Low‐Temperature Control of Twins and Abnormal Grain Growth in BaTiO₃

Abstract

The microstructure of polycrystalline barium titanate (BaTiO3) thin films processed with a liquid‐phase can be controlled by the crystallographic orientation of the underlying sapphire substrate. During postdeposition crystallization, the tendency for {111} twin nucleation, which drives subsequent abnormal grain growth, depends upon the specific sapphire facet. Specifically, tilting away from the close‐packed c‐plane modifies the orientation, morphology, and relative amount of an interfacial BaAl2O4 second phase. These factors control the density of twin formation, and thus overall grain size of the crystallized BaTiO3. As the substrate orientation transitions from c‐plane, to r‐plane, to a‐plane, the twin density is reduced, the average grain size decreases systematically from 270 to 130 nm, and the grain structure becomes overall more homogeneous. This twinning mechanism and abnormal grain growth occur by 900°C, several hundred degrees lower than reported previously.

Scaling Effects in Perovskite Ferroelectrics: Fundamental Limits and Process‐Structure‐Property Relations

“…shows permittivity measurements from room temperature to 200°C from several different reports. The systems shown were selected on the basis of high material density and overall quality and to illustrate the differences between a 75‐nm‐thick strain‐free single crystal, a 70 nm grain size bulk ceramic, a 55 nm grain size film (~180 nm thick) on platinized silicon, a 130 nm grain size film (~500 nm thick) on rigid a ‐sapphire (with top interdigitated contacts), and a 157 nm grain size film (~650 nm thick) on flexible copper foil . The latter two example thin films were processed with added BaO–B 2 O 3 (869°C eutectic composition) to enhance densification and grain growth at lower temperatures.…”

“…In this particular comparison, grain sizes are similar, processing temperatures are identical (900°C), and the liquid forming sintering aide is added to each. However, for films on sapphire the final dielectric constant is roughly 67% lower than for films on flexible substrates . Ferroelectric films on flexible substrates are one of few examples where bulk‐like permittivities, dielectric tuning, and piezoelectric coefficients are present at room temperature.…”

“…However, for films on sapphire the final dielectric constant is roughly 67% lower than for films on flexible substrates. 102,103 Ferroelectric films on flexible substrates are one of few examples where bulk-like permittivities, dielectric tuning, and piezoelectric coefficients are present at room temperature. In addition to the data shown in Fig.…”

“…Temperature dependence of permittivity for fine dimensioned BaTiO 3 materials: 75‐nm‐thick single crystal, 70 nm grain size ceramic, 130 nm grain size (500‐nm thick) film on a rigid a ‐plane sapphire substrate, 157 nm grain size (650‐nm thick) film on a flexible copper foil substrate, and a 55 nm grain size (178‐nm thick) film on a platinized silicon substrate …”

Water-Mediated Conversion of BaTiO3 Nanoparticles into BaCO3 Nanorods in Electrospun Polymer Fibers: Implications for Carbon Capture Applications

“…This may be particularly relevant for the production of BTO-based electroceramics, which involves sintering as the key process step after shaping the workable mass (powder or an aqueous paste). Our literature research revealed that there exist several reports about abnormal grain growth of BTO nanomaterials after processing and sintering at temperatures T > 1100 °C. − One study even described abnormal grain growth even within electrospun fibers, where water was also inevitably involved in the preceding materials processing. The authors clearly indicate that an intermediate BaCO 3 phase has formed, which is also consistent with independent report, but decomposes at temperatures above 700 °C.…”