Charge ordering in θ-(BEDT-TTF)2TIM(SCN)4 [M=Co, Zn] studied by vibrational spectroscopy

Raman and Infrared spectra of two types of charge transfer salts θ-(BEDT-TTF) 2 TlM(SCN) 4 [M=Co, Zn] were measured in the temperature range of 50-300 K. Vibrational spectra of θ-(BEDT-TTF) 2 TlCo(SCN)4 at low temperature suggest the charge ordering with a horizontal stripe accompanying a doubling of the unit cell. The θ-(BEDT-TTF) 2 TlZn(SCN) 4 salt also underwent a charge-ordering phase transition at 165 K. The fluctuation of the charge ordering appeared at 240 K.