@article{oai:nagoya.repo.nii.ac.jp:00007099, author = {Lee, kyu Hyoung and Kim, Sung Wng and Ohta, Hiromichi and Koumoto, Kunihito}, issue = {8}, journal = {JOURNAL OF APPLIED PHYSICS}, month = {Apr}, note = {The thermoelectric properties and crystallographic features of layered perovskite-type Ca-substituted (Sr1−xCax)3(Ti1−yNby)2O7 (y=0–0.2), Ruddlesden-Popper phases were investigated. The influence of crystal structure and carrier concentration on the carrier effective mass for Ti-based metal oxides based on TiO6 octahedra and having a significant Ca substitution effect are discussed. It was found from structural analysis that the large Seebeck coefficients of Ca-substituted compounds can be attributed to the high values of carrier effective mass, which originates from the enhancement of the symmetry of the TiO6 octahedra. Low thermal conductivities, 3.6–3.8 W m−1 K−1 at 300 K, were obtained for Ca-substituted compositions due to phonon scattering at SrO/ (SrTiO3)2 interfaces of the inherent superlattice structure and to mass-defect phonon scattering between Ca (MCa=40) and Sr (MSr=88). The highest ZT value obtained was 0.15 at 1000 K, for 10 at % Ca-substituted Sr3(Ti0.95Nb0.05)2O7.}, pages = {083707--083707}, title = {Thermoelectric properties of layered perovskite-type (Sr1_x Cax)3 (Ti1_y Nby)2 O7}, volume = {101}, year = {2007} }