Effect of ageing on optical and thermal properties of YBa 2 Cu 3 O 7 –δ

Photoacoustic phase and amplitude spectra of YBa 2 Cu 3 O 7 – δ samples synthesised 18 years ago were measured and numerically analysed. The value of thermal diffusivity obtained on the aged samples was lower than the values obtained for fresh samples. Far infrared spectra of YBa 2 Cu 3 O 7 – δ samples synthesised 18 years ago were recorded and analysed enabling determination of reflectivity peak phonon frequencies present at room temperature. X-ray diffraction analysis and far infrared reflectivity measurements enabled determination of a slight change of the oxygen content with time. The YBa 2 Cu 3 O 7 – δ samples synthesised 18 years ago still remained superconducting, which was confirmed by resistivity measurements of the samples between 50 K and room temperature where the critical temperature was reduced from 93 to 73 K. Atomic force microscopy, scanning electron microscopy and energy dispersive X-ray microanalytical measurements were also performed confirming the composition of the sample.