Synthesis, crystal structure, and characterization of Ba(Ti1/2Mn1/2)O3:: A high permittivity 12R-type hexagonal perovskite

A 12R-type hexagonal perovskite, Ba(Ti1/2Mn1/2)O-3, has been prepared by a mixed oxide route at 1250 degreesC in air and the crystal structure established by a joint Rietveld refinement of powder X-ray and neutron diffraction data at room temperature [space group Mm, a = 5.69135(2) Angstrom, and c = 27.91860(15) Angstrom]. The structure consists of a (hhcc)(3) stacking sequence of BaO3 close-packed layers along the c-axis with face sharing M3O12 trimers connected by a vertex sharing octahedron. Partial ordering of the Ti+IV and Mn+IV ions occurs in the B-site substructure; Mn+IV ions occupy the central octahedral site in the trimers, Ti+IV ions occupy the octahedral site in the vertex sharing octahedron, and both ions occupy the outer octahedral site of the trimers. Impedance spectroscopy and microwave dielectric resonance measurements on dense pellets (>97% of the theoretical X-ray density) show the title compound to be a modest dielectric insulator at room temperature with high permittivity, epsilon(r) similar to 45 (at both radio and microwave frequencies); a modest unloaded quality factor, Q(u) similar to 2026 (at similar to5.75 GHz); and a temperature coefficient of resonant frequency, TCf = -4 ppm K-1.