Stabilization Mechanism of the Tetragonal Structure in a Hydrothermally Synthesized BaTiO₃ Nanocrystal

Abstract

Higher OH concentration is identified in tetragonal barium titanate (BaTiO) nanorods synthesized by a hydrothermal method with a 10 vol % ethylene glycol solvent (Inada, M.; et al. Ceram. Int. 2015, 41, 5581-5587). This is apparently inconsistent with the known fact that higher OH concentration in the conventional hydrothermal synthesis makes pseudocubic BaTiO nanocrystals more stable than the tetragonal one. To understand where and how the introduced OH anions are located and behave in the nanocrystals, we applied ab initio analysis to several possible microscopic geometries of OH locations, confirming the relative stability of the tetragonal distortion over the pseudocubic one because of the preference of trans-type configurations of OH anions. We also performed Fourier transform infrared and X-ray diffraction analysis, all being consistent with the microscopic picture established by the ab initio geometrical optimizations.

Perovskite Oxides Prepared by Hydrothermal and Solvothermal Synthesis: A Review of Crystallisation, Chemistry, and Compositions

“…[29] Hongo et al proved that the ethylene glycol modified synthesis gave a level of hydroxide three times higher than in conventional aqueous synthesis and then used a combination of powder X-ray diffraction and modelling to identify likely locations of hydroxide defects in BaTiO3. [30] This work ascribed the stabilisation of the tetragonal perovskite, to a trans orientation of substituent hydroxide ions in the oxide sublattice. Defects have been reported in more complex titanate perovskites from hydrothermal synthesis, such as Na0.5Bi0.5TiO3 [31] and NaCe1-xLaxTi2O6 (0 < x <1), [32] where in the former, the piezoelectric properties showed evidence of polarisation pinning due to oxide vacancies after sintering.…”

TiO2-Seeded Hydrothermal Growth of Spherical BaTiO3 Nanocrystals for Capacitor Energy-Storage Application

“…It is not only time-consuming and labor-intensive but also easy to introduce impurities [29]. As an alternative to the solid-state process, various "wet chemical" methods, including sol-gel process [30,31], hydrothermal method [32], micro-emulsions [33], and oxalate process [34] have been developed to synthesize BaTiO 3 powders. These methods can produce high-purity, uniform, ultrafine BaTiO 3 powders.…”

Feature space of XRD patterns constructed by auto-encorder

“…[4] The technique has since been applied to extractions features of data [5], noise eliminations for image data [6], detections of signal anomalies [7], and to data generations to form images etc. [8] One of the promising topics in the MI is the recognitions of the peak patterns of X-ray diffraction (XRD) analysis, [9][10][11][12][13][14][15], which is common in crystal structure analysis in experiments [16] In terms of how to capture the features of patterns, all the previous studies above are based on the application of time-series signal recognition techniques. The Auto-encoder technique, on the other hand, takes a different approach to capture features: Putting features is regarded as a grouping operation made over all data, each of which has some data dimension (e.g., the number of data on time-axis).…”