Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

The coefficient of thermal expansion of highly enriched 28Si



Ernest G. Kessler Jr., Guido Bartl, Arnold Nicolaus, Rene Schodel, Peter Becker


For the new definition of the SI-unit mass based on a fundamental constant, a redetermination of Avogadro s constant is the goal of an international collaboration of numerous national laboratories and universities. Since a relative uncertainty of about 210-8 is aimed at, the macroscopic density, the isotopic composition and the volume of the unit cell of a silicon single crystal have to be measured with high precision. One step to improve the precision was the production of a silicon crystal of highly enriched 28Si. This paper addresses the effect of thermal expansion of that material in order to account for a possible discrepancy between the coefficient of thermal expansion (CTE) of natural silicon and that of 28Si. The results of two independent CTE measuring methods are presented and compared in this paper.


coefficient of thermal expansion, enriched Si, silicon sphere, Avogadro constant, sphere interferometer, length measurement, lattice parameter, X-ray diffraction


Kessler, E. , Bartl, G. , Nicolaus, A. , Schodel, R. and Becker, P. (2009), The coefficient of thermal expansion of highly enriched 28Si, Metrologia, [online], (Accessed June 13, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created October 1, 2009, Updated February 19, 2017