Effect of external fields on the memory effect of the incommensurate phase in the ferroelectric-semiconductor TlGaSe2

The effect of external fields (dc electric field, light illumination) on the memory effect of the incommensurate phase in the ferroelectric-semiconductor TlGaSe2 is studied using the measured dielectric constant. The results obtained are discussed. It is shown for the first time that the effect of external fields on the anomaly related to the memory effect in TlGaSe2 can be reduced to the following universal empirical rule: when a sample is held for many hours at a constant temperature T0 in the temperature range of the incommensurate phase in a dc electric field, the deflection amplitude in the low-temperature part of the anomaly in the temperature dependence of the relative change in the dielectric constant Δɛ/ɛ increases (the deflection in the high-temperature part of the Δɛ/ɛ anomaly disappears) as compared to this segment in the dependence obtained during isothermal annealing of this sample at the same temperature without an electric field. The crystal remembers its thermal history at a temperature that is several kelvins higher than T0. Light illumination increases the deflection amplitude in the high-temperature part of the Δɛ/ɛ(T) anomaly and shifts the temperature at which the crystal remembers its thermal history toward lower temperatures with respect to T0.