= Bednorz-Müller experiment
{c}
In 1986, <Johannes Georg Bednorz> and <Karl Alexander Müller> precipitated mixed <oxalates> from aqueous <barium>, <lanthanum> and <copper> <nitrates> using <oxalic acid>. Heating at $900\,{}^\circ\mathrm C$ for five hours preceded pressing at $4\,\mathrm{kbar}$ and reheating for <sintering>. <X-ray diffraction> resolved three phases. Rectangular pieces carried <gold> electrodes and <indium> wires; <four-terminal sensing> in a continuous-flow <cryostat> measured <electrical resistance> versus <temperature>. Annealing atmosphere and measuring <electric current density> were varied; larger <electric current densities> suppressed the drop. An onset near $35\,\mathrm K$ differed from the much lower <temperature> where the drop approached three orders of magnitude.<Possible high Tc superconductivity in the Ba-La-Cu-O system by Johannes Georg Bednorz and Karl Alexander Müller>[§II, pp.190–191; Figs.1–3]{ref}
This was evidence for possible granular <superconductivity>, with phase identification unfinished. The paper deferred <Meissner effect> and <heat capacity> tests; its proof note corrected bulk <lanthanum>/<barium> ratios. A resistive onset did not establish a uniform bulk <superconducting transition temperature>.<Possible high Tc superconductivity in the Ba-La-Cu-O system by Johannes Georg Bednorz and Karl Alexander Müller>[§IV, p.192; proof note, p.193]{ref}
Their 1987 authored lecture describes later <magnetometer> checks on <lead>, followed by <magnetic susceptibility> measurements: samples with a resistive drop developed <diamagnetism> at somewhat lower <temperatures>. Combining magnetic, transport and <X-ray diffraction> results identified <barium>-substituted $\mathrm{La_2CuO_4}$ as the superconducting phase. These later results strengthened the case beyond the initial mixed-phase transport evidence.<Perovskite-type oxides: The new approach to high-Tc superconductivity by Johannes Georg Bednorz and Karl Alexander Müller>[Part 1, pp.436–438; Figs.1.10–1.11]{ref}
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