INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH VOLUME 4, ISSUE 04, APRIL 2015 ISSN 2277-8616 37 IJSTR©2015 www.ijstr.org High Thermoelectric Performance Of Unsintered NaCo 2 O 4 Nanocrystal Mehmet OkanErdal, Mustafa Koyuncu, İbrahim Uslu Abstract: Sodium cobaltite (NaCo2O4) nano crystalline thermoelectric materials were obtained using electrospinning technique. Electrospunnanofibers was calcined at 800 o C and sintered at 850 o C in open air atmopshere. We have investigated the microstructure and thermoelectric properties of the sintered and unsintered samples for analysis sintering effect. The calcined sodium cobaltite crystal structures were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Products molded by cold pressing method, and one of the pellets were sintered at 850 o C by conventional sintering, the other not subjected to the sintering process. Thermoelectric properties of the both materials were measured by PPMS system in the temperature range 10-300 K. The dimensionless figure of merit (ZT) values at 300 K is 4 × 10 −5 and 9 × 10 −5 for sintered and unsintered samples respectively. Although conventional sintered technique increase thermoelectric power and thermal conductivity approximately % 50 but it 4-fold decreased electrical conductivity. Index Terms: Thermoelectric properties, Sodium Cobal OxideNanocrystalline, Electrospinning. ———————————————————— 1 INTRODUCTION THERMOELECTRIC is a generic name given to the event the conversion of heat energy directly into electrical energy or vice versa. This idea is very valuable in today's world which is rapidly increasing energy consumption. Thermoelectric energy conversion is considered to be the energy source of the future. A high performance thermoelectric material must have high thermoelectric power, electrical conductivity and, low thermal conductivity [1]. However, requirements for high- efficiency thermoelectric materials are not easily satisfied since these three parameters are interrelated [2], [3]. In recent years, different approaches have been used for improving the thermoelectric efficiency. The idea of using nanotechnology to further improve conventional thermoelectric materials has led to many exciting results to increase the electrical conductivity or to decrease the thermal conductivity [4], [5], [6].In addition, the molding and sintering technique is also very important for the yield of good thermoelectric material production [7], [8], [9], [10]. In recent years, Polymeric precursor such as poly vinyl alcohol (PVA) have been researched in thermoelectric devices recently due to solution-process-based fabrication, such as electrospinning, spin coating, and inkjet printing [11], [12]. It is found that long chain polymers have a substantial effect on the electrical conductivity. Also, the thermal conductivity of polymer increases with the increase of polymer chain length as has been shown by Zhao et al. [13]. In this study PVA polymeric precursor is used to prepare nanocomposite powders that, when sintered, convert to pure Sodium–cobalt oxide (NaCo 2 O 4 ). It has been revealed that NaCo 2 O 4 has potential as a thermoelectric material [2],[14], [15], [16] because of the sodium cobaltite have high Seebeck coefficient, low resistivity and low thermal conductivity. Since NaCo 2 O 4 is a ceramic material it can be used at high temperatures without deterioration of their performance due to oxidation [17], [18]. 2 Experimental Details In this study, PVA (average molecular weight of 85 000- 124000 g/mol) was obtained from Sigma Aldrich and sodium and cobalt acetate was obtained from Merck. Deionized water was used as a solvent. Aqueous PVA solution (10%) was first prepared by dissolving PVA powder in distilled water and heating at 80 o C with stirring for 3 h, then cooling to room temperature. Sodium and cobalt acetate solutions were added to the aqueous PVA at 60 o C separately and drop by drop and the solution was vigorously stirred for one hour at this temperature. Stirring was continued for 2 h at room temperature. Thus, a viscous gel of PVA/Na-Co acetate solution was obtained. The polymeric solution was first transferred to a 50 mL syringe, which was connected to a capillary needle with an inside diameter of 0.8 mm. A copper electrode was attached to the needle, a DC power supply produces 35 kV against a grounded collector screen distant 15cm. With the syringe pump set at 2 mL/h, the electric force overcomes the surface tension of the solution at the capillary tip, and a jet emerges. Nanofibers wascalcined at 800 o C for 12 h in atmospheric conditions and these powders was pelleted under 5000 MPa of pressure. The pellet samples was sintered at 850 o C for 12 h in atmospheric conditions. 3 MEASUREMENT AND CHARACTERIZATION Composite morphology was taken by scanning electron microscopy JEOL JSM 7000 on the samples sputtered with gold and observed at an accelerating voltage of 20 kV. SEM micrographs of the electrospun PVA/(Co–Na) acetate nanofibers, nanopowders and surface of pellets are presented in Fig 1, _______________________  Mehmet Okan ERDAL Institute of Science and Technology,Department of Physics,SelcukUniversity, Turkey. E-mail: mehmeterdal@ttmail.com  Mustafa KOYUNCU Science Faculty, Department of Physics,SelcukUniversity,Turkey. E-mail: mkoyuncu@selcuk.edu.tr  İbrahim USLU Education Faculty,Department of Chemistry,Gazi University, Turkey. E-mail: uslui_1955@yahoo.com