MICROSTRUCTURAL INVESTIGATION OF A NEW COMPLEX OXIDE Ho_2Mn2/3Nb4/3O_7 WITH A PYROCHLORE-RELATED STRUCTURE

摘要

A complex oxide Ho_2Mn2/3Nb4/3O_7 with a pyrochlore-related structure was synthesized from Ho_2O_3, MnO, and Nb_2O_5 in Ar containing l/100 H_2 atmo- sphere. Its structure was investigated by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The oxide, which was determined to be Ho_2.0Mn_0.6Nb_1.4O_7.1by an electron probe microanalyzer (EPMA), had a monoclinic symmetry (space group C2/c) with lattice parameters a = l.28l3(3), b = 0.7397(l), c = l. l625(2) nm, and 6 = l00.575(8). The oxide had a large number of lamellar domains bounded by planar defects on (00l), and such domains were composed of twinned structures on the twin axis < ll0>.