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Evidence for Pb-O covalency in tetragonal PbTiO3
Y Kuroiwa1, S Aoyagi, A Sawada
1Department of Physics, Okayama University, Okayama 700-8530, Japan. kuroiwa@science.okayama-u.ac.jp
Physical Review Letters
|December 12, 2001
Summary
The study reveals strong Pb-O hybridization in tetragonal lead titanate (PbTiO3), explaining its enhanced ferroelectricity compared to barium titanate (BaTiO3). This covalent bonding network is key to its unique layered structure.
Area of Science:
- Materials Science
- Solid-State Chemistry
- Crystallography
Background:
- Ferroelectric materials like lead titanate (PbTiO3) and barium titanate (BaTiO3) exhibit spontaneous electric polarization.
- Understanding the electronic structure and bonding is crucial for explaining their distinct ferroelectric properties.
Purpose of the Study:
- To accurately determine the charge-density distributions in cubic and tetragonal phases of PbTiO3 and BaTiO3.
- To elucidate the bonding characteristics responsible for the enhanced ferroelectricity in tetragonal PbTiO3.
Main Methods:
- Utilized synchrotron-radiation powder diffraction data.
- Performed analysis using the Maximum Entropy Method (MEM) combined with Rietveld refinement.
Main Results:
- Obtained accurate charge-density distributions for both cubic and tetragonal phases of PbTiO3 and BaTiO3.
- Identified strong covalency in Pb-O bonds for tetragonal PbTiO3, contrasting with ionic bonds in cubic PbTiO3.
- Observed a two-dimensional covalent-bonding network of Ti-O5 pyramids in tetragonal PbTiO3.
Conclusions:
- The observed Pb-O hybridization in tetragonal PbTiO3 provides clear evidence for its enhanced ferroelectricity.
- This hybridization, theoretically predicted, explains why tetragonal PbTiO3 is significantly more ferroelectric than BaTiO3.
- The layered structure with a covalent bonding network is a defining characteristic of tetragonal PbTiO3.