京都大学0048新制・課程博士博士(理学)甲第18098号理博第3976号新制||理||1573(附属図書館)30956京都大学大学院理学研究科化学専攻(主査)教授 吉村 一良, 教授 北川 宏, 教授 寺西 利治学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDGA

Makino, Yukio

Kyoto University Research Information Repository

Title Chemical Interpretation of Superconductivity by ValenceElectron Parameters( Digest_要約 )Author(s)Makino, YukioCitationKyoto University (京都大学)Issue Date2014-03-24URL http://dx.doi.org/10.14989/doctor.k18098Right学位規則第9条第2項により要約公開Type Thesis or DissertationTextversionnoneKyoto University学	 位	 論	 文	 の	 要	 約  題目 	 	 	 Chemical Interpretation of Superconductivity by Valence Electron Parameters  氏名	 	 	 	 Yukio MAKINO  序論	 	 	  It has been tried to interpret the generation of superconductivity in various materials and their critical temperatures (Tc) by the valence electron parameters based on the pseudopotential radii (r(s), r(p) and r(d)) for 65 elements, where r(s), r(p) and r(d) are the pseudopotential radii of s, p and d-electrons, respectively. Selecting the effective orbital electronegativity (χ(eff)=(N(v)/r(eff))1/2) and the effective electron number (N(v)) as the valence electron parameters, which are given in advance by assuming the hybridization states for 65 elements, the two-dimensional maps for various compounds have been constructed and the relations of Tc/N(atom-χ(eff) and Tc-N(v)r(eff)3 have been examined for the various compounds including high-Tc superconductors. It has been indicated that χ(eff) and the parameter N(v)r(eff)3 are the effective measures for the empirical search of a new superconductor.   Chapter 1  Introduction   The historical background and the purpose of the present thesis are explained. The importance of the physical parameters is stressed by exemplifying the construction of the crystal structure maps and syntheses of the pseudobinary nitrides in the previous papers. The purposes of the thesis are the understanding of the superconducting materials systematically by constructing the two-dimensional maps of various superconducting compounds and the perspective interpretation of superconducting critical temperature based on the pseudopotential radius and the concept of hybridization.  Chapter 2  Pseudopotential radius and orbital electronegativity   The reasons for selecting pseudopotential radius and orbital electronegativity as the two valence electron parameters and their meanings are explained from physical and chemical standpoints. Further, the possibility of applying these parameters to superconductivity is discussed.  Chapter 3  Superconductivity in elements and interpretation of critical temperature(Tc) by valence electron parameters   It has been tried to interpret the superconductivity and its critical temperature(Tc) in the elemental substances by the orbital electronegativity of the s electron, (Z/r(s))1/2, which is defined by the pseudopotential radius of the s electron, r(s), and the valence, Z. Dependence of critical temperature(Tc) on (Z/r(s))1/2 shows a concave curve with a maximum around (Z/r(s))1/2 =2.0, except for several substances and it is found that the elemental substances with higher Tc such as Nb and Pb have a (Z/r(s))1/2 value close to the threshold one corresponding to the change from metal to semiconductor. Many exceptional substances can be plotted close to the concave curve by considering the effect of the p electron or by changing the cohesion state from bulk to film, suggesting the increase of Tc value due to the increase of s- and/or p-characters, though the critical temperature for metastable elemental substances is not completely explained by the orbital electronegativity of the s electron.     