Single crystalline BaTi 2 O 5 was prepared by a floating zone method. The single crystal was transparent having a (001) cleavage plane. The space group was C2, and the lattice parameters were a ¼ 1:6909ð9Þ nm, b ¼ 0:3937ð1Þ nm, c ¼ 0:9419ð4Þ nm and ¼ 103:12ð6Þ. The permittivity perpendicular to a (010) plane showed the maximum value of 20500 at 748 K. The permittivity perpendicular to (100) and (001) planes were about 140 and 70, respectively, independent of temperature.
Single crystalline BaTi 2 O 5 was prepared by a floating zone method. The permittivity of single crystalline BaTi 2 O 5 perpendicular to a (010) plane showed the maximum value of 20500 at 748 K obeying the Curie-Weiss law at higher temperatures. The permittivity perpendicular to (100) and (001) planes were 140 and 70, respectively almost independent of temperature. A transition temperature measured by a dilatometer was in agreement with a Curie temperature. The relationship between polarization and electrical field perpendicular to the (010) plane showed ferroelectric hysteresis. No hysteresis was observed in the direction perpendicular to (100) and (001) planes. The electrical conductivity perpendicular to the (010) was larger than those of (100) and (001) planes. The activation energy of electrical conductivity was 147 to 180 kJ mol À1 independent of directions.
The crystal structure of monobarium dititanium pentaoxide, BaTi(2)O(5), synthesized by a floating-zone method, was studied by X-ray diffraction. Previous reports describe the structure as being in the monoclinic centrosymmetric space group C2/m. We have recently found that this material exhibits ferroelectricity, and therefore BaTi(2)O(5) should have lower symmetry. The crystal structure of BaTi(2)O(5) was refined in space group C2, revealing a displacement of the Ti atoms along the b axis. This result is consistent with the fact that the ferroelectricity of BaTi(2)O(5) was only observed along the b axis.
Structure
Structure D 2000A Ferroelectric Barium Titanate, BaTi 2 O 5 . -The structure of the title compound is redetermined by single crystal XRD using a colorless crystal grown by the floating zone method. The structure was previously described in the monoclinic centrosymmetric space group C2/m, but it should have lower symmetry because the material is found to exhibit ferroelectricity. The structure of BaTi2O5 is refined in space group C2 (Z = 6), revealing a displacement of the Ti atoms along the b-axis. This result is consistent with the fact that the ferroelectrocity of BaTi 2 O 5 is only observed along the b-axis. -(KIMURA*, T.; GOTO, T.; YAMANE, H.; IWATA, H.; KAJIWARA, T.; AKASHI, T.; Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 59 (2003) 12, i128-i130; Inst. Mater. Res., Tohoku Univ., Aoba, Sendai 980, Japan; Eng.) -Schramke 14-004
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