Temperature evolution of the crystal structure of La2-xSrxNiO4 (x=1/4 and 1/3) as revealed through neutron powder diffraction -: art. no. 174113

The crystal structure of La2-xSrxNiO4 (x=1/4 and 1/3) has been investigated by neutron powder diffraction. These compositions are well known to exhibit charge and spin ordering at T-co and T-so, respectively. The samples remain tetragonal with space group I4/mmm from 300 K down to 20 K. Small changes in the apical Ni-O1 and La/Sr-O1 bond lengths occur at the charge-ordering transition T-co. No unusual effects are found in the NiO2 plane. An analysis of the oxygen atom thermal parameters reveals on enhanced octahedral tilting above T-so, suggesting that charge or spin ordering relaxes the tilting. A static component to the tilting remains at 20 K, but is absent in the long-range symmetry of the structure. These observations suggest the existence of local structural distortions.