A silicon powder diffraction standard reference material

Abstract

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/2 is 3.525176. With 2(Cu Kel peak) taken as 1.5405981 ~, a= 5.430880 (35) ,X, 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.

A new theory for X-ray diffraction

“…Hart et al (1988) have discussed the ratio of transmission to reflection geometry based on scattering in the symmetrical 'Bragg condition' and estimated that it is dominated by transmission geometry. This would suggest that the refraction effect would be small and cannot account for the measured difference in lattice parameters between polycrystalline Si and bulk Si (Hubbard et al, 1975). Another important conclusion of the work of Hart et al is that the refractive index is negligible at large extinction distances: the extinction distance is smallest for intense Bragg reflections that have the largest dynamical effects.…”

The refractive-index correction in powder diffraction

“…Regrettably, this analysis adds nothing to the basic debate (Hubbard, Swanson & Mauer, 1975;Hubbard, 1983) about why d's derived by powder diffraction are in practice significantly different from those measured by single-crystal methods. We have, however, been able to give clear advice that small enough powder grains should Bragg reflect according to the exact Bragg equation 2d sin 01_= A with no refractive-index correction necessary.…”

HREM studies of intergrowth between NbO and perovskite in the Ba-, Sr and K-Nb-O systems

“…X-ray powder diffraction patterns were recorded in a focusing camera of Guinier-Hâgg type, using Cu Kal radiation, and silicon [10] was added as internal standard. The photographs were analysed with a film-scanner system [11].…”