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Negative or Zero Thermal Expansion in Silicon Dicarbodiimide, Si(NCN)2

Published online by Cambridge University Press:  01 February 2011

Peter Kroll
Affiliation:
[email protected], University of Texas at Arlington, Chemistry and Biochemsitry, 700 Planetarium Pl, Arlingtom, TX, 76019, United States
Xuehua Yan
Affiliation:
[email protected], Jiangsu University, School of Materials Science and Engineering, Zhenjiang, 212013, China, People's Republic of
Ralf Riedel
Affiliation:
[email protected], TU Darmstadt, Institut fuer Materialwissenschaft, Darmstadt, 64287, Germany
Helmut Ehrenberg
Affiliation:
[email protected], IFW Dresden, Institute for Complex Materials, Dresden, 01171, Germany
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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.

Type
Research Article
Copyright
Copyright © Materials Research Society 2008

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