Thermoelectric properties of Pb_2-xY_xRu₂O_7-z pyrochlore

Thermoelectric materials convert heat to electrical energy and are considered for various applications such as refrigeration or in power generations. Thermoelectric properties are characterized by a figure of merit (ZT), ZT=S²σT k^-1. ZT is a function of the Seebeck coefficient or Thermopower (S), electrical conductivity (σ), temperature (T) and thermal conductivity (k). This work aims to study the respective properties of lead ruthenate (Pb₂Ru₂O_6.5) doped with yttrium oxide in the temperature range of 25 to 300°C. Lead ruthenate has a defect pyrochlore crystal structure and has metal-like electrical conductivity. Y₂Ru₂O₇ is an insulator. Molar fractions of Pb have been substituted by yttrium, i.e., Pb_2-xY_xRu₂O_7-z with x varied between 0 and 1. The compounds were prepared by solid-state synthesis and characterized by XRF, X-ray diffraction, and SEM/EDX for composition, structure, phase content, morphology and crystal size. Micron-sized powders were pressed into pellets to measure the thermoelectric properties. The results will be discussed, particularly the transition from conductive to insulating and its effect of ZT.