Accession Number:

ADA278442

Title:

Displacive Transformation in Ceramics

Descriptive Note:

Final rept. 15 Mar 1990-30 Sep 1993

Corporate Author:

AIR FORCE OFFICE OF SCIENTIFIC RESEARCH ARLINGTON VA BIOMIMETICS/BIOMATERIALS AND BIOINTERFACIAL SCIENCES

Report Date:

1994-02-28

Pagination or Media Count:

578.0

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 YBa2Cu3O6x 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 YBa2Cu3O6x 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

Subject Categories:

  • Inorganic Chemistry
  • Physical Chemistry
  • Ceramics, Refractories and Glass
  • Crystallography

Distribution Statement:

APPROVED FOR PUBLIC RELEASE