LAUSR

The absolute length of a single-crystal silicon gauge block was measured by interferometry in the temperature range between 285 K and 320 K and at different air pressures from atmospheric conditions down to 10-5 hPa. From the obtained dataset, the coefficient of thermal expansion (CTE) was determined as well as the compressibility -- or the bulk modulus -- of single-crystal silicon in consideration of a systematic correction of the refractometer used. As the choice of the underlying model for the evaluation is not unambiguous, a Bayesian model averaging approach was applied to take into account possible model errors in the uncertainty evaluation. The result of the CTE is not only in agreement with the recommended reference data of CODATA, but provides a standard uncertainty of less than 1 × 10-9 K-1, which is less than half the uncertainty stated so far in the relevant temperature range.