Monoclinic structure of ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{Mn}}_z{\mathrm{O}}_3$ $(x=0.212,z=0.958)$

Single-crystal x-ray diffraction is used to show that the crystal structure of ${\mathrm{La}}_{0.788}{\mathrm{Sr}}_{0.212}{\mathrm{Mn}}_{0.958}{\mathrm{O}}_3$ is monoclinic at room temperature. The Curie temperature of this sample is 324 K. The space group is determined as $I2/c$ with lattice parameters $a=5.4863\mathrm{}$ (3) Å, $b=5.5361\mathrm{}$ (3) Å, $c=7.7941\mathrm{}$ (4) Å, and $\beta =90.74\mathrm{}$ $\mathrm{}\left(2\right)\mathrm{}°.$ The crystals are found to be multiply twinned with nonequal volume fractions of the twin domains. A structure refinement against the diffraction data of a twinned crystal converged at $R=\mathrm{0.040.}\mathrm{}$ The structure model involves the same pattern of tiltings of the ${\mathrm{MnO}}_6$ octahedra as was found in the rhombohedral structure. The principal distortions of the monoclinic structure as compared to the rhombohedral structure are deviations of the O-Mn-O bond angles within the ${\mathrm{MnO}}_6$ octahedra from $90°.$ It is argued that the small size of the monoclinic splitting and the very weak additional reflections might not have been visible in neutron diffraction. Our finding of monoclinic symmetry for this compound calls for a revision of the phase diagram of ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$ compounds $\mathrm{}(0<x<\mathrm{}1\mathrm{}).$