of freedom in the 2D limit but also holds promise for the development of high-efficiency thermal management and spin Seebeck devices.
The Cover Feature illustrates the enhanced mobility of ionic charge carriers after substitution of F− on the O2− site. Interestingly, weakened chemical bonds were observed between the cations (A or B site) and the oxygen ions by the anion doping strategy resulting in an improved oxygen mobility in the lattice. This finding suggests that targeted anion doping is a promising strategy for the development of a new generation of electrolyte materials. More information can be found in the Aricle by J. Gao et al.
Abstract With the continuous development of digital information and big data technologies, the ambient temperature and heat generation during the operation of magnetic storage devices play an increasingly crucial role in ensuring data security and device stability. In this study, we examined the lattice thermal conductivity of the van der Waals magnetic semiconductor CrSBr from bulk to monolayer structures using first-principles calculations and the phonon Boltzmann transport equation. Our results indicated that lattice thermal conductivity show anisotropy and CrSBr bilayer exhibits lower thermal conductivity at all temperatures. Through the analysis of phonon spectra. phonon lifetime, heat capacity, scattering probability, phonon-phonon interaction strength, we demonstrated that Cr-Br antisymmetrical stretching vibrations and phonon band gap are the main factors, which exhibit considerable dependence on layer number, magnetic ordering and strain effects. These results offer a comprehensive insight into phonon transport phenomena in van der Waals magnetic materials.
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