Hs. Luo et al., Compositional homogeneity and electrical properties of lead magnesium niobate titanate single crystals grown by a modified Bridgman technique, JPN J A P 1, 39(9B), 2000, pp. 5581-5585
Relaxer ferroelectric single crystals Pb((Mg1/3Nb2/3)(1-x)Ti-x)O-3 (PMNT 10
0(1-x)/100x) were grown directly from melt by a modified Bridgman technique
. The segregation during the growth of PMNT single crystals was studied by
means of differential thermal analysis (TGA), thermogravimetric analysis (D
TA), X-ray diffraction (XRD) and X-ray fluorescence analyzer (XRFA). The re
sults show that PbTiO3 content increases throughout the crystal growth. The
segregation coefficient is about 0.95 during the growth of PMNT 76/24 dire
ctly from melt. Therefore, the electric properties of PMNT single crystals
vary even in the same boule. It was demonstrated that the homogeneity of PM
NT single crystals can be improved by optimizing growth parameters, but it
cannot be eliminated because of the effect of segregation during the crysta
l growth. We have recently improved the growth process of the modified Brid
gman technique to increase the homogeneity of the crystals. Good-quality si
ngle crystals with a boule size of more than phi 40 x 80 mm or 30 x 30 x 1
mm plates have been achieved. For PMNT 67/33 crystals, their coupling facto
rs are k(33) approximate to 94% for the longitudinal mode, k'(33) approxima
te to 86% for the beam mode, and k(t) approximate to 62% for the thickness
mode, and they have the piezoelectric constant d(33) = 1500-3000 pC/N, and
dielectric. constant epsilon (33)/epsilon (0) = 3500-5500.