Structural parameters of bulk crystalline materials can be accessed in a damage-free manner by high-energy X-ray diffraction. Specific parts of the sample can be characterized if they are distinguished by the lattice spacings. This technique is applied for the first time to massive Si1-xGexcrystals with locally varying concentrations x. The data reveal e.g. an unusual lattice distortion with an in-plane expansion and an out-of-plane contraction if the samples are deposited at high temperature (1350 K). This is opposite to a distortion inferred from the difference in the lattice constants of Si and Ge. © 1995 IOP Publishing Ltd.