Optimization of High Thermoelectric Figure-of-Merit in p-type Ag 1-x (Pb 1-y Sn y ) m Sb 1-z Te m+2
- PDF / 173,927 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 5 Downloads / 192 Views
1044-U04-08
Optimization of High Thermoelectric Figure-of-Merit in p-type Ag1-x (Pb1-ySny) mSb1-zTem+2 Kyunghan Ahn, and Mercouri G Kanatzidis Chemistry, Northwestern University, Evanston, IL, 60208 ABSTRACT The Ag1-x(Pb1-ySny)mSb1-zTem+2 compounds have been found to exhibit high performance p-type thermoelectric properties and are now being considered for practical applications. In this paper, various m values and silver concentrations were investigated to determine the effect on thermoelectric properties. Also, the charge-compensated compounds were studied in order to eliminate the problem of excess tellurium evaporation at high temperature. INTRODUCTION The direct conversion of waste heat to electricity using thermoelectric materials may play an important role in the future energy production because of the potential for environmentally benign and cost-effective power generation.[1] Efficient thermoelectric-based power generation devices require both higher thermoelectric figure-of-merit n-type and p-type materials for practical thermoelectric modules.[2],[3] The search for high TE efficiency materials is a quest to maximize the dimensionless figure of merit ZT = (σS2/κ)T, where σ is electrical conductivity, S is the TE power (Seebeck coefficient), and κ is thermal conductivity. In 2004, we reported that n-type AgPbmSbTem+2 (m =18) materials can achieve a high ZT.[4] Later we described similarly efficient p-type materials based on the Agx(Pb1-ySny)mSbzTe2+m (LASTT) series (ZT ~ 1.45 at 630 K).[5] Investigations by tuning primarily m value and Pb/Sn ratio (y value) and secondarily the Ag and Sb concentrations (x and z values) on the TE properties of p-type Ag1-x(Pb1-ySny)mSb1-zTem+2 (LASTT) series showed that x and z are important in optimizing the properties. However if these two variables are varied independently of one another the resulting materials become biphasic or multi-phasic with one of the phases being Te. The latter can begin to evaporate at the temperatures of interest (~700K) causing undesirable complications in the absence of encapsulation. Therefore, we reinvestigated the compositions of the present the LASTT so that no Te phase is created. We report here the thermoelectric properties of these p-type LASTT materials. EXPERIMENTAL Polycrystalline ingots (~ 10 gram) of Ag1-x(Pb1-ySny)mSb1-zTem+2 were prepared by heating the evacuated quartz tubes containing Ag, Pb, Sn, Sb, and Te elements at 1323 K for 20 hrs, the furnace was rocked to homogenize the liquid phase at 1323 K for 6 hrs and kept at the same temperature for 24 hrs (or the furnace was not rocked sometimes, but the ingots from unrocked furnace show similar TE properties as those from rocked furnace), and then the furnace was slowly cooled from 1323 K to 973 K for 2 days followed by a fast cooling to room temperature over 12 hrs. Powder X-ray diffraction patterns for LASTT samples were collected using a Cu Kα radiation on an Inel diffractometer equipped with a position sensitive detector and operating at
40 kV and 20 A. Electrical conducti
Data Loading...
