Abstract
Several compositions in the Pb n Nb 2 O5+ n system have been ascribed nearly identical distorted pyrochlore symmetries, with the degree of distortion increasing with PbO content. Rietveld refinements of neutron diffraction data for the n =1.5 composition have confirmed its cubic structure. Defect layers form for n > 1.5, and their density increases with n . The temperature coefficient of resonant frequency (TCF) of Pb 2 Nb 2 O 7 is 814 MK −1 . The substitution of Ta for Nb decreases TCF significantly, down to 223 MK −1 for Pb 2 (Nb 0.5 Ta 1.5 )O 7 , and increases the defect density slightly. Further substitution of Ca for Pb significantly alters the structure of these defect layers, although the product remains single-phase. The structure and properties of Ca 2 Nb 2 O 7 and Ca 2 Ta 2 O 7 have also been studied. Ca 2 Nb 2 O 7 is monoclinic and ferroelectric at room temperature, containing (100) domains but no defect layers. Monoclinic Ca 2 Ta 2 O 7 , on the other hand, is not ferroelectric but does contain defect layers similar in appearance to those found in Pb-niobate-tantalates.
| Original language | American English |
|---|---|
| Journal | Journal of the European Ceramic Society |
| Volume | 24 |
| Issue number | 6 |
| State | Published - 2004 |
Keywords
- Defects; Dielectric properties
- Electron microscopy
- Niobates
- Tantalates
EGS Disciplines
- Materials Science and Engineering