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The effect of low-level CeO 2 addition and cooling rate on sintering, microstructures, phase formation, 1:2 ordering and microwave dielectric properties of Ba 3 Co 0.7 Zn 0.3 Nb 9 (BCZN) was investigated. It was found that low levels doping of CeO 2 (up to 0.5 wt.%) could significantly improve densification of the specimens and their properties. Dielectric properties of CeO 2 -doped samples were sensitive to 1:2 ordering in the B-site. Slow cooling after sintering improved the unloaded quality factor (Q × f values) significantly. The B-site ordering parameter (S) and lattice constant (c/a) values increased as the cooling rate decreased. Ba 5 Nb 4 O 15 (5/0/4) and Ba 8 (Co,Zn) 1 Nb 6 O 24 (8/1/6) secondary phases were found on the surface of all the samples. At 0.4 wt.% CeO 2 the specimens showed maximum Q × f of 84,000 GHz attributed to high density and the degree of cation ordering.

The structure of ceramic Ba4.5Nd9Ti18O54 was investigated by synchrotron x-ray powder diffraction from 10 to 295 K. Reitveld refinement and Le Bail profile analysis were applied to the data. Based on an orthorhombic structure, unit cell parameters of a = 22.3479(3) Å, b = 7.6955(1) Å, and c = 12.2021(2) Å were obtained at room temperature and a = 22.3367(5) Å, b = 7.6738(1) Å, and c = 12.1842(3) Å at 10 K. No evidence was found for any major structural change from 10 to 295 K. Within the tungsten bronze framework the two pentagonal channels were fully occupied by Ba; the remaining Ba atoms shared the rhombic channels with Nd. Thermal expansion of the unit cell was found to be anisotropic. The largest expansion occurs along the b cell edge, and the least along the a cell edge. It is proposed that the anisotropy is due to enhanced bending of the TiO6 polyhedra chains along the b direction.

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