Presentations

銅酸化物高温超伝導体に対して、水素雰囲気下で熱処理をほどこした際の、超伝導転移温度の変化について報告する。

Coをドープされた YBa2Cu3O7-δ (YBCO)の酸素発生反応電気化学触媒としての性質を、サイクリックボルタンメトリーにより明らかにした。Coドープは過電圧を下げ、電流量を増加する寄与がある。すなわち、触媒としての性能は向上する。

水素をドープされた鉄系高温超伝導体SmFeAsOの磁気イメージングを、磁気光学効果により測定した。その結果、ピン留めの機構に寄与する異相の分布が明らかとなった。

Zintl phase compound is one of the most promising thermoelectric materials. In particular, various high-performance thermoelectric materials were found in 122-Zintl phase compounds AM2X2 (A: alkali metal, alkaline-earth metal, M: transition metal, X: pnictogen). Recently, we found that 143-Zintl phase compounds of RbZn4As3, whose crystal structure is close to 122-Zintl phase compounds, exhibits relatively high thermoelectric performance with the value of the dimensionless figure-of-merit (ZT) to be 0.53 (T=797K) [1]. We proposed that 143-Zintl phase compound can be a new class of high-performance thermoelectric materials. In this study, we extended the study to Rb(Cd,Zn)4As3, where Zn was replaced by Cd to reduce the lattice thermal conductivity. We synthesized those samples by solid-state reactions. The total thermal conductivity of RbCd4As was extremely low to be 0.83 W/mK (T=470 K) that is advantageous for achieving high ZT value. Crystal structure analysis was conducted by powder neutron diffraction measurement. The results show that Rb atoms vibrate relatively large, which can be the origin of its low lattice thermal conductivity.

水の電気分解には、過電圧が生じるが、その過電圧を下げる効果のある電気化学触媒として、Co-doped YBa2Cu3O7-δを選択肢、触媒性能を報告する。複数の熱処理温度で得た試料の性能に対して報告する。

酸素発生反応(OER)電気化学触媒としての、Co-doped YBa2Cu3O7-δの性能について報告する。

鉄系高温超伝導体の内、最も高い超伝導転移温度(Tc)を示すSmFeAsOを母相とする化合物群の内、H-doped SmFeAsOに着目する。磁気光学効果を用いてH-doped SmFeAsOの磁気Jcの分布を20 K、30 K、40 K、50 Kで得た。

Several mixed anion layered compounds (MALCs) exhibit relatively high figure of merit (ZT).[1,2] Experimental and theoretical researches expect a promising functionality for the MALCs as thermoelectric materials, [3,4] however detailed carrier-doping mechanism and relations between crystallographic defect and resistivity are still controversial for representative mixed anion layered compounds, polycrystalline LaCu(S, Se)O bulk.[5,6,7,8] In the symposia, we demonstrate thermoelectric properties of polycrystalline LaCu(S, Se)O with a little deficient in Cu site. [1] L. D. Zhao et al., Appl. Phys. Lett. 97, 092118_1-3 (2010). Bi1−xSrxCuSeO oxyselenides as promising thermoelectric materials [2] Y. Liu et al., J. Am. Chem. Soc. 133, 20112-20115 (2011). Remarkable enhancement in thermoelectric performance of BiCuSeO by Cu deficiencies [3] For a review, W. Tang et al., Materials Today Physics 35, 101104_1-22 (2023). BiCuSeO based thermoelectric materials: Innovations and challenges [4] For a review, A. R. Natarajan et al., Phys. Rev. Mater. 7, 025405 (2023). High thermoelectric performance of layered LaAgXO (X = Se, Te) from electrical and thermal transport calculations [5] H. Hiramatsu et al., J. Am. Chem. Soc. 132, 15060-15067 (2010). Origins of hole doping and relevant optoelectronic properties of wide gap p-type semiconductor, LaCuOSe [6] Y. Goto et al., Appl. Phys. Lett. 105, 022104-022107 (2014). Effects of the Cu off-stoichiometry on transport properties of wide gap ptype semiconductor, layered oxysulfide LaCuSO [7] T. Kato et al., Mater. Sci. Tech. Jpn. 55, 67-71 (2018). Anisotropic thermoelectric exchange properties of high density polycrystalline layered oxychalcogenide, LaCuSeO obtained by uniaxial hot pressing (in Japanese) [8] N. Azuma et al., Mater. Sci. Tech. Jpn. 58, 64-68 (2021). In-gap-states of a mixed anion layered compound, polycrystalline LaCu1-deltaS0.5Se0.5O (delta~ 0.01) as a degenerate semiconductor (in Japanese)

複合アニオン層状化合物LnTMPnO (Ln : ランタノ イド. TM : Fe, Ni. Pn : P, As) は低温下で超伝導を示す。 このうち、TM = Ni, Pn = Pの試料を固相反応による合成し、磁気的性質を調べた。得られた試料は4.2 Kにおいて超伝導相を 示さなかった。これは、過去にMcQueenら(2009)によるLaNiPOの超伝導転移温度(Tc)の不定比性依存性と矛盾しない。

Layered oxychalcogenide RETMChO (RE: rare-earth, TM: transition metal, Ch: chalcogen) is known as a compound that exhibits various electronic properties such as transparent p-type conductivity and high thermoelectric efficiency. The crystallographic structure of RETMChO can be composed by variety of elements, which are replacd by several RE and TM as cations and Ch as anions. Furthermore, the carrier transport is seemed as two-dimensional because the carrier-conducting TMCh layer and the carrier-blocking REO layer are sandwiched in an unit cell. In the unit cell, a square lattice is formed by TM of the constituent elements. LaCuChO is a a representative RETMChO. In 2000-2010, several reserchers had tryed to generate p-type carrier in LaCuChO using aliovalent ion doping in the insulating TMCh layer. Hiramatsu et al. and Goto et al. reports that Cu deficient is a dominant factor to generate p-type carriers in LaCuChO. [H. Hiramatsu, T. Kamiya, T. Tohei, E. Ikenaga, T. Mizoguchi, Y. Ikuhara, K. Kobayashi, and H. Hosono, J. Am. Chem. Soc. 132, 15060 (2010). Y. Goto, M. Tanaki, Y. Okusa, T. Shibuya, K. Yasuoka, M. Matoba, and Y. Kamihara, Appl. Phys. Lett. 105, 022104 (2014).] In this study, polycrystalline LaCuS0.25Se0.75O samples were synthesized via solid state reaction. Purity of the obtained bulk samples was examined by X-ray diffraction (XRD) using CuK radiation (Rigaku Rint 2500). Total diffuse reflectance spectra were measured using a spectrometer equipped with integrating sphere (Hitachi High-Tech, U-4100). Electrical resistivity (r) was measured by the four-probe method. Thermal conductivity (k) and seebeck coefficient (S) were measured by the steady state method to evaluate dimensionless figure of merit (ZT) of the samples. The samples exhibit optical band gap ~ 2.83 eV. Broad optical absorption around 2.3 eV was also observed indicateing in-gap states due to Cu deficiency. r = 55 Ωcm, k = 5.2 Wm-1K-1, S = 339 micro VK-1, giving ZT ~ 2•10-5 at 673 K.

Bi2Sr2CaCu2O8+x (Bi-2212)に対してCoをドープを施した多結晶粉末をゾルゲル法により作製した。 CoをCuサイト、Biサイト、に部分置換を仕込み組成において試みた試料を作製した。それぞれの過電圧は、0.45 V, 0.38 Vであった。比較としてアセチレンブラックの過電圧は0.56 Vであった。すなわちBi-2212は電気化学触媒としての機能を示す。