Session: 17-15-01: Society-Wide Micro/Nano Poster Forum

Paper Number: 99068

99068 - Ab Initio Modeling of Phonon Transport in Refractory Di-Silicides 

Refractory di-silicides namely, MoSi₂, WSi₂, and VSi₂ possess high melting points, resistance to creep and high temperature oxidation resistance. Typical applications involve heating elements, heat shields and jet engines. We examine phonon transport in novel cation disordered di-silicides, namely, (MoW)₁Si₂,  (MoWNb)₁Si₂, (MoWNbTa)₁Si₂ and (MoWNbTaV)₁Si₂, with tetragonal C11b structure. Ab initio calculations predict that these materials possess high heat capacity (C_p), considerably low thermal expansion (α) and higher stability. An assessment of phonon (lattice vibration) scattering and band unfolding is presented to explain the correlation between configurational entropy and thermodynamic properties. It is seen that scattering is maximum for compound with the most disordered structure. This is the first effort to study disordered multicomponent (high entropy) refractory di-silicide via first principal calculations. There have been a few first principal studies on MoSi2 and its derivative compounds, mostly focused on elastic properties and anisotropy of thermal expansion. In this work we set a pathway for future of high entropy di-silicide as more stable with better thermal properties compared to the unitary di-silicide.  Phonons are the vibrational quanta responsible for phase transformation, thermal conductivity,  thermal expansion and other thermodynamic properties. Modelling phonons can give a detailed insight into design and optimization of better thermos-electric materials and heat transfer mechanism. Chemical disorder and structural perturbations have a significant effect on phonon properties. The extent of disorder directly affects the phonon scattering phenomenon. In this work we perform band unfolding and scattering using spectral function to unravel the underlying effects of high entropy on phononic characteristics. We find that quaternary and quinary compounds have largest scattering due to highest configurational disorder. Band unfolding simplifies the hard to read band structure or often called “Spaghetti diagram”. Phonon group velocities are a pivotal factor that indirectly hints about the nature of thermal properties like thermal conductivity, bulk modulus and acoustic softening. Predominantly group velocities are directly related to the phonon band structure. The reduction in group velocity with increase in configurational entropy also supports our prediction. Quinary di-silicide possess the highest Cp with ten times the value of MoSi₂ while the value of α shows significant decreases for multi component di-silicide. The thermal expansion of multicomponent silicide is reduced to 3/4^th of values for MoSi₂ above room temperature. Grüneisen parameter above room temperature is found to be have nearly equal slope for all di-silicide. MoSi₂ has highest value of Grüneisen parameter at all temperatures. Further studies into phononic and electronic transport phenomenon will establish multicomponent silicide as high temperature material.

Presenting Author: PRINCE SHARMA Lehigh University

Presenting Author Biography: Prince Sharma has received his Master of Technology in Materials Science and Engineering from the Indian Institute of Technology Hyderabad, India. He is a PhD student working in the mentorship of Dr. Ganesh Balasubramanian at Lehigh University. His research interests lies in alloy design, ab initio calculations and high temperature materials.

Authors:

PRINCE SHARMA Lehigh University
Ganesh Balasubramanian Lehigh University