UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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Conference: Bucharest University Faculty of Physics 2001 Meeting


Section: Solid State Physics and Materials Science


Title:
Pyroelectric measurements of doped TGS crystals


Authors:
M. Costache, L. Pintilie*, I. Matei*, H.V. Alexandru , C. Berbecaru


Affiliation:
Faculty of Physics, Bucharest University, Bucharest-Magurele, Romania

*National Institute of Materials Physics, Bucharest-Magurele, Romania


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Keywords:


Abstract:
Pyroelectric measurements were performed on L and D alanine doped TGS. Crystals were grown in paraelectric phase (~52 0C) from solutions by slow solvent evaporation. Silver-paint electrodes were used for samples cleaved from the crystals. Pyroelectric current was recorded with a computer controlled Keithley 6517 electrometer, crossing up and down the Curie point. The pyroelectric coefficient p(T) = dPS/dT was plotted versus temperature using the formula Ip = pA(dT/dt), where Ip -the pyroelectric current, A -the electrode area and dT/dt is the heating or cooling rate. Spontaneous polarization PS(T) was also recorded using the charge integration method. The pyroelectric coefficient of pure TGS samples along with the spontaneous polarization could be measured only on heating, using a similar procedure. Reliable data could not be obtained on cooling from the paraelectric phase. Ferroelectric domain reconstruction seems responsible for this effect. Partially or even totally compensated polarization, due to domain instability gives very small and uncertain values. Doped crystals show much more stable and reproducible ferroelectric parameters due to fixed polarization. However, a remarkable asymmetry of the temperature dependence of the pyroelectric coefficient for D and L alanine doped crystals, suggests a non-equivalent substitution of glycine in the host lattice. Higher pyroelectric coefficient values of D alanine, versus L alanine doped crystals; show this TGS doped crystal is more suitable for practical applications.