CHARGE-TRANSFER TO THE LOCAL SINGLET-STATES AS A FUNCTION OF LI CONTENT IN LA2CU1-XLIXO4 AND LA1.85SR0.15CU1-XLIXO4

Magnetic susceptibility (chi) and NMR/NQR measurements were performed on La2Cu1-xLixO4 (0 less than or equal to x less than or equal to 0.5) and La1.85Sr0.15Cu1-xLixO4 (0 less than or equal to x less than or equal to 0.425). The narrow Cu-63 NQR line at nu(Q)=46.3 MHz (1.3 K) is detected in La2Cu0.5Li0.5O4. This frequency is higher than all Cu-63-NQR frequencies found so far in all the cuprates. Moreover, a further increase of nu(Q) is observed in the solid solutions La2Cu1-xLixO4 with decreasing x. Corresponding electric field gradients (EFG's) are considered in terms of ionic and cluster models. The 3d hole density n(x2-y2) approximate to 1 and the radial average (r(-3)) approximate to 9.5 a.u. are derived from the EFG's, suggesting the d(9) (L) under bar state of the formally trivaIent copper. The antiferromagnetic ordering is rapidly suppressed as a function of x in La2Cu1-xLixO4, and for x greater than or equal to 0.03 we find T-N approximate to 0. The evolution of chi vs. x shows a gradual decrease of Cu spin susceptibility and its disappearance in the diamagnetic La2Cu0.5Li0.5O4, in which chi = -6.7 X 10(-5) cm(3)/mole is composed of Van Vleck and core terms. The electronic state is implied to be a local singlet ((1)A(1g)) Of primarily d(9) (L) under bar character. The quadrupole signature of the local singlet in the range 46.3 less than or equal to (63)nu(Q) less than or equal to 147.0 MHz is observed for x > 0.15 in both systems, La2Cu1-xLixO4 and La-1.85Sr0.15Cu1-xLixO4. The differentiation of charge between local singlet and conductivity band states is discussed.