Thermal Conductivity Studies Of Thermoelectric Oxide SrTiO₃

Defects are important physical mechanism in the thermal conductivity process of crystal. In this Paper, the research background and present situation of thermoelectric materials were briefly reviewed firstly. In order to study the influence of oxygen vacancies in SrTiO3on its thermal conductivity, SrTiO3single crystals were annealed in high temperature under vacuum. The thermal conductivities of the as-received and annealed samples were determined by measuring their specific heat Cp and their thermal diffusivities. By using experimental data and combining with Callaway model, fitting curves were obtained. The near edge X-ray absorption fine structure were used to study the influence of different annealing temperature on the oxygen vacancies in SrTiO3. Our results imply specific heat of sample increases along with temperature. In low temperature, specific heat increase rapidly, near the high temperature, specific heat tends to be the same, which conformed to the Debye model. According to Dulong and Peti’s law, the specific heat is proportional to the number of atoms. So the decreases of specific heat of annealed sample should be attributed to the produce of oxygen vacancies after annealing. After annealing, thermal conductivity of SrTiO3greatly decreased, this is due to oxygen vacancies. The oxygen vacancies act as strong phonon scattering centers, and decrease the mean free path of the phonons, effectively decreases the thermal conductivity of SrTiO3. The Callaway models show that the physical mechanism of vacancy defects affecting the thermal conductivity is the phonon scattering of oxygen vacancy, and the annealing temperature get higher it will produce more oxygen vacancies. The O-K edge X-ray absorption fine structure for the annealed and as-received sample indicate that the oxygen vacancies exist in the annealed SrTiO3. Further, in order to shed light on the relationship between annealing temperature and oxygen vacancies, the samples were characterized by NEXAFS of Ti L-edge. These results help in understanding thermal conductivity process, and facilitate the next research for improving the efficiency of the thermoelectric materials.