sci
hub

to open science
Ngai, K. L., & Liu, F.-S. (1981). Ionicity and charge density waves in layered transition-metal dichalcogenides. Physica B+C, 105(1-3), 410–413. doi:10.1016/0378-4363(81)90285-0 
10.1016/0378-4363(81)90285-0