Magnetization and Mössbauer spectroscopy results on aerosol processed YBa2 (Cu1-xFex)307–δ samples are presented. Systematics of Tc(x), x(x) and Fe dopant site occupancies In/I(x) as a function of dopant concentration ‘x’ are deduced and compared to those established on analogous solid-state- reacted samples. The absence of twinning in the aerosol processed grains leads to a random replacement of Cu for Fe in chains and planes of the host structure.

Stoichiometric Ca2CuO3, having square-planar Cu-chains [C. L. Teske and H. Müller-Buschbaum, Z. Anorg. Allg. Chem. 379, 234 (1970); M. Hjorth and J. Hyldtoft, Acta Chem. Scand. 44, 516 (1990)], is expectedly antiferromagnetic due to 1D intrachain superexchange [K. Okuda, S. Noguchi, K. Konishi, H. Deguchi, and K. Takeda, J. Magn. Magn. Mater. 104–107, 817 (1992)]. Nonetheless, we report remarkable spontaneous ferromagnetism at 293 K after sintering, prominently in oxygen. This apparently introduced excess oxygen at vacant quasioctahedral sites, promoting spin-flip and ferromagnetic interchain coupling. Thermogravimetry (TGA) revealed excess oxygen, ≈0.17 O/Cu. X-ray diffraction (XRD) yielded a comparatively smaller unit cell. Ferromagnetism disappeared by oxygen depletion, mimicking reported nonmagnetism of Ca2CuO3−δ [Okuda et al. (1992)]. Elemental analysis showed insignificant magnetic impurity traces. Tc ranged between 680 K and 723 K, depending on freshness and purity. Saturation magnetization varied with processing, optimally 0.30 A · m2/kg at 1.0 T applied field. Coercivity and remanence varied with purity.

Eine tetragonale Phase SrCuO2 bewirkt möglicherweise das supraleitende Verhalten von im Sol‐Gel‐Verfahren hergestellten Proben der nominalen Zusammensetzung Bi2Sr2CuO6. Die Meßergebnisse weisen auf eine Sprungtemperatur bis 70°C hin, wobei die Supraleitung auf eine zu weniger als 0.1% in der Probe vorhandene Phase zurückzuführen ist. Acht Proben zeigten Anzeichen von Raumtemperatursupraleitung, bei vierzehn weiteren lagen die Tc‐Werte zwischen 25 und 110 K.

A tetragonal phase SrCuO 2 possibly causes the superconducting behavior of the samples with the nominal composition Bi 2 Sr 2 CuO 6 prepared in the sol‐gel process. The results of the measurements indicate a critical temperature of 70 °C, and the superconductivity is attributed to a phase present in the sample in less than 0.1%. Eight samples show evidence of room‐temperature superconductivity, and an additional fourteen samples show superconductivity between 25 and 110 K.

A ferromagnetic series of alkaline earth cuprates has been synthesized utilizing sintering temperatures lower than those normally used. Curie point determinations for these compounds have been established and range from room temperature to 700°C.

$^{57}\mathrm{Fe}$ Mossbauer spectra of ${\mathrm{YBa}}_{2}$(${\mathrm{Cu}}_{0.985}$${\mathrm{Fe}}_{0.015}$${)}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ samples display multiple sites (n=A, B, C, and D) with the site intensity ratios ${I}_{n}$/I exhibiting profound thermal annealing effects in the temperature range 150 \ifmmode^\circ\else\textdegree\fi{}C${T}_{a}$550 \ifmmode^\circ\else\textdegree\fi{}C associated with oxygen desorption. Specifically, the ratio ${I}_{A}$/I is a function of ${T}_{a}$, and displays an activation enthalpy of site formation \ensuremath{\Delta}${H}_{A}$=104(3) meV. We ascribe it to the filling of O(1) oxygen vacancy sites in chains. The miniscule \ensuremath{\Delta}${H}_{A}$ is probably the consequence of the under-coordinated nature of the orthorhombic structure which globally promotes a superelastic (soft) lattice.

T-dependent $^{119}\mathrm{Sn}$ Mossbauer Debye-Waller factor f(T) in ${\mathrm{EuBa}}_{2}$${\mathrm{Cu}}_{2.98}$${\mathrm{Sn}}_{0.02}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ displays evidence of a substantial softening in lattice vibrations at T\ensuremath{\le}110 K. In a previous $^{151}\mathrm{Eu}$ study, no detectable softening in f(T) was found at the rare-earth site. These results taken together show that Sn atoms as a dilute impurity replace predominantly Cu(1) sites in the Cu-O chains of the orthorhombic structure. It appears that a softening in vibrational modes localized onto the Cu-O linear chains occurs as a precursor to the onset of superconductivity. These results show that phonons do appear to play an important role in electron pairing in these high-${T}_{c}$ oxide superconductors.