Barium orthotitanate

Barium orthotitanate is the inorganic compound with the chemical formula Ba₂TiO₄. It is a colourless solid that is of interest because of its relationship to barium titanate, a useful electroceramic.

Structure

Low-temperature Ba₂TiO₄ – TiO₄ tetrahedra shaded blue; Ba atoms green; O atoms red

The solid has two known phases: a low-temperature (β) phase with P2₁/n symmetry^[1] and a high-temperature (α′) phase with P2₁nb symmetry.^[2] The structure of Ba₂TiO₄ is unusual among the titanates because its titanium atoms sit in a four-oxygen tetrahedron rather than a six-oxygen octahedron.^[1][3]

Production

It forms as white crystals from a melt of BaCl₂, BaCO₃ and TiO₂^[4] or from just sintering BaCO₃ and TiO₂.^[5] Another method of preparation is heating pellets of Ba(OH)₂ and TiO₂.^[6] Additionally, there are polymer precursor, sol-gel and reverse micellar routes to Ba₂TiO₄ synthesis.^[3] Ba₂TiO₄ has also been successfully grown as a thin film with chemical vapor deposition.^[7]

Properties

• Room temperature entropy – 47.0 cal/deg. mol^[6]
• Dielectric constant – 20 (at 100 kHz)^[8]
• It is hygroscopic and decomposes with swelling in moist air.^[9]

Barium orthotitanate can remove up to 99.9% of CO
₂ from a high-temperature gas stream^[10] by the reaction:

Ba
₂TiO
₄ + CO
₂ → BaTiO
₃ + BaCO
₃

References

1. Wu, Kang Kun; Brown, I. D. (10 April 1973). "The Crystal Structure of β-Barium Orthotitanate, β-Ba₂TiO₄, and the Bond Strength-Bond Length Curve of Ti-O". Acta Crystallographica. B29 (9): 2009–2012. doi:10.1107/S0567740873005959.
2. Günter, John R.; Jameson, Geoffrey B. (14 September 1983). "Orthorhombic Barium Orthotitanate, α′-Ba₂TiO₄". Acta Crystallographica. C40: 207–210. doi:10.1107/S0108270184003619.
3. Shanker, Vishnu; Ahmad, Tokeer; Ganguli, Ashok K. (October 2004). "Investigation of Ba_2–xSr_xTiO₄: Structural aspects and dielectric properties". Bulletin of Materials Science. 27 (5): 421–427. doi:10.1007/BF02708558.
4. Bland, J. A. (August 1961). "The Crystal Structure of Barium Orthotitanate, Ba₂TiO₄". Acta Crystallographica. 14 (8): 875–881. Bibcode:1961AcCry..14..875B. doi:10.1107/S0365110X61002527.
5. Bobovich, Ya. S. "The Raman Scattering of Barium Orthotitanate". Optics and Spectroscopy. 13: 254–255.
6. Todd, S. S.; Lorenson, R.E. (August 1952). "Heat Capacities at Low Temperatures and Entropies at 298.16K. of Orthotitanates of Barium and Strontium". Journal of the American Chemical Society. 74 (15): 2043–2045. doi:10.1021/ja01135a014.
7. Guo, Dongyun; Goto, Takashi; Wang, Chuanbin; Shen, Qiang & Zhang, Lianmeng (2012). "High-speed growth of (103)-oriented Ba₂TiO₄ film by laser chemical vapor deposition". Materials Letters. 70: 135–137. doi:10.1016/j.matlet.2011.11.094.
8. Ahmad, Tokeer; Ganguli, Ashok K. (1 October 2004). "Synthesis of nanometer-sized particles of barium orthotitanate prepared through a modified reverse micellar route: Structural characterization, phase stability and dielectric properties". Journal of Materials Research. 19 (10): 2905–2912. Bibcode:2004JMatR..19.2905A. doi:10.1557/JMR.2004.0406.
9. Jaffe, Bernard; Cook Jr., William R.; Jaffe, Hans (1971). "5. Barium Titanate". Piezoelectric Ceramics. London and New York: Academic Press. p. 62. ISBN 0123795508.
10. Saito, Yoshinori; Sato, Hideto; Sakabe, Yukio (20 May 2008). "CO₂ Recovery at High Temperatures Using Ba₂TiO₄". Journal of Chemical Engineering of Japan. 41 (5): 441–446. doi:10.1252/jcej.07WE236.