A new series of niobates A6n+[Bxm+Nb12-x]Nb4O42(A=K,Ba;B=Ni,Cr,Fe,Ti and Zr) has been synthesized by solid state reaction and the flux method. The morphology, optical properties and chemical stability of the new compounds were studied. The composition of the compounds were determined by chemical analyses and electron probe X ray microanalysis(EPMA). The results of X ray powder diffraction(XRPD) analyses confirmed that the compounds crystallized in the hexagonal system with space group P63/mcm(193), and which are isostructure with K6CrNb15O42. X ray powder diffraction lines for these compounds were well indexed.
A New Niobate Ba 5LaTi 2Nb 3O 18 was synthesized by a high temperature solid state reaction in the BaO-La 2O 3-TiO 2-Nb 2O 5 system. The chemical compositions, crystal structure, microstructure, density and melting point of the new compound were characterized by EPMA, XRD, SEM, DTA and so on. Ba 5LaTi 2Nb 3O 18 crystallizes the rhombohedral system with unit cell parameters a=0 573 25(2) nm, c=4 213 9(2) nm, and space group R3m, Z=3. The structure may be described as five (Nb,Ti)O 6 octahedra corner-sharing along c axis to form perovskite layer connected by Ba atoms. The Ba 5LaTi 2Nb 3O 18 ceramic exhibits a high dielectric constant of 80.5, low dielectric loss of 6.5×10 -4 and small temperature coefficient of dielectric constant of -78×10 -6 K -1 at 1 MHz due to its close structure and relative high dielectric polarizabilities of Ba 2+, La 3+, Ti 4+ and Nb 5+. Ba 5LaTi 2Nb 3O 18 might be a suitable candidate of high ε r microwave dielectric ceramics.
