INTERFACIAL SEGREGATION IN PEROVSKITES .2. EXPERIMENTAL-EVIDENCE

Experimental evidence determined by scanning transmission electron microscopy, scanning Auger electron spectroscopy, and lattice parameter measurements is reported for interfacial segregation in pure and doped perovskite materials, e.g., BaTiO3 and SrTiO3. The segregation behavior for isovalent dopants (e.g., Sr2+, Ca2+, or Pb2+ at a Ba2+ site) is mainly associated with a strain energy contribution from ionic misfit. However, both strain energy and space charge contributions are important in determining the segregation behavior of aliovalent ions (e.g., La3+ or Nd3+ at a Ba2+ site and Fe3+ or Ni3+ at a Ti4+ site). Segregation depths for aliovlent dopants are typically 15 to 20 nm thick. Besides dopants, constituent alkaline‐earth ions also segregate to interfaces. Their segregation behavior is promoted by high temperatures, low partial pressures of oxygen, and the presence of acceptors. The results are explained in terms of a proposed theory of segregation presented in part I of the present series. Copyright © 1990, Wiley Blackwell. All rights reserved