論文の公開元へRedistribution of ionic species of the true congruent-melting LiNbO3 with stoichiometric structure during crystallization
概要
1.1 Crystal growth from LiNbO3 melt
LiNbO3 (LN) crystal is a ferroelectric material and belongs to the trigonal structure, which has attracted much attention because it can be applied to non- linear optical devices due to its excellent non-linear optical properties [1]. It is also applied to substrates for surface acoustic wave (SAW) devices because of its low acoustic losses [2]. To obtain a single crystal with uniform compositional distribution, LN is generally grown from a congruent melt (c-LN), of which the composition is Li2O:Nb2O5 = 48.38:51.62 mol% [3].
The crystallization process is a central topic for LN single crystals. During crystal growth from the melt (Fig. 1.1), it consists of three parts: bulk melt, interface and crystal. The transport and partitioning of solute occur at the interface, strongly affecting the variation of solute concentration in the crystal. Therefore, the research on the solid-liquid interface is significant. The segregation of solute is evaluated by the equilibrium partitioning coefficient k0, which is expressed as where XS and XL are the mole fractions of solute in the solid and liquid in equilibrium at a given temperature. As shown in Fig. 1.2, the degree of freedom (f) is zero at the congruent point and the equilibrium partitioning coefficient of solute is unity (𝑘Li2O = 1), that is, the solute concentration in the liquid equals that in the crystal. If k0 is not unity, the segregation of solute occurs at the solid-liquid interface and thus the solute concentration in the grown crystal is different in the bulk melt. When 𝑘Li2O > 1, the Li2O concentration in the solid is larger than that in the liquid; when 𝑘Li2O < 1, the Li2O concentration in the solid is smaller than that in the liquid.
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