Chapter 107 Rare earth pyrochlores
1993; Linguagem: Inglês
10.1016/s0168-1273(05)80018-2
AutoresM. A. Subramanian, A.W. Sleight,
Tópico(s)Radioactive element chemistry and processing
ResumoThis chapter provides an overview of rare earth pyrochlores. The occurrence of the pyrochlore structure is very common, because the vast majority of the elements in the periodic table are found in this structure. The ideal pyrochlore formula is A2M2X7, where A and M are cations and X is an anion, such as oxygen or fluorine. Some rare earth pyrochlores are electrical insulators; others are low-activation-energy semiconductors. Superconductivity might be expected to occur in the pyrochlore structure considering the wide variety of compositions and properties found for compounds with this structure. An interesting aspect of the pyrochlore structure is the unique coordination found for the rare earth at the A cation site. Two different descriptions of the pyrochlore structure are useful. One description views the structure as derived from the fluorite structure, and the other views the pyrochlore structure as a network structure. The network description of the pyrochlore structure has become more popular, because it leads to a natural description of defect pyrochlores, such as A2 M2 O6 and AM 2O6.
Referência(s)