Ultra-high-angle double-crystal X-ray diffractometry (U-HADOX) for determining a change in the lattice spacing: experiment

An experiment is reported on ultra-high-angle double-crystal X-ray diffractometry (U-HADOX) at the Bragg angle (theta)up to 89.5(degree), coupled with white X-rays from a conventional source. It is shown that the Bragg-peak shift associated with a change in the lattice spacing increases in proportion to tan(theta) as predicted; the relative accuracy of a change in the spacing to 10^-8 is attained. The performance is demonstrated for the determination of the linear thermal-expansion coefficient (alpha)of silicon and strontium titanate SrTiO3, a value with four significant figures being determined with the data in a temperature range narrower than 1  K; the value of (alpha) for silicon (2.621  +-  0.003)  *  10^-6  K^-1 at 300.4  K is compared with those in the literature based on experiments using the Bond method of X-ray diffraction and macroscopic thermal expansion. The advantages and characteristics of U-HADOX including the coupling with synchrotron X-rays are discussed.