Defects and Transport in YBa2 Cu3 O7 − x

  • G. M. Choi
  • H. L. Tuller
  • M-J. Tsai
Part of the NATO ASI Series book series (ASIC, volume 276)

Abstract

In an attempt to understand the role of stoichiometry in controlling the transport properties of the system YBa2Cu3O7−x (0 < x < 1), we have performed electrical conductivity (σ) and thermoelectric power (Q) measurements, in situ, as a careful function of temperature, oxygen partial pressure, and oxygen stoichiometry.

In the low temperature orthorhombic phase, a continuous transition from semiconducting to metallic conduction was observed as temperature decreases and Po2 increases as a result of exothermic generation of holes. Both the magnitude of Q and the Po2 dependence of σ and Q confirm the p-type nature of the carriers. In the high temperature tetragonal phase a p-n semiconducting transition is detected which shifts to higher temperature as the Po2 is increased. Based on these results and results of measurements performed as a function of temperature for fixed values of x, we conclude that the n-type contribution is a result of the disproportionation of Cu1+ to Cu0 and Cu2+ which is characterized by an energy of 1.24 eV. A preliminary defect model is proposed which provides a framework for understanding the Po2 dependence of σ and Q.

Keywords

Oxygen Partial Pressure Thermoelectric Power Oxygen Stoichiometry Mass Balance Relation Absolute Thermoelectric Power 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Kluwer Academic Publishers 1989

Authors and Affiliations

  • G. M. Choi
    • 1
  • H. L. Tuller
    • 1
  • M-J. Tsai
    • 1
  1. 1.Crystal Physics & Optical Electronics Laboratory Department of Materials Science & EngineeringMassachusetts Institute of TechnologyCambridgeUSA

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