Accurate determination and correction of the lattice parameter of LaB 6 (standard reference material 660) relative to that of Si (640b)

Abstract

X-ray powder diffraction and synchrotron radiation have been used to determine the lattice parameter of the NIST standard reference material (SRM 660) LaB6 as 4.156468 Å with an accuracy of 12 parts per million (p.p.m.), calibrated relative to the lattice parameter of the Si powder standard [a 0 = 5.430940 (11) Å, Si 640b]. A discrepancy of 0.00048 (5) Å, or nine standard deviations from the NIST reference, is observed between the currently accepted lattice spacing of LaB6 and the measured value. Twelve different measurements of the lattice parameter were made at beam energies between 10 and 20 keV. The observed discrepancy in the lattice parameter is consistent for the different energies us..