Softening of bulk modulus and negative Poisson ratio in barium titanate ceramic near the Curie point

Substantial softening in the bulk modulus (a factor of five) and a negative Poisson ratio (−0.25) have been observed via broadband viscoelastic spectroscopy in the vicinity of the Curie point of a barium titanate ceramic. These effects were observed under electrical short-circuit conditions at low deformation frequencies. Softening was less in an electric open circuit or at higher frequencies. Softening of individual elastic modulus tensor elements is known to occur near phase transformations, but softening of the bulk modulus has not previously been well reported.