Precise lattice-constant determinations using measured beam and crystal tilts

Bond's method [Bond (1960). Acta Cryst. 13, 814-818] has been commonly used to measure precise lattice constants of single crystals. One source of error is the uncertainty in the beam tilt which is usually fixed and unknown. A method is presented here whereby the beam and crystal tilts can be measured to ±0.5 milliradians (mrad). Data taken on a gadolinium gallium garnet single-crystal with the beam tilt set at - 6.0, 0 and + 5.0 mrad confirms the analysis of Burke & Tomkeieff [Acta Cryst. (1968), A24, 683-685; J. Appl. Cryst. (1969), 2, 247-248] and the separate analysis of Gruber & Black [J. Appl. Cryst. (1970), 3, 354-357].