LOW DETECTABILITY OF EXCESS YTTRIUM OR BARIUM BY X-RAY-DIFFRACTION IN YBA2CU3O7 PREPARED BY COPRECIPITATION

Excess CuO, BaCuO2, and Y2BaCuO5 (2-1-1) were each separately incorporated into YBa2Cu3O7 (1-2-3) samples, in order to test the sensitivity of powder X-ray diffraction to these common impurity phases. The additions were made by two methods: 1. (1) physical blending, by mixing a phase-pure impurity with phase-pure 1-2-3, and 2. (2) chemical addition, by adding the impurities as individual metal nitrates to a stoichiometric YBa2Cu3 nitrate solution, followed by precipitation and calcination. While chemically and physically incorporated CuO display similar X-ray detectabilities, low (2 wt.%) concentrations of chemically added BaCuO2 and 2-1-1 are far harder to detect than their physically blended counterparts. It was also found that nearly 10 at.% of yttrium in excess of stoichiometry (i.e. "1.1-2-3") can be chemically incorporated before 2-1-1 X-ray peaks are observed. © 1990.