Effect of particle size on the phase transformation behavior and equation of state of Si under hydrostatic loading

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Yesudhas, Sorb
Lin, Feng
Pandey, K. K.
Somayazulu, Maddury
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Aerospace Engineering

The Department of Aerospace Engineering seeks to instruct the design, analysis, testing, and operation of vehicles which operate in air, water, or space, including studies of aerodynamics, structure mechanics, propulsion, and the like.

The Department of Aerospace Engineering was organized as the Department of Aeronautical Engineering in 1942. Its name was changed to the Department of Aerospace Engineering in 1961. In 1990, the department absorbed the Department of Engineering Science and Mechanics and became the Department of Aerospace Engineering and Engineering Mechanics. In 2003 the name was changed back to the Department of Aerospace Engineering.

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Mechanical Engineering
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High-pressure synchrotron X-ray diffraction (XRD) studies have been conducted on three types of Si particles (micron, 100 nm, and 30 nm). The pressure for initiation of Si-I->Si-II phase transformation (PT) essentially increases with a reduction in particle size. For 30 nm Si particles, Si-I directly transforms to Si-XI by skipping the intermediate Si-II phase, which appears during the pressure release. The evolution of phase fractions of Si particles under hydrostatic compression is studied. The equation of state (EOS) of Si-I, Si-II, Si-V, and Si-XI for all three particle sizes is determined, and the results are compared with other studies. A simple iterative procedure is suggested to extract the EOS of Si-XI and Si-II from the data for a mixture of two and three phases with different pressures in each phase. Using previous atomistic simulations, EOS for Si-II is extended to ambient pressure, which is important for plastic strain-induced phase transformations. Surprisingly, the EOS of micron and 30 nm Si are identical, but different from 100 nm particles. In particular, the Si-I phase of 100 nm Si is less compressible than that of micron and 30 nm Si. The reverse Si-V->Si-I PT is observed for the first time after complete pressure release to the ambient for 100 nm particles.
This is a preprint from Yesudhas, Sorb, Valery I. Levitas, Feng Lin, K. K. Pandey, and Maddury Somayazulu. "Effect of particle size on the phase transformation behavior and equation of state of Si under hydrostatic loading." arXiv preprint arXiv:2402.15092 (2024). doi: https://doi.org/10.48550/arXiv.2402.15092. Copyright 2024 The Authors. CC-BY.