Crystal versus electronic structure

Crystal versus Electronic Structure Are There Really Polyacetylene-Like Gallium Chains in Li Ca. ... 

Here again certain trends were observed, and the most influential factor was the crystal structure which the superconducting material adopted. The most fruitful system was the NaCl-type structure (also referred to as the B1 structure by metallurgists). Many of the important superconductors in this ceramic class are based on this common structure, or one derived from it. Other crystal structures of importance for these ceramic materials include the Pu2C3 and MoB2 (or ThSi2) prototypes. A plot of transition temperature versus the number of valence electrons for binary and ternary carbides shows a broad maximum at 5 electrons per atom, with a Tc maximum at 13 K. 

We should also mention an early work by Slonimsky and Askadsky 74 who were apparently the first to observe structural changes taking place in extension under condition s of constant force. Three characteristic sections (see Fig. 20) were identified on the curves of strain versus tension time at F = const. These sections correspond to polymer flow in the amorphous state, the process of molecular ordering and crystallization, and, finally, to polymer flow in the crystalline state. The presence of crystalline formations on the latter section was detected with the help of X-ray-structural and electron-microscopic investigation of extended samples. As the tensile stress was lifted, the sample amorphised again and contracted. The occurrence of a drastic increase in strain on the second section was accounted for 74) by exhaustion of the longevity of supramolecular structures. 

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