Synthesis And Characterization Of New Anhydrous Phosphate Fluorides And Alkaline Earth Phosphates

Anhydrous compounds are crucially important for many technological applications,such as achieving high performance in lithium/sodium cells,but are often challenging to synthesize under hydrothermal conditions.Moreover,there are still a large number of hydroxyl groups and fluorine substituted interaction phenomenon in the synthesis process,leading to limit its practical application for their low thermal stability.Therefore,a new method for obtaining anhydrous phosphate compounds was proposed,and more than 10 new phosphate compounds were obtained in this paper.The main results are as follows:1.A modified solvo-/hydro-fluorothermal method with fluoride-rich and water-deficient condition is highly effective for synthesizing anhydrous compounds by the replacement of hydroxyl groups and water molecules with fluorine.Several novel anhydrous compounds Na3[GeF4(PO4)],K4[Ge2F9(PO4)],K2Ba2[Al2F9(PO4)]and Na2Ba2[Al2F9(PO4)]were successfully prepared by the solvothermal method of high concentration fluoride mineralization solution with triethylamine and phosphoric acid.Their crystal structures exhibit a one-dimensional chain structure,All F atoms exclusively coordinated to Ge/Al do not have any further connection,which demonstrates fluoride prefers to be terminals that act like"scissors".The results of TG-DTA tests showed that thermal stability of anhydrous phosphate compounds was significantly higher than that of aqueous or hydroxyl compounds.2.Several novel polyanionic phosphate compounds and pyrophosphate compounds were synthesized via solvothermal synthesis of the reaction raw materials with crystalline water with triethylamine and phosphoric acid.It is worth noting that,AlF5@[Ba4(PO3(OH))4]·2(H5O2)is a hydroxyl polyanionic phosphate,consists of per-fluorinated AlF6 octahedral linear chains which are enwrapped in the barrel shape tubes of barium polyhedra that forming a rod shape chain.The resulting rods are interconnected to each other to form a three dimensional(3-D)framework structure with 1-D channels running along the c-axis where the H5O2+ ions resided.And it shows the similar three-dimensional framework structure to molecular sieve materials,the pore diameter was up to 7.31 (?).Besides,Ba5(P3O10)(HPO4)2Cl also belongs to the polyanionic halide phosphate,which is.unique because of three different anionic groups:[P3O10]5-phosphate trimer,[HPO4]3-group,Cl-exist simultaneously in the structure.3.In the system of fluoro-germanophosphates,all F atoms exclusively coordinated to Ge were summarized.It is interesting to note that the Ge/P ratio increases with the increasing number of F-substitutions,which leads to the transformation of the compounds from the phosphorus-rich state to the germanium-rich state.Remarkably,the anhydrous phosphate K4[Ge2F9(PO4)is the highest proportion of Ge/P in the germanophosphates database.