Compositional Homogeneity and Electrical Properties of Lead Magnesium Niobate Titanate Single Crystals Grown by a Modified Bridgman Technique

Abstract

Relaxor ferroelectric single crystals Pb((Mg 1/3 Nb 2/3 ) 1- x Ti x )O 3 (PMNT 100(1- x )/100 x ) 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 (DTA), X-ray diffraction (XRD) and X-ray fluorescence analyzer (XRFA). The results show that PbTiO 3 content increases throughout the crystal growth. The segregation coefficient is about 0.95 during the growth of PMNT 76/24 directly from melt. Therefore, the electric properties of PMNT single crystals vary even in the same boule. It was demonstrated that the homogeneity of PMNT single crystals can be improved by optimizing growth parameters, but it cannot be eliminated because of the effect of segregation during the crystal growth. We have recently improved the growth process of the modified Bridgman technique to increase the homogeneity of the crystals. Good-quality single crystals with a boule size of more than φ40×80 mm or 30×30×1 mm plates have been achieved. For PMNT 67/33 crystals, their coupling factors are k 33 ≈94% for the longitudinal mode, k 33 ′ ≈86% for the beam mode, and k t ≈62% for the thickness mode, and they have the piezoelectric constant d 33 =1500–3000 pC/N, and dielectric constant ε 33 / ε 0 =3500–5500.