Dielectric and ferroelectric properties of phosphoric acid doped triglycine sulfate single crystals

Single crystals of triglycine sulfate (TGS) grown with 25-50 mol% phosphoric acid dopant in solution were investigated for their dielectric, ferroelectric and mechanical hardness properties. A 25 mol% of H3PO4 in solution yielded crystals with a large area in the uc plane without any seed crystal. The room temperature (300 K) dielectric constant (epsilon') and tan delta in the frequency range 0.1-100 kHz were found to increase with increasing phosphoric acid concentration. A maximum shift of 2.5 K in the phase transition temperature (T-c) is observed for crystals grown with 50 mol% of H3PO4. Systematic lowering of Curie-Weiss constant (C-f) in ferroelectric phase and an increase in the paraelectric phase (C-p) indicates domain wall clamping effects in the doped samples. The changes in the spontaneous polarization (2.6-3.2 muC cm(-2)) with phosphoric acid doping are insignificant, but the high coercive fields (E-c = 5 kV cm(-1)), and distorted loops indicate the presence of stresses and inhomogeneities. The activation energy (DeltaE) from temperature dependent d.c. conductivity measurements is lower in both the ferroelectric and the paraelectric phase for doped crystals indicating a strong influence of dopants on the conduction process. The microhardness of the doped crystals is lower in comparison to undoped TGS. (C) 2001 Elsevier Science B.V. All rights reserved.