The development and thermoelectric efficiency depend on the temperature of P-type Ca3Co4O9 structure in energy conversion

Thermoelectric materials generate electricity as a result of the movement of electrons in the hot region towards the cold region following the gaining of a certain activation energy. Many studies have been conducted in recent years on the production of high efficiency p-type and n-type materials via thermoelectric at high temperatures. P-type Ca3Co4O9 materials are made of high temperature thermoelectric materials has a high potential to be commercialized and used in future years. The objective of this study was to determine the formation temperature using mixtures at nano-dimensions with larger micron particle sizes for the production of Ca3Co4O9, stable temperature interval for temperature dependent phases, parameters effective in crystal growth and temperature dependent thermoelectric efficiency of samples sintered at different temperatures. For this purpose, thermal analyses of mixtures prepared at different dimensions were made and the critical temperatures were determined. High temperature XRD was applied at these temperatures after which the XRD analyses of the sintered samples were carried out and the generated phases were examined. Microstructural examinations of the sintered samples, UV-VIS measurements, electrical conductivity via thermal conductivity and diffusion, Seebeck Coefficient along with power factor were determined thus examining the temperature intervals with high thermoelectric efficiency. It was found according to the acquired results that Ca3Co4O9 formation started developing at 830°C in nano-dimensioned mixtures and at 980°C which is 150°C higher in micron-dimensioned mixtures. It has been found that the temperature interval at which Ca3Co4O9 crystal remains stable was 135°C for nano-dimensioned mixtures, 80°C for mixtures with large particle size and that the difference between the two mixtures was 55°C. It was found that the particle sizes of the raw materials used at the start were effective in the formation of the crystals and their stability. In addition, the temperature interval at which Ca3Co4O9 phase remains stable is higher in mixtures with smaller particle size. It was observed that sudden cooling or stoichiometric deviations were not effective in Ca3Co4O9 crystallization and that sintering has to be carried out for very long periods of time. It was pointed out that the post-sintering samples absorb wavelengths above 350nm and that the energy band interval was between 2.2eV and 2.4eV. Thermoelectric efficiency reached the best values in samples sintered between 750-1060°C and above 1200°C. It was also put forth that higher thermoelectric efficiency may be obtained when initial raw materials sintered between these temperature intervals with smaller particle sizes were used. In addition, it was also determined that the produced material is paramagnetic and that it has a tendency to be diamagnetic with increasing sintering temperature. It was put forth that high magnetic sensitivity with high dipole moment behavior in unit magnetic area would observed in materials sintered between 980-1020°C and above 1200°C. Keywords: Energy, Thermoelectric, Ca3Co4O9, Sintering, Thermoelectric efficiency