Abstract
We use time-of-flight neutron powder diffraction to examine static displacive disorder in three different pyrochlore A2B2O6O′ compounds with Bi on the A site. The compounds (Bi1.5Zn0.5)(Nb1.5Zn0.5)O6O′ (BZN), (Bi1.5Zn0.5)(Ta1.5Zn0.5)O6O′ (BZT), and (Bi1.5Zn0.5)(Sb1.5Zn0.5)O6O′ (BZS), are of interest - particularly BZN - for their high dielectric constants in the absence of any phase transition from the cubic high temperature phase. The local structures of the three compounds is characterized by displacive disorder from the ideal pyrochlore positions for both the A and O′ sites, with the precise nature of the disorder being quite similar. However the extent of displacive disorder is different, despite the B-O networks being nearly identical in the three compounds. The reported dielectric constants of the three compounds are related to the extent of local displacement, and BZN, with the largest extent of local atomic displacement of A and O′, is also reported to have the largest dielectric constant at 1 MHz. The dielectric constants are also related to the magnitudes of the thermal parameters of the different ions. The strongest correlation is found to involve the thermal parameter on the B site (Nb, Ta, or Sb).
Original language | English |
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Pages (from-to) | 961-966 |
Number of pages | 6 |
Journal | Materials Research Bulletin |
Volume | 41 |
Issue number | 5 |
DOIs | |
State | Published - May 25 2006 |
Externally published | Yes |
Funding
We thank Susanne Stemmer for suggesting the problem and Katharine Page for help with data collection. This work was supported by the National Science Foundation through the MRL program (DMR00-80034), through a Chemical Bonding Center (CHE04-34567) and through an IGERT fellowship to ER. Measurements at the Lujan Center at Los Alamos Neutron Science Center were supported by the Department of Energy Office of Basic Energy Sciences and Los Alamos National Laboratory funded by the Department of Energy under contract W-7405-ENG-36. MAH thanks the Royal Society for funding.
Keywords
- A. Electronic materials
- B. Dielectric properties