Influence of Pr substitution on acoustic gruneisen parameter and lattice vibrational anharmonicity contribution in ceramic superconductors

This paper reports the effect of Pr substitution on lattice anharmonicity contribution to temperature dependent longitudinal and shear ultrasonic velocity data in (Er 1-x Pr x )Ba 2 Cu 3 O 6.9 (x = 0.0, 0.1 and 0.2) and TlSr 2 (Ca 1-y Pr y )Cu 2 O 7 ( y = 0.5 and 1.0) superconductors. Pr was observed to influence the deviation of the elastic behaviour of both samples from the lattice anharmonicity curves at higher temperatures. The calculated effective Gruneisen parameter for the longitudinal mode (γ eff L ) for both compounds was found to increase with Pr content, indicating increasing anharmonicity contribution. In addition, both series also showed that γ eff L is larger than the effective Gruneisen parameter for the shear mode (γ eff L ) throughout the substitution. The influence of Pr substitution on γ eff and the BCS electron-phonon coupling constant (λ) as well as its possible relationship to superconductivity are discussed.