SPring-8, the large synchrotron radiation facility

Date : 16:00-17:00　June 27, 2007

Place : Main Auditorium of the Public Relation Center

Speaker : Masaki  AZUMA

Affiliation : Institute for Chemical Research , Kyoto University

Title : Structures and properties of Bi, Pb perovskites stabilized at high pressure

Abstract : Magnetic ferroelectrics attract much attention because of the  possible application for the memory device and the fascinating  coupling between magnetic and dielectric properties.
 A classical way  to obtain a magnetic ferroelectric is to locate Bi³⁺ or Pb²⁺ ions and  a magnetic transition metal ion on A and B sites of perovskite  structure. The 6s2 lone pair and the strong covalent character of Bi (Pb)-O bonds stabilize a noncentrosymmetric distorted structure.
 For  example, BiFeO₃ is an established antiferromagnetic ferroelectrics. 
We have studied structure, magnetic and electric properties of BiMO₃  with M=Cr, Co and Ni and PbVO₃ stabilized by high-pressure synthesis. 
 BiCoO₃ and PbVO₃ are found to have tetragonal PbTiO₃ type structures  with　expected polarizations of ~100mC/cm². BiNiO₃ crystallizes in a  triclinic structure where disproportionation into Bi³⁺ and Bi⁵⁺ took  place.
 We have also succeeded in preparing a designed ferromagnetic ferroelectric double provskite Bi2NiMnO6.
 In this compound, NaCl type  ordering of Ni²⁺ (eg1) and Mn⁴⁺ (t2g3) leads to ferromagnetism with Tc=140 K.

Organizer : Mizumaki (PHS 3870)