TY - JOUR
T1 - Oxygen-deficiency-induced 6H-polymorph of hexagonal perovskite Ba 4YMn 3O 11.5-δ
T2 - Synthesis, structure and properties
AU - Kuang, Xiaojun
AU - Zhu, Hong
AU - Allix, Mathieu
AU - Bridges, Craig A.
AU - Rosseinsky, Matthew J.
AU - Li, Yuexiang
PY - 2012/4/28
Y1 - 2012/4/28
N2 - The 12-layer hexagonal perovskite Ba 4YMn 3O 11.5 (R3m, referred to as 12R) was transformed to a 6-layer mixed valent Mn 3+/4+ hexagonal perovskite Ba 4YMn 3O 10.7 (P6 3/mmc, referred to as 6H) via a partial-reduction in a N 2 flow. This phase transformation between the 12R and 6H phases is redox-reversible. In contrast with the 12R-type Ba 4YMn 3O 11.5 structure containing c-BaO 2.75 and h-BaO 3 layers with a (cchh) 3 stacking, the 6H-type Ba 4YMn 3O 10.7 structure consists of the cubic (c) BaO 2.87 and hexagonal (h) BaO 2.33 layers with a (cch) 2 stacking, showing a preference of oxygen vacancy distribution in the hexagonal layers over the cubic layers. The h-BaO 2.33 layer in the 6H-type Ba 4YMn 3O 10.7 transforms two-thirds of face-sharing octahedral Mn 2O 9 dimers into edge-sharing pyramidal Mn 2O 8 units, sharing corners with Y octahedra/pyramids. Impedance measurements suggested that the 6H-type material is insulating with a bulk electrical resistivity of ∼10 7 Ω cm at 303 K, significantly higher than that for the 12R-type Ba 4YMn 3O 11.5 by ∼4 orders of magnitude.
AB - The 12-layer hexagonal perovskite Ba 4YMn 3O 11.5 (R3m, referred to as 12R) was transformed to a 6-layer mixed valent Mn 3+/4+ hexagonal perovskite Ba 4YMn 3O 10.7 (P6 3/mmc, referred to as 6H) via a partial-reduction in a N 2 flow. This phase transformation between the 12R and 6H phases is redox-reversible. In contrast with the 12R-type Ba 4YMn 3O 11.5 structure containing c-BaO 2.75 and h-BaO 3 layers with a (cchh) 3 stacking, the 6H-type Ba 4YMn 3O 10.7 structure consists of the cubic (c) BaO 2.87 and hexagonal (h) BaO 2.33 layers with a (cch) 2 stacking, showing a preference of oxygen vacancy distribution in the hexagonal layers over the cubic layers. The h-BaO 2.33 layer in the 6H-type Ba 4YMn 3O 10.7 transforms two-thirds of face-sharing octahedral Mn 2O 9 dimers into edge-sharing pyramidal Mn 2O 8 units, sharing corners with Y octahedra/pyramids. Impedance measurements suggested that the 6H-type material is insulating with a bulk electrical resistivity of ∼10 7 Ω cm at 303 K, significantly higher than that for the 12R-type Ba 4YMn 3O 11.5 by ∼4 orders of magnitude.
UR - http://www.scopus.com/inward/record.url?scp=84859224602&partnerID=8YFLogxK
U2 - 10.1039/c2jm15845k
DO - 10.1039/c2jm15845k
M3 - Article
AN - SCOPUS:84859224602
SN - 0959-9428
VL - 22
SP - 8103
EP - 8109
JO - Journal of Materials Chemistry
JF - Journal of Materials Chemistry
IS - 16
ER -