Doped versus pure TGS crystals

Pure and l- or d-alanine doped triglycine sulphate crystals (TGS) where grown in paraelectric phase around 52 °C. Doped crystals show lower and reproducible permittivities (crossing down the Curie point) and much lower losses versus pure crystals. Higher figures of merit have to be expected for highly doped crystals, suitable for IR detection. A remarkable difference of the experimental curves was noticed in the temperature dependence of the pyroelectric coefficients (p = dPS/dT) for l- and d-alanine doped samples. This fact suggests a non-equivalent l/d-alanine dopant substitution of the glycine group GI in the host lattice. Spontaneous polarization was calculated by integration of pyroelectric current data, and separately from the hysteresis loops recorded on a large temperature range, using Sawyer–Tower (phase compensated) circuit. Polarization values estimated from the two method compare reasonable well, except the temperature range in the proximity of the Curie point. Internal bias field of ∼1 kV/cm, induced by l-alanine dopant, stabilizes the polarization components P+ and P− in opposite directions, with a peculiar dependence on the ac electric field.