Structural and magnetic properties of the colossal magnetoresistance perovskite La0.85Ca0.15MnO3

A single phase sample of La0.85Ca0.15MnO3 with uniform cation distribution and complete oxygen stoichiometry was synthesized by freeze-drying technique and studied by a variety of methods. The sample is ferromagnetic below T-C= 170 K with mu(Mn)= 2.9(1) mu(B) at 10 K. Precise examination of the crystal structure by a combination of electron diffraction, high-resolution electron microscopy, and neutron powder diffraction revealed a monoclinic distortion of the GdFeO3-type structure [S.G. P2(1)/c, a=7.74476(6) Angstrom, b =5.50398(4) Angstrom, c = 5.47351(4) Angstrom, beta= 90.091(2)(0)] with nonequivalent MnO2 layers alternating along the a axis. The crystal structure is characterized by a specific pattern of Mn-O distances implying an unconventional orbital ordering type. A possible relation to charge ordering is described within the bond valence sum framework.