Abstract
The atomic structure of (1−x)PbTiO3-xBi(Zn0.5Ti0.5)O3 (x=0.1, 0.2, 0.25) is investigated across the tetragonal to cubic phase transition by neutron powder diffraction measurements up to temperature T=750°C. Both the long-range average structure and the local atomic distributions are studied from Rietveld refinements and atomic pair distribution function (PDF) analysis combined with reverse Monte-Carlo (RMC) modeling, respectively. In the tetragonal phase, the average structure is featured with a large shift of oxygen, which is responsible for an off-centering of cations. With increasing concentration x, the shift of the planar oxygen along the c-axis increases further. The increment of the oxygen displacement is larger than that of the Ti/Zn displacement. This makes the off-centering of cations larger at higher x, which enhances the stability of the tetragonal phase with higher transition temperature. On thermal displacements, the heaviest ion Pb/Bi in the structure exhibits the largest value and is also increased by the concentration x in both the tetragonal and cubic phases. The local structure from PDF and RMC modeling shows that the abnormal thermal displacements are due to a large distribution of Pb off-centering and a bond-length mismatch between Ti–O and Zn–O bonds. Based on these complementary local and average structures, a splitting between Ti and Zn displacements is discussed.
Published Version
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