Structure and negative thermal expansion in the PbTiO_3-BiFeO_3 system

摘要

The structures of (1-x)PbTiO_3-xBiFeO_3 (x=0.3 and 0.6) were investigated by means of the neutron powder diffraction. A splitting shift between Fe and Ti atoms was found along the c axis in 0.7PbTiO_3-0.3BiFeO_3; however, this splitting does not appear in 0.4PbTiO_3-0.6BiFeO_3. The tetragonal phase of PbTiO_3-BiFeO_3 exhibits a large spontaneous polarization. The negative thermal expansion of PbTiO_3 is significantly enhanced in a wide temperature range by the BiFeO_3 substitution. The average bulk thermal expansion coefficient of 0.4PbTiO_3-0.6BiFeO_3 is a_v =-3.92X10~(-5) ℃~(-1), which is much strong in the known negative thermal expansion oxides.