Temperature and pressure studies of the continuous neutral–ionic borderline in ClMePD–DMeDCNQI

Temperature- and pressure-induced neutral–ionic phase transitions in the mixed stack charge transfer crystal ClMePD–DMeDCNQI are studied and compared. Using vibrational spectroscopy, we show that the crossing of the neutral–ionic interface is different from previously studied cases. The ionicity change is continuous, and the onset of the stack dimerization precedes, rather than accompany, the neutral–ionic crossing. Moreover temperature- and pressure-induced phase transitions appear to be slightly different, suggesting that different mechanisms are involved.