Influence of cation size on the structural features of Ln{sub 1/2}A{sub 1/2}MnO{sub 3} perovskites at room temperature
- Brookhaven National Lab., Upton, NY (United States). Physics Dept.
- Indian Inst. of Science, Bangalore (India). Solid State and Structural Chemistry Unit
- Univ. of Oslo (Norway). Dept. of Chemistry
- Univ. of California, Santa Barbara, CA (United States). Materials Research Lab.
Polycrystalline samples of Ln{sub 1/2}Sr{sub 1/2}MnO{sub 3} (Ln = La, Pr, La{sub 0.33}Nd{sub 0.67}, Nd, Nd{sub 0.5}Sm{sub 0.5}, Sm, and Gd) and Ln{sub 1/2}Ca{sub 1/2}MnO{sub 3} (Ln = La, Pr, La{sub 0.5}Nd{sub 0.5}, Nd, Sm, and Y{sub 0.5}Sm{sub 0.5}) 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, (r{sub A}), decreases. The two crystallographically distinct Mn-O-Mn bonds are almost identical for Ln{sub 0.5}Ca{sub 0.5}MnO{sub 3} compounds, with the exception of La{sub 0.5}Ca{sub 0.5}MnO{sub 3}. All of the Ln{sub 0.5}Ca{sub 0.5}MnO{sub 3} compounds have Pnma symmetry, whereas across the Ln{sub 0.5}Sr{sub 0.5}MnO{sub 3} series with increasing (r{sub A}), an evolution from Pnma over Imma to I4/mcm symmetry is observed. Changes in the octahedral tilt system at room temperature are linked to changes in the low-temperature magnetic structure. In particular, the simultaneous onset of charge ordering and CE-type antiferromagnetism in the Ln{sub 0.5}Sr{sub 0.5}MnO{sub 3} series appears to be closely associated with the Imma structure. The average Mn-O bond distance is relatively constant across the entire series, but individual Mn-O bond distances show the presence of a cooperative Jahn-Teller effect (orbital ordering) at room temperature in Sm{sub 0.5}Ca{sub 0.5}MnO{sub 3} and Sm{sub 0.25}Y{sub 0.25}Ca{sub 0.5}MnO{sub 3}.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC02-98CH10886
- OSTI ID:
- 316253
- Journal Information:
- Chemistry of Materials, Vol. 10, Issue 11; Other Information: PBD: Nov 1998
- Country of Publication:
- United States
- Language:
- English
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