18. C. Xu^, W.J. Xiao^, T.C. Liu^, F. Sun, J.X. Zheng, S. Peng, X.Q. Liu, F. Pan*, W.G. Yang*, H.K. Mao, "Pressure-induced abnormal insulating state in triangular layered cobaltite LixCoO2 (x ¼ 0.9)", J. Mater. Chem. A, 2017, 5, 19390.