講演情報
[21a-P08-2]Direct Measurement of In-Plane Thermal Conductivity for Freestanding Oxide Films
〇(D)Kungwan Kang1, Fumiaki Kato2, Akitoshi Nakano2, Ichiro Terasaki2, Hyoungjeen Jeen3, Hiromichi Ohta4 (1.IST-Hokkaido Univ., 2.Physics-Nagoya Univ., 3.Physics-Pusan Nat'I Univ., 4.RIES-Hokkaido Univ.)
キーワード：
Thermal conductivity、Freestanding film、Ac-calorimetric method
Ba1/3CoO2 belongs to the layered crystal structure composed of rigid CoO2− layer and Ba2+ layer alternately stacked along the c-axis. Recently, we have reported Ba1/3CoO2 epitaxial films [1, 2] exhibit rather high ZT ~0.55 at 600 °C in air along the layered structure. This ZT value is the highest among reliable values of oxides and comparable to that of p-type PbTe and p-type SiGe at 600 °C. We fabricated the Ba1/3CoO2 epitaxial films by the reactive solid-phase epitaxy (Na3/4CoO2) followed by the ion exchange treatment. We measured the electrical conductivity and thermopower along the layered structure directly using the dc four-probe method and steady-state method, respectively. Further, we measured the thermal conductivity values of the Ba1/3CoO2 epitaxial films with two different crystallographic orientations perpendicular to the film surface by the time-domain thermoreflectance (TDTR) method. Then, we extracted the thermal conductivity along the layered structure (κ//). Here we show that the κ// values were correctly estimated. We fabricated 1 μm thick freestanding films of Sr1/3CoO2 and Ba1/3CoO2 by peeling off the epitaxial films grown on sapphire substrates using hot water.[3] Subsequently, we directly measured the κ// by the ac-calorimetric method (Figs. a and b).[4] The obtained κ// of Sr1/3CoO2 and Ba1/3CoO2 were 4.1 and 3.4 W m−1 K−1 (Fig. c), which were similar to those of the TDTR results, clearly revealing that the TDTR method can be used to extract κ// correctly.