Dense polycrystalline samples of the compound YBa2Cu4Osim;8, Y124, were prepared by a threehyphen;step procedure. In the first step a mixture of Y2O3, CuO and BaO2was reacted at 960thinsp;deg;C under an oxygen pressure of 55 bar. The compound did not sinter under these conditions but electrical resistivity and susceptibility measurements showed that the oxide mixture converted to Y124. In the second step densification was produced by hot isostatic pressing at 875thinsp;deg;C. This degraded the superconducting properties severely and a final highhyphen;temperature anneal in pressurized oxygen was required to restore optimum properties. This anneal consisted of a one hour hold at 1010thinsp;deg;C in 40hyphen;bar O2followed by a 24hyphen;h anneal at 950thinsp;deg;C in 55hyphen;bar O2. After this treatment the samples were sim;90percnt; dense, phase pure Y124. The maximum grain dimensions were about 10 mgr;m, and Auger spectroscopy data were obtained on a fracture surface. These data showed that the grain boundary composition does not differ significantly from the bulk values.
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