High-temperature thermoelectric properties of (1-x)DyBCO − xBNT ceramics

ABSTRACT Dysprosium barium copper oxide – bismuth sodium titanate ((1-x)DyBCO−xBNT) ceramics, where x = 0−0.07 mole fraction, were successfully prepared by a solid-state reaction and sintering method. The DyBa2Cu3O7-δ and (Bi0.5Na0.5)TiO3 powders were separately synthesized by calcining their stoichiometric mixtures at 900°C for 4 h and 800°C for 2 h, respectively. The (1-x)DyBCO−xBNT powders were compacted into pellets and sintered at 930°C for 2 h under normal air atmosphere. Phase identification and morphology of all samples were determined using X-ray diffractometer (XRD). The quantitative phase analysis was analyzed by fitting the XRD pattern using the GSAS-II program. Scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) was used to study microstructure and chemical composition. In all cases, the result of XRD shows that the DyBa2Cu3O7–δ (Dy-123) was identified as the main crystalline phases, due to the good agreement between the observed and calculated patterns after Rietveld refinement. All BNT-doped DyBCO ceramics showed slightly higher density values than the undoped sample, suggesting that BNT helped improve the densification process. The sign of the Seebeck coefficient ( ) was positive for all samples at all measured temperatures, confirming a p-type conduction mechanism. Low BNT doping improved the overall thermoelectric properties of DyBCO ceramics by affecting electrical conductivity ( ), Seebeck coefficient ( ), and thermal conductivity ( ). The dimensionless figure of merit ( ) of all samples increased with increasing temperature. The highest value of 5.67 × 10−2 was observed for the 0.97DyBCO−0.03BNT sample at 863 K.