Chemical-Pressure-Modulated BaTiO₃ Thin Films with Large Spontaneous Polarization and High Curie Temperature

Abstract

Although BaTiO3 is one of the most famous lead-free piezomaterials, it suffers from small spontaneous and low Curie temperature. Chemical pressure, as a mild way to modulate the structures and properties of materials by element doping, has been utilized to enhance the ferroelectricity of BaTiO3 but is not efficient enough. Here, we report a promoted chemical pressure route to prepare high-performance BaTiO3 films, achieving the highest remanent polarization, P r (100 μC/cm2), to date and high Curie temperature, T c (above 1000 °C). The negative chemical pressure (∼−5.7 GPa) was imposed by the coherent lattice strain from large cubic BaO to small tetragonal BaTiO3, generating high tetragonality (c/a = 1.12) and facilitating large displacements of Ti. Such negative pressure is especially significant to the bonding states, i.e., hybridization of Ba 5p–O 2p, whereas ionic bonding in bulk and strong bonding of Ti eg and O 2p, which contribute to the tremendously enhanced polarization. The promoted chemical pressure method shows general potential in improving ferroelectric and other functional materials.

Chemical pressure in functional materials

“…Since the nature of chemical pressure can also be considered as elastic lattice strain, in a chemical way instead of a physical one, we can describe chemical pressure by applying Eq. (1-2): 54 𝑑𝑃 = −𝐸 𝑑𝑥 𝑥 0…”

“…The "interphase strain" method can also be extended to other materials (111). 54 For BaTiO3/BaO, the negative chemical pressure (~ -5.7 GPa) was imposed by the coherent lattice strain from large cubic BaO to small tetragonal BaTiO3, generating high tetragonality (c/a = 1.12) and facilitating large displacements of Ti. This leads to the record remanent polarization Pr (100 μC/cm 2 ) in any forms of BaTiO3 to date with a high Curie temperature Tc (above 1000 °C), see Fig.…”

“…The interphase strain method has the advantage of providing not only isotropic negative chemical pressure but also isotropic positive chemical pressure, through selective phase matches, and the magnitude of chemical pressure can be modulated by adjusting the composition. 54 This review summarizes the development of chemical pressure and defines the concept as a methodology for material design: a lattice internal force caused by chemical modifications. The main feature of chemical pressure is that the lattice strain is caused by a chemical way, instead of physical one, and hence is diverse and does not require extreme conditions.…”

Efficient Production of Solar Hydrogen Peroxide Using Piezoelectric Polarization and Photoinduced Charge Transfer of Nanopiezoelectrics Sensitized by Carbon Quantum Dots

“…Analyses of the powder X‐ray diffraction (XRD) patterns in Figure 3b showed that both undoped and doped BaTiO 3 belonged to a tetragonal phase of the space group P 4 mm (99). [ 42 ] The half‐peak widths for the XRD lines were slightly wider for BaTiO 3 :Nb/C and BaTiO 3 :Nb than for BaTiO 3 (Figure S4 , Supporting Information). The tetragonal (101)/(110) diffraction peaks of BaTiO 3 :Nb/C and BaTiO 3 :Nb shifted to higher angles (about 0.12° shifts) when compared to pristine BaTiO 3 (Figure S4 , Supporting Information) as a result of Nb 5+/4+ (0.064/0.068 nm) replacing in part larger Ba 2+ (0.135 nm), according to the analysis using the Bragg equatio, 2 d sin θ = λ .…”

Ferroelectric thin films: performance modulation and application

“…62 Similar structures were also obtained in BaTiO 3 :BaO epitaxial composite films (c-BTO). 77 The cross-sectional HAADF-STEM image (Fig. 3d) of c-BTO shows that BaTiO 3 and BaO have a coherent interface and that interphase strain exists between them.…”