WELCOME TO SJSU JV Acrivos et al., Physical Chemistry in the XX to XXI Centuries: Chemistry

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¬ 3*a = 1.155 nm ®

¬ a ® ¬ a ®

Figures show SCF electron density contours, r_e>10^-3/bohr³_, TOTAL, HOMO, LUMO.

Many electron resonance interactions determine the bond distances in high temperature layer cuprate superconducting alloys, HTLSC: (Bi_1.7Pb_0.3Sr₂Ca_n-1Cu_nO_2n+4+δ)_2,n<24, (2s:2:n-1:n). Indexed in ideal D¹⁷_4h symmetry, {a_n,b_n,c_n}={3.815Ǻ,a(1+u_bn),2d_P(n+3)(1+u_cn)}_u<1% the structure gives the experimental evidence that resonance reduces the Pauling ionic radii: 2(r(Cu⁺²)+r(O^-2))= 4.2Å > a_n > d(CuO)+2^-3/2d(O₃). Oxide melts form clusters of n-1 perovskite: [P]º[½(CusO₂)/_Ca/½(CuO₂)] stacks (at ideal AB stacking sites along the Cu₄O₄ square diagonal), and its center of symmetry inverted, [P*]º[½(O₂Cu)/Ca_/½(O₂Cu)]; d_P»d(CuO)+2^-3/2d(O₃) thick along the c-axis, that are intercalated in between high melting point, [S]º [½(CuO₂)/OSr/BiO/OBi/SrO/½(O₂Cu)], hard stacks of layers, to obtain [P]_½(n-1)[S][P*]_½(n-1), c_n/2 long chains of nm cross section, where the CuO₂ exposed planes control the activity. An ideal D¹⁷_4h symmetry stoichiometric n-polymorph obtains by pairing of chains, according to the Gibbs free enthalpy of formation, DG^≠_n. But, the addition of perovskite stacks, by proximity reactions gives rise to mixed n'-polymorphs when c_n'/2=Nc_n, N=1,2,. or n'=Nn+3(N-1). A relation between the cluster size and the transition temperature to the superconducting state, T_c,n indicates that polarized free electron pairing, 2e^-Ûe₂⁼, proposed to induce the phase transition, is favored in the intercalated perovskite stacks over the entire unit cell by: -DG^≠_n/k_BT»ln((n+3)/(n-1)) »20meV/T-1.1 near T_c,n=2=87K, T_c,n=3=107K, to T_c,n'>7Þ190K within the skin depth of the lower density n'-polymorphs, that float to the alloy surface on fast cooling and annealing at 848^oC ±5^oC .