Charge Density Study on Phase Transition in BaTi2O5 Ferroelectric

概要

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The accurate crystal structure of BaTi2O5 ferroelectric has been derived at the charge density levels from 100 to 900 K in both the paraelectric and ferroelectric phases. High-energy synchrotron-radiation powder-diffraction data were taken and analyzed by the maximum entropy method (MEM)/Rietveld method. Three independent Ti–O6 octahedra in the structure of BaTi2O5 are distorted, two of which can be regarded as having five-oxygen coordination in both phases. The structural change associated with the ferroelectric phase transition is characterized by the occurrence of extra distortion in Ti1–O6, which is the least distorted octahedron above $T_{\text{C}}$. The spontaneous polarization calculated from the determined crystal structure is $P_{\text{s}} = 15$ μC/cm2 at room temperature. The contribution of the distortion of Ti1–O6 to $P_{\text{s}}$ is about 80%.
2009-09-25