A Method for the Accurate Comparison of Lattice Parameters

A new method of comparison of lattice parameters is described. The method uses a standard double‐crystal diffractometer, fitted with a specimen rotation stage, which compensates for tilt errors on the specimen setting. Some improvement is possible through the use of a monochromatizing system with a well defined wavelength. The use of a single reference standard enables the instrument zero to be accurately determined; the use of a second reference or a different reflection from the first allows the wavelength to be accurately determined. The errors are carefully assessed and it is shown that some errors important in other methods are self‐cancelling through the use of the rotation stage, which need not itself be an ultraprecision component. Peak location to a confidence level of 10′′ permits absolute traceable lattice parameter determination to a few tens of parts in 106, with much greater relative sensitivity. The method is verified using both a tangent‐arm‐driven and direct‐drive double‐axis diffractometer at room temperature on samples of semi‐insulating gallium arsenide. Comparison of the lattice parameter of a sample using this method and the conventional Bond technique is satisfactory.