Structure and enhancement of negative thermal expansion in the PbTiO_3-CdTiO_3 system

摘要

The structures of Pb_(1-x)Cd_xTiO_3 (x=0.03 and 0.06) were investigated by the x-ray Rietveld method at room temperature. It is surprising to find that the spontaneous polarization displacements of Pb/Cd and Ti atoms according to the oxygen polyhedron decrease, although the c/a ratio increases with doping-cadmium content. Cadmium substitution plays a unique role of enhancement of the negative thermal expansion in PbTiO_3. The average bulk thermal expansion coefficient decreases from a=-1.99X10~(-5)/℃ for pure PbTiO_3 to a = -2.40X10~(-5)/℃ for Pb_(0.94)Cd_(0.06)TiO_3. The negative thermal expansion of PbTiO_3 might be a consequence of hybridization between Pb and O atoms.