Application Study Of The Chemical Bond Method On Functional Inorganic Crystal

With the continuous development of science and technology, the complex relationship between the constituent, structure, crystal growth and property of crystals has been widely investigated in order to explore, design and synthesize new functional inorganic crystal materials. The chemical bond method provides an important theoretical tool for studying the relationship between the crystal structure and property, which is widely applied to the structural evaluation and property prediction of functional inorganic crystals. Starting from the microscopic structure of lithium niobate (LN) and potassium dihydrogen phosphate (KDP) crystals, study on the structure, growth and property of these functional inorganic crystals was carried out on the basis of the chemical bond method.LN crystals have attracted much attention due to their excellent physical properties and potential applications in the modern science and technology. However, it is very difficult to grow LN crystals with a high quality and large size, which can match different kinds of practical needs. The theoretical development is thus necessary for directing the growth of LN crystals. Therefore, on the basis of the crystallographic characteristics of LN crystals, Law of Bravais and Pauling's third rule were employed with the aim to find the relationship between the crystal structure and growth behaviors of LN crystals. It can be found that both octahedra linking and chemical bond behaviors of constituent elements within the crystallographic frame play dramatic roles in affecting the crystal growth. In addition, the calculated results indicated that the crystal plane with the highest reticular density and bonding energy in the LN crystal has the slowest growth rate, and is the most influential face for the LN crystal growth. The current work showed starting from the viewpoint of the microscopic behaviors of constituent chemical bonds and polyhedra in the crystallographic frame, we may comprehensively understand the crystallization process, and build up a link between the crystal structure and growth behaviors of LN crystals, which provides a theoretical tool for us to control the LN crystal growth.Curie temperature (Tc) of LN crystals is a composition-dependent property, which may be applied to determine the crystal composition and estimate the crystal quanlity. A general expression of Tc and spontaneous polarization (Ps) of LN crystals was energetically proposed by employing the viewpoint of the bond energy of constituent chemical bonds within the LN crystallographic frame. The present work showed Tc and Ps of LN crystals are strongly dependent on the Li site within the LN crystallographic structure. Therefore, the Li site is a sensitive lattice position to dominate the ferroelectricity of LN crystals. In addition, domain characteristics (such as the domain shape, domain switching, and etching rate) at±Z surfaces of LN single crystals were comprehensively studied from the chemical bond viewpoint. The present work indicated that domain characteristics are closely correlated to anisotropic bond behaviors of constituent atoms, which may be regarded as a microscopic reflection of the chemical bond behaviors in the LN crystallographic frame. Chemcial bond method provides us a good understanding of ferroelectric behaviors of LN crystals, which may be very helpful to the estimation of ferroelectric behaviors of LN-type solids.Controlling the crystal morphology has become increasingly important, since many of their physical and chemical properties are highly shape dependent. Here we proposed a kinetic model that was applied to the cases of KDP crystals grown from the solution with different surpersaturation on the basis of the structural analysis of the crystal surface. Then, we can predict the growth behaviors of KDP crystals according to the relative growth rate that is quantitatively calculated by using the kinetic model. Seeding experiments with the kinetic model may have significant potential towards the development of shape-controlled growth with defined conditions.