Z. Yang

Manifestation of anisotropy in melting systematics of RBa2Cu3O7−δ (R=lanthanides)

The conventional isotropic Debye temperature fails to account for the trend of melting temperatures for the high Tc superconductors, RBa2Cu3O7−δ (R-123), as a function of the ionic radius of R3+. We overcame this problem by calculating Debye temperatures using mean sound velocity along the c axis that features an anisotropic layered structure. Using the “improved” Debye temperature, the trend of derived melting temperatures based on the “Lindemann law” matches well with experimental data. This trend is also confirmed by comparing theoretical and experimental Raman active modes corresponding to the Cu–O (plane copper and apical oxygen) and Ba–O (in-plane) bonds in R-123 series.

Synthesis and crystal structure of Na1−xGe3+z: a novel zeolite-like framework phase in the Na–Ge system

A novel crystalline binary phase is reported in the Na-Ge system, with an entirely new, zeolite-like crystal structure solved and refined by the combination of synchrotron X-ray and neutron powder diffraction techniques.

A phase relation study of Ba–Y–Cu–O coated-conductor films using the combinatorial approach

Phase relationships in bulk and thin film Ba–Y–Cu–O high-Tc superconductor system were determined at processing conditions relevant for industrial production of coated conductors. Our results demonstrated that the absence of BaY2CuO5 (which has a critical effect on flux pinning) at 735 °C—a typical temperature employed in production of coated conductors—in thin films processed in situ from the BaF2 precursor is caused by the sluggish reaction kinetics rather than by the presence of fluorine in the system. Thermodynamic calculations combined with annealing experiments confirmed that BaY2CuO5 is thermodynamically stable but forms at temperatures higher than 735 °C.