Unveiling phonon frequency-dependent mechanism of heat transport across stacking fault in silicon carbide

Stacking faults(SFs)are often present in silicon carbide(SiC)and affect its thermal and heat-transport properties.However,it is unclear how SFs influence thermal transport.Using non-equilibrium molecular dynamics and lattice dynamics simulations,we studied phonon transport in SiC materials with an SF.Compared to perfect SiC materials,the SF can reduce thermal conductivity.This is caused by the additional interface thermal resistance(ITR)of SF,which is difficult to capture by the previous phenomenological models.By analyzing the spectral heat flux,we find that SF reduces the contribution of low-frequency(7.5 THz-12 THz)phonons to the heat flux,which can be attributed to SF reducing the phonon lifetime and group velocity,especially in the low-frequency range.The SF hinders phonon transport and results in an effective interface thermal resistance around the SF.Our results provide insight into the microscopic mechanism of the effect of defects on heat transport and have guiding significance for the regulation of the thermal conductivity of materials.

Alunite spectral features and mineral chemistry of the ZijinshanDafanshan lithocap in SE China:Implications for mineral exploration

Lithocaps are composed of silicic and advanced argillic altered rocks,and represent an important target for porphyry-epithermal Cu-Au exploration.Previous studies showed that integrating alunite spectral and composition with lithocap whole-rock geochemistry can effectively aid exploration for concealed Cu-Au mineralization.The Zijinshan Cu-Au and Dafanshan alunite deposits are located in the Coastal Volcanic Belt in SE China,where alunite is an indicator of hypogene mineralization and alteration.Detailed mineralogical studies of alunite from these two deposits were performed with short-wavelength infrared spectroscopy(SWIR),whole-rock geochemistry and laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS).For Zijinshan,wavelength variation of the SWIR alunite absorption peak at 1480 nm is proportional to the whole-rock Na/(Na+K)molar ratio of alunitebearing samples.Different percentage of alunite and mineral assemblages in the lithocap samples would both affect the wavelength of the SWIR alunite absorption peak at1480 nm.We suggest that the alunite Ba-Bi contents and the whole-rock Nb/La value(of alunite-bearing rocks)are reliable vectoring tools for detecting magmatic-hydrothermal mineralization center in the district.Comparing the alunite SWIR spectral and mineral geochemical features and whole-rock geochemistry of alunite-bearing rocks between the Zijinshan and Dafanshan deposits,Au–Ag mineralization may be concealed at depth in northwestern Dafanshan.

Strong phonon localization in PbTe with dislocations and large deviation to Matthiessen’s rule

Dislocations can greatly enhance the figure of merit of thermoelectric materials by prominently reducing thermal conductivity.However,the evolution of phonon modes with different energies when they propagate through a single dislocation is unknown.Here we perform non-equilibrium molecular dynamics simulation to study phonon transport in PbTe crystal with dislocations by excluding boundary scattering and strain coupling effect.The frequency-dependent heat flux,phonon mode analysis,and frequency-dependent phonon mean free paths(MFPs)are presented.The thermal conductivity of PbTe with dislocation density on the order of 10^(15)m^(−2) is decreased by 62%.We provide solid evidence of strong localization of phonon modes in dislocation sample.Moreover,by comparing the frequency-dependent phonon MFPs between atomistic modeling and traditional theory,it is found that the conventional theories are inadequate to describe the phonon behavior throughout the full phonon spectrum,and large deviation to the well-known semi-classical Matthiessen’s rule is observed.These results provide insightful guidance for the development of PbTe based thermoelectrics and shed light on new routes for enhancing the performance of existing thermoelectrics by incorporating dislocations.