Lattice Parameter Determinations with an X-Ray Spectrogoniometer by the Debye-Scherrer Method and the Effect of Specimen Condition

Abstract

It is shown that the Debye-Scherrer method can be used successfully on an x-ray spectrogoniometer by removing the bisecting mechanism. Complete profiles of the diffraction lines have been recorded and the center of gravity (CG) determined with an accuracy of ±0.005°2θ. Monochromated CuKα1 radiation was employed and the complete x-ray unit housed in a room maintained at constant temperature to within ±1°C. The lattice constant was calculated from each reflection and plotted against the Nelson-Riley function; a straight line could be drawn through all the points. The limiting factors in the accuracy of the lattice constant determination are the uncertainties in the correction for vertical divergence, monochromatization, and tail effects in measuring the CG (and in the x-ray wavelength). Solid rods as well as compacts made of filings were examined after annealing and after deformation. The lattice constant of pure Al was found to be unaffected (within ±0.00005 A) by the condition in which it was examined, contrary to observations by certain other investigators. However, the lattice constants of single-phase alloys are in general quite sensitive to their state of preparation. The influence of short-range ordering, stacking faults, solute clustering, quenching stresses, etc., are discussed and their relative importance assessed.