Chapter 4 Two-dimensional mapping of superconducting materials based on pseudopotential radii   Two dimensional diagrams for superconducting elements and AnB(n=1, 2, 3) compounds have been constructed by using the difference (ΔrENav) between Zunger’s pseudopotential radii and the orbital electronegativity(  ! [( Z / r( sn pm ))1 / 2 ]ENav) derived from the pseudopotential radii. It is found that both superconducting elements and AnB compounds are well placed in the same domain surrounded by four boundary lines in the ΔrENav-   ! [( Z / r( sn pm ))1 / 2 ]ENav diagram. For sp-bonded elements, the boundary for superconducting/non-superconducting(SC/non-SC) is determined by a constant orbital electronegativity of   ! [( Z / r( sn pm ))1 / 2 ]ENav " 2.3 , which is close to the boundary (   ! [( Z / r( sn pm ))1 / 2 ]ENav = 2.046 ) for the metal-semiconductor transition. Superconducting elements and compounds with relatively high Tc values have an orbital electronegativity close to the value ranging between SC/non-SC and metal-semiconductor transition boundaries. It is suggested that arithmetically averaging of electronegativity is inadequate in AB-type transition metal nitrides and carbides.   Chapter 5  Dependence of superconducting critical temperature on the pseudopotential radii 	 Relation between the critical temperature and the pseudopotential radii has been examined in the superconducting elements, AB-type compounds, Fe- and Cu-based compounds by using the effective pseudooptential radii(r(eff)) assumed from the pseudopotential radii of s-, p- and d-electrons in advance. It has been indicated that the critical temperature(Tc) for many superconducting materials can be estimated by the functional form, N(v)r(eff)3, of the effective number of valence electron(N(v)) and the effective pseudopotential radius. The value of Tc shows a highly linear relation to N(v)r(eff)3 by assuming the p3dn or sp2dn hybridization for the elements connected with relatively high Tc such as V, Nb and Tc in elements and AB compounds, Cu in cuprates and Fe in pnictides and chalcogenides. The findings suggest that the p3dn or sp2dn hybridization is a key bonding character for generating high Tc in various superconducting materials.  Chapter 6  Relations between the critical temperature and the valence electron parameters 	 It has been tried to empirically understand the superconducting critical temperature Tc of various materials (24 elements, 286 AnB(n=1, 2, 3) compounds, 34 Fe- and 49 Cu-based compounds) by the effective pseudopotential radius, r(eff), and the effective orbital electronegativity, χ(eff)(=[N(v)/r(eff)]1/2). By giving the sets of values of r(eff) and the number of effective electron, N(v), for 65 elements in advance under the assumption that both the respective hybridization state and N(v) can be assigned to 65 elements by considering their chemical characters, both the Tc/N(atom)-χ(eff) and Tc-Ν((v)r(eff)3 relations are examined, where N(atom) is the number of atom in compounds.    It is found that a convex triangle-like relation between Tc/N(atom) and χ(eff) is obtained for the elements, AnB(n=1, 2, 3) compounds and both Fe- and Cu-based superconductors, in which the maximum of Tc/N(atom) is placed at around the value of χ(eff)=2.046 corresponding to the threshold of metal-semiconductor (M-S) transition. It is indicated that the cuprates and Fe-compounds with the orbital electronegativity closer to the threshold χ(eff) value show the higher Tc value, respectively.    Examining the Tc-Ν((v)r(eff)3 relation for the elements by using the sets of values of r(eff) and N(v), a linear relation (given by Tc=1.70Ν((v)r(eff)3–0.70) is obtained empirically. About two-thirds of AnB compounds as well as the Fe- and Cu-based compounds are well placed along the linear relation obtained from the elements. These results allow us to estimate the Tc value in compounds empirically based on the effective pseudopotential radius determined by the assumed hybridization.  Chapter 7  Summary of the thesis 	 	 It has been indicated that the critical temperature (Tc) can be empirically estimated by the valence electron parameters of χ(eff) and Ν((v)r(eff)3 based on pseudopotential radius. The availability of the empirical relations of both the Tc/N(atom)-χ(eff) and Tc-Ν((v)r(eff)3 are expecting for the search of new superconductors.      

価電子パラメーターによる超伝導の化学的解釈

http://repository.kulib.kyoto-u.ac.jp/dspace/bitstream/2433/188509/1/grigk03976.pdf

価電子パラメーターによる超伝導の化学的解釈

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