Local structure and oxide-ion motion in defective perovskites

• Published in: Solid state ionics Vol. 68; no. 3; pp. 193 - 211
• Main Authors: Adler, Stuart, Russek, Steven, Reimer, Jeffrey, Fendorf, Mark, Stacy, Angelica, Huang, Qingzhen, Santoro, Antonio, Lynn, Jeffrey, Baltisberger, Jay, Werner, Ulrike
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.1994
• ISSN: 0167-2738; 1872-7689
• DOI: 10.1016/0167-2738(94)90177-5

Macroscopic thermodynamic and transport properties of disordered materials are determined largely by their local structure, which may differ substantially from long-range crystalline symmetry. In order to better understand local structure and ionic motion in highly disordered perovskite oxides, we have investigated several cubic perovskites using high-temperature oxygen-17 NMR in conjunction with other experimental techniques. Materials we have studied include Ba(In 0.67Zr 0.33)O y , Ba(In 0.67Ce 0.33) O y , (La 0.5Ba 0.5) (Co 0.7Cu 0.3O y , and (La 0.6Sr 0.4) (Co 0.8Cu 0.2) O y . We show that despite having the long-range cubic symmetry as determined by X-ray and neutron powder diffraction, these materials possess microdomains with layered structures on a short length scale (50–500 Å). These microdomains are apparent in HRTEM images of these materials, and manifest themselves as unit cell doublings in the electron diffraction patterns. Neutron powder profile refinements and oxygen- 17 DAS NMR both suggest that oxygen nuclei are displaced from sites of cubic symmetry in a manner reminiscent of layered perovskite-related structures. As is the case with known layered materials, the high temperature oxygen- 17 spectra and relaxation measurements show that few oxygen atoms are mobile below 800°C due to trapping of oxygen-ion vacancies in ordered layers. In the case of (La 0.6Sr 0.4) (Co 0.8Cu 0.2) O y , estimates of the vacancy trapping energy and the vacancy migration energy, extracted from NMR, appear to rationalize macroscopic transport measurements.