Invited Talks: Transition Metal Oxides - University Blog Service - The ...

The John B. Goodenough Symposium in Materials Science & Engineering–
In Honor of His 90 th Birthday
The University of Texas at Austin, Austin, Texas
October 26-27, 2012
Perovskites of p-block elements: influence of the lone electron pair
José-Antonio Alonso
Instituto de ciencia de Materiales de Madrid, C.S.I.C., Cantoblanco, 28049 Madrid
Email: ja.alonso@icmm.csic.es Website: http://www.icmm.csic.es/matfuelcells/
Perovskite oxides containing p-block elements at the A positions provide the possibility of investigating
the stereochemical effect of the lone electron pair on the crystal structure and properties of these materials.
In this work we will address the singular features of two families of perovskites: Se(Te)MO 3 (M=
Mn,Co,Ni) and Pb 2 (M,Sb)O 6 (M= rare earths). The former oxides are only accesses via high-pressure
synthesis, given the small size of Se 4+ (Te 4+ ) and the extremely distorted MO 6 octahedral framework. The
irregular oxygen environment around Se(Te) is the result of the presence of the Se 4+ (Te 4+ ) non-bonded
lone 4s 2 electron pair, which is thought to be directed towards the apex of each trigonal pyramid.
Additionally, three short Se-O bond lengths, implying very covalent Se-O bonds in a trigonal pyramidal
configuration, are an important ingredient for the stability of this family of SeMO 3 perovskites. The highpressure
structural evolution also provides with clues to understand the nature of the chemical bond in
these materials. The family of Pb 2 (M,Sb)O 6 oxides, typified by Pb 2 TmSbO 6 , exhibit a room-temperature
structure never observed in double perovskites, and an original sequence of phase transitions with
temperature; in the different structures an asymmetrical distribution of the chemical bonds driven by the
strong interaction between the Pb 2+ non-bonded 6s 2 electron pair and the oxygen p states is observed,
which has been visualized from the electron localization function obtained from DFT calculations by
using accurate structural data for the room temperature crystal structure. Moreover, the presence of an
unexpected hybridization between Y and oxygen has been observed in Pb 2 YSbO 6 . This behavior involves
the oxygen atoms that form the PbO 4 polyhedron, suggesting a strong effect of the chemical pressure of
the non-bonded electron pair of lead in the whole structure of these compounds.