Presentations

Mixed anion layered compounds (MACLs) demonstrate several functional electronic properties; i.e., thermoelectric conversion1, superconductivity2, and transparent semiconductivity3. These functionalities strongly depend on the chemical compositions, that had been controversial on a complex mixed anion compound. Semiconducting MALC LaCu1−deltaS0.5Se0.5O are synthesized via solid state reaction. We synthesized several nominal LaCu1−deltaS0.5Se0.5O (delta = 0, ~0.01, and ~0.02). A degenerated semiconducting bulk LaCu1−deltaS0.5Se0.5O appears at delta ~ 0.014. p-type carriers are doped due to Cu deficient Cu1−deltaS0.5Se0.5 layers in LaCu1−deltaS0.5Se0.5O. In-gap states, which dominate electrical conduction, are observed at energy ~0.5 eV higher than that of the valence band in an energy band diagram for delta ~ 0.01.

緒言 　GoldsmidとDouglasによるBi2Te3系材料の開発1)以来, 60年以上,実用を目指した熱電変換の研究は,材料の素子化やモジュール化に重点が置かれた. 近年は新たな結晶構造の材料候補が提案されつづけている. 磁性トポロジカル絶縁体としての物性の有無についての議論2,3)のある2次元磁性体EuSn2Pn2は, 熱電変換性についてSakagamiらにより報告された.4,5) EuSn2Pn2は,層状構造をとる点,空間群がR3mである点, vdW結合を有する点,および, 孤立電子対を有する点で, Bi2Te3の結晶と共通する特徴を示す. この層状化合物においては, 孤立電子対に起因する熱伝導率低減が着目されている. 実験方法 　Euは購入時,油漬されているため, 短時間, アセトンで超音波洗浄し,その表面をキムワイプで拭き取り,アルゴン雰囲気のGB内へ移動して使用した. Euは金属ヤスリを用いて, 粉末化した. P粒を, めのう乳鉢・乳棒で摩砕し得られたP粉末と,Sn粉末を,化学量比でSn：P＝１：１になるように,かつ,Sn及びPの合計の質量が0.6623ｇになるように秤量し,めのう乳鉢・乳棒で混合・摩砕した.その油圧20MPaの一軸加圧でペレット状に成型し,Sn-Pペレットを得た.化学量論比でEu:Sn:P=1:2:2となるように, Sn-PペレットとEu片を,カーボンるつぼ内に入れた.これらの作業はGB内で行った.得られた出発物入りカーボンるつぼを石英ガラス管内に真空封入し,熱処理した.熱処理後,石英ガラス管を割り,試料入りカーボンるつぼを取り出した.これをアルミ箔で包みハンマで叩き割り,試料を回収した.切り出された試料片を,めのう乳鉢・乳棒で粉砕し,XRD測定し相同定した.

超伝導は転移温度以下で電気抵抗が 0 になる現象で, 超伝導磁石や送電線に応用されている. 今回扱う鉄 系超伝導体 SmFeAsO1-xHx は, SmO 層と FeAs 層が積み重なった構造を取る. 水素負イオンをドープすると生 じた電子が鉄の反強磁性相を消し, 55 K 以下で超伝導相になる. 水素負イオンドープは多量の電子を供給で き, 超伝導転移温度を上げることが可能となる利点がある. LaFeAsO 由来の超伝導体は転移温度が約 7 K 上昇 して 35 K になる[1] . 我々は試料 SmFeAsO0.77H0.14の磁気測定により, この試料の臨界電流密度を明らかにした.

After the discovery of graphene in 2004, 2D magnetic materials have earned a great interest among condensed matter physicists and material engineers due to their fascinating magnetic properties. The 2D magnetic materials have proven that they are worth of investigating as they gave birth to van der Waals materials or topological insulators. They are the type of materials that will introduce the new era for information and semiconductor technology. The previous paper by R. Sakagami et el1,2 demonstrated that EuSn2As2 samples were prepared from Eu ingots and Sn-As pallets through a liquid phase reaction in carbon crucibles within vacuum silica tubes.1) The resulting crystal structure of EuSn2As2 has a sandwich shape where top and bottom layers are Eu, and SnAs bilayer is positioned in between Eu layers. After successful synthesis, heat capacity measurement was performed through physical property measurement system (PPMS) from Quantum Design Inc. As shown in Figure 1, we observed that there was a sudden increase of heat capacity around 24 K which implies that antiferromagnetic transition occurred. It is noted that the heat capacity of EuSn2As2 tends to follow Dulong-Petit limit at high temperature which means ultimately it would reach C = 3nR where n is the number of atoms per formula and R is the molar-gas constant. Nevertheless, at sufficiently low temperature, Dulong-Petit law does not hold anymore. It is necessary to take account for lattice vibration which is involving Debye model into our formula to obtain a value of electronic heat capacity4), Sommerfeld constant. In the conference, we will demonstrate a Sommerfeld constant for polycrystalline EuSn2As2. Acknowledgement This work was performed using facilities of the Institute for Solid State Physics, the University of Tokyo.

熱電変換材料の研究の際，性能指数の測定値の不確かさにまで注意を向けないと，極端な楽観主義に陥る恐れがある．また，熱電変換素子は，通常，定常状態で使用されるから，定常法での熱伝導率測定は重要である．本研究では，試料片からの放射熱の漏れが定常法熱伝導率に及ぼす影響を見積もった．