Polarized Raman spectra of single and polycrystalline R 1Ϫx A x MnO 3 (RϭLa,Pr; AϭCa,Sr) ceramic samples were studied as a function of temperature. For the rhombohedral LaMnO 3.1 and La 0.7 Sr 0.3 MnO 3 , the observed Raman peaks were associated with modes arising from the folding of the Brillouin zone under lattice deformation. For the orthorhombic LaMnO 3.0 , the Raman spectra are consistent with the Pnma structure and show an anomalous softening of the 494 and 604 cm Ϫ1 modes below the antiferromagnetic ordering temperature T N Ӎ140 K. Polycrystalline samples of La 0.5 Ca 0.5 MnO 3 show a dramatic change of the Raman spectra between 100 and 160 K, which was associated with the increase of the orthorhombic distortion observed by others for TՇ240 K. Other R 1Ϫx A x MnO 3 single crystals, with small orthorhombic distortions, show Raman spectra which are similar to those observed in the rhombohedral samples.

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Ion irradiation experiments and atomistic simulations were used to demonstrate that irradiation-induced lattice swelling in a complex oxide, Lu2Ti2O7, is due initially to the formation of cation antisite defects. X-ray diffraction revealed that cation antisite formation correlates directly with lattice swelling and indicates that the volume per antisite pair is approximately 12  Å3. First principles calculations revealed that lattice swelling is best explained by cation antisite defects. Temperature accelerated dynamics simulations indicate that cation Frenkel defects are metastable and decay to form antisite defects.