Pressure dependence of the electric field gradient at the⁶³Cu nucleus of Cu₂O and CuO; implications for the analysis of NQR measurements on high T_csuperconductors

Abstract

The electric field gradient (EFG) at the 63Cu nucleus of Cu2O and CuO has been measured as a function of pressure using the nuclear quadrupole resonance frequency (vQ). The value of ( delta ln vQ/ delta P)T was 1.40+or-0.02(1.33+or-0.05) Mbar-1 for Cu2O at 295 (77) K and 5.4+or-0.1 Mbar-1 for CuO at 295 K. The value of ( delta ln vQ/ delta ln V) for Cu2O is -1.5, showing that Cu2O is not a purely ionic compound, as is often assumed in the analysis of the EFG of high Tc superconductors. The magnitude of ( delta ln vQ/ delta P) tau for 63Cu in CuO suggests that meaningful measurements of the pressure dependence of vQ in the high Tc superconductors can be made at easily accessible pressures.