The phase transitions of the anion radical salts containing mixed cations; [(C6H5)(3)PCH3](1-x)(+)[(C6H5)(3)AsCH3](x)(+)(TCNQ)(2)(-), (0 <= x <= 1)

The phase transitions of the anion radical salts containing mixed cations represented by [(C6H5)(3)PCH3] (1-x) +[(C6H5) 3AsCH3](x) + (TCNQ) (2) (-) (O <= x <= 1) were investigated. The transition temperature, T., and the magnitude of the heat, Delta H, of the transition were determined as a function of the composition parameter, x, by means of a differential scanning calorimeter. It was found that T, increases, and Delta H decreases, monotonously with an increase in the value of x, and that the phase transition disappears with x= 1.00. The mechanism of the phase transitions was discussed on the basis of the theory of triplet exciton-exciton interaction proposed by Chesnut. The theoretical values of the entropy changes of the transitions were found to be much less than those observed. In view of these results it was concluded that the anomalies in the magnetic susceptibilities of these salts were induced y the change in the crystal structure.