Abstract
Polycrystalline samples of Ln1/2Sr1/2MnO3 (Ln = La, Pr, La0.33Nd0.67, Nd, Nd0.5Sm0.5, Sm, and Gd) and Ln1/2Ca1/2MnO3 (Ln = La, Pr, La0.5Nd0.5, Nd, Sm, and Y0.5Sm0.5) have been prepared, and structure determinations have been carried out at room temperature using high-resolution synchrotron X-ray powder diffraction data. The octahedral tilting distortion increases as the average ionic radius of the Ln/A cations, 〈rA〉, decreases. The two crystallographically distinct Mn−O−Mn bonds [Mn−O(eq)−Mn and Mn−O(ax)−Mn] are almost identical for Ln0.5Ca0.5MnO3 compounds, with the exception of La0.5Ca0.5MnO3. The La0.5Ca0.5MnO3 compound and the entire Ln0.5Sr0.5MnO3 series adopt structures where the Mn−O(eq)−Mn bond angle is consistently and significantly larger (2−6°) than the Mn−O(ax)−Mn bond angle. All of the Ln0.5Ca0.5MnO3 compounds have Pnma symmetry, whereas across the Ln0.5Sr0.5MnO3 series with increasing 〈rA〉, an evolution from Pnma (tilt system a-b+a-) over Imma (tilt system a-b0a-) to I4/mcm (tilt system a0a0...
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