Comparison of the Two Orthorhombic--Tetragonal Transitions in Iron-Doped Y sub 1 Ba sub 2 Cu sub 3 O sub y

• Published in: Journal of the less-common metals 1988-11, Vol.150 (1-2), p.159-166
• Main Authors: Krebs, H U, Bremert, O
• Format: Article
• Language: English
• ISSN: 0022-5088

Undoped and Fe-doped Y sub 1 Ba sub 2 Cu sub 3 O sub y samples were investigated by in situ X-ray experiments, differential scanning calorimetry, thermogravimetrical analysis. Mossbauer spectroscopy and resistivity measurements. In these systems two different orthorhombic--tetragonal (O-T) transitions occur. The first--for undoped samples or those with low iron content--is induced by annealing experiments with an oxygen content of approx 6.5. The decrease of O content leads to a drastic reduction of T sub c and large changes of the Mossbauer spectra. The second O-T transition occurs at an Fe content of about 2.3%. The substitution by Fe in the (001) plane does not greatly affect the superconducting properties, but leads to the attraction of additional O, which is strongly bonded to the lattice, and to the formation of a microdomain structure. This increases the heat of absorption and the activation energy for diffusion. 13 ref.--AA