Influence of defects on the thermal conductivity of compressed LiF

The thermal conductivities along the basal and hexagonal directions of α-quartz silica, the low-temperature form of crystalline SiO2, are predicted from the solution of the Boltzmann transport equation combined with the van Beest, Kramer, and van Santen potential for the temperature up to 900 K and the pressure as high as 4 GPa. The thermal conductivities at atmospheric pressure, which show a negative and nonlinear dependence on temperature, are in reasonable agreement with the experimental data. The influence of pressure on thermal conductivity is positive and linear. The pressure (P) and temperature (T) dependences of the thermal conductivity (λ) in basal and hexagonal directions are fitted to a function of the form λ=(b+cP)Ta. The thermal conductivity, influenced by temperature and pressure, is analyzed based on phonon properties, including spectral thermal conductivity, dispersion relation, phonon density of states, phonon lifetime, and phonon probability density distribution function.

Lattice thermal conductivity of quartz at high pressure and temperature from the Boltzmann transport equation

Ragasa

Chernatynskiy

Phillpot

2019

Optical absorption spectra of MgO single crystals under shock compression between 50 and 132 GPa

Liu

Xue²,

Li³

et al. 2022

Optical properties of transparent windows at high pressures are of essential importance in dynamic experiments. To investigate the effects of plastic deformation-induced defects on optical transparency of MgO single crystals, real-time absorption spectra are measured via impact experiments and fast multi-color pyrometry. Shock pressure ranges from 50 to 132 GPa. Optical transmission histories are measured in each experiment via an on-board light source generated by shock-wave, from which absorption coefficient [Formula: see text] is determined as a function of the wavelength [Formula: see text]. The resultant real-time absorption spectrum ([Formula: see text] vs [Formula: see text]) peaks around 520 nm ([Formula: see text]2.39 eV), which blueshifts with increasing pressure. These featured spectra are possibly attributed to defective absorption at defect-centers (color-centers) in MgO single crystals generated by shock-waves. Plasticity-induced defects are most likely responsible for the decrease in transparency. MgO single crystals are not suited to be used as an optical window for thermometric in the visible light spectrum under shock pressures above 129 GPa.

Dynamic interaction between phonons and edge dislocations in LiF

Li,

Zheng,

Chen

et al. 2023

The dynamic interaction between phonons and dislocations in LiF has been studied using molecular dynamics simulations. The simulations have captured the strong dynamic interactions between low-frequency slow transverse acoustic phonons and dislocations that were observed in experiments. Simulation results reveal that the strong dynamic interaction is attributed to resonant interactions between dislocations and slow transverse acoustic phonons. Each dislocation segment is found to possess a set of resonant modes characterized by large-amplitude out-of-phase vibrations of atoms on both sides of the dislocation slip plane. The resonant frequencies associated with these modes exhibit a nearly linear distribution with respect to the mode order. Contrary to previous beliefs, the resonant frequencies of dislocations exhibit only a weak correlation with the dislocation length. Additionally, each dislocation exhibits a dominant resonant mode that corresponds to the strongest vibration mode in response to phonons. This dominant resonant mode is not always the first resonant mode with the lowest frequency. Its specific order depends on the dislocation length. Simulation results have also demonstrated that the resonant modes of dislocations can be influenced by the interactions from neighboring dislocations.