Investigation Of Chemical Bond And Structure-Property Relationship Of Crystal Materials

With the increasing development in the study of functional materials,more and more attentions are paid on the internal factors that determine materials properties.The chemical bond method provides an important tool for studying the relationship between the crystal structure and properties,which is widely applied to the structural evaluation and property prediction of functional materials,and even offers some valuable information for further materials design.On the basis of the microscopic characteristics of crystals,this thesis exploringly applies the chemical bond method to the study of borates and hydrogen bonds.Borates possess excellent nonlinear optical(NLO) properties,which are strongly related to their various structural configurations.The discrepancy of the chemical bonding parameters d₀ should not be ignored when investigating the microscopic structures of borate crystals, which reflects the chemical bonding behaviors of central cations in the crystallographic framework.Therefore,the parameters d₀ of B-O bonds were systematically calculated in the 758 investigated oxoborates.By considering the factors that influence the d₀ parameters, including the detailed configurations of borate fundamental building blocks(FBBs), anhydrous or hydrous,the interstitial halogen anions and the substitution of other anionic groups,more precise d₀ data were recommended for various kinds of FBBs.On the basis of the cooperative trend between the d₀ parameter of various FBBs and the calculated largest NLO tensor coefficient of different borates,d₀ values for the unique configuration of FBBs may serve as a useful parameter for pre-investigating the NLO properties of borates,and even for designing novel borate crystals.Hydrogen bonds widely exist in hydrated borates,and often have dominant NLO contributions to the total nonlinearity of crystals.Two-center O-H…O hydrogen bonds in hydrated borates were investigated,in order to reveal their effect on materials properties and further effectively utilize them as functional bonds.With the notion that the stronger O-H and the weaker H…O bonds are two different types of bonds and should have different chemical bonding parameters d₀,two different approaches,respectively basing on the electrostatic interaction(Coulomb's law) and geometric configuration(Golden ratio),were used to calculate d₀ values.The linear correlation between the parameter d₀ and the corresponding bond length was found,which can be employed in the structural design of borate crystals with hydrogen bonds by tuning the structural packing or modifying the electric and optical properties.With deeper studying of general systems beyond the limit of borates,the potential energy function that reflects the actual bonding environment was successfully constructed for a variety of homonuclear O-H…O hydrogen bonds in inorganic solids,including two-center, three-center and multicenter types.Two polynomial functions exhibiting different length sensitivities were respectively proposed for the bond valence calculation of O-H and H…O bonds,the validity of which was proved by evaluating the bond valence sums around not only the central H atoms but also the proton donor and acceptor O atoms in O-H…O systems.The interaction energies of O-H and H…O bonds were analyzed in detail,and the geometric parameters were also connected to the force constants and stretching frequencies of hydrogen bonds.This analysis method from the energy viewpoint can be readily extended to other systems of homonuclear hydrogen bonds,and may be hopefully applied in heteronuclear systems.Due to the simplification of complicated O-H…O interactions,the bond valences were calculated and then the microscopic interactions were studied in hydrogen bond systems. Therefore,this work may shed light on understanding the underlying nature of hydrogen bonds in the actual crystals on the basis of the quantitative analysis of energy,which may also give people some exciting advances to reasonably analyze and employ O-H…O hydrogen bonds in inorganic solids.