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Negative or Zero Thermal Expansion in Silicon Dicarbodiimide, Si(NCN)2
Published online by Cambridge University Press: 01 February 2011
Abstract
Using ab-initio molecular dynamics simulation we investigate the thermal expansion of β-Si(NCN)2 for temperatures up to 700 K. We find that the structure behaves isotropic, although its optimized ground state is tetragonal. Studying the zero-pressure volume as a function of temperature we find a negative expansion of the structure and a linear expansion coefficient αL of -2·10−5 K-1. We attribute this effect to a strong bending of the Si-N=C angle within the structure which increases on increasing the temperature. The stretching of Si-N and C=N bonds on the other side is regular.
Experiments motivated by the computational study were carried out on nano-crystalline Si(NCN)2 powders. The XRD Mo Kα data shows a negative thermal expansion for β-Si(NCN)2 up to 600 K. Synchrotron data indicates zero expansion of β-Si(NCN)2 between 460K and 800 K.
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- Copyright © Materials Research Society 2008