A silicon powder diffraction standard reference material

A silicon powder Standard Reference Material, SRM-640, has been prepared for use as a standard in powder diffractometry. Powder diffraction measurements were performed with a tungsten internal standard and a high-angle goniometer. The measured a/λ is 3.525176. With λ(Cu Kα₁ peak) taken as 1.5405981 Å, a = 5.430880 (35) Å, uncorrected for refraction. Comparison of a with values obtained with a single-crystal from one of the boules reveals a difference of 3 parts in 10⁵. This difference suggests a subtle systematic error in powder diffractometry or a change in lattice spacing near crystal boundaries. Use of the SRM should permit individual measurements of lattice parameters to be made reproducible to near 1 part in 10⁵ and an absolute accuracy of at least 3 parts in 10⁵.