Doped TGS crystals for IR detection and sensors

Triglycine sulfate crystals (TGS) doped With L- and D-alanine, respectively, where grown in paraelectric phase at 52 degreesC. They show stable parameters versus pure TGS crystals, lower permittivities and losses, i.e. higher pyroelectric figure of merit. L- and D-alanine-doped crystals show a mirror asymmetry of the growth habit along the ferroelectric axis. Hysteresis loop of pure and doped samples were automatically recorded. Internal bias field of about I kV/cm, induced by the two dopants, stabilizes the polarization components P+ and P- in opposite directions. Spontaneous polarization of doped crystals shows two unequal P+/P- components, having a peculiar dependence on the ac applied electric field. Dopage simulation of pure TGS samples, using several bias fields, shows even more complicated pattern. Pyroelectric coefficients were evaluated from pyroelectric current measurements. A remarkable asymmetry of the pyroelectric coefficient peak values for the enantiomorphous-doped crystals was noticed, crossing up and down the Curie point. This fact suggests a non-equivalent L/D-alanine dopant substitution of the glycine group GI in the host lattice. It has been shown that the pyroelectric coefficient can be increased at room temperature, under an optimized dc electric field applied on the pyroelectric wafer. Doped crystals are suitable for IR detector and for more stable gas sensors applications in pollution monitoring. (C) 2004 Elsevier B.V. All rights reserved.