Syntheses And Properties Of Novel Inorganic Borophosphates

Inorganic phosphates have attracted considerable interest in materials chemistry,since they have been widely used as nonlinear optical?NLO?materials,cathode materials,ionic conductors,and ion-exchange materials,etc.At present,simple phosphates have been systematacially studied.In order to obtain new phosphates with novel structures and excellent NLO properties,reaearchers have gradually focused on combining[PO₄]units with other anionic groups,such as BO₃^3-,CO₃^2-,NO₃^-,SeO₃^2-and TeO₄^2-.The combination of borate and phosphate groups has been most widely studied.Many borophosphates with excellent nonlinear optical properties have been reported.This thesis focuses on exploring the structures and properties of borophosphate materials.On one hand,we have attempted to introduce fluorine into the borophosphate,which can make the cut-off edge blue-shifted which is effective to obtain new deep ultraviolet nonlinear optical materials.We have also tried to introduce different cations into borophosphate system to synthesize mixed-cation borophosphates.On the other hand,based on simple phosphates,we tried to introduce transitional metal into phosphates to synthesize mixed-cation phosphates with excellent NLO properties.Based on the above two aspects,we have successfully synthesized a series of borophosphates and mixed-cation phosphates by hydrothermal methods.The main results are as follows:First,in the borophosphate system,eight borophosphate compounds were successfully synthesized hydrothermally:RbBPO₄F?1?,CsBPO₄F?2?,?NH₄?₂BPO₄F₂?3?,NH₄PbBP₂O₈?4?,NaMgBP₂O₈?OH?₂?5?,KMgBP₂O₇?OH?₂?6?,Rb₂Ni₃?H₂O?₂B₄P₆O₂₄?OH?₂?7?and Na₆Mn₃B₂P₅O₂₁Cl·H₂O?8?.In compounds 1-3,the F atoms replace the oxygen atoms of BO₄ tetrahedra to form BO₃F/BO₂F₂ groups,which futher share oxygen atoms with the PO₄ tetrahedra to form an anionic framework,and then interact with the metal ions to form its three-dimensional structure.All three compounds crystallized in noncentrosymmetric space groups and display second-harmonic generation?SHG?signals approximately 0.4,0.6 and 0.8 times that of KH₂PO₄?KDP?respectively.These compounds exhibit short UV absorption edges?<200 nm?,indicating that they are potential deep UV nonlinear optical materials.In compounds of 4-7,the BO₄ and PO₄ groups are connected by sharing oxygen atoms to form a three-dimensional framework,and the cations are filled in different coordination modes.Wherein compound 4 is an acentric compound which displays a SHG signal of approximately 0.5 times KDP.Magnetic measurements indicate that the metal ions of compound 7 have an antiferromagnetic interaction,while the metal ions in compound8 have a paramagnetic interaction.Second,in the phosphates system,due to the variety of the coordination configuration of transition metal ions and easy to form distorted polyhedron,it is an effective method to improve the SHG properties by introducing transitional metal ions.We have attempted to introduce transitional metal ions into phosphates and successfully synthesized two mixed-cation phosphates:LiHgPO₄?9?and Li₂Fe?HPO₄?₂?10?.Compound 9 crystallizes in a noncentrosymmetric space group P-42₁m,exhibiting a strong SHG signal of approximately 11 times that of KDP.Besides,the distorted HgO₆octahedra with larger polarizability share O atoms with PO₄ groups to form the layered structure,which leads to a high anisotropy and large birefringence large enough to achieve phase-matching at 1064 nm.