Syntheses,Structures And Properties Of Zinc Phosphates And Zinc Borates

The main purpose of this dissertation mainly explores and synthesizes the novel structures in zinc phosphates and zinc borates because of their abundant structure types and the special role of ZnO₄ in structural construction.In MO?M=Pb,Ba?-ZnO-P₂O₅ system,Pb₄Zn₈?PO₄?₈ and?-BaZn₂?PO₄?₂ compounds have been synthesized,in addition Pb₂Mg?PO₄?₂ has also been obtained by element substitution.In PbO-ZnO-B₂O₃ system,three Pb₅Zn₄B₆O₁₈8 polymorphs have been synthesized.In PbO-BaO-ZnO-B₂O₃ system,two new borates,Pb₃Ba₃Zn₆?BO₃?₈ and?-Ba Zn₂?BO₃?₂have been synthesized.The crystal structures and properties of the eight compounds have been investigated.1.Zinc phosphates contain Zn-P-O layers.Two new zinc phosphates containing Zn-P-O layers have been synthesized by the standard solid-state reaction and their structures were determined by single crystal X-ray diffraction for the first time.Besides,Pb₂Mg?PO₄?₂ has also been synthesized for the first time.Pb₄Zn₈?PO₄?₈ and?-BaZn₂?PO₄?₂ crystallize in the monoclinic crystal system,C2/c and trigonal crystal system,P^<sub>3m1,respectively.Pb₂Mg?PO₄?₂crystallize in the monoclinic crystal system P2₁/c.The structure of Pb₂Mg?PO₄?₂exists three-dimensional framework consisting of the MgO₆ octahedra and the PO₄tetrahedra and the Pb²⁺cations resided in the[Mg₆P₆O₁₂]tunnels.Pb₄Zn₈?PO₄?₈ and?-Ba Zn₂?PO₄?₂ are two-dimension layered structures and exit[Zn₄P₄O₁₆]_?layers for Pb₄Zn₈?PO₄?₈ and[Zn₃P₃O₁₂]_?honeycomb double layers for?-BaZn₂?PO₄?₂.And Pb₄Zn₈?PO₄?₈ contains four different type of Zn-P-O layers,which is reported for the first time in zinc phosphates.Thermal behavior analyses verified that Pb₂Mg?PO₄?₂and Pb₄Zn₈?PO₄?₈ may exist phase transition.The IR spectra confirm the existence of the PO₄ units.The first principles studies reveal that Pb₂Mg?PO₄?₂ is direct-gap compound with the band gap energy value of 3.62 eV,while Pb₄Zn₈?PO₄?₈ and?-Ba Zn₂?PO₄?₂ are indirect band gap compounds with the band gap energy value of3.78 eV and 3.65eV,respectively.2.The Pb₅Zn₄B₆O₁₈8 Polymorph.Three Pb₅Zn₄B₆O₁₈8 polymorphs were synthesized by high temperature solution method.Their structures were determined by single crystal X-ray diffraction and they crystallize in P2₁/c for?-and?-Pb₅Zn₄B₆O₁₈8 and P^-1 for?-Pb₅Zn₄B₆O₁₈.It is interesting that?-Pb₅Zn₄B₆O₁₈8 and?-Pb₅Zn₄B₆O₁₈8 crystallize in different space group,but their structures are very similar,while?-Pb₅Zn₄B₆O₁₈8 and?-Pb₅Zn₄B₆O₁₈crystallize in the same space group,but their structures are totally different.In?-and?-Pb₅Zn₄B₆O₁₈,the ZnO₄ tetrahedra connect with isolated BO₃ to construct the two dimensional?2D?layers,while in?-Pb₅Zn₄B₆O₁₈,the 2D Zn-B-O layers changed to3D framework.In addition,the structure comparisons were discussed based on the coordination environments of the Pb atoms and the distortion of Zn₂BO₈ rings.Furthermore,combining TG-DSC analysis with PXRD,the results show that the transformation of?-to?-Pb₅Zn₄B₆O₁₈8 and?-to?-Pb₅Zn₄B₆O₁₈8 began around 420°C and they are irreversible.The calculated Madelung energy shows the differences among their thermal stability,and?-Pb₅Zn₄B₆O₁₈8 is more stable than?-and?-Pb₅Zn₄B₆O₁₈.3.Pb₃Ba₃Zn₆?BO₃?₈ and?-BaZn₂?BO₃?₂Pb₃Ba₃Zn₆?BO₃?₈ and?-BaZn₂?BO₃?₂ were synthesized by high temperature solution method.Their structures were determined by single crystal X-ray diffraction and they crystallize in C2/c for Pb₃Ba₃Zn₆?BO₃?₈ and P2₁/n for?-Ba Zn₂?BO₃?₂.Their structures both contain 0D and 1D Zn-O structure units which is reported in zinc borates.Additional functional properties including UV-vis-IR diffuse reflectance and IR spectra,have been investigated.