Larmor diffraction measurement of the temperature dependence of lattice constants in CuGeO sub(3)

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 CuGeO sub(3) 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 T sub(SP)=14.1(1) K in our sample, we observe a large distribution of lattice constants ([detla]d/d[inline image]3x10[super]-3), while the mosaicity of the sample appears to be quite reasonable (20').