TY - CONF A1 - Chen, Cong A1 - Müller, Bernd R. A1 - Lebedev, O.I. A1 - Giovannelli, F. A1 - Bruno, Giovanni A1 - Delorme, F. T1 - Stability of the low thermal conductivity in Fe2TiO5 ceramics N2 - An increase in the thermal diffusivity of Fe2TiO5 is observed after only three cycles of measurement. X-ray refraction shows an increase in the mean specific surface. A segregation of Ca- and F-rich nanocrystals at grain boundaries is also observed by SEM and STEM-EDX. This emphasizes the importance of precursor purity and the influence of redistribution of impurities on thermoelectric properties. T2 - 10th Joint BER II and BESSY II User Meeting CY - Berlin, Germany DA - 05.12.2018 KW - X-ray refraction KW - Fe2TiO5 KW - Thermoelectrics PY - 2018 AN - OPUS4-47267 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Chen, Cong A1 - Müller, Bernd R. A1 - Lebedev, O. A1 - Giovannelli, F. A1 - Bruno, Giovanni A1 - Delorme, F. T1 - Effects of impurities on the stability of the low thermal conductivity in Fe2TiO5 ceramics N2 - The stability of the low thermal conductivity in Fe2TiO5 pseudobrookite ceramics has been studied. An increase in thermal diffusivity is observed after only three cycles of measurement. X-ray refraction shows an increase in the mean value of specific surface after the thermal diffusivity measurements. By using scanning electron microscopy and high‐angle annular dark‐field scanning transmission electron microscope equipped with energy dispersive X-ray spectroscopy, we observe a segregation of Ca- and F-rich nanocrystals at grain boundaries after three cycles of thermal diffusivity measurement. Therefore, impurities seem to be more efficient to scatter phonons as point defects in the pseudobrookite lattice rather than as nanocrystals at pseudobrookite grain boundaries. This emphasizes the importance of precursor purity and the influence of redistribution of impurities on thermoelectric properties: stability of micro-/nano-structures is a key point, and repeated thermoelectric measurements may allow detecting such metastable micro- /nano-structures and producing stable and reliable data. KW - Fe2TiO5 KW - Impurity segregation KW - Thermoelectrics KW - X-ray refraction KW - Scanning transmission electron microscopy PY - 2019 UR - http://www.sciencedirect.com/science/article/pii/S1044580318329309 U6 - https://doi.org/10.1016/j.matchar.2019.01.021 SN - 1044-5803 SN - 1873-4189 VL - 149 SP - 111 EP - 117 PB - Elsevier Inc. AN - OPUS4-47255 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Chen, Cong A1 - Giovannelli, F. A1 - Delorme, F. T1 - Thermoelectric properties of Fe2-xTi1+xO5 solid solutions: Influence of microcracking and Nb substitution N2 - The synthesis route and thermoelectric characterization of n-type Fe2-xTi1+xO5 (0 ≤ x ≤ 0.5) and Fe1.75(Ti1-yNby)1.25O5 (0 ≤ y ≤ 0.05) are presented. Their electrical conductivity obeys the small polaron model and their Seebeck coefficient is weakly dependent on temperature. The carrier concentration is increased with increasing Ti content in Fe2-xTi1+xO5, thus improving the electrical conductivity and decreasing the absolute values of the Seebeck coefficient. The composition with x = 0.5 shows reduced electrical conductivity contradicting the change in the carrier concentration, as it contains more microcracks than the other compositions. Fe2-xTi1+xO5 exhibits extremely low thermal conductivity. Fe2-xTi1+xO5 with x = 0.25 exhibits the highest ZT, ~ 0.014 at 1000 K. Therefore, a limited extent microcracks are beneficial to thermoelectric properties; however, when they are too extended they can be detrimental. On the contrary to Fe2TiO5, Nb substitution into Fe1.75Ti1.25O5 does not obviously improve its thermoelectric properties. KW - Thermoelectric KW - Pseudobrookite KW - Fe2TiO5 PY - 2018 U6 - https://doi.org/10.1016/j.ceramint.2018.08.282 SN - 0272-8842 SN - 1873-3956 VL - 44 IS - 17 SP - 21794 EP - 21799 PB - Elsevier CY - Amsterdam AN - OPUS4-46299 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -