Depending on the preparation method

Depending on the preparation method, the surface of asprepared BaTiO3 NCs can be covered with different molecular adsorbates, such as hydroxyl groups (OH) if prepared by sol–gel or hydrothermal techniques, or carbonaceous species if synthesized from various precursor routes.104 More importantly, most of these atomic or molecular adsorbates can better stabilize the ferroelectricity of nanoscale BaTiO3. In this regard, many efforts have been made to tailor the surface of BaTiO3 NCs for manipulating their dielectric and ferroelectric properties. To date, surface modification has been widely achieved through chemical bonding with surface ligands104,106 and coatings.In one study, the n-hexylphosphonic acid (HPA)-functionalized BaTiO3 NCs possess improved dielectric constant but displayed decreased sensitivity to temperature and frequency in comparison to unmodified BaTiO3 NCs.104 Another study involving coating of a manganese (Mn) layer on 40 nm BaTiO3 nanoparticles demonstrates that surface coating can preserve the ferroelectricity of extremely small particles, enabling them to adopt a pure tetragonal ferroelectric phase.