High-temperature thermoelectric characterization of filled strontium barium niobates: power factors and carrier concentr
- PDF / 351,900 Bytes
- 8 Pages / 584.957 x 782.986 pts Page_size
- 34 Downloads / 184 Views
Thermoelectric properties of oxygen-deficient filled strontium barium niobates (SBN, SrxBa6xNb10O30d) in the composition range from the barium end member to a Sr:Ba ratio of 80:20 were investigated. The electrical conductivity, Seebeck coefficients, and power factors for ceramic samples annealed at 1300–1310 °C for 30 h under forming gas (;1016 pO2 atm) were evaluated from ;350 to 970 K. The conduction mechanism in the filled SBNs was found to be similar to that of the heavily-reduced unfilled SBNs reported in literature. However, relative to the unfilled counterparts heat-treated at 1016 atm pO2, larger power factors were observed in the filled SBNs. The thermoelectric performance of these filled SBNs was composition-sensitive; lower Sr contents showed higher electrical conductivities, and power factors. Electron diffraction and Hall experiments suggest that both mobility and carrier concentration are enhanced with decreasing Sr. For ceramic samples, the highest power factors achievable were found for low Sr, heavily-reduced filled compositions.
I. INTRODUCTION
Thermoelectric materials may play a pivotal role in improving energy sustainability. Thermoelectric devices are not expected to replace current methods of energy generation, but instead, to harness the waste heat that evolves from burning of fossil fuels in automobiles or power plants. Thermoelectric generators are especially attractive in that they are silent and house no moving components.1 Other advantages include reliability (exceeding 100,000 h of steady-state operation) and the scalability of size to meet the required application.2 The primary factor that prevents thermoelectrics from wider implementation is the low efficiency-to-cost ratio.1 For example, tellurium, a component in some of the most-utilized thermoelectrics, has a cost that is comparable to Pt.3 SiGe alloys are among the most efficient thermoelectric materials at high temperatures, but only possess an efficiency of around 8%.4 Currently, thermoelectrics are constrained to niche uses, especially where cost concerns are outweighed by other factors, such as in military or space applications.2 Thus, there is interest in developing less-expensive alternative thermoelectrics. Despite the ubiquity of oxides in other electronic applications, only a handful of useful oxide thermoelectrics have been reported. Layered cobaltites still lead by almost a factor of 2 in terms of zT.5 However, oxygen-deficient unfilled strontium barium niobate (or SBN, Sr5xBaxNb10O30),
which crystallizes in the tungsten bronze structure, was reported to have an upper bound of zT that was on par with the layered cobaltites.6 The term “unfilled” refers to a tungsten bronze system in which only 5 out of the 6 A-sites of the structure are occupied.7 The high figure of merit of SBN was attributed to the remarkable increase in the electrical conductivity when processed under sufficiently-reducing atmospheres.8 While oxygen vacancies act as a dopant species contributing to the electrical conductivity of SBN, only modest increase were sh
Data Loading...
