Composition−Structure−Property Relationships of 6H- and 12R-Type Hexagonal Ba(Mn,Ti)O_3−δPerovskites

Abstract

The crystal structures of 6H-type BaMn 0.15 Ti 0.85 O 3 , BaMn 1/4 Ti 3/4 O 2.95 , and BaMn 1/2 Ti 1/2 O 2.84 and 12Rtype BaMn 2/3 Ti 1/3 O 3 have been established by a combination of X-ray, neutron, and electron diffraction, and high-resolution electron microscopy. The 6H-type structure (space group P6 3 /mmc) can be described by a stacking sequence (hcc) 2 along the c-axis with any anion deficiency located exclusively in the h-BaO 3 layers. Ti atoms display a strong preference for the corner-shared octahedral site, whereas both Mn and Ti are distributed over the octahedral sites in the face sharing dimers. The 12R-type structure (space group R3 j m) can be described by a stacking sequence (hhcc) 3 . Ti atoms again display a strong preference for the isolated corner-sharing octahedral site, whereas Mn atoms occupy the central site of the facesharing trimers. The electrical properties have been characterized by impedance spectroscopy and reveal the fully oxidized compounds to be electrical insulators with relative permittivity values of ∼45-55 at 300 K. The oxygen-deficient compounds are semiconductors, which is attributed to the presence of mixed Mn 3+ and Mn 4+ ions on the B-site sublattice. Antiferromagnetic (AFM) interactions occur within the face-sharing units of the respective structures. The AFM interactions inside the dimers (6H-type) and trimers (12R-type) become stronger with increasing Mn content and result in an increase in the magnitude of the Curie-Weiss constant.

Magnetic dimers and trimers in the disorderedS=32spin systemBaTi1/2Mn1/

“…A good agreement of the atomic positions and bond distances is found with respect to previously published data [8,21]. Table I: Refined structural parameters and relevant bond lengths for BaTi 1/2 Mn 1/2 O3 at room temperature.…”

“…A 12R-type perovskite structure was employed in the refinement, see Fig 3(a). It consists of face-sharing trimers of octahedra connected by corner-sharing octahedra along the c axis, under the space group R3m [8,21]. All atomic occupancy factors were fixed at the stoichiometric values in our Rietveld refinement of the Neutron diffraction data.…”

Structural and magnetic properties of single perovskite Ca(Ti1/2Mn1/2)O3

“…From dw/dT as a function of temperature, the paramagnetic-antiferromagnetic transition temperature T c was determined to be 11.7 K. ZFC and FC curves diverge at about 50 K, indicating history dependence of magnetization.Similar divergence was also found in Sr(Ti 1/2 Mn 1/2 )O 3 [18] and Ba(Ti 1/2 Mn 1/2 )O 3 . Miranda et al [19] suggested that the magnetic transition of undetectable impurity Mn 3 O 4 should be responsible for this feature. In Fig.…”

Microwave dielectric properties of Ba[Ti0.4Ga0.3Nb0.3(1−x)Sb0.3x]O3 perovskite ceramics

“…ABO 3 perovskites have attracted considerable attentions for their superior electrical properties [1,2], such as ferroelectric, piezoelectric, and microwave dielectric properties. In the latter case, many cubic perovskites have been extensively studied [3][4][5] for their applications at microwave frequency.…”

“…And the structurecomposition-property relationships among them have been established. In recent years, some researches have been focused on the hexagonal perovskites for their interesting crystal structures and special physical properties [2,6]. But the formation mechanism of the hexagonal perovskites and the relationships between structures and properties are still not well clear.…”