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

The electric field gradient (EFG) at the 63 Cu nucleus of Cu 2 O and CuO has been measured as a function of pressure using the nuclear quadrupole resonance frequency (v Q ). The value of ( delta ln v Q / delta P) T was 1.40+or-0.02(1.33+or-0.05) Mbar -1 for Cu 2 O at 295 (77) K and 5.4+or-0.1 Mbar -1 for CuO at 295 K. The value of ( delta ln v Q / delta ln V) for Cu 2 O is -1.5, showing that Cu 2 O is not a purely ionic compound, as is often assumed in the analysis of the EFG of high T c superconductors. The magnitude of ( delta ln v Q / delta P) tau for 63 Cu in CuO suggests that meaningful measurements of the pressure dependence of v Q in the high T c superconductors can be made at easily accessible pressures.