Chemical Pressure Effect on Superconductivity of BiS^sub 2^-Based Ce^sub 1-x^Nd^sub x^O^sub 1-y^F^sub y^BiS^sub 2^ and Nd^sub 1-z^Sm^sub z^O^sub 1-y^F^sub y^BiS^sub 2

We have studied crystal structure and physical properties of REO...F...BiS... (Ce...Nd...O...F...BiS... and Nd...Sm...O...F...BiS...) with three different F concentration (y = 0.7, 0.5, and 0.3) to investigate relationship between the emergence of superconductivity and crystal structure in the REO...F...BiS... series. REO...F...BiS... is suitable for discussing chemical pressure effect on physical properties because the RE site at the blocking layer can be fully or partially substituted by various RE... ions, which could systematically tune the lattice volume. With increasing chemical pressure (with decreasing lattice volume), lattice constant of a-axis systematically decreases while lattice constant of c-axis does not show a remarkable change, indicating that the RE site substitution basically affect the lattice constant of a-axis. On the other hand, lattice constant of c-axis can be tuned by F concentration. On the basis of magnetic susceptibility measurements, we have obtained three kinds of superconductivity phase diagram with y = 0.7, 0.5, and 0.3 as a function of RE concentration (chemical pressure). For all the systems with y = 0.7, 0.5, and 0.3, chemical pressure basically increases superconducting transition temperature (T...) with increasing chemical pressure. Having compared these three phase diagrams, we have suggested that there are at least two important structure parameters, (1) lattice contraction along a-axis, (2) optimal lattice contraction ratio (c/a), are essential for the emergence of superconductivity and increase in T... in REO...F...BiS... (ProQuest: ... denotes formulae/symbols omitted.)