Significant Increase of Curie Temperature in Nano-scale BaTiO3

ABSTRACT: The low Curie temperature (Tc  = 130 °C) of bulk BaTiO3 greatly limits its applications. In this work, the phase structures of BaTiO3 nanoparticles with sizes ranging from 2.5 nm to 10 nm were studied at various temperatures by using aberration-corrected transmission electron microscopy (TEM) equipped with an in-situ heating holder. The results implied that each BaTiO3 nanoparticle was composed of different phases, and the ferroelectric ones were observed in the shells due to the complicated surface structure. The ferroelectric phases in BaTiO3 nanoparticles remained at 600 °C, suggesting a significant increase of Tc . Based on the in-situ TEM results and the data reported by others, temperature-size phase diagrams for BaTiO3 particles and ceramics were proposed, showing that the phase transition became diffused and the Tc obviously increased with decreasing size. The present work sheds light on the design and fabrication of advanced devices for high temperature applications.

Figure left: (a)–(c) Atomic resolved TEM images of BaTiO3 nanoparticles with the incident electron beam parallel to (100), (110), and (111), recorded at 200 °C, 25 °C, and 400 °C, respectively. (d)–(f). The distribution mappings of possible phases related with the corresponding symmetry, where phase with high symmetry locates in cool areas and low symmetric phases locate in warm areas.

Figure left: Phase distribution maps of six different particles with the similar size (4-5 nm) at (a) 25 C, (b) 100 C, (c) 200 C, (d) 300 C, (e) 400 C, and (f) 600 C, respectively. All the particles are composed of various phases including ferroelectric phases with lower symmetry, implying that ferroelectric phases could remain at 600 C and the Tc increases to at least 600 C in BaTiO3 nanoparticle.

DENSsolutions Comments:

Developing better technologies for efficient use of our nature resource relies on advances in new and improved nanostructure and nanomaterials. Understanding size-property relation play a crucial role in designing functional devices. (S)TEM, with enhanced by recent aberration correction, has become a powerful tool for nanomaterials characterization. It has the unique ability to image the size, shape, bulk/surface/interface structures of individual nano objects at sub-angstrom scale. Characterization of the particles over the whole temperature range provides a direct measurement of  the thermal stability of the nano-objects. The link between the size and the thermal property of the particles is then able to be obtained.
The DENSsolutions heating system provides the minimal specimen drift at elevated temperature. The atomic structure of the sample, even light atoms, e.g. Oxygen, can be clearly imaged with high precision at elevated temperature, allowing different domain structures determined within nm size particles.