Defects and Impurities Influences on Phase Transformations in Rare-Earth Oxides

Abstract

Several types of defects are observed on thin films (up to 2500 A) of pure rare-earth oxides of type A-Ln2 O3 and B-Ln2O3. They are (a) structural steps connected with the layered character of the structures which contain the (LnO)n n+ entities parallel to the thin-film surface, (b) reciprocal twins in B-Ln2 O3 of type I [twin plane (313)] and of type II [twin axis (132)] whose combination yields microtwinned zones; (c) planar defects; (d) dislocations; and possibly (e) antiphase boundaries. The twinning in B-Ln2 O3 is directly seen, under the electron microscope, securing the syntaxy conditions between the two phases when the A → B-Ln2 O3 or B → A-Ln2 O3 transition takes place. A small amount of yttrium in A-Nd2 O3 induces the formation of domains of B-Nd2 O3. The transformation is, from X-ray investigation, complete at 10 atomic percent yttrium, and consequently the B-Nd2 O3 phase is stabilized. An electron microscopy investigation of thin films of mixed oxides containing up to 10 atomic percent yttrium suggests the possibility that microdomains of C-Ln2 O3 are operative in the transition from A to B-Nd2 O3, which can be produced in the pure phase by a mechanical stress. A well-defined epitaxy between C and B-Ln2 O3 was determined in the mixed oxides thin films.