Temperature Dependence of Structural Phase Transitions in La_1-xSr_xMnO₃ (x=0.12 and 0.17). T. Iglesias, D. E. Cox and G. Shirane, Physics Department, Brookhaven National Laboratory, Upton N.Y. 11973 USA; K. Hirota and Y. Endoh, Tohoku University, Sendai, 980 Japan.

High resolution synchrotron X-ray powder diffraction measurements have been made on samples of La_1-xSr_xMnO₃ (x=0.12 and 0.17) over the temperature interval 100-325 K. For the x=0.17 sample a very wide coexistence region was found for the rhombohedral (R-3c)-orthorhombic (Pnma) phase transition at 310 K previously reported by several groups. Although about 90 % of the rhombohedral phase transformed in the temperature region between 320-300 K, a small residual fraction persisted down to 220 K, as revealed by the presence of well-resolved diffraction peaks characteristic of both phases. Between 220-325 K the variation of the lattice parameters of the two phases did not show any marked discontinuity in the vicinity of the paramagnetic-ferromagnetic transition at about 260 K.

For the x=0.12 sample the coexistence of at least two closely-related orthorhombic phases at 300 K with Pnma symmetry was observed, the lattice parameters being respectively a=5.574(1) b=7.743(2) c=5.555(1) Å and a=5.542(2), b=7.788(3) and c=5.548(3) Å corresponding to the O' and O* phases reported in [1]. Temperature dependence measurements are currently in progress and will be discussed.

References:

[1] H. Kawano, R. Kajimoto, M. Kubota and H. Yoshizawa, Phys. Rev. B , 53 14709 (1996).

This work was supported by the US Department of Energy, Division of Materials Sciences, under contract no. DE-AC02-76CH00016.