Precision measurements of lattice parameters of non-cubic crystals

It is shown that lattice parameters of non-cubic crystals can be accurately determined by linear extrapolation against the function ½(cos e 0/sin 0-b cos ~ 0/0) by selecting lines with suitable indices.Use can be made of the slope of the extrapolation curve of one of the parameters to derive the slope of the extrapolation curve of a second parameter.By this means, a true extrapolated value of the second parameter may be obtained when only a single appropriate reflexion is available.It is also shown that the observed sin e 0 values can be accurately corrected for drift by means of an expression of the form D sin e 0(cos ~ 0/sin 0-b cos e 0/0).Examples of lattice-parameter determinations and drift corrections are given for cobalt and for NiaTi.