FREYHARDT H. C, R. WORDENWEBER, G. V. SASTRY, K. HEINEMANN, ULLMAN В., and O. BREMERT, High-tempature superconductors. The influen¬ce of substitutions on their structure, microstructure and critical currents., Low Temp. Phys. 16, (1990) [Fiz. Nizk. Temp. 16, 605-605, (1990)].