The temperature-dependent domains, SHG effect and piezoelectric coefficient of TGS

The temperature-dependent, second-order, nonlinear, optical coefficient (X(2)), piezoelectric coefficient (d33), pyroelectric coefficient (Ps) and domains on triglycine sulfate (TGS) reported herein provide a clue for us to investigate these as a typical second-order phase transition. The symmetry breaking occurrence is definitely confirmed by the temperature-dependent X(2) in which X(2) displays a limited value at the ferroelectric phase, indicating the space group (P21) chosen is correct, and when X(2) basically maintains a zero value at the paraelectric phase, indicating the space group should be centric. Interestingly, after normalization of X(2), d33 or Ps, the change trend with temperature is basically overlapped, probably abiding by Landau theory. Moreover, temperature-dependent domains directly show the symmetry breaking occurrence.