"Barium titanate was one of the first useful piezoelectric materials, developed in the 1940s and 1950s. Although this material does not have a very high piezoelectric constant, it has a very high permittivity, making it a good material for capacitors. ... [Barium titanate] exhibits a relatively low Curie temperature, however, and therefore has not seen many developments in recent years for applications in piezoelectric devices" . The barium titanate can be synthesized as a white powder of nanoparticles or as a transparent large crystal. The solid exists in one of four polymorphisms depending on temperature. From high to low temperature, the crystal symmetries are cubic, tetragonal, orthorhombic and rhombohedral crystal structure. In the Fig. by Aksel and Jones, we can see the diagrams of the polymorphic phase transitions in barium titanate single crystals, of the spontaneous polarization and dielectric constant changing with temperature. "The low Curie temperature of barium titanate results from the tetragonal to paraelectric cubic phase transition at 120 °C. Barium titanate undergoes several additional structural phase transitions upon decreasing temperature, ... recent studies by Wada et al. on single crystal barium titanate found that these phase transitions can also be induced by applied electric field" . "BaTiO3 is known to undergo a ferroelectric transition at ∼120 °C ... Above transition temperature, BaTiO3 has cubic (O 1 h or Pm3m) symmetry with all oxygen atoms at 3c sites (Wyckoff notation), which have 4/mmm symmetry. Below transition temperature, BaTiO3 has tetragonal (C 1 4V or P4mm) symmetry with two nonequivalent oxygen sites denoted as OI and OII" .