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|Author(s):||Norman A. Sanford; J A. Aust;|
|Title:||Crystal Growth, Characterization, and Domain Studies in Lithium Niobate and Lithium Tantalate Ferroelectrics|
|Published:||January 01, 2001|
|Abstract:||rroelectricity in lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) crystals was discovered by Matthias and Remeika in 1949 . They emerged as key technological materials in the areas of nonlinear optics,  integrated optics , acoustic wave devices , and optical holography . An unprecedented interest in these materials was seen in 1990s. This is seen from Figure 1 which shows the results of a literature search for technical publications relating to either lithium niobate or lithium tantalate. This trend was driven by many factors. The emergence of photonics (6) for communications, data storage, display, biomedical, and defense applications resulted in an increasing need for a versatile solid-state platform with a range of linear and nonlinear optical properties, much as silcon in semiconductor industry. The crystal growth for lithium niobate and lithium tantalate is perfected to an extent that high quality, single crystal, single domain wafers of these materials are available commercially and inexpensively in up to 4 in wafers. Their high electro-optic and nonlinear optical coefficients, transparency in a wavelength range from near UV to far infrared, large photovoltaic, and photocurrents in doped crystals, and the possibility of patterning ferroelectric domains into various shapes and sizes created this surge in interest. As is often the case, a widespread technological application of these materials preceded a complete understanding of many of the fundamental physical processes occurring in these materials. This chapter focuses on four specific areas where significant progress was made in understanding these materials. The first is the growth of single crystals with noncongruent melt compositions. While congruent crystals are excess in Niobium.the growth of crystals with varying [Li] resulted in the discovery that many physical properties sensitively depend on [Li]/[ND] ratio in the crystal. The second area of focus is the study of uniformity in crystal composition. wafer thickness. and strains using the sensitive Maker fringe technique. The third area of focus is a variety of experimental studies on the structure of a ferroelectric domain wall, and strains, electric fields, and optical birefringence associated with these walls. Advances in the phenomenological theory of domain wall structure in LiNbO3 and LiTiO3 are also reviewed in the light of these new experimental studies. The fourth area reviews the advances in the real-time studies of the dynamics of antiparallel ferroelectric domains in these materials under external driving forces. While one can observe a moving domain wall on a video monitor today, it is interesting to note that ferroelectric domain reversal in these materials was believed to be impossible at room temperature.hence the nicknamefrozen ferroelectric given to LiNbO3 by Megaw. The organization of this chapter is as follows. Section 2 discusses the crystal structure and growth of noncongruent single crystals of lithium niobate and lithium tantalate using double crucible Czochralski technique. Section 3 discusses in detail the technique theory and analysis of using Maker fringes to characterize ferroelectric crystals Section 4 focuses on the phenomena of ferroelectric domains and discusses ferroelectric hysteresis internal fields the role of nonstoichiometry in domain reversal, the structure of a domain wall and its interaction with lattice defects and phenomenological modeling of domain wall structure in these materials Section 5 covers the real-time studies of the dyamics of ferroelectric domains under external driving forces Section 6 summarizes the current status of understainding of physical processes in these materials, and the open issues that still need to be addressed. Two excellent reviews on lithium niobate already exist in literature covering a period from early days of discovery to the late 1980s[8, 9]. Considering the curren|
|Citation:||Handbook of Advanced Electronic and Photonic Materials and Devices|
|Publisher:||Academic Press, St. Louis, MO|
|Keywords:||crystal growth,Lithium Niobate,Lithium Tantalate|