K. Allakhverdiev et al., Second harmonic generation in layered TlInS2 in the vicinity of the low-temperature phase transitions, PHASE TRAN, 73(4), 2001, pp. 579-588
Second-harmonic generation in the ternary layered semiconductor T1InS(2) ex
cited with the wavelength lambda = 1.06 mum of YAG:Nd3+ laser is investigat
ed in the temperature range corresponding to the low-temperature phase tran
sitions. It is shown that the intensity of the second-harmonic signal corre
sponding to the non-linear coefficients d(eff), d(21), d(22) reveals peculi
arities close to the commensurate-incommensurate phase transitions. The tem
perature hysteresis of the second-harmonic signal in the low-temperature re
gion (below and close to T-i2=206K) is explained assuming that an incomplet
e lock-in transition in T1InS2 takes place at T-c1 = 204 K within the tempe
rature range between a ferroelectric (T-c2 = 201 K) and an incommensurate (
T-i2 = 206 K) phases. II is shown that the monoclinic point group symmetry
Ca is preserved also at temperatures lower than the phase transition temper
ature T-c4 = 79K to a weak ferroelectric state.