Larmor diffraction measurement of the temperature dependence of lattice constants in CuGeO3

By using the neutron Larmor diffraction method and a setup based on the improved neutron resonant spin echo option ZETA recently installed on the three-axis spectrometer IN22 (CRG beam line at the ILL), we have determined the precise relative evolution of the inter- and intra-chain lattice constants of the paradigmatic spin-Peierls compound CuGeO3 as a function of temperature. Our results are consistent with previous results obtained by conventional high-resolution diffraction. This method also allows to retrieve independently the sample mosaicities, as well as the widths of various lattice-spacings distributions, thus offering an evaluation of the intrinsic sample quality. In spite of the good definition of the spin-Peierls transition at TSP=14.1(1) K in our sample, we observe a large distribution of lattice constants (Δd/d≃3×10−3), while the mosaicity of the sample appears to be quite reasonable (≲20′).