The electrical properties of A2[Ru2−xAx]O7−y (A = Pb or Bi) pyrochlores as a function of composition and temperature
1988; Elsevier BV; Volume: 72; Issue: 1 Linguagem: Inglês
10.1016/0022-4596(88)90002-3
ISSN1095-726X
AutoresR. A. Beyerlein, H.S. Horowitz, John M. Longo,
Tópico(s)Ferroelectric and Piezoelectric Materials
ResumoThe variable stoichiometry pyrochlore compounds A2[Ru2−xAx]O7−y (A = Pb or Bi) exhibit high electrical conductivity with room temperature values ranging from 10 to 1000 (ohm-cm)−1, dependent upon composition. For the lead-containing series, resistivity vs temperature data show that there is a smooth variation from a positive to a negative temperature coefficient of resistivity (TCR) as a function of increasing lead content. Substitution of ∼20% of the ruthenium by lead results in a material with essentially temperature-independent resistivity. In the bismuth-containing series, the essentially zero TCR at zero substitution is made progressively more negative as the extent of bismuth substitution is increased. The electrical conductivity of these pyrochlore compounds is discussed in terms of electron transfer between large conducting segments consisting of connected networks of RuO6 octahedra. It is postulated that the thermally activated conductivity behavior exhibited by the negative TCR materials is associated with the presence of thin barrier regions resulting from the introduction of Pb or Bi on the Ru site. Results of infrared absorption measurements showing active modes associated with PbO but not with RuO bonds support this picture.
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