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Crystal. -As revealed by single crystal XRD, the title compound (tetragonal, space group P42/mnm) transforms into a new phase upon annealing at 453 K (10 d; very slow cooling). The new BaEu2Mn2O7 phase crystallizes in the orthorhombic space group Ccmm with Z = 4. The structure contains slightly distorted corner-sharing MnO6 octahedra. The orthorhombic phase changes into a tetragonal one with superstructure (P4 2 /mnm) at 402 K and changes once more into the fundamental tetragonal phase (I4/mmm) above 552 K. -(KAMEGASHIRA*, N.; MENG, J.; FUJITA, K.; SATOH, H.; SHISHIDO, T.; NAKAJIMA, K.; J. Alloys Compd. 408-412 (2006) 603-607; Dep. Mater. Sci., Toyohashi Univ. Technol., Toyohashi, Aichi 441, Japan; Eng.) -W. Pewestorf 20-008