Abstract
This paper reports ultrasonic longitudinal and shear attenuation measurements performed on non-superconducting PrBa2Cu3Ox (x = 6.5 and 6.9) between 80 and 300 K. Longitudinal attenuation profile for orthorhombic PrBa2Cu3O6.9 showed attenuation peaks around 185, 205 and 240 K. No attenuation peaks were observed for tetragonal PrBa2Cu3O6.5 in the longitudinal mode. Shear attenuation in PrBa2Cu3O6.5 showed a broad attenuation peak centred around 140 K. The longitudinal attenuation peaks in PrBa2Cu3O6.9 are oxygen-related and are explained in relation to a possible phase transition involving oxygen ordering. In addition, we also report the longitudinal and shear attenuation and velocity measurements on pseudo-tetragonal PrBa2Cu3O6.6. A strong stiffening tendency was observed upon cooling from 270 to 220 K for the longitudinal mode. A thermally anelastic relaxation process involving oxygen hopping was suggested to cause the large change in velocity.
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