Displacive Transformation in Ceramics

Abstract : An interdisciplinary study of displacive phase transformations in ceramics has been undertaken. The unifying themes were to obtain an in-depth understanding of (1) nucleation and (2) transformation mechanisms. The ceramic systems focused on, and studied from different perspective, included lead titanate (PbTiO3), potassium niobate (KNbO3), yttrium barium copper oxide (YBa2Cu3O6+x) and dicalcium silicate (Ca2SiO4). The cubic to tetragonal transformation in PbTiO3 was proven to be martensitic, and the experimental observations illustrated a predicted theoretical mechanism of common habit plane variants which had not yet been observed in any other system. Shape memory and superelasticity effects were discovered in doped PbTiO3 ceramics which exhibited field-induced antiferroelectric to ferroelectric transformations. The effect of oxygen partial pressures on the transformation mechanism and microstructure in YBa2Cu3O6+x single crystals, leading to elastic deformation, has been ascertained. A comprehensive understanding of the complex sequence of ferroelastic transformations in Ca2SiO4 with volume changes up to 12 % has been achieved. For the first time, a case study of martensitic nucleation in a KNbO3 ceramic has almost been assembled, with complementary aspects of theoretical lattice dynamics, phonon properties, (RT) elastic moduli and in situ hot stage TEM microstructural studies having been determined prior to and during transformation. Ceramics, Displacive phase transformations, Martensitic nucleation, Precursor phenomena, Plastic properties, Mechanisms, Crystallography, Lattice dynamic theory