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:
Peculiar aspects in doped ferroelectric crystals


Authors:
Gabriela Conache, C. Berbecaru, H.V. Alexandru


Affiliation:
Faculty of Physics, University of Bucharest, PO Box Mg 11, 76900 Bucharest, Romania


E-mail


Keywords:


Abstract:
Ferroelectric TGS crystals doped with L or D alanine, grown from solutions in the paraelectric phase, show peculiar aspects versus the pure ones. Doped crystals show much lower and stable er versus temperature and losses are more than one order of magnitude lower in the ferroelectric phase [1,2]. Hysteresis loops (HL) of pure and doped samples were automatically recorded using a Sawyer-Tower assembly in line with a Tektronics digital oscilloscope, interface and Computer. Essential parameters: er, tgd, P+, P-, EC+, EC- and the bias field EB have been measured in relation with the intensity of a.c. electric field and temperature. Several distortions of the HL were noticed in particular samples. To study such distortions, the upper electrode of a TGS:D-alanine doped sample (0.7 cm2) was divided in 6x4 smaller square samples of ~2x2 mm and several HL were analyzed. Conclusions: (1) Dopage concentration related to several HL distortions (the bias field particularly and P+/ P- ratio) are connected to the growth zones of the crystal faces. (2) The largest dopant concentration in the zone of (101) face is clearly related to the lowest growth rate, according to the crystal habit. (3) The non-compensated HL (P+ > P-), even at saturation (E~ > 4 EC), seems to be related to the border of specific growth zones, were lattice distortions may hinder domains reversal. (4) The pyroelectric coefficient measurements [3] of L and D alanine doped samples suggest a non-equivalent substitution of glycine group in the lattice. References. [1] H.V.Alexandru, C.Berbecaru, Ferroelectric 202 (1997) 173-182. [2] H.V.Alexandru et all, J.of Optoelectronics and Adv. Materials 1, nr.4 (1999) 57-63. [3] M.Costache, I.Matei, L.Pintilie, H.V.Alexandru, C.Berbecaru, J.of Optoelectronics and Adv. Materials 3, nr.1 (2000) 75-81.