Elastic and thermal properties of hexagonal perovskites

We systematically investigate the mechanical and thermal properties of the P6₃cm hexagonal perovskites with composition A³+B³+O₃ for potential use in thermal barrier coatings. In spite of the structural anisotropy, the elastic constants are essentially isotropic. The thermal expansion is, however, strongly anisotropic, while the thermal conductivity is relatively isotropic. The thermal conductivities of the hexagonal perovskites are much larger than those of the orthorhombic perovskites

Building-Block Approach to the Discovery of Na8Mn2(Ge2Se6)2: A Polar Chalcogenide Exhibiting Promising Harmonic Generation Signals with a High Laser-Induced Damage Threshold

A new polar quaternary chalcogenide, Na8Mn2(Ge2Se6)2, has been synthesized using the building-block approach by reacting preformed Na6Ge2Se6 and MnCl2 at 750 °C. The structure consists of layers of [Na(1)Mn(Ge2Se6)]3– stacked perpendicular to the c-axis and sodium ions occupying the interlayer space. An indirect bandgap of 1.52 eV has been calculated using density functional theory, which is expectedly underestimated compared to the observed optical bandgap of 1.95 eV derived from diffuse reflectance spectroscopic measurements in the UV/Vis/NIR region. Magnetic measurements confirm the paramagnetic nature of Na8Mn2(Ge2Se6)2 with an experimental magnetic moment of 5.8 μB in good agreement with the theoretical spin only moment of 5.92 μB for high spin Mn2+. Na8Mn2(Ge2Se6)2 exhibits a potentially wide region of transparency in the measured range of 2.5–25 µm. Na8Mn2(Ge2Se6)2 shows a modest second-harmonic generation (SHG) response but with a high laser-induced damage threshold (LIDT) of ~9x AgGaSe2. Third harmonic generation (THG) measurements indicate that Na8Mn2(Ge2Se6)2 displays a high THG coefficient (1.9x AgGaSe2) at λ = 1800 nm

Phonon Transport Simulator (PhonTS)

This program has been imported from the CPC Program Library held at Queen's University Belfast (1969-2018) Abstract Thermal conductivity prediction remains an important subject in many scientific and engineering areas. Only recently has such prediction become possible on the basis of the first principles calculations, thus ensuring high quality results. Implementation of the methodology, however, is technically challenging and requires a lengthy development process. We thus introduce the Phonon Transport Simulator (PhonTS), a Fortran90, fully parallel code to perform such calculations. PhonTS possesses a l... Title of program: PhonTS Catalogue Id: AEVO_v1_0 Nature of problem Computes thermal conductivity in crystal solids from the level of the interatomic interactions. Versions of this program held in the CPC repository in Mendeley Data AEVO_v1_0; PhonTS; 10.1016/j.cpc.2015.01.008 AEVO_v1_0; PhonTS; 10.1016/j.cpc.2015.01.00

Uncertainty Quantification in Multiscale Simulation of Materials: A Prospective

Simulation has long since joined experiment and theory as a valuable tool to address materials problems. Analysis of errors and uncertainties in experiment and theory is well developed; such analysis for simulations, particularly for simulations linked across length scales and timescales, is much less advanced. In this prospective, we discuss salient issues concerning uncertainty quantification (UQ) from a variety of fields and review the sparse literature on UQ in materials simulations. As specific examples, we examine the development of atomistic potentials and multiscale simulations of crystal plasticity. We identify needs for conceptual advances, needs for the development of best practices, and needs for specific implementations

Phonon lifetime investigation of anharmonicity and thermal conductivity of UO2 by neutron scattering and theory

Inelastic neutron scattering measurements of individual phonon lifetimes and dispersion at 295 and 1200 K have been used to probe anharmonicity and thermal conductivity in UO2. They show that longitudinal optic phonon modes carry the largest amount of heat, in contrast to past simulations and that the total conductivity demonstrates a quantitative correspondence between microscopic and macroscopic phonon physics. We have further performed first-principles simulations for UO2 showing semiquantitative agreement with phonon lifetimes at 295 K, but larger anharmonicity than measured at 1200 K. \ua9 2013 American Physical Society.Peer reviewed: YesNRC publication: Ye

Thermal Conductivity of UO₂ Fuel: Predicting Fuel Performance from Simulation

Recent progress in understanding the thermal-transport properties of UO2 for fission reactors is reviewed from the perspective of computer simulations. A path to incorporating more accurate materials models into fuel performance codes is outlined. In particular, it is argued that a judiciously integrated program of atomic-level simulations and mesoscale simulations offers the possibility of both better predicting the thermal-transport properties of UO2 in light-water reactors and enabling the assessment of the thermal performances of novel fuel systems for which extensive experimental databases are not available

Investigations of thermal conductivity of simple van der Waals crystal-based nanocomposites

The experimental setup for obtaining and determination of the thermal conductivity of simple van der Waals crystal-based nanocomposites is described. Preliminary thermal conductivity results of measurements carried out in the temperature range 1–40 K on two samples of methane crystals containing nanoparticles of hydroxyapatite are presented. These results confirm usability of the setup and its suitability as a proper experimental method for investigations of the thermal conductivity of the nanocomposites

Anisotropic Thermal Properties in Orthorhombic Perovskites

The structure, elastic properties, thermal expansion, and thermal conductivity of the orthorhombic-structured A3+B3+O3 perovskites are determined using atomistic simulations with classical potentials. When considered as pseudo-cubic monoclinic systems, they show relatively small deviations in structure and properties from their cubic perovskite parent phase. The variations in properties are shown to be related to the magnitude of the tilting of the BO6 octahedra, which in turn is related to the relative sizes of the A and B ions, as encapsulated in the tolerance factor