Method for simultaneously enhancing the transition temperature and increasing mechanical strength of yttrium barium copper oxide (YBa2Cu4O8). Technical report, June 1992-May 1994

Y124 can be heated to 850 deg C without serious O2 loss, and also Y123 loses O2 from its structure at temperatures above 400 deg C. Partial substitution of Ca for Y and of Li for Cu raised the transition temperature (Tc) and enhanced sintering in Y1 Ba2Cu4O8. The authors measured the critical temperature by two methods; a microwave technique (RF) which measures the surface resistivity at 35 GHz, and an AC technique which measures the magnetic screening provided by the whole sample. Twelve samples of Y124 or Y(1-z)Ca(z)Ba2Cu(4-x)Li(x)O8 were prepared; a summary is presented. It is desirable to have a thin film of Y124 for device applications; the authors have not been successful at this endeavor.