The {111} Growth Twins in Tetragonal Barium Titanate |
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| Authors: | Yu-Chuan Wu Che-Chi Lee Hong-Yang Lu Daniel E McCauley Mike SH Chu |
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| Affiliation: | Centre for Nanoscience, Institute of Materials Science and Engineering, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan; Ferro Electronic Materials Systems, Penn Yan, New York 14527 |
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| Abstract: | The {1 1 1} twins frequently observed in pressureless-sintered BaTiO3 ceramics have been analyzed by the X-ray diffractometry, scanning and transmission electron microscopy. Both the single twins and double lamellar twins are growth (or annealing) twins. The twins lying in the {1 1 1} mirror planes, which is not one of the symmetry elements of the (basic) crystal lattice's but that of the superlattice's, are therefore superlattice twins. The {1 1 1} twins, particularly the double twins, were found more frequently from samples sintered in an Ar atmosphere of lower oxygen partial pressure (pO2). Further decreasing of pO2 using the Ar-5% H2 mixture has rendered the sintered samples entirely of hexagonal BaTiO3, the 6H-polytype. The formation of such twins is attributed to changing of the corner-sharing TiO6 octahedra to Ti2O9 face-sharing octahedra, which accommodates for local oxygen deficiency in tetragonal BaTiO3. The stacking sequence alters accordingly from c-layer (constituting the 3C-polytype, treating tetragonal pseudo-cubic) to h-layer (as in (chc)1(chc)2 of 6H). |
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